上次我们讲解的cglib的动态代理的实现,今天我们看下JDK proxy的实现原理
- 对类Subject的方法执行前和执行后显示当前时间戳
import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
public class TestProxy {
public static interface ISubject {
void sayHi();
}
public static class Subject implements ISubject {
public void sayHi() {
System.out.println("Subject1-sayHi");
}
}
static class ProxyInvocationHandler<T> implements InvocationHandler {
public ProxyInvocationHandler(T target) {
this.target = target;
}
private T target;
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
System.out.println("开始时间:"+System.currentTimeMillis());
Object result = method.invoke(target, args);
System.out.println("结束时间:"+System.currentTimeMillis());
return result;
}
}
public static void main(String[] args) throws Exception {
RuntimeMXBean runtimeMXBean = ManagementFactory.getRuntimeMXBean();
System.out.println("pid=" + runtimeMXBean.getName().split("@")[0]);
System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");
ISubject subject = (ISubject) Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(),
new Class[]{ISubject.class}, new ProxyInvocationHandler<ISubject>(new Subject()));
System.out.println("ProxyInstance的类型:"+subject.getClass().getSimpleName());
subject.sayHi();
}
}
pid=3320
ProxyInstance的类型:$Proxy0
开始时间:1543648238358
Subject1-sayHi
结束时间:1543648238358
- 在1中的结果看到Proxy.newProxyInstance生成的类subject,它的类型为
Proxy0代码如下:
package com.sun.proxy;
import TestProxy.ISubject;
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 ISubject {
private static Method m1;
private static Method m3;
private static Method m2;
private static Method m0;
public $Proxy0(InvocationHandler var1) throws {
super(var1);
}
public final boolean equals(Object var1) throws {
try {
return ((Boolean)super.h.invoke(this, m1, new Object[]{var1})).booleanValue();
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
public final void sayHi() throws {
try {
super.h.invoke(this, m3, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
public final String toString() throws {
try {
return (String)super.h.invoke(this, m2, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
public final int hashCode() throws {
try {
return ((Integer)super.h.invoke(this, m0, (Object[])null)).intValue();
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
static {
try {
m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[]{Class.forName("java.lang.Object")});
m3 = Class.forName("TestProxy$ISubject").getMethod("sayHi", 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]);
} catch (NoSuchMethodException var2) {
throw new NoSuchMethodError(var2.getMessage());
} catch (ClassNotFoundException var3) {
throw new NoClassDefFoundError(var3.getMessage());
}
}
}
- 原理分析
&Proxy0实现ISubject接口,并将sayHi重写为执行InvocationHandler#invoke方法,在InvocationHandler中我们使用反射Method进行执行代码,并前后包装打印当前时间戳（反射method执行原理） - &Proxy0生成:ProxyGenerator.generateProxyClass生成字节码文件并使用类加载器进行加载(Proxy.newProxyInstancede的第一个参数为类加载器)他们名称就是proxyClassNamePrefix+nextUniqueNumber.getAndIncrement();
private static final class ProxyClassFactory
implements BiFunction<ClassLoader, Class<?>[], Class<?>>
{
// prefix for all proxy class names
private static final String proxyClassNamePrefix = "$Proxy";
// next number to use for generation of unique proxy class names
private static final AtomicLong nextUniqueNumber = new AtomicLong();
@Override
public Class<?> apply(ClassLoader loader, Class<?>[] interfaces) {
.........
long num = nextUniqueNumber.getAndIncrement();
String proxyName = proxyPkg + proxyClassNamePrefix + num;
byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
proxyName, interfaces, accessFlags);
try {
return defineClass0(loader, proxyName,
proxyClassFile, 0, proxyClassFile.length);
} catch (ClassFormatError e) {
throw new IllegalArgumentException(e.toString());
}
}
}
5.&Proxy0的方法包含hashCodeMethod,equalsMethod,toStringMethod,interfaces.getMethods()
this.addProxyMethod(hashCodeMethod, Object.class);
this.addProxyMethod(equalsMethod, Object.class);
this.addProxyMethod(toStringMethod, Object.class);
Class[] var1 = this.interfaces;
int var2 = var1.length;
int var3;
Class var4;
for(var3 = 0; var3 < var2; ++var3) {
var4 = var1[var3];
Method[] var5 = var4.getMethods();
int var6 = var5.length;
for(int var7 = 0; var7 < var6; ++var7) {
Method var8 = var5[var7];
this.addProxyMethod(var8, var4);
}
}
