7 1 Java Script Execution Environment The Java

7. 2 The Document Object Model - Under development by w 3 c since

7. 3 Events and Event Handling - In event-driven programming, code is executed as

7. 4 Events, Attributes, and Tags Event Tag Attribute abort blur change click error

7. 5 Using the load and unload Events - These events are triggered when

7. 6 Event Handlers for Button Events - Radio buttons <input type = "radio"

7. 6 Event Handlers for Button Events (continued) --> SHOW ch 7_2. html -

7. 6 Event Handlers for Button Events (continued) - Disadvantage of specifying handlers by

7. 7 Checking Form Input (continued) - The focus function puts the element in

7. Checking Form Input (continued) - Handler actions: 1. If no password has been

7. 8 The navigator object - Indicates which browser is being used - Two

7. 9 Event Propagation (continued) - Events that are allowed to bubble can be

Chapter 8 Sebesta: Programming the World Wide Web Chapter 7 © 2001 by Addison

8. 1 Browser Support for Dynamic Documents - IE 5 supports most of CSS

8. 1 Browser Support for Dynamic Documents (continued) - The standard DOM allows base

8. 1 Browser Support for Dynamic Documents (continued) - The script can determine the

8. 2 Element Positioning - This is CSS-P, not DHTML - Without CSS-P, the

8. 2 Element Positioning (continued) --> SHOW abs. Pos 2. html and Figure 8.

8. 3 Moving Elements - If position is set to either absolute or relative,

8. 5 Dynamic Colors and Fonts - Supported by IE 5 and NN 6

8. 5 Dynamic Colors and Fonts (continued) function set. Color(where, new. Color) { if

8. 6 Dynamic Content - The content of an HTML element is addressed with

8. 7. Stacking Elements (continued) - The stacking order can be changed dynamically -

Chapter 9 Sebesta: Programming the World Wide Web Chapter 7 © 2001 by Addison

9. 1 Introduction - Applets are relatively small Java programs whose execution is triggered

9. 1 Introduction (continued) - Applets are an alternative to CGI and embedded scripts

9. 2 Primary Applet Activities - Browser actions: a. Download and instantiate the applet

9. 3 The paint Method - Always called by the browser (not the applet

9. 3 The paint Method (continued) /* welcome. Message. java An applet to illustrate

9. 3 The paint Method (continued) /* welcome. Message_2. java An applet to illustrate

9. 4 The <object> Tag (continued) <object codetype = "application/java" code = "applet_class_file" width

9. 4 The <object> Tag (continued) 9. 5 Applet Parameters - Applets can be

9. 5 Applet Parameters (continued) - If no parameter with the given name has

9. 5 Applet Parameters (continued) <body> <object codetype = "application/java" code = "welcome. Message_3.

9. 6 Simple Graphics (AWT) (continued) - Rectangles are drawn with draw. Rect and

9. 6 Simple Graphics (AWT) (continued) - 3 D rectangles can be created with

9. 6 Simple Graphics (AWT) (continued) - draw. Polygon can also take a single

9. 7 Color (continued) - An object for any color can be created with

9. 8 Interactive Applets (continued) - Labels - Label objects are static strings Label

9. 8 Interactive Applets (continued) - Text boxes Text. Field my. Name = new

9. 8 Interactive Applets (continued) Chapter 7 © 2001 by Addison Wesley Longman, Inc.

9. 8 Interactive Applets (continued) - The Java Event Model - Related to the

9. 8 Interactive Applets (continued) - Semantic Events Action. Event click a button, select

9. 8 Interactive Applets (continued) - Event handlers get an event object as a

9. 9 Concurrency in Java - Our only interest in concurrency here is to

9. 9 Concurrency in Java (continued) - All Java programs run in threads -

9. 9 Concurrency in Java (continued) - Thread methods - yield is a request

9. 9 Concurrency in Java (continued) - Our applet is named Clock - Its

Chapter 10 Sebesta: Programming the World Wide Web Chapter 7 © 2001 by Addison

10. 1 Introduction - SGML is a meta-markup language - Developed in the early

10. 1 Introduction (continued) - Problem with using SGML: - It’s too large and

10. 1 Introduction (continued) - We will refer to an XML-based markup language as

10. 2 The Syntax of XML (continued) - XML names: - Must begin with

10. 2 The Syntax of XML (continued) - Nested tags are better than attributes,

10. 3 XML Document Structure - An XML document often uses two auxiliary files:

10. 3 XML Document Structure (continued) - When the XML parser encounters a reference

10. 4 Data Type Definitions - A DTD is a set of structural rules

10. 4 Data Type Definitions (continued) - Declaring Elements - Element declarations are similar

10. 4 Data Type Definitions (continued) - Declaring Elements (continued) - Child elements can

10. 4 Data Type Definitions (continued) - Declaring Attributes (continued) - Attribute types: there

10. 4 Data Type Definitions (continued) - Declaring Entities - Two kinds: - A

10. 4 Data Type Definitions (continued) - Declaring Entities (continued) - General form of

10. 4 Data Type Definitions (continued) - Internal DTDs <!DOCTYPE root_name [ … ]>

10. 5 Namespaces - A markup vocabulary is the collection of all of the

10. 5 Namespaces (continued) - Can declare two namespaces on one element <gmcars xmlns:

10. 7 Displaying XML Documents with CSS - A CSS style sheet for an

10. 8 XML Transformations and Style Sheets (continued) - An XSLT processor merges an

10. 8 XML Transformations and Style Sheets (continued) - An XSLT style sheet is

10. 8 XML Transformations and Style Sheets (continued) <span style = "font-size: 14"> Happy

Chapter 11 Sebesta: Programming the World Wide Web Chapter 7 © 2001 by Addison

11. 1 Web Server Operation - Client-server systems - When two computers are connected,

11. 2 General Server Characteristics - Web servers have two separate directories - The

11. 2 General Server Characteristics (continued) - The server root is the root directory

11. 3 Apache under UNIX - Apache is available for other platforms, but it

11. 3 Apache under UNIX (continued) - Changes to configuration files affect Apache only

11. 3 Apache under UNIX (continued) - Server. Root - to set the server

11. 3 Apache under UNIX (continued) - Alias - to specify a virtual document

11. 3 Apache under UNIX (continued) - Redirect - to redirect requests to another

11. 3 Apache under UNIX (continued) - User. Dir - to specify whether local

11. 4 Overview of Servlets - A servlet is a compiled Java class -

11. 4 Overview of Servlets (continued) - Servlets are used 1) as alternatives to

11. 5 Servlet Details (continued) - The Servlet interface declares three methods that are

11. 5 Servlet Details (continued) - Two other necessary interfaces: - Servlet. Response –

11. 5 Servlet Details (continued) - The protocol of do. Get is: protected void

11. 6 A Survey Example --> Show ch 11_2. html (consumer electronics survey form)

11. 6 A Survey Example (continued) - The servlet must access the form data

11. 6 A Survey Example (continued) - The file structure is an array of

11. 7 Storing Information about Clients - A session is the collection of all

11. 7 Storing Information about Clients (continued) - Every HTTP communication between the browser

11. 7 Storing Information about Clients (continued) - By default, a cookie’s lifetime is

11. 7 Storing Information about Clients (continued) - Vote counting servlet activities: - See

11. 7 Storing Information about Clients (continued) - Create a Session object - Put

Chapter 12 Sebesta: Programming the World Wide Web Chapter 7 © 2001 by Addison

12. 1 Relational Databases - A database is a collection of data organized to

12. 1 Relational Databases (continued) - Logical model Corvettes States Corvettes_ Equipment - Implementation

12. 1 Relational Databases (continued) State_id 1 2 3 4 5 6 7 8

12. 1 Relational Databases (continued) Vette_id 1 1 1 2 2 2 3 3

12. 2 Intro to SQL - A standard language to create, query, and modify

12. 2 Intro to SQL (continued) - There are several constraints possible e. g.

12. 2 Intro to SQL (continued) - The INSERT Command - General form: INSERT

12. 2 Intro to SQL (continued) UPDATE table_name SET col_name 1 = value 1,

12. 2 Intro to SQL (continued) - Joins - If you want all cars

12. 2 Intro to SQL (continued) SELECT Corvettes. Vette_id, Corvettes. Body_style, Corvettes. Miles, Corvettes.

12. 3 Architectures for Database Access - Client-Server Database Architectures - Usual database client

12. 3 Architectures for Database Access (continued) - One solution to the problems of

12. 3 Architectures for Database Access (continued) - Disadvantage (of embedded SQL): - Portability

12. 3 Architectures for Database Access (continued) - The Java JDBC Architecture: - Related

12. 4 Approaches to Using JDBC (continued) - The classes that implement the JDBC

12. 4 Approaches to Using JDBC (continued) 3. Use a third-tier computer to run

12. 5 Java JDBC Applications (continued) - The general form of a reference to

12. 5 Java JDBC Applications (continued) 2. Manual registration, using the for. Name method

12. 5 Java JDBC Applications (continued) - SQL commands are String objects final String

12. 5 Java JDBC Applications (continued) Result. Set result; final String sql_com = "SELECT

12. 5 Java JDBC Applications (continued) 1993 -2001 Corvettes For Sale Vette_id Body_style Miles

12. 5 Java JDBC Applications (continued) - The get. Tables method of Database. Meta.

