9.6 Deployment

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JSP pages are typically deployed as is in the public document structure of a web application. The container converts each JSP file to a Java class file the first time it's requested , or possibly as part of the web application deployment process. Deploying the source files is not the only option, though.

9.6.1 Consider Precompilation

An alternative to deploying JSP pages directly is to precompile them into the corresponding JSP page implementation classes and deploy only the class files. The main advantage is that the container invokes the class file immediately instead of going through the JSP container and checking if the source file has changed, resulting in slightly better performance. If you deliver applications to third parties, the fact that the JSP pages cannot be modified can be an advantage, but it can also be a disadvantage because the customer might want to adjust the look and feel of the application.

The class files for the JSP pages can be packaged in a JAR file and dropped in the WEB-INF/lib directory. In addition, the web.xml file must include mappings for all JSP page URLs to the corresponding class files:

 <web-app>    . . .    <servlet>     <servlet-name>mypage</servlet-name>     <servlet-class>org.apache.jsp.mypage$jsp</servlet-class>   </servlet>    . . .    <servlet-mapping>     <servlet-name>mypage</servlet-name>     <url-pattern>mypage.jsp</url-pattern>   </servlet-mapping>    . . .  </web-app> 

Most containers include a tool for precompiling the JSP pages in a web application. Tomcat 4, for instance, comes with a command-line tool called JspC, which can be used to compile all JSP pages and generate the required web.xml declarations, like this:

 [tomcat@frontier tomcat]$  cd /usr/local/jakarta-tomcat-4.0.4/bin  [tomcat@frontier bin]$  jspc -d ~/jspsrc -webinc ~/jspsrc/web.inc   -webapp ../webapps/ora  

The command creates servlet source files for all JSP files in the application located in the directory specified by the -webapp option and saves the generated files in the directory specified by the -d option. It also writes all servlet and URL mapping elements needed for web.xml in the file specified by the -webinc option. To compile the source files, you must set the classpath to include all classes that your application uses ”for instance, all the tag libraries and beans, as well as the Tomcat JAR files common/lib/servlet.jar and lib/jasper-runtime.jar . When you deploy the compiled JSP pages, the classes in the Tomcat lib/jasper-runtime.jar file must also be deployed because the generated JSP classes depend on them. If you use a different container, read the documentation to see which compile time and runtime classes you need to include, as well as how to use their compilers.

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The OReilly Java Authors - JavaT Enterprise Best Practices
The OReilly Java Authors - JavaT Enterprise Best Practices
Year: 2002
Pages: 96

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