jdk动态代理的实现原理
2017-11-30 03:01
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jdk动态代理实际上是jvm帮我们建成的类实现我们传入的接口,加载字节码到jvm。实际上就是帮我们拼接的字符串和我们传进去的接口进行拼接,然后生成字节码加载进虚拟机。代理类持有InvocationHandler的引用,当我们调用方法时实际上调用的是InvocationHandler的引用的invoke方法,invoke方法中再进行反射调用方法。jdk动态代理只能代理接口
接口类:
实现类:
InvocationHandler的实现类:
测试类:
System.getProperties().put(“sun.misc.ProxyGenerator.saveGeneratedFiles”,”true”);会保存生成的动态代理类$Proxy0,生成的代理类会自动新建文件夹存放在com/sun/proxy下
反编译后如下:
接口类:
public interface Person { public void eat(); }
实现类:
public class Man implements Person{ @Override public void eat() { System.out.print("我吃饭了"); } }
InvocationHandler的实现类:
public class MyHandler implements InvocationHandler{ private Object object; public MyHandler(Object object) { this.object=object; } @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { // TODO Auto-generated method stub doBefore(); Object result; result=method.invoke(this.object, args);//这里是不是很熟悉,可以看看反射 doAfter(); return result; } private void doBefore(){ System.out.println("方法执行前"); } private void doAfter(){ System.out.println("方法执行后"); } }
测试类:
public class Test { public static void main(String[] args) { System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles","true"); Person man=new Man(); MyHandler handler=new MyHandler(man); Person proxy=(Person) Proxy.newProxyInstance(man.getClass().getClassLoader(), man.getClass().getInterfaces(), handler); System.out.println(proxy.getClass()); proxy.eat(); } }
System.getProperties().put(“sun.misc.ProxyGenerator.saveGeneratedFiles”,”true”);会保存生成的动态代理类$Proxy0,生成的代理类会自动新建文件夹存放在com/sun/proxy下
反编译后如下:
package com.sun.proxy; import com.gjh.test.Person; 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 Person { private static Method m1; private static Method m3; private static Method m2; private static Method m0; 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 (RuntimeException localRuntimeException) { throw localRuntimeException; } catch (Throwable localThrowable) { } throw new UndeclaredThrowableException(localThrowable); } public final void eat() throws { try { this.h.invoke(this, m3, null); return; } catch (RuntimeException localRuntimeException) { throw localRuntimeException; } catch (Throwable localThrowable) { } throw new UndeclaredThrowableException(localThrowable); } public final String toString() throws { try { return (String)this.h.invoke(this, m2, null); } catch (RuntimeException localRuntimeException) { throw localRuntimeException; } catch (Throwable localThrowable) { } throw new UndeclaredThrowableException(localThrowable); } public final int hashCode() throws { try { return ((Integer)this.h.invoke(this, m0, null)).intValue(); } catch (RuntimeException localRuntimeException) { throw localRuntimeException; } 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("com.gjh.test.Person").getMethod("eat", new Class[0]); m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]); m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]); return; } catch (NoSuchMethodException localNoSuchMethodException) { throw new NoSuchMethodError(localNoSuchMethodException.getMessage()); } catch (ClassNotFoundException localClassNotFoundException) { } throw new NoClassDefFoundError(localClassNotFoundException.getMessage()); } }
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