12. 5 Java JDBC Applications (continued) Result. Set. Meta. Data result. Md = result.

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7. 1 Java. Script Execution Environment - The Java. Script Window object represents the window in which the browser displays documents - The Window object provides the largest enclosing referencing environment for scripts - Its properties are visible to all scripts in the document (they are the globals) - Other Window properties: - document - a reference to the Document object that the window displays - frames - an array of references to the frames of the document - forms - an array of references to the forms of the document - Each Form object has an elements array, which has references to the form’s elements - Form elements are usually referenced by name, but this is a problem for radio buttons Chapter 7 © 2001 by Addison Wesley Longman, Inc. 1

7. 2 The Document Object Model - Under development by w 3 c since the mid-90 s - DOM 2 is the latest approved standard - The DOM is an abstract model that defines the interface between HTML documents and application programs - It is an OO model - document elements are objects - A language that supports the DOM must have a binding to the DOM constructs - In the Java. Script binding, HTML elements are represented as objects and element attributes are represented as properties e. g. , <input type = "text" name = "address"> would be represented as an object with two properties, type and name, with the values "text" and "address" - The property names in Java. Script are usually just lowercase versions of the corresponding HTML attribute names Chapter 7 © 2001 by Addison Wesley Longman, Inc. 2

7. 3 Events and Event Handling - In event-driven programming, code is executed as a result of a user or browser action - An event is a notification that something specific has occurred, either with the browser or an action of the browser user - An event handler is a script that is implicitly executed in response to the appearance of an event - Because events are Java. Script objects, their names are case sensitive - all are in lowercase only - Event handlers can be specified in two ways: 1. An HTML tag can have an attribute that is associated with a specific event and the handler code, in the form of a string literal, is assigned to the attribute 2. The handler can be implemented as a function and the function’s name is assigned to the object property associated with the event at the HTML element - Don’t use document. write in an event handler, because the output may go on top of the display Chapter 7 © 2001 by Addison Wesley Longman, Inc. 3

7. 4 Events, Attributes, and Tags Event Tag Attribute abort blur change click error focus load mouseout mouseover reset resize select submit unload on. Abort on. Blur on. Change on. Click on. Error on. Focus on. Load on. Mouse. Out on. Mouse. Over on. Reset on. Resize on. Select on. Submit on. Unload - The same attribute can appear in several different tags e. g. , The on. Click attribute can be in <a> and <input> --> SHOW Tables 7. 1 and 7. 2 - Specifying a handler by assigning the attribute: on. Click = "alert('Mouse click!'); " on. Click = "my. Handler(); " Chapter 7 © 2001 by Addison Wesley Longman, Inc. 4

7. 5 Using the load and unload Events - These events are triggered when the loading or unloading of a document is completed  <html> <head> <title> on. Load and on. Unload event handlers </title> <script language = "Java. Script"> // The onload event handler function load_hello () { alert("Your page has been loaded - hello!"); } // The onunload event handler function unload_goodbye () { alert("Your page is now unloaded - goodbye!"); } </script> <head> <body on. Load = "load_hello(); " on. Unload = "unload_goodbye(); "> </body> </html> Chapter 7 © 2001 by Addison Wesley Longman, Inc. 5

7. 6 Event Handlers for Button Events - Radio buttons <input type = "radio" name = "button_group" value = "blue" on. Click = "handler()"> - Can’t use the element’s name to identify it, because all buttons in the group have the same name - Must use the DOM address of the element, e. g. , var radio. Element = document. my. Form. elements; - Now we have the name of the array of elements of the form for (var index = 0; index < radio. Element. length; index++) { if (radio. Element[index]. checked) { element = radio. Element[index]. value; break; } } - NOTE: There is no error checking in this code - Now, we can use a switch on element, as in switch(element) {. . . Chapter 7 © 2001 by Addison Wesley Longman, Inc. 6

7. 6 Event Handlers for Button Events (continued) --> SHOW ch 7_2. html - Event handlers can be specified by assigning them to properties of the Java. Script objects associated with the HTML elements - The property names are lowercase versions of the attribute names - If the event handler is a function, just assign its name to the property, as in document. my. Form. elements[0]. onclick = my. Handler; - This sets the handler for the first element in the form -This would need to follow both the handler function and the HTML form - If this is done for a radio button group, each element of the elements array must be assigned --> SHOW ch 7_2 x. html Chapter 7 © 2001 by Addison Wesley Longman, Inc. 7

7. 6 Event Handlers for Button Events (continued) - Disadvantage of specifying handlers by assigning them to event properties is that there is no way to use parameters - The advantage of specifying handlers by assigning them to event properties are: 1. It is good to keep HTML and Java. Script separate 2. The handler could be changed during use 7. 7 Checking Form Input - A good use of Java. Script, because it finds errors in form input before it is sent to the server for processing - Things that must be done: 1. Detect the error and produce an alert message 2. Put the element in focus (the focus function) 3. Select the element (the select function) Chapter 7 © 2001 by Addison Wesley Longman, Inc. 8

7. 7 Checking Form Input (continued) - The focus function puts the element in focus, which puts the cursor in the element document. my. Form. phone. focus(); - The select function highlights the text in the element - To keep the form active after the event handler is finished, have it return false - Example – comparing passwords - If a password will be used later, the user is asked to type it in twice - The program must verify that the second typing of the password is the same as the first - The form just has two password input boxes to get the passwords and Reset and Submit buttons - The event handler is triggered by the Submit button Chapter 7 © 2001 by Addison Wesley Longman, Inc. 9

7. Checking Form Input (continued) - Handler actions: 1. If no password has been typed in the first box, focus on that box and return false 2. If the two passwords are not the same, focus and select the first box and return false if they are the same, return true --> SHOW ch 7_3. html & its output - Another Example – Checking the format of a name and phone number - The event handler will be triggered by the change event of the text boxes for the name and phone number - If an error is found in either, an alert message is produced and both focus and select are called on the text box element - Another event handler is used to produce a thank you alert message when the input is ok Chapter 7 © 2001 by Addison Wesley Longman, Inc. 10

7. 8 The navigator object - Indicates which browser is being used - Two useful properties 1. The app. Name property has the browser’s name 2. The app. Version property has the version # - Microsoft has chosen to set the app. Version of IE 5 to 4 (? ) 7. 9 Event Propagation - As with exception handling, it is valuable to be able to propagate events, so that one handler can deal with events from more than one source - The DOM 2 model of event propagation bubbles events upward in the hierarchy, toward the document or window level - There are two categories of events – those that bubble and those that don’t Chapter 7 © 2001 by Addison Wesley Longman, Inc. 11

7. 9 Event Propagation (continued) - Events that are allowed to bubble can be handled at the element level, but they also bubble upward unless told not to with stop. Propagation - IE 5 and NN 6 support bubbling, but NN 4 does not Chapter 7 © 2001 by Addison Wesley Longman, Inc. 12

8. 1 Browser Support for Dynamic Documents - IE 5 supports most of CSS and dynamic HTML standards - IE 5 also supports some non-standard things, such as advanced visual effects - NN 4 supports Netscape JSS and layers, but few of the standard things (except CSS-P) - NN 6 support for standards is similar to that of IE 5 - A dynamic HTML document is one whose tag attributes, tag contents, or element style properties can be changed after the document has been and is still being displayed by a browser - To make changes in a document, a script must be able to address the elements of the document using the DOM addresses of those elements - NN 4 uses a non-standard DOM structure, which makes the few changes it can make more difficult Chapter 7 © 2001 by Addison Wesley Longman, Inc. 14

8. 1 Browser Support for Dynamic Documents (continued) - The standard DOM allows base element addresses to be gotten through their names, but the NN 4 DOM does not support this - Example: <body> <form id = "my. Form" > <input type = "button" id = "on. Button"> … </form> </body> - The standard DOM address of the button can be gotten with the get. Element. By. Id method, as in document. get. Element. By. Id("on. Button"). style - For NN 4, the whole path must be included, as in document. my. Form. on. Button - To build scripts that work for both NN 4 and the standard, you must determine whether NN 4 is being used and set the DOM address accordingly Chapter 7 © 2001 by Addison Wesley Longman, Inc. 15

8. 1 Browser Support for Dynamic Documents (continued) - The script can determine the browser using the navigator object if ((navigator. app. Name == "Netscape" && (parse. Int(navigator. app. Version) == 4)) dom = document. my. Form. on. Button; else dom = document. get. Element. By. Id("on. Button"). style; - HTML elements are sometimes referenced through a value of a variable or a function parameter, rather than through its id - In these cases, the DOM address must be built for NN 4 with eval and string catenation, as in function changer(elem. Id) { if ((navigator. app. Name == "Netscape") && (parse. Int(navigator. app. Version) == 4)) dom = eval('document. ' + elem. Id); else dom = document. get. Element. By. Id(elem. Id). style; . . . } Chapter 7 © 2001 by Addison Wesley Longman, Inc. 16

