自己写的一个 CGBLIB 动态代理【原创】

CGLIB代理类，用CGLIB来实现一个代理类。大致原理描述如下：

1、使用Enhancer类来生成一个继续于被代理类的子类，此子类会重写被代理类（父类）中所有的非final的public方法；

2、当调用代理类的某个方法时实际上通过一个MethodInterceptor委托来间接调用的；

3、MethodInterceptor的intercept方法会对被代理类的方法进行增强（增强的逻辑是通过Interceptor接口来实现的）并调用被代理类（super class）的相关方法。

调用过程如下图：

CglibProxy类实现核心代理逻辑，并提供一个Interceptor接口供客户端来实现增强逻辑。

package proxy;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import lombok.AccessLevel;
import lombok.RequiredArgsConstructor;
import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;

/**
 * @author xfyou
 */
@RequiredArgsConstructor(access = AccessLevel.PRIVATE)
public class CglibProxy<T> {

  private final Class<T> targetClass;
  private final MethodInterceptor methodInterceptor;

  public static <T> CglibProxy<T> newInstance(Class<T> targetClass, Interceptor interceptor) {
    return new CglibProxy<>(targetClass, new MethodInterceptor() {
      @Override
      public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
        interceptor.before(obj);
        Object invokeResult;
        try {
          invokeResult = proxy.invokeSuper(obj, args);
        } catch (Throwable e) {
          interceptor.exception(obj, e);
          throw new InvocationTargetException(e);
        }
        interceptor.after(obj);
        return invokeResult;
      }
    });
  }

  @SuppressWarnings("unchecked")
  public T createNewObj() {
    return (T) createNewEnhancer().create();
  }

  private Enhancer createNewEnhancer() {
    Enhancer enhancer = new Enhancer();
    enhancer.setSuperclass(targetClass);
    enhancer.setCallback(methodInterceptor);
    return enhancer;
  }

  public interface Interceptor {

    /**
     * Do something before invoke the super class method
     *
     * @param obj Instances of proxied objects
     */
    void before(Object obj);

    /**
     * Do something after invoked the super class method
     *
     * @param obj Instances of proxied objects
     */
    void after(Object obj);

    /**
     * Do something when exception occurred when invoke the super class method
     *
     * @param obj Instances of proxied objects
     * @param e Exception
     */
    void exception(Object obj, Throwable e);

  }

}

WorkProxy类用来对Work类进行代理，生成的是一个单例的代理类。

package proxy;

import proxy.CglibProxy.Interceptor;

/**
 * @author xfyou
 * @date 2019/10/15
 */
public class WorkProxy {

  private static Work proxyObject;

  private static Interceptor interceptor = new Interceptor() {

    @Override
    public void before(Object obj) {
      System.out.println("before");
    }

    @Override
    public void after(Object obj) {
      System.out.println("after");
    }

    @Override
    public void exception(Object obj, Throwable e) {
      System.out.println("exception");
    }

  };

  static {
    proxyObject = CglibProxy.newInstance(Work.class, interceptor).createNewObj();
  }

  public static Work get() {
    return proxyObject;
  }

}

被代理的Work类如下：

package proxy;

/**
 * Work
 */
public class Work {

    public void doWork() {
        System.out.println("Do work");
    }

}

测试代码：

package proxy;

/**
 * @author xfyou
 * @date 2019/10/15
 */
public class Test {

  public static void main(String[] args) {
    WorkProxy.get().doWork();
  }

}