CG Compilation Framework

Compilation Framework

JDK Compiler

The "JDK compiler" uses the built-in Java compiler (which is, in modern Java, available in the JRE itself.) Java compilation in Java itself is based on the JavaCompiler class. The javax.tools provides a dynamic compilation framework. The IBM article provides a sample app that compiles Java classes from in-memory sources.

Drill's implementation is similar to the approach outlined in the IBM article. The DrillJavaFileManager manages the (virtual) source and class files, DrillJavaFileObject manages each file.

Debugging Hints

You can view the generated code in one of three ways:

• Enable debug logging for AbstractClassCompiler. The generated code is written to the log file. Set the config option drill.exec.compile.debug to true if you want line numbers added to each line.
• Uncomment the obvious block of code in AbstractClassCompiler to write each generated class to /tmp. This version is handy as it uses the class name to name each file.
• Pass the following to the command line when starting Drill: -Dorg.codehaus.janino.source_debugging.enable=true -Dorg.codehaus.janino.source_debugging.dir=/tmp. (See this post for more information.) This version writes all files using generic temporary names, making it hard to find the particular file of interest.

You can gain access to the generated class files by uncommenting the obvious lines near line 256 in MergeAdapter.