8. 2 Element Positioning - This is CSS-P, not DHTML - Without CSS-P, the only ability to position elements in the display of a document is with tables - CSS-P is completely supported by IE 5 and NN 6, and partially by NN 4 - The position of any element can be dictated by the three style properties: position, left, and top - The three possible values of position are absolute, relative, and static - Absolute Positioning <p style = "position: absolute; left: 50 px; top: 100 px; "> --> SHOW abs. Pos. html and Figure 8. 1 - If an element is nested inside another element and is absolutely positioned, the top and left properties are relative to the enclosing element Chapter 7 © 2001 by Addison Wesley Longman, Inc. 17

8. 2 Element Positioning (continued) --> SHOW abs. Pos 2. html and Figure 8. 2 - Relative Positioning - If no top and left properties are specified, the element is placed exactly where it would have been placed if no position property were given - But it can be moved later - If top and left properties are given, they are offsets from where it would have placed without the position property being specified - If negative values are given for top and left, the displacement is upward and to the left --> SHOW rel. Pos. html Figure 8. 3 - Static Positioning - The default value if position is not specified - Neither top nor left can be initially set, nor can they be changed later Chapter 7 © 2001 by Addison Wesley Longman, Inc. 18

8. 3 Moving Elements - If position is set to either absolute or relative, the element can be moved after it is displayed - Just change the top and left property values with a script --> SHOW mover. html & Figures 8. 4 and 8. 5 8. 4 Element Visibility - The visibility property of an element controls whether it is displayed - The standard values are visible and hidden - The NN 4 values, show and hide, are used internally, though NN 4 recognizes the std. values - Suppose we want to toggle between hidden and visible, and the element’s DOM address is dom if (dom. visibility == "visible" || dom. visibility == "show") dom. visibility = "hidden"; else dom. visibility = "visible"; --> SHOW show. Hide. html Chapter 7 © 2001 by Addison Wesley Longman, Inc. 19

8. 5 Dynamic Colors and Fonts - Supported by IE 5 and NN 6 - Background color is controlled by the background. Color property - Foreground color is controlled by the color property - Can use a function to change these two properties - Let the user input colors through text buttons - Have the text button elements call the function with the element address and the new color Background color: <input type = "text" size = "10" name = "background" onchange = "set. Color('background', this. value)"> - The actual parameter this. value works because at the time of the call, this is a reference to the text button Chapter 7 © 2001 by Addison Wesley Longman, Inc. 20

8. 5 Dynamic Colors and Fonts (continued) function set. Color(where, new. Color) { if (where == "background") document. body. style. background. Color = new. Color; else document. body. style. color = new. Color; } --> SHOW dyn. Colors. html - Changing fonts - Can change the font properties of a link by using the mouseover and mouseout events to trigger a script that makes the changes - In this case, we can put the script in the HTML onmouseover = "this. style. color = 'blue'; this. style. font = 'italic 16 pt Times'; " onmouseout = "this. style. color = 'black'; this. style. font = 'normal 16 pt Times'; ” --> SHOW dyn. Link. html and Figures 8. 6 & 8. 7 Chapter 7 © 2001 by Addison Wesley Longman, Inc. 21

8. 6 Dynamic Content - The content of an HTML element is addressed with the value property of its associated Java. Script object --> SHOW dyn. Value. html and Figure 8. 8 8. 7 Stacking Elements - The top and left properties determine the position of an element on the display screen, which is a two-dimensional device - We can create the appearance of a third dimension by having overlapping elements, one of which covers the others (like windows) - This is done with the z-index property, which determines which element is in front and which are covered by the front element - The Java. Script variable associated with the z-index property is z. Index - Element stacking is supported by IE 5, NN 6, & NN 4 Chapter 7 © 2001 by Addison Wesley Longman, Inc. 22

8. 7. Stacking Elements (continued) - The stacking order can be changed dynamically - Make the elements anchors, so they respond to mouse clicking - The href attribute can be set to call a Java. Script function by assigning it the call, with 'JAVASCRIPT' attached to the call code <a href = "JAVASCRIPT: fun()"> - The function must change the z. Index value of the element - A call to the function from an element sets the z. Index value of the new top element to 10 and the z. Index value of the old top element to 0 - It also sets the current top to the new top --> SHOW stacking. html and Figures 8. 9, 8. 10, & 8. 11 Chapter 7 © 2001 by Addison Wesley Longman, Inc. 23

9. 1 Introduction - Applets are relatively small Java programs whose execution is triggered by a browser - The purpose of an applet is to provide processing capability and interactivity for HTML documents - The ‘standard’ operations of applets are provided by the parent class, Applet public class_name extends Applet { … } - The Applet class descends directly from Panel, which descends directly from Component - The use of applets has been restrained by the lack of support for Swing - Specifically, the JVM that comes with NN 4 does not support Swing, so NN 4 users cannot execute applets that use it - Use of applets is still widespread, and there is heavy use in intranets, where all browsers can be required to support the latest JVM Chapter 7 © 2001 by Addison Wesley Longman, Inc. 25

9. 1 Introduction (continued) - Applets are an alternative to CGI and embedded scripts - Comparisons: - CGI is faster than applets and Java. Script, but it is run on the server - Java. Script is easier to learn and use than Java, but less expressive - Java is faster than Java. Script - Java graphics are powerful, even with just AWT (Java. Script has none) - Java. Script does not require the additional download from the server that is required for applets - Java may become more of a server-side tool, in the form of servlets, than a client-side tool Chapter 7 © 2001 by Addison Wesley Longman, Inc. 26

9. 2 Primary Applet Activities - Browser actions: a. Download and instantiate the applet class b. Call the applet’s init method c. Call the applet’s start method - This starts the execution of the applet - When the user takes a link from the document that has the applet, the browser calls the applet’s stop method - When the browser is stopped by the user, the browser calls the applet’s destroy method - Every applet must override at least one of the three methods, init, start, or paint (paint is inherited from Component) Chapter 7 © 2001 by Addison Wesley Longman, Inc. 27

9. 3 The paint Method - Always called by the browser (not the applet itself) - Takes one parameter, of class Graphics, which is defined in java. awt - The parameter object is created by the browser - The protocol is: public void paint(Graphics graf. Obj) { … } - The simplest use of paint is to display text, using the draw. String method - Three parameters: a String literal, the x coordinate of the left end of the string, and the y coordinate of the base of the string (the coordinates are given in pixels) Chapter 7 © 2001 by Addison Wesley Longman, Inc. 28

9. 3 The paint Method (continued) /* welcome. Message. java An applet to illustrate the display of a string */ import java. applet. Applet; import java. awt. *; public class welcome. Message extends Applet { public void paint(Graphics graf. Obj) { graf. Obj. draw. String( "Welcome to my home page!", 50); } } - Font Control - The Font class, defined in java. awt. Font, has three variables that specify the font name, style, and size of the font used by draw. String The size parameter is in points - The styles are PLAIN, BOLD, and ITALIC - To change the font, create a Font object with the desired parameters and set it with the set. Font method of Graphics, which takes a Font parameter Chapter 7 © 2001 by Addison Wesley Longman, Inc. 29

9. 3 The paint Method (continued) /* welcome. Message_2. java An applet to illustrate the display of a string in specific font, font style, and font size */ import java. applet. Applet; import java. awt. *; public class welcome. Message_2 extends Applet { Font my. Font = new Font("Times. Roman", Font. ITALIC, 24); public void paint(Graphics graf. Obj) { graf. Obj. set. Font(my. Font); graf. Obj. draw. String( "Welcome to my home page!", 50); } } 9. 4 The <object> Tag - Used to specify an applet in an HTML document - Creates a space in the document display for applet output (like <img> does) Chapter 7 © 2001 by Addison Wesley Longman, Inc. 30

9. 4 The <object> Tag (continued) <object codetype = "application/java" code = "applet_class_file" width = "applet display width" height = "applet display height"> </object> - The display width and height are in pixels - The applet_class_file is the compiled version  <html> <head> <title> Test welcome. Message_2 </title> </head> <body> <object codetype = "application/java" code = "welcome. Message_2. class" width = "500" height = "100"> </object> </body> </html> Chapter 7 © 2001 by Addison Wesley Longman, Inc. 31

9. 4 The <object> Tag (continued) 9. 5 Applet Parameters - Applets can be sent parameters through HTML, using the <param> tag and its two attributes, name and value - Parameter values are strings - e. g. , <param name = "fruit" value = "apple"> - The applet gets the parameter values with get. Parameter, which takes a string parameter, which is the name of the parameter String my. Fruit = get. Parameter("fruit"); Chapter 7 © 2001 by Addison Wesley Longman, Inc. 32

9. 5 Applet Parameters (continued) - If no parameter with the given name has been specified in the HTML document, get. Parameter returns null - By checking the return value against null, a default value can be set - If the parameter value is not really a string (although parameters are all sent as strings), the value returned from get. Parameter must be converted, as in String p. String = get. Parameter("size"); if (p. String == null) my. Size = 24; else my. Size = Integer. parse. Int(p. String); - The best place to put the code to get parameter values is in init - Parameters are stored in instance variables Chapter 7 © 2001 by Addison Wesley Longman, Inc. 33

