详解JAVA动态代理

public interface Personal {

  /**
   * 被代理的方法
   */
  void introduction();

}

public class PersonalImpl implements Personal {
  @Override
  public void introduction() {
    System.out.println("我是程序员！");
  }
}

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class JDKProxyFactory<T> implements InvocationHandler {

  /**
   * 目标对象
   */
  private T target;

  /**
   * 构造函数传入目标对象
   *
   * @param target 目标对象
   */
  public JDKProxyFactory(T target) {
    this.target = target;
  }

  /**
   * 获取代理对象
   *
   * @return 获取代理
   */
  public T getProxy() {
    return (T) Proxy.newProxyInstance(target.getClass().getClassLoader(), target.getClass().getInterfaces(), this);
  }

  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    // 对方法增强
    System.out.println("大家好！");
    // 调用原方法
    Object result = method.invoke(target, args);
    // 方法增强
    System.out.println("再见！");
    return result;
  }
}

import org.junit.Test;
import sun.misc.ProxyGenerator;

import java.io.FileOutputStream;
import java.io.IOException;

public class ProxyTest {

  @Test
  public void testJdkProxy() {
    // 生成目标对象
    Personal personal = new PersonalImpl();
    // 获取代理对象
    JDKProxyFactory<Personal> proxyFactory = new JDKProxyFactory<>(personal);
    Personal proxy = proxyFactory.getProxy();

    // 将proxy的class字节码输出到文件
    generatorClass(proxy);

    // 调用代理对象
    proxy.introduction();
  }

  /**
   * 将对象的class字节码输出到文件
   *
   * @param proxy 代理类
   */
  private void generatorClass(Object proxy) {
    FileOutputStream out = null;
    try {
      byte[] generateProxyClass = ProxyGenerator.generateProxyClass(proxy.getClass().getSimpleName(), new Class[]{proxy.getClass()});
      out = new FileOutputStream(proxy.getClass().getSimpleName() + ".class");
      out.write(generateProxyClass);
    } catch (Exception e) {
      e.printStackTrace();
    } finally {
      if (out != null) {
        try {
          out.close();
        } catch (IOException e) {
          // TODO Auto-generated catch block
        }
      }
    }

  }

}

/**
* the invocation handler for this proxy instance.
* @serial
*/
protected InvocationHandler h;

protected Proxy(InvocationHandler h) {
  Objects.requireNonNull(h);
  this.h = h;
}

public final void introduction() throws {
    try {
      super.h.invoke(this, m3, (Object[])null);
    } catch (RuntimeException | Error var2) {
      throw var2;
    } catch (Throwable var3) {
      throw new UndeclaredThrowableException(var3);
    }
  }

public class PersonalImpl {
  public void introduction() {
    System.out.println("我是程序员！");
  }
}

import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;

import java.lang.reflect.Method;

public class CgLibProxyFactory<T> implements MethodInterceptor {

  /**
   * 获取代理对象
   *
   * @param tClass 被代理的目标对象
   * @return 代理对象
   */
  public T getProxyByCgLib(Class<T> tClass) {
    // 创建增强器
    Enhancer enhancer = new Enhancer();

    // 设置需要增强的类的类对象
    enhancer.setSuperclass(tClass);

    // 设置回调函数
    enhancer.setCallback(this);

    // 获取增强之后的代理对象
    return (T) enhancer.create();
  }

   /**
   * 代理类方法调用回调
   * 
   * @param obj 这是代理对象，也就是[目标对象]的子类
   * @param method [目标对象]的方法
   * @param args 参数
   * @param proxy 代理对象的方法
   * @return 返回结果，返回给调用者
   * @throws Throwable
   */
  @Override
  public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {

    System.out.println("大家好！");

    Object result = proxy.invokeSuper(obj, args);

    System.out.println("再见！");

    return result;
  }
}

@Test
public void testCgLibProxy() {
  // 生成被代理的目标对象
  PersonalImpl personal = new PersonalImpl();
  
  // 获取代理类
  CgLibProxyFactory<PersonalImpl> proxyFactory = new CgLibProxyFactory<>();
  PersonalImpl proxy = proxyFactory.getProxyByCgLib((Class<PersonalImpl>) personal.getClass());

  // 将proxy的class字节码输出到文件
  generatorClass(proxy);

  // 调用代理对象
  proxy.introduction();
}

public final void introduction() throws {
  try {
    super.h.invoke(this, m7, (Object[])null);
  } catch (RuntimeException | Error var2) {
    throw var2;
  } catch (Throwable var3) {
    throw new UndeclaredThrowableException(var3);
  }
}