Generating methods with generic types with Asm bytecode generator (ClassWriter)

Question

Defining simple getters and setters is easy using Asm (and fortunately it is even explained in their FAQ). But one thing that is not mentioned, and for which I have been unable

Answer 1

You can build the signature using ASM's SignatureWriter class.

For example, suppose you wish to write the signature for this method:

public <K> void doSomething(K thing)

You could use this code:

SignatureWriter signature = new SignatureWriter();
signature.visitFormalTypeParameter("K");

// Ensure that <K> extends java.lang.Object
{
    SignatureVisitor classBound = signature.visitClassBound();
    classBound.visitClassType(Type.getInternalName(Object.class));
    classBound.visitEnd();
}

// The parameter uses the <K> type variable
signature.visitParameterType().visitTypeVariable("K");

// The return type uses the void primitive ('V')
signature.visitReturnType().visitBaseType('V');

signature.visitEnd();

String signatureString = signature.toString();

Which is equivalent to:

String signatureString = "<K:Ljava/lang/Object;>(TK;)V;"

Answer 2

In my experience most on-the-fly bytecode generation libraries don't have good support for generic types; however erased classes work just fine (unless you want to introspect those classes later, of course).