9. 5 Applet Parameters (continued) <body> <object codetype = "application/java" code = "welcome. Message_3. class" width = "500" height = "100"> <param name = "size" value = "35"> </object> </body> 9. 6 Simple Graphics (AWT) - Coordinate system: (0, 0) is at the upper left corner - The methods that draw graphic figures are called through the Graphics object (the parameter to paint) - Lines are drawn with draw. Line(x 1, y 1, x 2, y 2) - Draws a line from (x 1, y 1) to (x 2, y 2) Chapter 7 © 2001 by Addison Wesley Longman, Inc. 34

9. 6 Simple Graphics (AWT) (continued) - Rectangles are drawn with draw. Rect and fill. Rect - Both take four parameters, the coordinates of the upper left corner of the rectangle and the width and height of the rectangle (width and height are in pixels) - Rectangles with rounded corners can be drawn with draw. Round. Rect and fill. Round. Rect - These two take two more parameters, which specify the numbers of horizontal pixels and vertical pixels in the rounding /* rectangles. java */ import java. applet. Applet; import java. awt. *; public class rectangles extends Applet { public void paint(Graphics graf. Obj) { graf. Obj. draw. Rect(10, 80, 60); graf. Obj. fill. Rect(120, 10, 60, 80); graf. Obj. draw. Round. Rect(10, 120, 80, 60, 20, 30); graf. Obj. fill. Round. Rect(120, 60, 80, 40); } } Chapter 7 © 2001 by Addison Wesley Longman, Inc. 35

9. 6 Simple Graphics (AWT) (continued) - 3 D rectangles can be created with a 5 th parameter, true (not pushed) or false (pushed) - Polygons are drawn with draw. Polygon, which takes three parameters, two arrays of coordinates of edge endpoints, and the number of edges public void paint(Graphics graf. Obj) { int x. Coordinates [] = {30, 50, 64, 50, 30, 16, 30}; int y. Coordinates [] = {10, 24, 44, 58, 44, 24, 10}; graf. Obj. draw. Polygon(x. Coordinates, y. Coordinates, 9); } Chapter 7 © 2001 by Addison Wesley Longman, Inc. 36

9. 6 Simple Graphics (AWT) (continued) - draw. Polygon can also take a single parameter, which is a Polygon object, whose constructor takes the same three parameters as draw. Polygon - Ovals are like rectangles (same parameters) 9. 7 Color - The Color class has predefined objects for common colors Color. white, Color. black, Color. gray, Color. red, Color. green, Color. blue, Color. yellow, Color. magenta, Color. cyan, Color. pink, Color. orange Chapter 7 © 2001 by Addison Wesley Longman, Inc. 37

9. 7 Color (continued) - An object for any color can be created with the Color constructor, as in Color my. Color = new Color(x, y, z); - The color of the Graphics object can be set with set. Color, as in graf. Obj. set. Color(Color. cyan); - The foreground and background colors of the applet display are set with methods from Panel 9. 8 Interactive Applets - Applet extends Panel, which extends Component - The Component class includes GUI components as subclasses - Panel objects are used to enclose GUI components - The Applet class is itself a GUI component Chapter 7 © 2001 by Addison Wesley Longman, Inc. 38

9. 8 Interactive Applets (continued) - Labels - Label objects are static strings Label labl 1 = new Label("Click this button"); - Plain buttons Button my. Button = new Button( "Click here for fun"); - Checkboxes Checkbox 1 = new Checkbox("Beer"); Checkbox 2 = new Checkbox("Pretzels"); - Radio buttons – just checkboxes in a Checkbox. Group pop = new Checkbox. Group(); Checkbox 1 = new Checkbox("Coke", pop, true); Checkbox 2 = new Checkbox("Pepsi", pop, false); Chapter 7 © 2001 by Addison Wesley Longman, Inc. 39

9. 8 Interactive Applets (continued) - Text boxes Text. Field my. Name = new Text. Field(30); - A Panel object is needed to contain components Panel my. Panel = new Panel(); my. Panel. set. Background(Color. yellow); my. Panel. set. Foreground(Color. blue); my. Panel. add(box 1); - Layout Managers - Default is Flow. Layout – just like a browser - Grid. Layout is like HTML document panels Panel button. Panel = new Panel(); button. Panel. set. Layout( new Grid. Layout(3, 2, 10)); - Three rows of two components each, with 10 pixels between the components --> SHOW Pizza. java Chapter 7 © 2001 by Addison Wesley Longman, Inc. 40

9. 8 Interactive Applets (continued) - The Java Event Model - Related to the Java. Script event model - Event handlers are called event listeners - Connection of an event to a listener is through event listener registration - Done with a method of the class that implements the listener interface - The panel object that holds the components can be the event listener for those components - Event generators send messages (call methods) to registered event listeners when events occur - Event handling methods must conform to a standard protocol, which comes from an interface - We only consider the “semantic” events (there also “low-level” events) Chapter 7 © 2001 by Addison Wesley Longman, Inc. 42

9. 8 Interactive Applets (continued) - Semantic Events Action. Event click a button, select from a menu or list, or type the enter button in a text field Adjustment. Event adjust a scroll bar Item. Event select a checkbox or list item Text. Event change the contents of a text field or text area - For these four events, we have the following interfaces and handler methods: Interface Handler method Action. Listener Adjustment. Listener Item. Listener Text. Listener action. Performed adjustment. Value. Changed item. State. Changed text. Value. Changed - The methods to register the listener is the interface name with “add” prepended - e. g. , button 1. add. Action. Listener(my. Panel); Chapter 7 © 2001 by Addison Wesley Longman, Inc. 43

9. 8 Interactive Applets (continued) - Event handlers get an event object as a parameter, through which information about the event can be gotten with methods, such as get. State - e. g. , button 1. get. State() returns true if the button is on, false otherwise - When an event handler has just a few lines, it can be implemented as an instance of an anonymous nested class - Example: a button that sets a font button. add. Action. Listener(new Action. Listener(){ public void action. Performed(Action. Event e) { text. set. Font(new. Font); } }); --> SHOW Radio. B. java Chapter 7 © 2001 by Addison Wesley Longman, Inc. 44

9. 9 Concurrency in Java - Our only interest in concurrency here is to illustrate how threads can be used to create animation in an applet - A thread of control is a sequence of program points reached as execution flows through the program - A nonconcurrent program has a single thread of control; a concurrent program has more than one - Java supports lightweight concurrency through its threads - The concurrent program units in Java are methods named run, whose code can be in concurrent execution with other run methods and with main - There are two ways to implement threads, as a subclass of Thread and by implementing the interface Runnable - The Thread class - Two essential methods, run and start - run is the concurrent method - start tells the run method to begin execution Chapter 7 © 2001 by Addison Wesley Longman, Inc. 45

9. 9 Concurrency in Java (continued) - All Java programs run in threads - For applications, when execution is to begin, a thread is created for main and its start method is called - For applets, when the browser finds one, it creates a thread and calls the applet --> SHOW Names. java, output, delayer, and output - Thread States - New - created, but start hasn’t been called - Runnable or ready - ready to run, but is not currently running - In the ready queue - Running - actually has the processor - Blocked - was running, but is not now, because it was interrupted (i/o, end of time slot, gave up its time slot, etc. ) - Dead - either its stop was called or its run method completed its execution Chapter 7 © 2001 by Addison Wesley Longman, Inc. 46

9. 9 Concurrency in Java (continued) - Thread methods - yield is a request from the running thread to give up the processor; a static method - sleep(time) - blocks the thread for at least as many milliseconds as the parameter specifies; also a static method - sleep can throw Interrupted. Exception, which must be caught - stop - now deprecated, because of safety problems - Now we override it and just set the thread reference to null (destroys the thread) - An example - an animated digital clock - An applet must implement Runnable, its start and stop methods, and the repaint method of Graphics - repaint is called after the applet display has changed Chapter 7 © 2001 by Addison Wesley Longman, Inc. 47

9. 9 Concurrency in Java (continued) - Our applet is named Clock - Its start method creates a new Thread object, sending this to the constructor. This sets the new Thread object’s target to the Clock object, which forces the thread to get its run method from the Clock object - After creating the Thread object, start is called to start its execution - The run method sets a variable to the currently executing thread, and then loops as long as the thread is clock. Thread - The loop gets the new time with a new Date object and repaints the display every second Chapter 7 © 2001 by Addison Wesley Longman, Inc. 48

10. 1 Introduction - SGML is a meta-markup language - Developed in the early 1980 s; ISO std. In 1986 - HTML was developed using SGML in the early 1990 s - specifically for Web documents - Two problems with HTML: 1. Fixed set of tags and attributes - User cannot invent new tags or attributes - So, the given tags must fit every kind of document, and the tags cannot connote any particular meaning 2. There are no restrictions on arrangement or order of tag appearance in a document - One solution to the first of these problems: Let users define their own tags (with assigned meanings) (i. e. , design their own “HTML”s using SGML) Chapter 7 © 2001 by Addison Wesley Longman, Inc. 50

