Faculty of Information Technology 3124232549 Advanced Internet Programming

Faculty of Information Technology 31242/32549 Advanced Internet Programming Java Server Pages (JSP) V 5 © Copyright UTS Faculty of Information Technology 2008 – JSP 1

Topics Faculty of Information Technology • JSP architecture • JSP syntax • • • objects directives scripting elements standard actions expression language JSP and Java. Beans Tag libraries JSP deployment Model 1 and Model 2 JSP architectures © Copyright UTS Faculty of Information Technology 2008 – JSP 3

J 2 EE & JSP © Copyright UTS Faculty of Information Technology 2008 – JSP Faculty of Information Technology 4

JSP architecture HTTP Faculty of Information Technology Web Server JVM Compile + Execute JSP JDBC HTML + JSP file © Copyright UTS Faculty of Information Technology 2008 – JSP 5

JSP architecture Faculty of Information Technology • Advantages: – all the advantages of servlets • efficient, robust, secure, access to Java libraries – uses "page-centric" coding • HTML that contains embedded code • Disadvantages: – minor performance issue first time a JSP is loaded • has to be compiled on-the-fly • only affects very first request to a JSP • after first request, compiled code is cached for faster execution © Copyright UTS Faculty of Information Technology 2008 – JSP 6

Topics Faculty of Information Technology • JSP architecture • JSP syntax • • • objects directives scripting elements standard actions execution JSP and Java. Beans Tag libraries JSP deployment Model 1 and Model 2 JSP architectures © Copyright UTS Faculty of Information Technology 2008 – JSP 7

Not JSP syntax Faculty of Information Technology • JSP is an embedded language like ASP, PHP <P>This is my ASP Hello World program. So <% First. Name = Request. Form("FIRSTNAME") Response. Write "hi " & First. Name & vb. Cr. Lf %> </P> <P>This is my PHP Hello World program. So <? php $firstname = $HTTP_POST_VARS['FIRSTNAME']; echo "hi ". $firstname. "n"; ? > </P> © Copyright UTS Faculty of Information Technology 2008 – JSP 8

JSP syntax Faculty of Information Technology <P>This is my JSP Hello World program. So <% String first. Name = request. get. Parameter("FIRSTNAME"); out. println("hi " + first. Name); %> </P> • Java code is enclosed by <%. . . %> • Outside those tags, it is normal HTML • e. g. : http: //127. 0. 0. 1: 7001/My. App/hw. jsp? FIRSTNAME=Wayne This is my JSP Hello World program. So hi Wayne © Copyright UTS Faculty of Information Technology 2008 – JSP 9

JSP Objects Faculty of Information Technology • You can access Java objects from within JSP’s • Main types of objects – Implicit objects (provided by the container) – Application-specific objects • Local, instance & class variables • Java. Beans • EJBs • Web container provides a context to provide scope of object © Copyright UTS Faculty of Information Technology 2008 – JSP 10

JSP implicit objects © Copyright UTS Faculty of Information Technology 2008 – JSP Faculty of Information Technology 11

JSP implicit objects © Copyright UTS Faculty of Information Technology 2008 – JSP Faculty of Information Technology 12

Kinds of embedded JSP code Faculty of Information Technology 1. Directives 2. Scripting Elements • declarations • scriptlets • expressions 3. Actions • • include forward use. Bean get/set. Property 4. expression language (EL) © Copyright UTS Faculty of Information Technology 2008 – JSP 13

JSP Directives Faculty of Information Technology <%@ directivename attribute=“value” %> • Note: <%@directive %> tags • Directives are instructions to the JSP compiler – e. g. "include", includes at compile-time, NOT run-time • Main directives – page – include – taglibs (later) © Copyright UTS Faculty of Information Technology 2008 – JSP 14

JSP Directives Faculty of Information Technology • page Directive <%@ page import=“java. util. *, java. io. *” %> • include Directive [not at runtime!] <%@ include file=“copyright. html” %> <%@ page language="java" import="java. util. *" info="My wonderful JSP example" %> <%@ include file="other_file. html"> © Copyright UTS Faculty of Information Technology 2008 – JSP 15

