Tomcat: The Definitive Guide, 2nd Edition

Changing the JSP Compiler

By default, Tomcat version 5.5 and higher compiles JSP pages using a bundled Eclipse JDT compiler. See the Eclipse JDT core page at http://www.eclipse.org/jdt/core for more information about this Java compiler. The JDT compiler is written in pure Java and performs the same job for Tomcat as the JDK's javac command. It is a relatively new Java compiler, and as such may not be as mature or as robust as javac, or other older compilers.

Since Tomcat bundles the JDT compiler, Tomcat can compile and serve JSP page content when running on top of either a JRE or the full JDK. Even though the JDK has a javac compiler, since Tomcat contains its own Java compiler, Tomcat does not need the JDK's Java compiler, as long as Tomcat's bundled Java compiler can compile everything that javac can. Because the JDT compiler is newer, it is still maturing, and you may find that some Java 1.5 or 1.6 source code language features are not fully implemented yet. Because it is the Java compiler that the Eclipse IDE uses, quite a bit of effort is going into making it both complete and robust, and there are a large number of people using it and testing it. Still, you may run into a situation where you want to switch Tomcat between the JDT compiler and your JDK's javac compiler.

The way Tomcat 5.5 is written, you have two main Java compiler choices:

• Use the built-in JDT Java compiler, which is the default.

• Make some changes to enable Tomcat to use Apache Ant to compile the JSP pages.

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