I would also recommend ASM, but have a look at Jasmin, I used it (or, rather, had to use it) for a university project, and it worked quite well. I wrote a lexer-parser-analyzer-optimizer-generator combination for a programing language using Java and Jasmin, so it was generating JVM Code. I uploaded the code here; the interesting part should be the source code itself. In the folder bytecode/InsanelyFastByteCodeCreator.java
, you find a piece of code which transforms an AST Tree into the input format of Jasmin assembler. It is quite straightforward.
The source language (which was transformed to the AST by the lexer-parser-analyzer) is a subset of Java called MiniJava. It lacks some “complicated” features like inheritance, constructors, static methods, private fields and methods. None of those features are difficult to implement, but there was another task to write an x86 backend (so to generate machine assembler), and those things tend to get difficult if you got no JVM which handles some of those things.
In case you wonder about the strange class name: The task of the university project was to transform the AST into an SSA Graph (representing the input code), optimize the graph, and then turn it into Java bytecode. That was about ¾ of the work of the project and the InsanlyFastByteCodeCreator
was just a short-cut to test everything.
Have a look at the “Java Virtual Machine” book from Jon Meyer and Troy Downing. This book heavily references the Jasmin Assembler; it’s quite helpful for understanding the JVM internals.