When you r checking out that the method invoke(Object proxy, Method method, Object[] args) declaration & the doc statement,you will find that the input parameter proxy
proxy - the proxy instance that the method was invoked on
when I am doing a test on java dynamic proxy,I find this proxy is produced by vm.So I do want to know why the method invoke has this param,which is surely nothing except that is just an object ($proxy0 )but don't have the actual action for our usage?
This very useful if you have single invocation handle for multiple proxy objects. So you can use hash map to store proxy states information. For example - Mokito test framework store proxy invocation history.
if you are chinese ,you can read this article http://rejoy.iteye.com/blog/1627405
he makes a decompliation of $proxy0.class, you should know that $proxy0 extends Proxy
public final class $Proxy0 extends Proxy implements UserService and there is a function in $proxy0:
public final void add() { try { //the h(invocationhandler) is in Proxy class,so we need pass this $proxy0 instance to super ,so the super(Proxy) can invoke($proxy0,method,args) super.h.invoke(this, m3, null); return; } catch(Error _ex) { } catch(Throwable throwable) { throw new UndeclaredThrowableException(throwable); } } we can use System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true"); to generate $proxy.class file.
decomplie the .class file, we will find this class every java methods (except native method) are invoked by InvocationHandler
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); } } super.h object is the InvocationHandler instance.
use System.out.println(proxy) in invocationHandler.invoke will cause infinite recursion and StackOverflowException.
so I think the only function about proxy parameter is use getClass() method to get the GeneratedProxy.class information, like which interfaces are implemented.
In InvocationHandler invoke method implemention, we can know the type of proxy object
So we can use an single InvocationHander class to deal with multiple proxy interfaces.
