我的目前对于java动态代理浅显的理解

时间 2020-11-23

标签 java spring ide 测试 this 代理 code 对象继承接口栏目 Java 繁體版

原文原文链接

java动态代理主要可经过jdk动态代理和cglib动态代理实现，其主要区别是jdk动态代理须要被代理类实现某个接口，而后生成的实际代理类也会实现这个接口并对被代理类的方法进行加强；cglib动态代理不须要被代理类实现接口，能够直接对被代理类进行代理，生成的代理类能够直接继承被代理类，并对其方法进行加强。
jdk动态代理实现：
首先编写被代理类接口与被代理类
接口：java

public interface Animal {
      void say();
  }

被代理类spring

public class Dog implements Animal {
      @Override
      public void say() {
          System.out.println("I am a dog");
            }
  }

建立jdk动态代理类（这个并非实际生成的代理类）须要实现InvocationHandleride

public class JDKProxy implements InvocationHandler {
/**
 * 被代理对象
 */
private Object target;
public JDKProxy(Object target) {
    this.target = target;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    System.out.println("jdk动态代理前置方法");
    Object result = method.invoke(target,args);
    System.out.println("jdk动态代理后置方法");
    return result;
      }
}

测试测试

public class TestApplication {
public static void main(String[] args) {
    // 保存生成的代理类的字节码文件
    System.getProperties().put("jdk.proxy.ProxyGenerator.saveGeneratedFiles", "true");
    Dog dog1 = new Dog();
    Animal animal = (Animal) Proxy.newProxyInstance(Dog.class.getClassLoader(),Dog.class.getInterfaces(),new JDKProxy(dog1));
    animal.say();
      }
  }

测试结果：this

jdk动态代理前置方法
  I am a dog
  jdk动态代理后置方法

查看生成的代理类代理

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 Animal {
  private static Method m1;
  private static Method m2;
  private static Method m3;
  private static Method m0;

  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 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 void say() throws  {
    try {
        super.h.invoke(this, m3, (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"));
        m2 = Class.forName("java.lang.Object").getMethod("toString");
        m3 = Class.forName("Animal").getMethod("say");
        m0 = Class.forName("java.lang.Object").getMethod("hashCode");
    } catch (NoSuchMethodException var2) {
        throw new NoSuchMethodError(var2.getMessage());
    } catch (ClassNotFoundException var3) {
        throw new NoClassDefFoundError(var3.getMessage());
          }
      }
  }

咱们能够发现代理类继承了Proxy类并实现了咱们写的Animal接口code

这里咱们能够看到代理类是如何调用say()这个方法的对象

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

它使用了父类Proxy的InvocationHandler属性去调用，也就是经过咱们编写的JDkPoxy去调用say()方法，从而达到加强的效果继承

Cglib动态代理的实现接口

一样咱们先创建被代理类，但此时咱们不须要它去实现某个接口
public class Dog {
public void say(){
System.out.println("I am a dog");
}
}

这里咱们须要编写methodInterceptor类去实现MethodInterceptor（方法拦截）接口

import org.springframework.cglib.proxy.MethodInterceptor;
  import org.springframework.cglib.proxy.MethodProxy;

  import java.lang.reflect.Method;

  public class DogMethodInterceptor implements MethodInterceptor {
  /**
  *
  * @param o 代理对象
  * @param method 被代理方法
  * @param objects 方法的参数
  * @param methodProxy 代理方法
  * @return
  * @throws Throwable
  */
 @Override
 public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
    System.out.println("前置增强");
    Object result = methodProxy.invokeSuper(o,objects);
    System.out.println("后置增强");
    return result;
      }
  }

这里能够实现对代理方法的加强
编写测试类
import org.springframework.cglib.core.DebuggingClassWriter;
import org.springframework.cglib.proxy.Enhancer;

public class MainApplication {
      public static void main(String[] args) {
      // 保存生成的代理类字节码文件
      System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "D:\\mail\\CglibDynamicProxy\\target\\classes");
      //建立加强器对象
      Enhancer enhancer = new Enhancer();
      //设置父类
      enhancer.setSuperclass(Dog.class);
      //设置回调方法（也就是设置咱们以前编写的方法拦截器）
      enhancer.setCallback(new DogMethodInterceptor());
      Dog dog = (Dog)enhancer.create();
      dog.say();
            }
  }

