如何编译将.class文件直接放入JAR的Java文件

Question

First some reference:
1st Link
2nd link

The first article 1st Link mentions about compiling the Java files directly into JAR files and avoiding one step in the build process. Does anyone know this?

-Vadiraj

Answer 1

As you linked to my blog post I thought it was only fair to give you an update.

Compiling directly to a Jar is actually fairly simple to do. Basically you extend

javax.tools.ForwardingJavaFileObject

Then override openOutputStream method and direct it to your Jar. As the Java Compiler is highly concurrent but writing to a jar file is highly sequential I'd recommend that you buffer to byte arrays and then have a background thread that writes the byte arrays as they arrive.

I do exactly this is my experimental build tool JCompilo https://code.google.com/p/jcompilo/ This tool is completely undocumented but crazy fast. Currently it's about 20-80% faster than any other Java build tool and about 10x faster than the Scala compiler for the same code.

Answer 2

As the author is talking about extending the compiler itself, it is possible that he has knowledge of the built-in capabilities of the compiler (that is what the compiler is capable of, maybe with a little encouragement by tweaking the code).

Right now I'm investigating extending the Java 6 compiler to remove the unneeded file exists checks and possible jaring the class files directly in the compiler. [emphasis mine]

That capability, however, is certainly not supported officially (no documentation exist about it on the javac webpage ).

At best, the feature is compiler dependent; possibly requiring modification of the compiler's source code.