Java Dynamic Code Generation with support for generics

Is there any tool which provides Java dynamic code generation and that also supports gen开发者_C百科erics?

Javassist for example, is the kind of tool that I need, but it does not support generics.

I wrote a small lib which uses the Java 6 Compiler API, however as far as I know it depends on JDK. Is there a way to specify another compiler? Or to ship with my application only the parts that I need to invoke with the Java Compiler API?

It seems you can manipulate and read generic info with Javaassist. See

http://www.mail-archive.com/jboss-user@lists.jboss.org/msg101222.html

[jboss-user] [Javassist user questions] - Re: Altering Generics Information of Methods using Javassist SimonRinguette Thu, 20 Dec 2007 12:22:14 -0800

I have done further reading on how this is implemented by the compiler and finally found out the answer I was looking for.

You can defenitely do that with javaassist. The key class is javassist.bytecode.SignatureAttribute.

From a CtMethod, i've obtained the methodInfo I add a Signature attribute. You can do it with something like:

CtMethod method = ....
   MethodInfo methodInfo = method.getMethodInfo();
   SignatureAttribute signatureAttribute = new 
SignatureAttribute(methodInfo.getConstPool(),
   "()Ljava/util/List<Ljava/lang/String;>;");
   methodInfo.addAttribute(signatureAttribute);

If your more interesed in reading the signature with the generics inside, you can use the methodInfo.getAttribute(SignatureAttribute.tag).

I hope this helped.

If you are comfortable with writing bytecode then ASM is quite a good library for that kind of thing. That will let you generate a class file on the fly without having to worry about the nitty-gritty of the classfile format. You can then use a classloader to dynamically load it into your application.

If I recall correctly, it is sufficient to have tools.jar in the classpath in order to use the Java compiler at runtime.

Actually, javaassist can handle generics using SignatureAttribute.

SignatureAttribute.Type retType = new SignatureAttribute.BaseType(Void.TYPE.getName());
SignatureAttribute.Type[] argType = getArgType();
SignatureAttribute.MethodSignature signature = new SignatureAttribute.MethodSignature(null, argType, retType, null);
method.setGenericSignature(signature.encode());

This project has a lot of very good examples. Hop they are helpful.