Scripting Elements: Declarations Faculty of Information Technology ! <% Java variable and method declarations %> • Declarations executed when page is initialised – used to define class-wide variables and methods – declarations must produce no output <%! int i = 0; %> <%! int icubed = 0; %> <%! public int cubed (int j) { return (j * j); } %> © Copyright UTS Faculty of Information Technology 2008 – JSP 16

Scripting Elements: Scriptlets Faculty of Information Technology • Basically any Java code can go in a scriptlet • Executed during the request-processing time <% Valid Java code statements %> <% try { i = Integer. parse. Int(request. get. Parameter("mynum")); } catch (Number. Format. Exception nfe) { out. println("Go back and enter a valid number. "); i = 0; } icubed = cubed(i); %> © Copyright UTS Faculty of Information Technology 2008 – JSP 17

Scripting Elements: Expressions <% Faculty of Information Technology = Java expression to be evaluated %> • Expressions are primarily for inserting values of Java variables into HTML code without having to type in full as a scriptlet: – eg: <% out. print(i); %> vs <%= i %> No ; <BODY> <P>You entered the value <%= i %></P> <P>That number cubed is <%= icubed %></P> <P>I can say the same thing with <%= cubed(i) %></P> </BODY> © Copyright UTS Faculty of Information Technology 2008 – JSP 18

Standard Actions Faculty of Information Technology • Well-known tags that affect the runtime behaviour • Generates the Java code that corresponds to the required task - during conversion < jsp: include page=“myjsp. jsp” flush=“true” /> • Other standard actions – – <jsp: use. Bean> <jsp: set. Property> <jsp: get. Property> etc. © Copyright UTS Faculty of Information Technology 2008 – JSP 19

Standard Actions Faculty of Information Technology <jsp: forward page="My. Other. Servlet" /> <jsp: include page="My. Included. Servlet" /> <jsp: param name=“var” value=“something”/> <jsp: use. Bean id="myperson" class="au. edu. uts. it. Person. Bean" scope="session" /> • Uses XML syntax. • Actions are run-time behaviours – "jsp: include" includes a page at run-time – “jsp: param” adds parameters to the included page © Copyright UTS Faculty of Information Technology 2008 – JSP 20

Expression Language Faculty of Information Technology ${object} • Expression Language ( EL) introduced with JSP 2. 4 & J 2 EE 1. 4 • It complements JSP Expressions with simpler syntax. Each ${object } would be same as <%= object %> • Supports: – JSP implicit objects – Java. Beans – simple calculations © Copyright UTS Faculty of Information Technology 2008 – JSP 21

Expression Language Object param Faculty of Information Technology example ${param. newcol } header Description Request params & values HTTP headers cookie Cookie names & value ${cookie[“id”] } init. Param Init params in web. xml ${init. Param. name } ${header. Host } page. Context Use this to get ${page. Context. request, response, remote. Host } session • Use page. Context to get servlet parameter. eg: the example is same as <%= request. get. Remote. Host() %> © Copyright UTS Faculty of Information Technology 2008 – JSP 22

EL operators Faculty of Information Technology • EL also has some common programming operators ie: – – – Math: + - * / div % mod relational: == eq != ne < lt > gt <= le >= ge negative: logical: && and ||or ! not empty: empty (used to test for null or “”) • You can also access Java collections using array syntax eg: – ${myarray [1]} © Copyright UTS Faculty of Information Technology 2008 – JSP 23

JSP Execution • • In practice, JSPs are converted into servlets for execution Conversion involves: 1. 2. 3. 4. • Faculty of Information Technology Container generates Java source code Container invokes Java compiler Class file is executed as with a normal servlet A copy of the class file is kept (cached) to avoid unnecessary recompilation in future See for yourself! – weblogic specific: /home/chw/weblogic/Admin. Server/tmp/_WL_user/_app sdir_labs_war/fr 8116/jsp_servlet/__jspfilename. java) !!! © Copyright UTS Faculty of Information Technology 2008 – JSP 24

