Support using currently loaded classes as TypePool

When writing an agent, I might want to formulate a transformation based on a type description like this:

    Resolution httpServlet = typePool.describe("javax.servlet.http.HttpServlet");
    if (httpServlet.isResolved()) {
      TypeDescription httpServletType = httpServlet.resolve();
      transformer = agentBuilder.type(subTypeOf(httpServletType)))

Now, there are a couple of ways to obtain the typePool. Like typePool = TypePool.Default.ofClassPath(); The problem here is that HttpServlet is not on the classpath. it is however contained in “allLoadedClasses” of “Instrumentation”

So how about an Instrumentation based type pool which works like this?

  private void initByteBuddy(final Instrumentation inst) {
    typePool = TypePool.Default.of(new ClassFileLocator() {

      @Override
      public Resolution locate(String typeName) throws IOException {
        Class<?>[] allLoadedClasses = inst.getAllLoadedClasses();
        for (Class<?> clazz : allLoadedClasses) {
          if (clazz.getName().equals(typeName)) {
            return ClassFileLocator.ForClassLoader.read(clazz);
          }
        }
        return Resolution.Illegal.INSTANCE;
      }

    });
 }

This works, but I am unsure about performance and other implications. For example I assume that the type pool will only have loaded classes, so using a Typedescription for the initial load of something might not work.

[CodingFabian]

I hired a consultant to fix this issue for us. He will probably send a PR soon 😃

[CodingFabian]

I guess we can close this. The type pool is the wrong solution and we should use raw matchers.