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Getting the arguments for the bytecode using Javassist

The disassembled code (using javap -c) of http://lpaste.net/338173 looks like this: http://lpaste.net/338175 , on the third column, there is 200 as an argument to "sipush" how can I get this from a class file using javassist?

Solution

  • sipush is a bytecode which takes a single two byte argument which is a number to push onto the operand stack. In Javassist, you can iterate over all bytecode of a method via the CodeAttribute that is available from the CtMethod's MethodInfo. In your case, it would be the first byte code, but you can check that you reached Opcode.SIPUSH. Once you iterated to this instruction you can read the 2 byte argument via the s16bitAt method from the iterator. The method takes a zero-based index. In your case, this makes the argument zero for sipush, returning 200 as a value.