Topics Faculty of Information Technology • JSP architecture • JSP syntax • • • objects directives scripting elements standard actions execution JSP and Java. Beans Tag libraries JSP deployment Model 1 and Model 2 JSP architectures © Copyright UTS Faculty of Information Technology 2008 – JSP 25

Page View with Bean Faculty of Information Technology • Refinement Request JSP Response Java utility Bean class © Copyright UTS Faculty of Information Technology 2008 – JSP Business Processing 26

Using Java. Beans Faculty of Information Technology • Java. Beans are a client-side component model – not to be confused with Enterprise Java. Beans • Allows you to encapsulate reusable functionality in a "bean" – a Bean is a normal Java class that follows some rules – called "design patterns" • One basic design pattern is for "properties" – using a getter and/or a setter method – more complex patterns too – see a Java. Beans tutorial © Copyright UTS Faculty of Information Technology 2008 – JSP 27

Using Java. Beans Faculty of Information Technology public class Person { private String yourname; public String get. Name() { return yourname; } public void set. Name (String yourname) { this. yourname = yourname; } Person +name other. Method() public void other. Method () { //. . . } } • Note: method naming convention is important © Copyright UTS Faculty of Information Technology 2008 – JSP 28

Using Java. Beans Faculty of Information Technology • Using beans – <jsp: use. Bean id=“fred” class=“com. myapp. Person” scope=“page” /> • com. myapp. Person fred = new com. myapp. Person() • Setting properties – <jsp: set. Property name=“fred” property=“name” value=“Fred Jones” /> • fred. set. Name(“Fred Jones”) • Getting properties – <jsp: get. Property name=“fred” property=“name” /> • fred. get. Name() © Copyright UTS Faculty of Information Technology 2008 – JSP 29

JSP Scopes Faculty of Information Technology • JSP allows you to save data into a scope • Scopes can be one of: Scope Where saved page Only for the currentpage, destroyed when you leave the page. request kept while request is active. session saved in the current session. *** application saved for the whole application © Copyright UTS Faculty of Information Technology 2008 – JSP 30

EL and Java. Beans Faculty of Information Technology • Expression Language also can access Java. Beans • Instead of: <jsp: use. Bean id="fred" class="com. myapp. Person" /> <jsp: get. Property name=“fred” property=“name” /> • [note: this invokes fred. get. Name() ] • use: ${fred. name} instead © Copyright UTS Faculty of Information Technology 2008 – JSP 31

Topics Faculty of Information Technology • JSP architecture • JSP syntax • • • objects directives scripting elements standard actions execution JSP and Java. Beans Tag libraries JSP deployment Model 1 and Model 2 JSP architectures © Copyright UTS Faculty of Information Technology 2008 – JSP 32

Tag libraries Faculty of Information Technology • Create your own custom tags that can be used in documents – encapsulate reusable functionality – simplify page coding – Apache Jakarta project has large range of taglibs http: //jakarta. apache. org/taglibs – J 2 EE 1. 4 adopted some of these as the Java Standard Tag Library (JSTL) http: //java. sun. com/products/jsp/jstl <%@ taglib uri=“/hello” prefix=“examples” /> <html> <p>Hello message is: <examples: hello /> </html> © Copyright UTS Faculty of Information Technology 2008 – JSP 33

Tag libraries • Faculty of Information Technology Four things needed: 1. in JSP file: <%@ taglib uri=“/hello” prefix=“examples” /> <html> <p>Hello message is: <examples: hello /> </html> 2. Update web. xml with the taglib declaration <web-app> <taglib-uri>/hello</taglib-uri> <taglib-location>/WEB-INF/hellotags. tld</taglib-location> </taglib> </web-app> © Copyright UTS Faculty of Information Technology 2008 – JSP 34