10. 1 Introduction (continued) - Problem with using SGML: - It’s too large and complex to use, and it is very difficult to build a parser for it - A better solution: Define a lite version of SGML - That’s what the e. Xtensible Markup Language is - XML is not a replacement for HTML - HTML is a markup language used to describe the layout of any kind of information - XML is a meta-markup language that can be used to define markup languages that can define the meaning of specific kinds of information - XML is a very simple and universal way of storing and transferring data of any kind - All documents described with an XML-derived markup language can be parsed with a single parser Chapter 7 © 2001 by Addison Wesley Longman, Inc. 51

10. 1 Introduction (continued) - We will refer to an XML-based markup language as a tag set - Strictly speaking, a tag set is an XML application, but that terminology can be confusing - IE 5 has an XML parser (although it is based on an early XML standard) - NN 4 does not support XML, but NN 6 does 10. 2 The Syntax of XML - XML documents have data elements, markup declarations (instructions for the XML parser), and processing instructions (for the application program that is processing the data in the document) - All XML documents begin with an XML declaration: <? xml version = "1. 0"? > Chapter 7 © 2001 by Addison Wesley Longman, Inc. 52

10. 2 The Syntax of XML (continued) - XML names: - Must begin with a letter or an underscore - They can include digits, hyphens, and periods - There is no length limitation - They are case sensitive (unlike HTML names) - Syntax rules for XML: (similar to those for XHTML) - Every element that has content must have a closing tag - Tags must be properly nested - All attribute values must be quoted - An XML document that follows all of these rules is well formed - Attributes are not used in XML the way they are in HTML - In XML, you often define a new nested tag to provide more info about the content of a tag Chapter 7 © 2001 by Addison Wesley Longman, Inc. 53

10. 2 The Syntax of XML (continued) - Nested tags are better than attributes, because attributes cannot describe structure and the structural complexity may grow  <patient name = "Maggie Dee Magpie">. . . </patient>  <patient> <name> Maggie Dee Magpie </name>. . . </patient>  <patient> <name> <first> Maggie </first> <middle> Dee </middle> <last> Magpie </last> </name>. . . </patient> Chapter 7 © 2001 by Addison Wesley Longman, Inc. 54

10. 3 XML Document Structure - An XML document often uses two auxiliary files: - A Data Type Definition (rules about structure) - A style or presentation specification - An XML document has a single root element - An XML document consists of one or more entities - Entities range from a single special character to a book chapter - An XML document has one document entity - All other entities are referenced in the document entity - Reasons for entity structure: 1. Large documents are easier to manage 2. Repeated entities need not be literally repeated 3. Binary entities can only be referenced in the document entities (XML is all text!) Chapter 7 © 2001 by Addison Wesley Longman, Inc. 55

10. 3 XML Document Structure (continued) - When the XML parser encounters a reference to a non-binary entity, the entity is merged in - Entity names: - Do not have a length limitation - Must begin with a letter, a dash, or a colon - Can include letters, digits, periods, dashes, underscores, or colons - A reference to an entity has the form: &entity_name; - One common use of entities is for special characters that may be used for markup delimiters - These are predefined: < > & " ' < > & " ' - The user can only define entities in a DTD Chapter 7 © 2001 by Addison Wesley Longman, Inc. 56

10. 4 Data Type Definitions - A DTD is a set of structural rules called declarations - These rules specify how and where a set of elements can appear in a document - Not all XML documents have or need a DTD - The DTD for a document can be internal or external - All of the declarations of a DTD are enclosed in the block of a DOCTYPE markup declaration - DTD declarations have the form: <!keyword … > - There are four possible declaration keywords: ELEMENT, ATTLIST, ENTITY, and NOTATION Chapter 7 © 2001 by Addison Wesley Longman, Inc. 57

10. 4 Data Type Definitions (continued) - Declaring Elements - Element declarations are similar to BNF - An element declaration specifies the element’s structure - If the element is a leaf node of the document tree, its structure is in terms of characters - If it is an internal node, its structure is a list of children elements (either leaf or internal nodes) - General form: <!ELEMENT element_name (list of child names)> e. g. , <!ELEMENT memo (from, to, date, re, body)> memo from Chapter 7 to date re body © 2001 by Addison Wesley Longman, Inc. 58

10. 4 Data Type Definitions (continued) - Declaring Elements (continued) - Child elements can have modifiers, +, *, ? e. g. , <!ELEMENT person (parent+, age, spouse? , sibling*)> - Leaf nodes specify data types, most often PCDATA, which is an acronym for parsable character data - Data type could also be EMPTY (no content) and ANY (can have any content) - Example of a leaf declaration: <!ELEMENT name (#PCDATA)> - Declaring Attributes - General form: <!ATTLIST el_name at_type [default]> Chapter 7 © 2001 by Addison Wesley Longman, Inc. 59

10. 4 Data Type Definitions (continued) - Declaring Attributes (continued) - Attribute types: there are many possible, but we will consider only CDATA - Default values: a value #FIXED value (every element will have this value), #REQUIRED (every instance of the element must have a value specified), or #IMPLIED (no default value and need not specify a value) - e. g. , <!ATTLIST car car doors CDATA "4"> engine_type CDATA #REQUIRED> price CDATA #IMPLIED> make CDATA #FIXED "Ford"> <car doors = "2" engine_type = "V 8">. . . </car> Chapter 7 © 2001 by Addison Wesley Longman, Inc. 60

10. 4 Data Type Definitions (continued) - Declaring Entities - Two kinds: - A general entity can be referenced anywhere in the content of an XML document - A parameter entity can be referenced only in a markup declaration - If several predefined entities must appear near each other in a document, it is better to avoid using entity references - Character data section <![CDATA[ content ]]> e. g. , instead of Start > HERE < use <![CDATA[Start >>>> HERE <<<<]]> - If the CDATA content has an entity reference, it is taken literally Chapter 7 © 2001 by Addison Wesley Longman, Inc. 61

10. 4 Data Type Definitions (continued) - Declaring Entities (continued) - General form of declaration: <!ENTITY [%] entity_name "entity_value"> e. g. , <!ENTITY jfk "John Fitzgerald Kennedy"> - A reference: &jfk; - If the entity value is longer than a line, define it in a separate file (an external text entity) <!ENTITY entity_name SYSTEM "file_location"> --> SHOW planes. dtd - XML Parsers - Always check for well formedness - Some check for validity, relative to a given DTD - Called validating XML parsers - You can download a validating XML parser from: http: //xml. apache. org/xerces-j/index. html Chapter 7 © 2001 by Addison Wesley Longman, Inc. 62

10. 4 Data Type Definitions (continued) - Internal DTDs <!DOCTYPE root_name [ … ]> - External DTDs <!DOCTYPE XML_doc_root_name SYSTEM “DTD_file_name” > --> SHOW planes. xml - Problems with DTDs: 1. Syntax is different from XML - cannot be parsed with an XML parser 2. Do not allow specification of a particular kind of data - XML Schema are a solution to these problems - We don’t cover them because the popular browsers don’t support them, yet Chapter 7 © 2001 by Addison Wesley Longman, Inc. 63

10. 5 Namespaces - A markup vocabulary is the collection of all of the element types and attribute names of a markup language (a tag set) - An XML document may define its own tag set and also use that of another tag set - CONFLICTS! - An XML namespace is a collection of names used in XML documents as element types and attribute names - The name of an XML namespace has the form of a URI - A namespace declaration has the form: <element_name xmlns[: prefix] = URI> - The prefix is a short name for the namespace, which is attached to names from the namespace in the XML document <gmcars xmlns: gm = "http: //www. gm. com/names"> - In the document, you can use <gm: pontiac> - Purposes of the prefix: 1. Shorthand 2. URI includes characters that are illegal in XML Chapter 7 © 2001 by Addison Wesley Longman, Inc. 64

10. 5 Namespaces (continued) - Can declare two namespaces on one element <gmcars xmlns: gm = "http: //www. gm. com/names" xmlns: html = "http: //www. w 3. org/TR/REC-html 40"> - The gmcars element can now use gm names and html names - One namespace can be made the default by leaving the prefix out of the declaration 6. Displaying Raw XML Documents - There is no presentation information in an XML document - An XML browser should have a default style sheet for an XML document that does not specify one - You get a stylized listing of the XML --> SHOW Figure 10. 2 --> SHOW Figure 10. 3 Chapter 7 © 2001 by Addison Wesley Longman, Inc. 65

10. 7 Displaying XML Documents with CSS - A CSS style sheet for an XML document is just a list of its tags and associated styles - The connection of an XML document and its style sheet is made through an xml-stylesheet processing instruction <? xml-stylesheet type = "text/css" href = "mydoc. css"? > --> SHOW planes. css and Figure 10. 4 10. 8 XML Transformations and Style Sheets - XSL began as a standard for presentations of XML documents - Split into two parts: - XSLT - Transformations - XSL-FO - Formatting objects - XSLT uses style sheets to specify transformations Chapter 7 © 2001 by Addison Wesley Longman, Inc. 66