运行结果

前置增强
  I am a dog
  后置增强

一样咱们观察生成的代理类
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

import java.lang.reflect.Method;
  import org.springframework.cglib.core.ReflectUtils;
  import org.springframework.cglib.core.Signature;
  import org.springframework.cglib.proxy.Callback;
  import org.springframework.cglib.proxy.Factory;
  import org.springframework.cglib.proxy.MethodInterceptor;
  import org.springframework.cglib.proxy.MethodProxy;

  public class Dog$$EnhancerByCGLIB$$da0f95a7 extends Dog implements Factory {
  private boolean CGLIB$BOUND;
  public static Object CGLIB$FACTORY_DATA;
  private static final ThreadLocal CGLIB$THREAD_CALLBACKS;
  private static final Callback[] CGLIB$STATIC_CALLBACKS;
  private MethodInterceptor CGLIB$CALLBACK_0;
  private static Object CGLIB$CALLBACK_FILTER;
  private static final Method CGLIB$say$0$Method;
  private static final MethodProxy CGLIB$say$0$Proxy;
  private static final Object[] CGLIB$emptyArgs;
  private static final Method CGLIB$equals$1$Method;
  private static final MethodProxy CGLIB$equals$1$Proxy;
  private static final Method CGLIB$toString$2$Method;
  private static final MethodProxy CGLIB$toString$2$Proxy;
  private static final Method CGLIB$hashCode$3$Method;
  private static final MethodProxy CGLIB$hashCode$3$Proxy;
  private static final Method CGLIB$clone$4$Method;
  private static final MethodProxy CGLIB$clone$4$Proxy;

  static void CGLIB$STATICHOOK1() {
    CGLIB$THREAD_CALLBACKS = new ThreadLocal();
    CGLIB$emptyArgs = new Object[0];
    Class var0 = Class.forName("Dog$$EnhancerByCGLIB$$da0f95a7");
    Class var1;
    CGLIB$say$0$Method = ReflectUtils.findMethods(new String[]{"say", "()V"}, (var1 = Class.forName("Dog")).getDeclaredMethods())[0];
    CGLIB$say$0$Proxy = MethodProxy.create(var1, var0, "()V", "say", "CGLIB$say$0");
    Method[] var10000 = ReflectUtils.findMethods(new String[]{"equals", "(Ljava/lang/Object;)Z", "toString", "()Ljava/lang/String;", "hashCode", "()I", "clone", "                        
    ()Ljava/lang/Object;"}, (var1 = Class.forName("java.lang.Object")).getDeclaredMethods());
    CGLIB$equals$1$Method = var10000[0];
    CGLIB$equals$1$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/Object;)Z", "equals", "CGLIB$equals$1");
    CGLIB$toString$2$Method = var10000[1];
    CGLIB$toString$2$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/String;", "toString", "CGLIB$toString$2");
    CGLIB$hashCode$3$Method = var10000[2];
    CGLIB$hashCode$3$Proxy = MethodProxy.create(var1, var0, "()I", "hashCode", "CGLIB$hashCode$3");
    CGLIB$clone$4$Method = var10000[3];
    CGLIB$clone$4$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/Object;", "clone", "CGLIB$clone$4");
}

final void CGLIB$say$0() {
    super.say();
}

public final void say() {
    MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
    if (var10000 == null) {
        CGLIB$BIND_CALLBACKS(this);
        var10000 = this.CGLIB$CALLBACK_0;
    }

    if (var10000 != null) {
        var10000.intercept(this, CGLIB$say$0$Method, CGLIB$emptyArgs, CGLIB$say$0$Proxy);
    } else {
        super.say();
    }
}

final boolean CGLIB$equals$1(Object var1) {
    return super.equals(var1);
}

public final boolean equals(Object var1) {
    MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
    if (var10000 == null) {
        CGLIB$BIND_CALLBACKS(this);
        var10000 = this.CGLIB$CALLBACK_0;
    }

    if (var10000 != null) {
        Object var2 = var10000.intercept(this, CGLIB$equals$1$Method, new Object[]{var1}, CGLIB$equals$1$Proxy);
        return var2 == null ? false : (Boolean)var2;
    } else {
        return super.equals(var1);
    }
}

final String CGLIB$toString$2() {
    return super.toString();
}

public final String toString() {
    MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
    if (var10000 == null) {
        CGLIB$BIND_CALLBACKS(this);
        var10000 = this.CGLIB$CALLBACK_0;
    }

    return var10000 != null ? (String)var10000.intercept(this, CGLIB$toString$2$Method, CGLIB$emptyArgs, CGLIB$toString$2$Proxy) : super.toString();
}

final int CGLIB$hashCode$3() {
    return super.hashCode();
}

public final int hashCode() {
    MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
    if (var10000 == null) {
        CGLIB$BIND_CALLBACKS(this);
        var10000 = this.CGLIB$CALLBACK_0;
    }

    if (var10000 != null) {
        Object var1 = var10000.intercept(this, CGLIB$hashCode$3$Method, CGLIB$emptyArgs, CGLIB$hashCode$3$Proxy);
        return var1 == null ? 0 : ((Number)var1).intValue();
    } else {
        return super.hashCode();
    }
}

final Object CGLIB$clone$4() throws CloneNotSupportedException {
    return super.clone();
}

