JDK与CGLIB动态代理

JDK动态代理

实现InovactionHandler接口

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
  
/**
 * 耗时统计
 */
public class LogInvocationHandler implements InvocationHandler {
  
    private UserService userService;
  
    public LogInvocationHandler(UserService userService) {
        this.userService = userService;
    }
  
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        long start = System.currentTimeMillis();
        Object invoke = method.invoke(userService, args);
        long end = System.currentTimeMillis();
        System.out.println(method.getName() + " 耗时: " + (end - start));
        return invoke;
    }
}
  

业务类与接口

public interface UserService {
  
    /**
     * 根据用户id查询用户名称
     *
     * @param userId UserId
     * @return userName
     */
    String getUserNameById(long userId);
}
  
  
import java.util.concurrent.TimeUnit;
public class UserServiceImpl implements UserService {
  
  
    @Override
    public String getUserNameById(long userId) {
        try {
            //模拟数据库查询
            TimeUnit.MICROSECONDS.sleep(2);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
        return "proxy" + userId;
    }
}
  

创建代理对象

public static void main(String[] args) {
        //输出生成的代理类
        System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles","true");
        UserService userService = new UserServiceImpl();
        LogInvocationHandler invocationHandler = new LogInvocationHandler(userService);
        UserService userServiceProxy = (UserService) Proxy.newProxyInstance(userService.getClass().getClassLoader(), userService.getClass().getInterfaces(), invocationHandler);
    
        System.out.println(userServiceProxy.getUserNameById(1));
        //输出: getUserNameById 耗时: 2
        //     proxy1
    }

生成的代理类Class

package com.sun.proxy;
  
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;
  
public final class $Proxy0 extends Proxy implements UserService {
    private static Method m1;
    private static Method m3;
    private static Method m2;
    private static Method m0;
  
    //构造方法
    public $Proxy0(InvocationHandler var1) throws  {
        super(var1);
    }
  
    public final boolean equals(Object var1) throws  {
        try {
            return (Boolean)super.h.invoke(this, m1, new Object[]{var1});
        } catch (RuntimeException | Error var3) {
            throw var3;
        } catch (Throwable var4) {
            throw new UndeclaredThrowableException(var4);
        }
    }
  
    public final String getUserNameById(long var1) throws  {
        try {
            return (String)super.h.invoke(this, m3, new Object[]{var1});
        } catch (RuntimeException | Error var4) {
            throw var4;
        } catch (Throwable var5) {
            throw new UndeclaredThrowableException(var5);
        }
    }
  
    public final String toString() throws  {
        try {
            return (String)super.h.invoke(this, m2, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }
  
    public final int hashCode() throws  {
        try {
            return (Integer)super.h.invoke(this, m0, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }
  
    static {
        try {
            m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
            m3 = Class.forName("com.github.xdshent.design.proxy.UserService").getMethod("getUserNameById", Long.TYPE);
            m2 = Class.forName("java.lang.Object").getMethod("toString");
            m0 = Class.forName("java.lang.Object").getMethod("hashCode");
        } catch (NoSuchMethodException var2) {
            throw new NoSuchMethodError(var2.getMessage());
        } catch (ClassNotFoundException var3) {
            throw new NoClassDefFoundError(var3.getMessage());
        }
    }
}

原理
- $Proxy0类实现了业务接口UserService并且继承了java.lang.reflect.Proxy
- $Proxy0加载时类静态方法中通过反射获取了java.lang.Object中的equals、hashCode、toString以及业务对象中的getUserNameById方法对应的Method对象
- Proxy.newProxyInstance在生成代理对象时会把传入的InvocationHandler放入$Proxy0的构造函数中
- 生成的代理对象在通过业务接口UserService调用时会调用父类Proxy的InvocationHandler h字段, 进而进入用户所写的LogInvocationHandler, 参数为:
  - 当前 $Proxy0对象
  - 第2步获取到的对应Method对象
  - 方法参数
图示

CGLIB动态代理

依赖

        <dependency>
            <groupId>cglib</groupId>
            <artifactId>cglib</artifactId>
            <version>3.3.0</version>
        </dependency>

实现MethodInterceptor

public class LogMethodInterceptor implements MethodInterceptor {
  
    @Override
    public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
  
        long start = System.currentTimeMillis();
        Object invoke = proxy.invokeSuper(obj, args);
        long end = System.currentTimeMillis();
        System.out.println(method.getName() + " 耗时: " + (end - start));
        return invoke;
    }
}

创建代理对象

       public static void main(String[] args) {
        //设置生成的class对象输出到当前目录
        System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "./");
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(UserServiceImpl.class);
        enhancer.setCallback(new LogMethodInterceptor());
  
        UserServiceImpl userService = (UserServiceImpl)enhancer.create();
        System.out.println(userService.getUserNameById(1));
    }

生成的Class

FastClass机制根据方法签名获取对应的索引, 执行时根据索引找到对应的方法直接执行
- 代理类
- 代理类的FastClass
- 目标类FastClass
整体概览
调用流程

JDK与CGLIB动态代理

JDK动态代理

CGLIB动态代理

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