Reading a Java .class file

Question

I want to write a tool which generates some code using a compiled .class file as input. Specifically, I want to read from this class file:

• Methods, with annotations
• Method parameters, with annotations

The input class file will likely refer to several types that are not in the tool's classpath. This is ok, I don't need to do anything with them, just need to read fully qualified type names as strings. I do need to get some information from the annotations, but they will be in the tool's classpath.

Is there a library which I can use for this purpose? It would be nice if the API was a bit like the reflection API, but it doesn't have to be.

Answer 1

ASM http://asm.ow2.org/ allows you to read a class from a file/input stream without class loading it. It allows you to see annotations which are not loaded at runtime. It can also be used to modify the class byte code/annotations/method etc.

Answer 2

The javap tool included with the JDK probably already does what you're after.

Answer 3

You need to look at two things Reflection API and Decompiler

Answer 4

I think you could use spring class scanning.

ClassPathScanningCandidateComponentProvider provider = new ClassPathScanningCandidateComponentProvider(true);
String basePackage = "org/springframework/samples/petclinic";
Set<BeanDefinition> components = provider.findCandidateComponents(basePackage);
for (BeanDefinition component : components) {
    System.out.printf("Component: %s\n", component.getBeanClassName());
}

for more information you can look into spring docs

Answer 5

I'm using asm for finding out all the methods.

Answer 6

If you have access to generating the .class file then the Reflection API should be able to help.