Is there a Java library to generate class files from an AST?

Question

This page describes how I can use the code generator in javac to generate code given that I can build an AST (using a separate parser which I wrote). The technique involves editing javac's source code to basically bypass the Java parser, so that one could supply his/her own AST to the code generator. This could work, but I was hoping to do it in a slightly cleaner way. I want to include the code generating part of javac as a library in my project so I can use it to generate code, without bringing with it the rest of javac's source.

Is there a way to do this with javac, or is there perhaps a better library?

Also, feel free to change the question's title. I couldn't think of a better one, but it's a little ambiguous. If you suggest an edit for a better title, I'll accept it.

Answer 1

I think what you might be interested in is a java library like BCEL(ByteCode Engineering Library)

I played around with it back when I took a class on compiler construction, basically, it has a nice wrapper for generating the constant pool, inserting named bytecode instructions into a method and whatnot, then when you are done, you can either load the class at runtime with a custom classloader, or write it out to a file in the normal way.

With BCEL, it should be relatively easy to go from the syntax tree to the java bytecodes, albeit a bit tedious, but you may want to just use BCEL to generate the raw bytecode without building the tree as well in some cases.

Answer 2

Another cool framework is ASM, a bytecode analysis and manipulation framework.

In case you do not want to use a framework, as of now (2014), it is not possible to generate bytecode from a tree using the arbitrary representations of com.sun.source.tree.* as said here.