protected final Object clone() throws CloneNotSupportedException {
    MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
    if (var10000 == null) {
        CGLIB$BIND_CALLBACKS(this);
        var10000 = this.CGLIB$CALLBACK_0;
    }

    return var10000 != null ? var10000.intercept(this, CGLIB$clone$4$Method, CGLIB$emptyArgs, CGLIB$clone$4$Proxy) : super.clone();
}

public static MethodProxy CGLIB$findMethodProxy(Signature var0) {
    String var10000 = var0.toString();
    switch(var10000.hashCode()) {
    case -909388886:
        if (var10000.equals("say()V")) {
            return CGLIB$say$0$Proxy;
        }
        break;
    case -508378822:
        if (var10000.equals("clone()Ljava/lang/Object;")) {
            return CGLIB$clone$4$Proxy;
        }
        break;
    case 1826985398:
        if (var10000.equals("equals(Ljava/lang/Object;)Z")) {
            return CGLIB$equals$1$Proxy;
        }
        break;
    case 1913648695:
        if (var10000.equals("toString()Ljava/lang/String;")) {
            return CGLIB$toString$2$Proxy;
        }
        break;
    case 1984935277:
        if (var10000.equals("hashCode()I")) {
            return CGLIB$hashCode$3$Proxy;
        }
    }

    return null;
}

public Dog$$EnhancerByCGLIB$$da0f95a7() {
    CGLIB$BIND_CALLBACKS(this);
}

public static void CGLIB$SET_THREAD_CALLBACKS(Callback[] var0) {
    CGLIB$THREAD_CALLBACKS.set(var0);
}

public static void CGLIB$SET_STATIC_CALLBACKS(Callback[] var0) {
    CGLIB$STATIC_CALLBACKS = var0;
}

private static final void CGLIB$BIND_CALLBACKS(Object var0) {
    Dog$$EnhancerByCGLIB$$da0f95a7 var1 = (Dog$$EnhancerByCGLIB$$da0f95a7)var0;
    if (!var1.CGLIB$BOUND) {
        var1.CGLIB$BOUND = true;
        Object var10000 = CGLIB$THREAD_CALLBACKS.get();
        if (var10000 == null) {
            var10000 = CGLIB$STATIC_CALLBACKS;
            if (var10000 == null) {
                return;
            }
        }

        var1.CGLIB$CALLBACK_0 = (MethodInterceptor)((Callback[])var10000)[0];
    }

}

public Object newInstance(Callback[] var1) {
    CGLIB$SET_THREAD_CALLBACKS(var1);
    Dog$$EnhancerByCGLIB$$da0f95a7 var10000 = new Dog$$EnhancerByCGLIB$$da0f95a7();
    CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
    return var10000;
}

public Object newInstance(Callback var1) {
    CGLIB$SET_THREAD_CALLBACKS(new Callback[]{var1});
    Dog$$EnhancerByCGLIB$$da0f95a7 var10000 = new Dog$$EnhancerByCGLIB$$da0f95a7();
    CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
    return var10000;
}

public Object newInstance(Class[] var1, Object[] var2, Callback[] var3) {
    CGLIB$SET_THREAD_CALLBACKS(var3);
    Dog$$EnhancerByCGLIB$$da0f95a7 var10000 = new Dog$$EnhancerByCGLIB$$da0f95a7;
    switch(var1.length) {
    case 0:
        var10000.<init>();
        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
        return var10000;
    default:
        throw new IllegalArgumentException("Constructor not found");
    }
}

public Callback getCallback(int var1) {
    CGLIB$BIND_CALLBACKS(this);
    MethodInterceptor var10000;
    switch(var1) {
    case 0:
        var10000 = this.CGLIB$CALLBACK_0;
        break;
    default:
        var10000 = null;
    }

    return var10000;
}

public void setCallback(int var1, Callback var2) {
    switch(var1) {
    case 0:
        this.CGLIB$CALLBACK_0 = (MethodInterceptor)var2;
    default:
    }
}

public Callback[] getCallbacks() {
    CGLIB$BIND_CALLBACKS(this);
    return new Callback[]{this.CGLIB$CALLBACK_0};
}

public void setCallbacks(Callback[] var1) {
    this.CGLIB$CALLBACK_0 = (MethodInterceptor)var1[0];
}

static {
    CGLIB$STATICHOOK1();
      }
  }

能够观察到生成的代理类继承了Dog类
这里咱们看它是如何调用say()方法的
public final void say() {
MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
if (var10000 == null) {
CGLIB$BIND_CALLBACKS(this);
var10000 = this.CGLIB$CALLBACK_0;
}

if (var10000 != null) {
        var10000.intercept(this, CGLIB$say$0$Method, CGLIB$emptyArgs, CGLIB$say$0$Proxy);
    } else {
        super.say();
    }
}

咱们也能够观察到它是经过咱们以前编写的MethodIntecerptor去实现对代理方法的加强的