10. 8 XML Transformations and Style Sheets (continued) - An XSLT processor merges an XML document into an XSLT style sheet - This merging is a template-driven process - An XSLT style sheet can specify page layout, page orientation, writing direction, margins, page numbering, etc. - The processing instruction we used for connecting a CSS style sheet to an XML document is used to connect an XSLT style sheet to an XML document <? xml: stylesheet type = "text/xsl" href = "XSL style sheet"? > - An example: <? xml version = "1. 0"? >  <? xml: stylesheet type = "text/xsl" href = "xslplane. xsl" ? > <plane> <year> 1977 </year> <make> Cessna </make> <model> Skyhawk </model> <color> Light blue and white </color> </plane> Chapter 7 © 2001 by Addison Wesley Longman, Inc. 67

10. 8 XML Transformations and Style Sheets (continued) - An XSLT style sheet is an XML document with a single element, stylesheet, which defines namespaces <xsl: stylesheet xmlns: xsl = "http: //www. w 3. org/1999/XSL/Format"> - For IE 5, you must use the earlier namespace, http: //www. w 3. org/TR/WD-xsl - If a style sheet matches the root element of the XML document, it is matched with the template: <xsl: template match = "/"> - A template can match any element, just by naming it (in place of /) - XSLT elements include two different kinds of elements, those with content and those for which the content will be merged from the XML doc - Elements with content often represent HTML elements Chapter 7 © 2001 by Addison Wesley Longman, Inc. 68

10. 8 XML Transformations and Style Sheets (continued) <span style = "font-size: 14"> Happy Easter! </span> - XSLT elements that represent HTML elements are simply copied to the merged document - The XSLT value-of element - Has no content - Uses a select attribute to specify part of the XML data to be merged into the XSLT document <xsl: value-of select = ”CAR/ENGINE" /> - The value of select can be any branch of the document tree --> SHOW xslplane. xsl and Figure 10. 5 - The XSLT for-each element - Used when an XML document has a sequence of the same elements --> SHOW xslplanes. xml --> SHOW xslplanes. xsl & Figure 10. 6 Chapter 7 © 2001 by Addison Wesley Longman, Inc. 69

11. 1 Web Server Operation - Client-server systems - When two computers are connected, either could be the client - The client initiates the communication, which the server accepts - Generally, clients are human consumers of information, while servers are machine suppliers - Client/server systems have an efficient division of work - All communications between Web clients and servers use HTTP - When a Web server starts, it tell its OS it is ready to accept communications through a specific port, usually 8080 - All current Web servers are descendents of the first two (CERN and NCSA) - Most servers are Apache running under UNIX Chapter 7 © 2001 by Addison Wesley Longman, Inc. 71

11. 2 General Server Characteristics - Web servers have two separate directories - The document root is the root directory of all servable documents (well, not really all) e. g. Suppose the site name is www. bloomers. com and the document root is named topdocs, and it is stored in the /admin/web directory So, /admin/web/topdocs is the document directory address If a request URL is http: //www. bloomers. com/bulbs/tulips. html the server will search for the file named /admin/web/topdocs/bulbs/tulips. html - The server can have virtual document trees - Sometimes a different disk, possibly on a different machine, is used after the original disk is filled Chapter 7 © 2001 by Addison Wesley Longman, Inc. 72

11. 2 General Server Characteristics (continued) - The server root is the root directory for all of the code that implements the server - The server root usually has four files - One is the code for the server itself - Three others are subdirectories - conf - for configuration information - logs - to store what has happened - cgi-bin - for executable scripts - Contemporary servers provide many services: - Virtual hosts - multiple sites on the same system - Proxy servers - to serve documents from the document roots of other sites - Besides HTTP, support for FTP, Gopher, News, email - Support for database access Chapter 7 © 2001 by Addison Wesley Longman, Inc. 73

11. 3 Apache under UNIX - Apache is available for other platforms, but it is most commonly used under UNIX - Apache is now a large and complex system - The configuration file is named httpd. conf - The directives in the configuration file control the operation of the server - Configuration file format: - Comments begin with a # - Blank lines are ignored - Non-blank lines that do not begin with # must begin with a directive name, which may take parameters, separated by white space - When Apache begins, it reads the configuration files and sets its parameters according to what it reads Chapter 7 © 2001 by Addison Wesley Longman, Inc. 74

11. 3 Apache under UNIX (continued) - Changes to configuration files affect Apache only if it is forced to reset - Use the following UNIX commands to force Apache to reset: cd /usr/local/etc/httpd/logs kill -HUP `cat httpd. pid` - This creates a hangup signal - It works because Apache write its process id (pid) into httpd. pid when it starts - Directives - Server. Name - default is what is returned by the hostname command, but it may be only the first part Server. Name Chapter 7 www. bloomers. com © 2001 by Addison Wesley Longman, Inc. 75

11. 3 Apache under UNIX (continued) - Server. Root - to set the server root address - Default is /usr/local/etc/httpd - If it is stored elsewhere, tell Apache with: Server. Root /usr/local/httpd - Server. Admin - email address of the site admin Server. Admin webguy@www. bloomers. com - Document. Root - set the document root address - Default is /usr/local/etc/httpd/htdocs - If it is elsewhere, tell Apache with: Document. Root Chapter 7 /local/webdocs © 2001 by Addison Wesley Longman, Inc. 76

11. 3 Apache under UNIX (continued) - Alias - to specify a virtual document tree - Takes two parameters, virtual path for URLs and the actual path - Example: Alias /bushes /usr/local/plants/bushes - Now, http: //www. bloomers. com/bushes/roses. html will be mapped to /usr/local/plants/bushes/roses. html - Script. Alias - to create a secure place for CGI scripts - Creates a virtual directory Script. Alias Chapter 7 /cgi-bin/ /usr/local/etc/httpd/cgi-bin/ © 2001 by Addison Wesley Longman, Inc. 77

11. 3 Apache under UNIX (continued) - Redirect - to redirect requests to another system e. g. , To move the bushes directory to www. bloomers 2. com Redirect /bushes http: //www. bloomers 2. com/local/web/bushes - Directory. Index - URL-specified directories - When a request includes a URL that ends with a slash, Apache searches for a document to return, called the welcome page - Default welcome page is index. html - If there is no index. html, Apache may try to build a directory listing for the home directory (unless automatic directory listings are turned off) - To avoid this, provide more than one welcome page names Directory. Index Chapter 7 index. html contents. html © 2001 by Addison Wesley Longman, Inc. 78

11. 3 Apache under UNIX (continued) - User. Dir - to specify whether local users can or cannot add or delete documents; default is: User. Dir public_html - Now, if user bob stores stuff. html in his public_html directory, the URL http: //site-name/~bob/stuff. html will work - To make a subdirectory of public_html available, include it in the parameter User. Dir public_html/special_stuff - To disallow additions and deletions: User. Dir disabled - Logs - Access logs record all accesses (time, date, HTTP command, URL, status, etc. ) - Error logs have the form: [date/time] The error message Chapter 7 © 2001 by Addison Wesley Longman, Inc. 79

11. 4 Overview of Servlets - A servlet is a compiled Java class - Servlets are executed on the server system under the control of the Web server - Servlets are managed by the servlet container, or servlet engine - Servlets are called through HTML - Servlets receive requests and return responses, both of which are supported by the HTTP protocol - When the Web server receives a request that is for a servlet, the request is passed to the servlet container - The container makes sure the servlet is loaded and calls it - The servlet call has two parameter objects, one with the request and one for the response - When the servlet is finished, the container reinitializes itself and returns control to the Web server Chapter 7 © 2001 by Addison Wesley Longman, Inc. 80

11. 4 Overview of Servlets (continued) - Servlets are used 1) as alternatives to CGI, and 2) as alternatives to Apache modules - Servlet Advantages: - Can be faster than CGI, because they are run in the server process - Have direct access to Java APIs - Because they continue to run (unlike CGI programs), they can save state information - Have the usual benefits of being written in Java (platform independence, ease of programming) 11. 5 Servlet Details - All servlets are classes that either implement the Servlet interface or extend a class that implements the Servlet interface - The Servlet interface provides the interfaces for the methods that manage servlets and their interactions with clients Chapter 7 © 2001 by Addison Wesley Longman, Inc. 81

11. 5 Servlet Details (continued) - The Servlet interface declares three methods that are called by the servlet container (the life-cycle methods) - initializes the servlet and prepares it to respond to client requests - service - controls how the servlet responds to requests - destroy - takes the servlet out of service - The Servlet interface declares two methods that are used by the servlet: - get. Servlet. Config - to get initialization and startup parameters for itself - get. Servlet. Info - to allow the servlet to return info about itself (author, version #, etc. ) to clients - Most user-written servlet classes are extensions to Http. Servlet (which is an extension of Generic. Servlet, which implements the Servlet Interface) Chapter 7 © 2001 by Addison Wesley Longman, Inc. 82

11. 5 Servlet Details (continued) - Two other necessary interfaces: - Servlet. Response – to encapsulate the communications, client to server - Servlet. Request – to encapsulate the communications, server to client - Provides servlet access to Servlet. Output. Stream - Http. Servlet – an abstract class - Extends Generic. Servlet - Implements java. io. Serializable - Every subclass of Http. Servlet MUST override at least one of the methods of Http. Servlet do. Get* do. Post* do. Put* do. Delete* init destroy get. Servlet. Info * Called by the server Chapter 7 © 2001 by Addison Wesley Longman, Inc. 83