Tag libraries • Faculty of Information Technology Four things needed (continued): 3. Create a Tag Library Descriptor (TLD) file in WEB-INF directory: (hellotags. tld) <taglib> <tag> <name>hello</name> <tagclass>Hello. Tag</tagclass> </taglib> 4. Create Java class that implements the tag handler public class Hello. Tag extends Tag. Support { public int do. Start. Tag() throws Jsp. Tag. Exception {. . . } } © Copyright UTS Faculty of Information Technology 2008 – JSP 35

Topics Faculty of Information Technology • JSP architecture • JSP syntax • • • objects directives scripting elements standard actions execution JSP and Java. Beans Tag libraries JSP deployment Model 1 and Model 2 JSP architectures © Copyright UTS Faculty of Information Technology 2008 – JSP 36

JSP deployment Faculty of Information Technology • For a simple JSP, just include it in a WAR file, no need to put anything in web. xml file • If you want to call your JSP by a different name, you can map it in web. xml, e. g. <servlet> <servlet-name>My. First. JSP</servlet-name> <jsp-file>foobar. jsp</jsp-file> </servlet> <servlet-mapping> <servlet-name>My. First. JSP</servlet-name> <url-pattern>/foobar/*</url-pattern> </servlet-mapping> © Copyright UTS Faculty of Information Technology 2008 – JSP 37

JSP deployment – tag libraries Faculty of Information Technology • For tag libraries, need to specify in web. xml: <web-app> <taglib-uri>/hello</taglib-uri> <taglib-location>/WEB-INF/tlds/hellotags. tld</tagliblocation> </taglib> </web-app> © Copyright UTS Faculty of Information Technology 2008 – JSP 38

WAR file directory structure Faculty of Information Technology Same as servlets: – Put JSP same place as html/gif etc, ie: top level directory or subdirectory – *NOT* in WEB-INF Not same as servlets: • WEB-INF/classes – Java classes required to implement tag libs or supporting classes • WEB-INF/lib – JAR files containing additional classes for tag libs • WEB-INF/tlds – contains TLDs (not mandatory though) - conventional – not tag handler classes © Copyright UTS Faculty of Information Technology 2008 – JSP 39

JSTL Faculty of Information Technology • J 2 EE 1. 4 provides Java Standard Tag Library (JSTL) – <%@ taglib prefix=“c” uri=“http: //java. sun. com/jsp/jstl/core” %> • Core tags: – – – <c: set> <c: remove> set/remove attributes from JSP <c: catch> catch Java errors! <c: for. Each> equivalent of Java for loop <c: for. Tokens> iterate over tokens in string <c: if> equivalent to Java if but no else ! <c: choose><c: when> <c: otherwise> equivalent to Java switch – <c: out value=“${x}”> like ${x} but escapes XML chars © Copyright UTS Faculty of Information Technology 2008 – JSP 40

JSTL – more libraries Faculty of Information Technology • More JSTL tag libraries: just use @taglib with the following parameters: Function prefix URL http: //java. sun. com/jsp/. . . XML processing x xml Internationalisation, fmt formatting fmt SQL access sql String, Collection functions fn functions © Copyright UTS Faculty of Information Technology 2008 – JSP 41

JSTL example • Scriptlet based <ul> <% for (int i=0; i< arr. length; i++) { String msg = arr[i]; %> <li><%= msg %></li> <% } %> </ul> Faculty of Information Technology • JSTL based <ul> <c: for. Each var=“msg” items=“${arr}”> <li>${msg}<li> </c: for. Each> • No java code needed!! • This also works if arr[] was a java collection! © Copyright UTS Faculty of Information Technology 2008 – JSP 42

Topics Faculty of Information Technology • JSP architecture • JSP syntax • • • objects directives scripting elements standard actions execution JSP and Java. Beans Tag libraries JSP deployment Model 1 and Model 2 JSP architectures © Copyright UTS Faculty of Information Technology 2008 – JSP 43

