我的目前對於java動態代理淺顯的理解

時間 2020-11-23

標籤 java spring ide 測試 this 代理 code 對象繼承接口欄目 Java 简体版

原文原文鏈接

java動態代理主要可經過jdk動態代理和cglib動態代理實現，其主要區別是jdk動態代理須要被代理類實現某個接口，而後生成的實際代理類也會實現這個接口並對被代理類的方法進行加強；cglib動態代理不須要被代理類實現接口，能夠直接對被代理類進行代理，生成的代理類能夠直接繼承被代理類，並對其方法進行加強。
jdk動態代理實現：
首先編寫被代理類接口與被代理類
接口：java

public interface Animal {
      void say();
  }

被代理類spring

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

建立jdk動態代理類（這個並非實際生成的代理類）須要實現InvocationHandleride

public class JDKProxy implements InvocationHandler {
/**
 * 被代理對象
 */
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動態代理前置方法");
    Object result = method.invoke(target,args);
    System.out.println("jdk動態代理後置方法");
    return result;
      }
}

測試測試

public class TestApplication {
public static void main(String[] args) {
    // 保存生成的代理類的字節碼文件
    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();
      }
  }

測試結果：this

jdk動態代理前置方法
  I am a dog
  jdk動態代理後置方法

查看生成的代理類代理

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());
          }
      }
  }

咱們能夠發現代理類繼承了Proxy類並實現了咱們寫的Animal接口code

這裏咱們能夠看到代理類是如何調用say()這個方法的對象

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);
    }
}

它使用了父類Proxy的InvocationHandler屬性去調用，也就是經過咱們編寫的JDkPoxy去調用say()方法，從而達到加強的效果繼承

Cglib動態代理的實現接口

一樣咱們先創建被代理類，但此時咱們不須要它去實現某個接口
public class Dog {
public void say(){
System.out.println("I am a dog");
}
}

這裏咱們須要編寫methodInterceptor類去實現MethodInterceptor（方法攔截）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 代理對象
  * @param method 被代理方法
  * @param objects 方法的參數
  * @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("前置增強");
    Object result = methodProxy.invokeSuper(o,objects);
    System.out.println("後置增強");
    return result;
      }
  }

這裏能夠實現對代理方法的加強
編寫測試類
import org.springframework.cglib.core.DebuggingClassWriter;
import org.springframework.cglib.proxy.Enhancer;

public class MainApplication {
      public static void main(String[] args) {
      // 保存生成的代理類字節碼文件
      System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "D:\\mail\\CglibDynamicProxy\\target\\classes");
      //建立加強器對象
      Enhancer enhancer = new Enhancer();
      //設置父類
      enhancer.setSuperclass(Dog.class);
      //設置回調方法（也就是設置咱們以前編寫的方法攔截器）
      enhancer.setCallback(new DogMethodInterceptor());
      Dog dog = (Dog)enhancer.create();
      dog.say();
            }
  }

運行結果

前置增強
  I am a dog
  後置增強

一樣咱們觀察生成的代理類
//
// 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();
      }
  }

能夠觀察到生成的代理類繼承了Dog類
這裏咱們看它是如何調用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();
    }
}

咱們也能夠觀察到它是經過咱們以前編寫的MethodIntecerptor去實現對代理方法的加強的