11. 5 Servlet Details (continued) - The protocol of do. Get is: protected void do. Get(Http. Servlet. Request request, Http. Servlet. Response response) throws Servlet. Exception, java. io. IOException - Servlet. Exception is thrown if the GET request could not be handled - The protocol of do. Post is the similar - Servlet output – HTML 1. Use the set. Content. Type method of the response object to set the content type to text/html response. set. Content. Type("text/html"); 2. Create a Print. Writer object with the get. Writer method of the response object Print. Writer servlet. Out = response. get. Writer(); - Example – Respond to a GET request with no data àShow ch 11_1. html and Greeting. java Chapter 7 © 2001 by Addison Wesley Longman, Inc. 84

11. 6 A Survey Example --> Show ch 11_2. html (consumer electronics survey form) and Figure 11. 3 - The servlet: - To accumulate voting totals, it must write a file on the server - The file will be read and written as an object (the array of vote totals) using Object. Input. Stream - An object of this class is created with its constructor, passing an object of class File. Input. Stream, whose constructor is called with the file variable name as a parameter Object. Input. Stream indat = new Object. Input. Stream( new File. Input. Stream(File_variable_name)); - On input, the contents of the file will be cast to integer array - For output, the file is written as a single object Chapter 7 © 2001 by Addison Wesley Longman, Inc. 85

11. 6 A Survey Example (continued) - The servlet must access the form data from the client - This is done with the get. Parameter method of the request object, passing a literal string with the name of the form element e. g. , if the form has an element named zip = request. get. Parameter("zip"); - If an element has no value and its value is requested by get. Parameter, the returned value is null - If a form value is not a string, the returned string must be parsed to get the value - e. g. , suppose the value is an integer literal - A string that contains an integer literal can be converted to an integer with the parse. Int method of the wrapper class for int, Integer price = Integer. parse. Int( request. get. Parameter("price")); Chapter 7 © 2001 by Addison Wesley Longman, Inc. 86

11. 6 A Survey Example (continued) - The file structure is an array of 14 integers, 7 votes for females and 7 votes for males - Servlet actions: If the votes data array exists read the votes array from the data file else create the votes array Get the gender form value Get the form value for the new vote and convert it to an integer Add the vote to the votes array Write the votes array to the votes file Produce the return HTML document that shows the current results of the survey - Every voter will get the current totals --> Show the servlet, Survey. java --> Show the results of running Survey Chapter 7 © 2001 by Addison Wesley Longman, Inc. 87

11. 7 Storing Information about Clients - A session is the collection of all of the requests made by a particular browser from the time the browser is started until the user exits the browser - The HTTP protocol is stateless - But, there are several reasons why it is useful for the server to relate a request to a session - Shopping carts for many different simultaneous customers - Customer profiling for advertising - Customized interfaces for specific clients - Approaches to storing client information: - Store it on the server – too much to store! - Store it on the client machine - this works - Cookies - A cookie is an object sent by the server to the client Chapter 7 © 2001 by Addison Wesley Longman, Inc. 88

11. 7 Storing Information about Clients (continued) - Every HTTP communication between the browser and the server includes information in its header about the message - At the time a cookie is created, it is given a lifetime - Every time the browser sends a request to the server that created the cookie, while the cookie is still alive, the cookie is included - A browser can be set to reject all cookies - A cookie object has data members and methods - Data members to store lifetime, name, and a value (the cookies’ value) - Methods: set. Comment, set. Max. Age, set. Value, get. Max. Age, get. Name, and get. Value - Cookies are created with the Cookie constructor Cookie new. Cookie = new Cookie(gender, vote); Chapter 7 © 2001 by Addison Wesley Longman, Inc. 89

11. 7 Storing Information about Clients (continued) - By default, a cookie’s lifetime is the current session - If you want it to be longer, use set. Max. Age - A cookie is attached to the response with add. Cookie - Order in which the response must be built: 1. Add cookies 2. Set content type 3. Get response output stream 4. Place info in the response - The browser does nothing with cookies, other than storing them and passing them back - A servlet gets a cookie from the browser with the get. Cookies method Cookie the Cookies []; … the. Cookies = request. get. Cookies(); - A Vote Counting Example Show ch 11_3. html Chapter 7 © 2001 by Addison Wesley Longman, Inc. 90

11. 7 Storing Information about Clients (continued) - Vote counting servlet activities: - See if a vote was cast - Make sure the voter hasn’t voted before - Tally real votes and give the client the totals - Store votes in a file àShow the Vote. Counter algorithm -> Show Vote. Counter output (Figure 11. 6) - Session Tracking - An alternative to cookies - Use the Http. Session object, which can store a list of names and values Chapter 7 © 2001 by Addison Wesley Longman, Inc. 91

11. 7 Storing Information about Clients (continued) - Create a Session object - Put value in the session object with put. Value my. Session. put. Value("i. Voted", "true"); - A session can be killed with the invalidate method - A value can be removed with remove. Value - A value can be gotten with get. Value(name) - All names of values can be gotten with get. Value. Names Chapter 7 © 2001 by Addison Wesley Longman, Inc. 92

12. 1 Relational Databases - A database is a collection of data organized to allow relatively easy access for retrievals, additions, and deletions - A relational database is a collection of tables of data, each of which has one special column that stores the primary keys of the table - An Example Relational Database: - A relational database for used Corvettes that are for sale - Could just put all data in a single table, whose primary key would be a simple sequence number - The table could have information about various equipment the cars could have - However, it is better to put the equipment in a different table and use a cross-reference table to relate cars to equipment - Use a separate table for state names, with only references in the main table Chapter 7 © 2001 by Addison Wesley Longman, Inc. 94

12. 1 Relational Databases (continued) - Logical model Corvettes States Corvettes_ Equipment - Implementation Vette_id 1 2 3 4 5 6 7 8 9 10 Body_style coupe hatchback convertible hatchback hardtop coupe convertible hardtop hatchback Miles 18. 0 58. 0 13. 5 19. 0 25. 0 15. 0 55. 0 17. 0 50. 0 Year 1997 1996 2001 1995 1991 2000 1979 1999 2000 1995 State 4 7 1 2 5 2 10 5 5 7 Figure 12. 2 The Corvettes table Chapter 7 © 2001 by Addison Wesley Longman, Inc. 95

12. 1 Relational Databases (continued) State_id 1 2 3 4 5 6 7 8 9 10 State Alabama Alaska Arizona Arkansas California Colorado Connecticut Delaware Florida Georgia Figure 12. 3 The States table Equip_id 1 2 3 4 5 6 Equip Automatic 4 -speed 5 -speed 6 -speed CD leather Figure 12. 4 The Equipment table Chapter 7 © 2001 by Addison Wesley Longman, Inc. 96

12. 1 Relational Databases (continued) Vette_id 1 1 1 2 2 2 3 3 4 4 5 5 6 7 7 8 8 8 9 9 9 10 10 Equip 1 5 6 1 6 2 4 6 4 5 6 1 5 Figure 12. 5 The Corvettes_Equipment cross-reference table Chapter 7 © 2001 by Addison Wesley Longman, Inc. 97

12. 2 Intro to SQL - A standard language to create, query, and modify databases - Supported by all major database vendors - More similar to structured English than a programming language - We cover only five basic commands: CREATE TABLE, SELECT, INSERT, UPDATE, and DELETE - SQL reserved words are case insensitive - The CREATE TABLE command: CREATE TABLE table_name ( column_name 1 data_type constraints, … column_namen data_type constraints) - There are many different data types (INTEGER, FLOAT, CHAR(length), …) Chapter 7 © 2001 by Addison Wesley Longman, Inc. 98

12. 2 Intro to SQL (continued) - There are several constraints possible e. g. , NOT NULL, PRIMARY KEY CREATE TABLE States ( State_id INTEGER PRIMARY KEY State CHAR(20)) NOT NULL, - The SELECT Command - Used to specify queries - Three clauses: SELECT, FROM, and WHERE - General form: SELECT column names FROM table names WHERE condition SELECT Body_style FROM Corvettes WHERE Year > 1994 - An asterisk for the column names means all columns Chapter 7 © 2001 by Addison Wesley Longman, Inc. 99

12. 2 Intro to SQL (continued) - The INSERT Command - General form: INSERT INTO table_name (col_name 1, … col_namen) VALUES (value 1, …, valuen) - The correspondence between column names and values is positional INSERT INTO Corvettes(Vette_id, Body_style, Miles, Year, State) VALUES (37, 'convertible', 25. 5, 1986, 17) - The UPDATE Command - To change one or more values of a row in a table - General form: Chapter 7 © 2001 by Addison Wesley Longman, Inc. 100

12. 2 Intro to SQL (continued) UPDATE table_name SET col_name 1 = value 1, … col_namen = valuen WHERE col_name = value - The WHERE clause is the primary key of the row to be updated - Example: UPDATE Corvettes SET Year = 1996 WHERE Vette_id = 17 - The DELETE Command - Example: DELETE FROM Corvettes WHERE Vette_id = 27 - The WHERE clause could specify more than one row of the table Chapter 7 © 2001 by Addison Wesley Longman, Inc. 101