Web application architectures Faculty of Information Technology • In theory, you can use servlets and JSPs interchangeably • However current best practice is to design the web part of your application according to a particular architecture – Model 1 architecture – Model 2 architecture © Copyright UTS Faculty of Information Technology 2008 – JSP 44

JSP Model 1 Architecture Faculty of Information Technology 1 HTTP JSP 4 Browser 2 Java. Beans Client Web Server © Copyright UTS Faculty of Information Technology 2008 – JSP 3 Data Source(s) 45

JSP Model 1 Arch (cont'd) Faculty of Information Technology 1. Browser makes HTTP request to JSP performs control logic 2. JSP may make use of Java. Beans for accessing either state information or database data 3. Java. Bean may retrieve its data from an external data source (optional) 4. JSP finishes execution and returns result to browser © Copyright UTS Faculty of Information Technology 2008 – JSP 46

Limitations of Model 1 • Faculty of Information Technology Model 1 applications have no structured way of keeping track of "what to do next" – JSPs can call each other in random patterns • Model 1 applications also have no separation between "design" and "coding" functions – typically these are performed by different people • • Model 1 is okay for simple applications For larger applications it becomes hard to keep track of JSP interdependences © Copyright UTS Faculty of Information Technology 2008 – JSP 47

Model-View-Controller Faculty of Information Technology • Model-View-Controller (MVC) – a design pattern for building applications that interact with a user (not web-specific, not Java-specific) • Model – code for internal representation of system state (data) • View – code for displaying information to user (GUI) • Controller – code for changing system state (logic) © Copyright UTS Faculty of Information Technology 2008 – JSP 48

JSP Model 2 Architecture Faculty of Information Technology 1 n ti a 2 te 4 Java. Beans JSP 5 (View) Client ta Browser (Controller) s 6 Servlet in HTTP (Model) Web Server 3 Data Source(s) • Model 2 = MVC for web applications © Copyright UTS Faculty of Information Technology 2008 – JSP 49

JSP Model 2 Arch (cont'd) Faculty of Information Technology 1. Browser makes HTTP request to controller servlet 2. Controller servlet instantiates any Java. Beans that might be needed for data displayed to user 3. Java. Bean may retrieve external data (parallel to step 4) 4. Controller forwards request to appropriate JSP only contains presentation/view code 5. JSP accesses Java. Bean data set up by controller 6. Execution finishes and result is returned to browser © Copyright UTS Faculty of Information Technology 2008 – JSP 50

Advantages of Model 2 • • Faculty of Information Technology Introducing a "controller" provides more structure to the application Also provides clearer separation of "design" and "coding" – web designers create JSPs without much coding – programmers write the controller servlet without being concerned by design issues • A large application may contain many controllers – e. g. one for each use case / piece of functionality © Copyright UTS Faculty of Information Technology 2008 – JSP 51

Model 2 Architecture Summary Faculty of Information Technology • Building web applications using the Model 2 architecture is current best practice • We'll revisit Model 2 again when we consider EJBs – EJBs change the picture, but only slightly • If you design a three-tier application using Model 2, migrating it to an N-tier application (with EJBs) should involve minimal code changes – changes only to the Java. Beans, in theory © Copyright UTS Faculty of Information Technology 2008 – JSP 52

Model 2 Implementations • • • Faculty of Information Technology The Struts framework http: //struts. apache. org/ is a common implementation of MVC architecture. Consists of a controller servlet + config file + JSP taglib You write View(JSP), Action and Model classes © Copyright UTS Faculty of Information Technology 2008 – JSP 53

Summary Faculty of Information Technology • JSP has many similarities to servlets • Again a fair amount of information to know about – use the documentation as a reference • Many ways to modularise and simplify coding – include directive – forward and include actions – tag libraries, especially Apache Jakata & JSTL • Tag libraries complex, but useful for big projects • Model 2 is best practice application architecture © Copyright UTS Faculty of Information Technology 2008 – JSP 54