Tomcat Configuration A Very Very Brief Overview Topics

Tomcat Configuration A Very, Very Brief Overview

Topics F Tomcat – Creating a new server. – Adding servlets to the web. xml file. – Initiating requests both with and without the translations inside the web. xml file. – Added initialization parameters to the web. xml file. – Starting and stopping Tomcat.

Servlet Engines F In order to execute a servlet, you must be running a servlet engine. – This is software that accepts and processes requests for servlets. – A servlet engine is usually a key component in an application server. F The application server, and hence the servlet engine, generally exists independently of the web server. – Application servers are tied to web servers via connectors.

Web Connectors F When a web server receives a request for static content such as an HTML document, it can handle the request itself. F When a request for dynamic content, such as a servlet, is received, the web server must hand that request off to the application server for processing. F The software that coordinates this effort is called a web connector.

Jakarta - Tomcat F Tomcat is the servlet and Java. Server Pages engine from the Apache group. – http: //jakarta. apache. org/tomcat F It’s small, installs quickly, and free. F For the purposes of this class, Tomcat is acting as both a web and application server.

Tomcat Root F The directory where you installed Tomcat is called the Tomcat Root. For instance: – c: program filesapache grouptomcat-3. 1 F We’ll use the Tomcat Root as our point-ofreference for all Tomcat configuration stuff. F One installation of Tomcat can host multiple web applications. This is discussed on the next slide.

Document Root F Change to the webapps directory under the Tomcat Root. For example: – c: program filesapache grouptomcat-3. 1webapps F Create a new subdirectory called the document root. For example: – SE 491 F A separate document root is created for each application we wish to host.

Directory Structure F Within your document root, create the following directory structure: – WEB-INF/classes/ – WEB-INF/lib/ F WEB-INF is where Tomcat looks for elements relating to your application. F /classes is used for all of your servlets. F /lib is used for third-party APIs and classes.

Server Configuration F Once you have chosen a document root, it’s a good idea to make Tomcat aware of it. – In theory Tomcat can locate your new document root implicitly, but you’re always better off controlling the configuration explicitly. F If any part of your Tomcat configuration is incorrect, Tomcat will fail to start and will record the problem in the <tomcat-root>/logs subdirectory. For instance: – c: program filesapache grouptomcat-3. 1logs

Server Configuration F Find and edit the following file: <tomcat root>/conf/server. xml F Add a new entry at the bottom of the file: <Context path="/se 491" doc. Base="webapps/se 491" debug="0" reloadable="true"> </Context>

Server Configuration (cont. ) F The context path should be the document root directory you just created. This is the place that Tomcat will use to derive all other locations. F The doc. Base is where Tomcat looks for nondynamic elements such as HTML. F The debug suggests that you aren’t debugging the servlet request. Change this value to “ 1” to get more information in the Tomcat logs.

Server Configuration (cont. ) F The reloadable entry suggests that if Tomcat notices that a class file has changed, it should reload that class the next time it is requested. – This feature of application servers allows us to have 7 x 24 availability; we don’t need to shut down the server to deploy enhancements and fixes to the application.

Server Configuration (cont. ) F You should add a new entry to server. xml for each document root you create. – We typically create a single document root for each application being hosted by the application server. – In a development environment we might host multiple application environments. For instance we might have document roots for development, string testing, system testing, acceptance testing, and performance testing. – We can use a similar approach if we’re doing both enhancements and regular maintenance concurrently.

Servlet Installation F Before we can execute the servlet, we need to install it on the application server. F Each application server has its own method for performing this installation. – The following instructions apply to Tomcat only.

Class File Location F Compile the servlet like any other Java program. F Copy the servlet’s. class file to the WEBINF/classes subdirectory. F If you are using packages, make certain that you use the same directory structure under WEBINF/classes that you did when developing your source code. – This ensures that the class loader is able to find all of the required resources.

web. xml F As with the Tomcat server configuration, when we add a new servlet to our application we should make Tomcat aware of it. – This is accomplished through the web. xml file. F Every application has its own web. xml file. F This file contains important configuration information that Tomcat uses to translate a browser request into a servlet execution.

web. xml (cont. ) <? xml version="1. 0" encoding="ISO-8859 -1"? > <!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc. //DTD Web Application 2. 2//EN" "http: //java. sun. com/j 2 ee/dtds/web-app_2. 2. dtd"> <web-app> <servlet-name> howdy </servlet-name> <servlet-class> Hello. World. Example </servlet-class> </servlet> <servlet-mapping> <servlet-name> howdy </servlet-name> <url-pattern> /howdy </url-pattern> </servlet-mapping> </web-app>

web. xml (cont. ) F The first part of this file provides a translation from the “pretty” name that users see in the browser to the servlet’s class name: <servlet> <servlet-name> howdy </servlet-name> <servlet-class> Hello. World. Example </servlet-class> </servlet>

web. xml (cont. ) F The second part of this file provides a translation from groups of names to the servlet name identified in the first part of the file: <servlet-mapping> <servlet-name> howdy </servlet-name> <url-pattern> /greetings </url-pattern> </servlet-mapping>

Bouncing the Server F Whenever you make configuration changes to Tomcat you should “bounce” the server. – “Bouncing” is a euphemism for shutting the server down and then immediately restarting it. F To bounce Tomcat, follow these steps: – Change to the <tomcat root>/bin directory – At the command line enter tomcat stop to stop the Tomcat server. – At the command line enter tomcat start to start the Tomcat server.

Running a Servlet F To execute a servlet you need to issue a request to Tomcat using your browser. F By default Tomcat listens for requests on port 8080. This can be configured, but for this class this value is fine.

Running a Servlet (cont. ) F To execute the Hello. World. Example servlet, use the following URI: – http: //localhost: 8080/se 491/greetings F Because we have a servlet mapping from /greetings to howdy, and howdy has been associated with the Hello. World. Example servlet in our web. xml file, Tomcat can translate this request into a servlet call.

Running a Servlet (cont. ) F All of these URIs invoke the same servlet: – http: //localhost: 8080/se 491/greetings – http: //localhost: 8080/se 491/servlet/howdy – http: //localhost: 8080/se 491/servlet/Hello. World. Example F This works because of the translations we defined in the web. xml file.

Servlet Lifecycle Reprise F You issue a request to the application server (Tomcat) using the client of your choice. F Tomcat looks at your request and attempts to locate the servlet within the URI. F Tomcat then looks at the servlet mappings that were defined in the web. xml file to determine the class name of the servlet that was requested.

Initialization Parameters F Sometimes we want to initialize a servlet when it’s first loaded by the servlet engine. – For instance, we may wish to load some configuration settings before allowing the servlet to process requests. F This can be useful for testing when you don’t want to configure a web page to initiate the test.

Tomcat Initialization Parameters F Tomcat allows you to place the initialization parameters within the web. xml file. F It requires a slight modification from the original format: <servlet> <servlet-name> message </servlet-name> <servlet-class> Message. Servlet </servlet-class> <init-param> <param-name>msg</param-name> <param-value>this is a message. . </param-value> </init-param> </servlet>

Changing Initialization Parameters F If you change the initialization parameters for a servlet, you should bounce the servlet engine to ensure that those changes are accepted. F Recycling the server forces it to reload the server. xml and web. xml files.