12. 2 Intro to SQL (continued) - Joins - If you want all cars that have CD players, you need information from two tables, Corvettes and Equipment - SELECT can build a temporary table with info from two tables, from which the desired results can be obtained - this is called a join of the two tables - A SELECT that does a join operation specifies two tables in its FROM clause and also has a compound WHERE clause - For our example, we must have three WHERE conditions 1. Vette_ids from Corvettes and Corvettes_Equipment must match 2. Equip from Corvette_Equipment must match the Equip_id from Equipment 3. The Equip from Equipment must be CD Chapter 7 © 2001 by Addison Wesley Longman, Inc. 102

12. 2 Intro to SQL (continued) SELECT Corvettes. Vette_id, Corvettes. Body_style, Corvettes. Miles, Corvettes. Year, Corvettes. State, Equipment. Equip FROM Corvettes, Equipment WHERE Corvettes. Vette_id = Corvettes_Equipment. Vette_id AND Corvettes_Equipment. Equip = Equipment. Equip_id AND Equipment. Equip = 'CD' This query produces VETTE_ID BODY_STYLE MILES YEAR STATE EQUIP. 1 2 8 9 10 18. 0 58. 0 17. 0 50. 0 4 7 5 5 7 coupe hatchback convertible hardtop hatchback Chapter 7 1996 1999 2000 1995 © 2001 by Addison Wesley Longman, Inc. CD CD CD 103

12. 3 Architectures for Database Access - Client-Server Database Architectures - Usual database client tasks: - Provide a way for users to submit queries - Run applications that use the results of queries - Display results of queries - Database server task: - Implement a data manipulation language, which can directly access and update the database - A two-tier system has clients that are connected directly to the server - Potential problems with a two-tier system: - Because the relative power of clients has grown considerably, we could shift processing to the client, but then maintaining data integrity is difficult Chapter 7 © 2001 by Addison Wesley Longman, Inc. 104

12. 3 Architectures for Database Access (continued) - One solution to the problems of two-tier systems is to add a component in the middle - create a three-tier system - For Web-based database access, the middle tier can run applications (client just gets results) Client Middle tier JDBC Database server - Database Access with Embedded SQL - SQL commands are embedded in programs written in a host programming language, whose compiler is extended to accept some form of SQL commands - Advantage: - One package has computational support of the programming language, as well as database access with SQL Chapter 7 © 2001 by Addison Wesley Longman, Inc. 105

12. 3 Architectures for Database Access (continued) - Disadvantage (of embedded SQL): - Portability among database systems - Microsoft Access Architecture - A tool to access any common database structure - Use either the Jet database engine, or go through the Other Database Connectivity (ODBC) standard - ODBC is an API for a set of objects and methods that are an interface to different databases - Database vendors provide ODBC drivers for their products – the drivers implement the ODBC objects and methods - An application can include SQL statements that work for any database for which a driver is available Chapter 7 © 2001 by Addison Wesley Longman, Inc. 106

12. 3 Architectures for Database Access (continued) - The Java JDBC Architecture: - Related to both embedded languages and to ODBC - JDBC is a standard protocol that can be implemented as a driver for any database system - JDBC allows SQL to be embedded in Java applications, applets, and servlets - JDBC has the advantage of portability over embedded SQL - A JDBC application will work with any database system for which there is a JDBC driver 12. 4 Approaches to Using JDBC - SQL commands are issued against a database system through JDBC methods - JDBC interfaces are in the java. sql package Chapter 7 © 2001 by Addison Wesley Longman, Inc. 107

12. 4 Approaches to Using JDBC (continued) - The classes that implement the JDBC interfaces serve as the client - Configurations for using JDBC: 1. The JDBC-ODBC bridge converts JDBC database interactions to ODBC database interactions - Not meant for commercial applications 2. If the target database has a JDBC driver, a two-tier configuration can be used - The application talks to the JDBC driver, which talks to the database server - Disadvantage: Every database needs its own driver, and every driver that the client may use must be installed on the client machine 3. Use a third-tier computer to run middleware - Client runs as a client of the middleware server, which talks to the database server Chapter 7 © 2001 by Addison Wesley Longman, Inc. 108

12. 4 Approaches to Using JDBC (continued) 3. Use a third-tier computer to run middleware (continued) - Advantages: a. The middleware supports all databases, so even though vendors may implement JDBC interfaces differently (extensions), the application on the client is database independent b. The client never needs to connect directly to the database server, which allows applets to be used for JDBC database access 12. 5 Java JDBC Applications - We use the Point. Base system, from www. pointbase. com - Connecting the application to the driver - The get. Connection method of Driver. Manager, which select the correct driver from those that are registered Chapter 7 © 2001 by Addison Wesley Longman, Inc. 109

12. 5 Java JDBC Applications (continued) - The general form of a reference to a database for the connection operation is: jdbc: subprotocol_name: more_info - The “subprotocol” specifies the driver - For the JDBC-ODBC bridge, it is odbc - For the Point. Base, it is pointbase - The “more info” part depends on the specific database being used - If the database is local, it is just the name of the database - Otherwise, it is the URL of the database - Two ways to register a database driver: 1. The general way is to have the system property jdbc. drivers maintain a list of registered drivers - Add one with jdbc. drivers = com. pointbase. jdbc. jbdc. Driver; Chapter 7 © 2001 by Addison Wesley Longman, Inc. 110

12. 5 Java JDBC Applications (continued) 2. Manual registration, using the for. Name method of the Class class, passing the name of the driver Class. for. Name( "com. pointbase. jdbc. Driver"); - The actual connection is made by creating a Connection object with the get. Connection method of the Driver. Manager class Driver. Manager. get. Connection(database_address, database_user_id, password) - If the application owner owns the database, public can be used for both the user id and the password my. Con = Driver. Manager. get. Connection( "jdbc: pointbase: vette", "public"); - SQL commands through JDBC - First, you need a Statement object Statement my. Stmt = my. Con. create. Statement(); Chapter 7 © 2001 by Addison Wesley Longman, Inc. 111

12. 5 Java JDBC Applications (continued) - SQL commands are String objects final String sql_com = "UPDATE Corvettes " + "Year = 1991 WHERE Vette_id = 7"); - Categories of SQL commands - Action - INSERT, UPDATE, DELETE, CREATE TABLE, and DROP TABLE - Query - SELECT - The action commands are executed with the execute. Update method of Statement my. Stmt. execute. Update(sql_com); - Returns the number of affected rows - A SELECT is executed by sending it as the actual parameter to the execute. Query method of Statement - The execute. Query method returns an object of class Result. Set - Get rows from Result. Set with next iterator Chapter 7 © 2001 by Addison Wesley Longman, Inc. 112

12. 5 Java JDBC Applications (continued) Result. Set result; final String sql_com = "SELECT * FROM Corvettes WHERE Year <= 1990" result = my. Stmt. execute. Query(sql_com); while(result. next()) { // access and process the current element } - Information is extracted from the Result. Set object with an access method, for which there is one for each data type e. g. , If an extracted row is 3, "convertible", 13. 5, 2001, 1 String style; style = result. get. String("Body_style"); or style = result. get. String(2); Chapter 7 © 2001 by Addison Wesley Longman, Inc. 113

12. 5 Java JDBC Applications (continued) 1993 -2001 Corvettes For Sale Vette_id Body_style Miles Year State 1 2 3 6 8 9 10 coupe hatchback convertible hardtop hatchback 18. 0 58. 0 13. 5 15. 0 17. 0 50. 0 1997 1996 2001 2000 1999 2000 1995 4 7 1 2 5 5 7 - Metadata - to get table and column names from a database - Two kinds of metadata: 1. Metadata that describes the database (tables and columns) 2. Metadata that describes a Result. Set object - A Connection method, get. Meta. Data, creates an object of class Database. Meta. Data dbmd = my. Con. get. Meta. Data(); Chapter 7 © 2001 by Addison Wesley Longman, Inc. 114

12. 5 Java JDBC Applications (continued) - The get. Tables method of Database. Meta. Data takes four parameters, only one of which is necessary (the string, "TABLE") String tbl[] = {"TABLE"}; Database. Meta. Data dbmd = my. Con. get. Meta. Data(); result = dbmd. get. Tables( null, tbl); System. out. println( "The tables in the database are: nn"); while (result. next()) { System. out. println(result. get. String(3)); } - Output from this: The tables in this database are: CORVETTES_EQUIPMENT STATES - Metadata about query results has a different structure than general database metadata - Result. Set. Meta. Data object Chapter 7 © 2001 by Addison Wesley Longman, Inc. 115

12. 5 Java JDBC Applications (continued) Result. Set. Meta. Data result. Md = result. get. Meta. Data(); - We can get the number of columns, their names, types, and sizes from the result. Md object, using its methods - get. Column. Count returns the number of columns - get. Column. Lable(i) returns the column names // Create an object for the metadata Result. Set. Meta. Data result. Md = result. get. Meta. Data(); // Loop to fetch and display the column names for (int i = 1; i" <= result. Md. get. Column. Count(); i++) { String column. Name = result. Md. get. Column. Label(i); System. out. print(column. Name + "t"); } System. out. println("n"); Output: Vette_id Body_style Chapter 7 Miles Year State © 2001 by Addison Wesley Longman, Inc. 116