Java 动态代理实现解析

小鱼儿 2022-08-26 12:15 175阅读 0赞

Java动态代理只能针对接口进行动态代理。如果需要对类进行实现代理可以使用:CGLIB,ASM等相关的操作字节码实现（在这里先只介绍下SUN 基于接口动态代理的实现）。

代码如下：

import java.lang.reflect.InvocationHandler;
    import java.lang.reflect.Method;
    import java.lang.reflect.Proxy;
    
    public class ProxyTest {
    	public static void main(String[] args) {
    		/* 设置此系统属性,让JVM生成的Proxy类写入文件.保存路径为：com/sun/proxy(如果不存在请手工创建) */
    		System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");
    		System.out.println(Proxy.getProxyClass(IUser.class.getClassLoader(), IUser.class));
    		IUser userImpl = (IUser) new DynamicProxy().bind(new UserImpl());
    		System.out.println(userImpl.sayHello(" kevin LUAN"));
    	}
    
    	public static class DynamicProxy implements InvocationHandler {
    		public Object target;
    
    		public Object bind(Object target) {
    			this.target = target;
    			return Proxy.newProxyInstance(target.getClass().getClassLoader(), target.getClass().getInterfaces(), this);
    		}
    
    		@Override
    		public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    			return method.invoke(target, args);
    		}
    	}
    
    	public static interface IUser {
    		public String sayHello(String speakString);
    	}
    
    	public static class UserImpl implements IUser {
    
    		@Override
    		public String sayHello(String speakString) {
    			return "welcome " + speakString;
    		}
    
    	}
    }

执行结果输出：

class com.sun.proxy.$Proxy0

welcome  kevin LUAN

接下来我们去看看生成的$Proxy0.class文件。

反编译后内容如下：

package com.sun.proxy;
    
    import ProxyTest.IUser;
    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 ProxyTest.IUser
    {
      private static Method m1;
      private static Method m3;
      private static Method m0;
      private static Method m2;
    
      public $Proxy0(InvocationHandler paramInvocationHandler)
        throws 
      {
        super(paramInvocationHandler);
      }
    
      public final boolean equals(Object paramObject)
        throws 
      {
        try
        {
          return ((Boolean)this.h.invoke(this, m1, new Object[] { paramObject })).booleanValue();
        }
        catch (Error|RuntimeException localError)
        {
          throw localError;
        }
        catch (Throwable localThrowable)
        {
          throw new UndeclaredThrowableException(localThrowable);
        }
      }
    
      public final String sayHello(String paramString)
        throws 
      {
        try
        {
          return (String)this.h.invoke(this, m3, new Object[] { paramString });
        }
        catch (Error|RuntimeException localError)
        {
          throw localError;
        }
        catch (Throwable localThrowable)
        {
          throw new UndeclaredThrowableException(localThrowable);
        }
      }
    
      public final int hashCode()
        throws 
      {
        try
        {
          return ((Integer)this.h.invoke(this, m0, null)).intValue();
        }
        catch (Error|RuntimeException localError)
        {
          throw localError;
        }
        catch (Throwable localThrowable)
        {
          throw new UndeclaredThrowableException(localThrowable);
        }
      }
    
      public final String toString()
        throws 
      {
        try
        {
          return (String)this.h.invoke(this, m2, null);
        }
        catch (Error|RuntimeException localError)
        {
          throw localError;
        }
        catch (Throwable localThrowable)
        {
          throw new UndeclaredThrowableException(localThrowable);
        }
      }
    
      static
      {
        try
        {
          m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") });
          m3 = Class.forName("ProxyTest$IUser").getMethod("sayHello", new Class[] { Class.forName("java.lang.String") });
          m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
          m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
          return;
        }
        catch (NoSuchMethodException localNoSuchMethodException)
        {
          throw new NoSuchMethodError(localNoSuchMethodException.getMessage());
        }
        catch (ClassNotFoundException localClassNotFoundException)
        {
          throw new NoClassDefFoundError(localClassNotFoundException.getMessage());
        }
      }
    }

所有生成的Proxy对象都默认继承了Proxy类，并实现了代理目标对象所实现的接口。

从代码可知，代理类做的事其实很简单，所有的方法处理都会交到：InvocationHandler来处理