More complex generic example

[dyorgio]

Documentation has only one example about using generics.

I couldn't find on internet how extend a class that defines more than one generic parameter
using javassist.

I have a class that I want to extend at runtime using javassist, but generic parameter need to exists at runtime for reflection (hibernate needs it).

So, I´m not posting this issue to get a response for my problem.

The issue is true, have no documentation and examples with use of generics in the real world (extends, implements, < T extends MyType < X < V > > , X, V >).

[chibash]

Multiple generic parameters are not so different from a single one.
Just build a class file as if all the parameters are of type java.lang.Object.
Then attach appropriate generic signatures to the class and the methods.

[dyorgio]

Hi @chibash , thank you for reply 😃

Sometimes what is easy to us is hard to another people that don´t use javassist every day.

I solve my problem, trying a lot....many, many, many times...

I will put here, so if you or another dev of javassist put it on a example/tutorial file it will be cool:

Problem: retain ParametrizedType generic info at runtime for hibernate read it from AttributeConverter interface.

Solution: Use

ClassPool pool = ClassPool.getDefault();
CtClass cc = pool.get("your.base.generic.enum.converter.Type");
cc.setName("someRandomName");

ClassSignature cs = new ClassSignature(null, null,
                                  // Set interface and its generic params
                                  new ClassType[]{new ClassType(AttributeConverter.class.getName(),
                                    new TypeArgument[]{
                                      new TypeArgument(new ClassType("user.enum.Type")),
                                        new TypeArgument(new ClassType("database.Type"))
                                    })});

cc.setGenericSignature(cs.encode());

// Constructor that call base class constructor with argument
CtConstructor ctConstructor = new CtConstructor(new CtClass[]{}, cc);
ctConstructor.setBody("this(" + "user.enum.Type" + ".class);");
cc.addConstructor(ctConstructor);