如何劫持Java应用的HTTP请求

public class Agent implements ClassFileTransformer {

  public static void premain(String args, Instrumentation instrumentation) {
    instrumentation.addTransformer(new Agent());
  }

  @Override
  public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
    if ("org/apache/http/HttpHost".equals(className)) {
      ClassPool pool = ClassPool.getDefault();
      try {
        CtClass httpHost = pool.get("org.apache.http.HttpHost");
        CtClass string = pool.get("java.lang.String");
        CtConstructor constructor = httpHost.getDeclaredConstructor(new CtClass[]{string, CtClass.intType, string});
        constructor.insertBefore("hostname = \"www.163.com\";");
        byte[] bytes = httpHost.toBytecode();
        FileOutputStream fos = new FileOutputStream("/Users/fangfeng/a.class");
        fos.write(bytes);
        return bytes;
      } catch(NotFoundException | CannotCompileException | IOException e){
        e.printStackTrace();
      }
    }
    return classfileBuffer;
  }
}