Java:在同一个JVM中从运行时获取类的字节码

import java.lang.instrument.Instrumentation;

public class MyAgent {
    public static void premain(String agentArgs, Instrumentation inst) {
        // 注册一个ClassFileTransformer来获取类的字节码
        inst.addTransformer(new MyClassFileTransformer());
    }
}

import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.security.ProtectionDomain;

import javassist.ClassPool;
import javassist.CtClass;

public class MyClassFileTransformer implements ClassFileTransformer {

    @Override
    public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined,
                            ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
        if (className == null || !className.startsWith("your/package/")) {
            return null; // 只处理特定包下的类
        }

        try {
            ClassPool classPool = ClassPool.getDefault();
            CtClass ctClass = classPool.get(className.replace('/', '.'));
            byte[] byteCode = ctClass.toBytecode();
            ctClass.detach(); // 释放CtClass对象
            return byteCode;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}

Manifest-Version: 1.0
Premain-Class: MyAgent
Can-Redefine-Classes: true
Can-Retransform-Classes: true

java -javaagent:/path/to/your/agent.jar -jar your-application.jar