java -- java.lang.reflect.proxy分析

proxy使用
实例1

实例2

简述
应用场景

分析javalangreflectProxy
静态方法

源码

proxy使用

实例1

http://www.cnblogs.com/linjiqin/archive/2011/02/18/1957600.html

实例2

/*
*Copyright (c) 2016, gp.inc and/or its affiliates. All rights reserved.
*/
package com.proxy.demo2;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;

public class ProxyStudy {

@SuppressWarnings("all")
public static void main(String[] args) throws Exception {
ClassLoader loader = Collection.class.getClassLoader();
Class<?>[] interfaces = new Class[] { Collection.class };

InvocationHandler h = new InvocationHandler() {
// proxyBuildColl是对ArrayList进行代理
ArrayList target = new ArrayList();

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
System.out.println(method.getName() + "执行之前...");
if (null != args) {
System.out.println("方法的参数：" + Arrays.asList(args));
} else {
System.out.println("方法的参数：" + null);
}
Object result = method.invoke(target, args);
System.out.println(method.getName() + "执行之后...");
return result;
}
};

Collection proxyBuildCollection2 = (Collection) Proxy.newProxyInstance(loader, interfaces, h);

proxyBuildCollection2.add("abc");
proxyBuildCollection2.size();
proxyBuildCollection2.clear();
proxyBuildCollection2.getClass().getName();
}
}

简述

动态代理，代理一个对象，间接执行相关操作，并且在执行操作前后可以增加额外操作，如日志。

应用场景

spring框架AOP中核心采用动态代理

org.springframework.aop.framework.CglibAopProxy

org.springframework.aop.framework.JdkDynamicAopProxy

两种动态代理的实现。

分析java.lang.reflect.Proxy

静态方法

方法

newProxyInstance

是我们经常用到的，返回目标对象。

Collection proxyBuildCollection2 = (Collection) Proxy.newProxyInstance(loader, interfaces, h);

源码

@CallerSensitive
public static Object newProxyInstance(ClassLoader loader,
Class<?>[] interfaces,
InvocationHandler h)
throws IllegalArgumentException
{
if (h == null) {
throw new NullPointerException();
}

final Class<?>[] intfs = interfaces.clone();
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
}

/*
* Look up or generate the designated proxy class.
*/
Class<?> cl = getProxyClass0(loader, intfs);

/*
* Invoke its constructor with the designated invocation handler.
*/
try {
final Constructor<?> cons = cl.getConstructor(constructorParams);
final InvocationHandler ih = h;
if (sm != null && ProxyAccessHelper.needsNewInstanceCheck(cl)) {
// create proxy instance with doPrivilege as the proxy class may
// implement non-public interfaces that requires a special permission
return AccessController.doPrivileged(new PrivilegedAction<Object>() {
public Object run() {
return newInstance(cons, ih);
}
});
} else {
return newInstance(cons, ih);
}
} catch (NoSuchMethodException e) {
throw new InternalError(e.toString());
}
}

看这行代码

Class<?> cl = getProxyClass0(loader, intfs);

private static Class<?> getProxyClass0(ClassLoader loader,
Class<?>... interfaces) {
if (interfaces.length > 65535) {
throw new IllegalArgumentException("interface limit exceeded");
}

// If the proxy class defined by the given loader implementing
// the given interfaces exists, this will simply return the cached copy;
// otherwise, it will create the proxy class via the ProxyClassFactory
return proxyClassCache.get(loader, interfaces);
}

proxyClassCache.get(loader, interfaces);

这行代码返回类对象

public V get(K key, P parameter) {
Objects.requireNonNull(parameter);

expungeStaleEntries();

Object cacheKey = CacheKey.valueOf(key, refQueue);

// lazily install the 2nd level valuesMap for the particular cacheKey
ConcurrentMap<Object, Supplier<V>> valuesMap = map.get(cacheKey);
if (valuesMap == null) {
ConcurrentMap<Object, Supplier<V>> oldValuesMap
= map.putIfAbsent(cacheKey,
valuesMap = new ConcurrentHashMap<>());
if (oldValuesMap != null) {
valuesMap = oldValuesMap;
}
}

// create subKey and retrieve the possible Supplier<V> stored by that
// subKey from valuesMap
Object subKey = Objects.requireNonNull(subKeyFactory.apply(key, parameter));
Supplier<V> supplier = valuesMap.get(subKey);
Factory factory = null;

while (true) {
if (supplier != null) {
// supplier might be a Factory or a CacheValue<V> instance
V value = supplier.get();
if (value != null) {
return value;
}
}
// else no supplier in cache
// or a supplier that returned null (could be a cleared CacheValue
// or a Factory that wasn't successful in installing the CacheValue)

// lazily construct a Factory
if (factory == null) {
factory = new Factory(key, parameter, subKey, valuesMap);
}

if (supplier == null) {
supplier = valuesMap.putIfAbsent(subKey, factory);
if (supplier == null) {
// successfully installed Factory
supplier = factory;
}
// else retry with winning supplier
} else {
if (valuesMap.replace(subKey, supplier, factory)) {
// successfully replaced
// cleared CacheEntry / unsuccessful Factory
// with our Factory
supplier = factory;
} else {
// retry with current supplier
supplier = valuesMap.get(subKey);
}
}
}
}

Object subKey = Objects.requireNonNull(subKeyFactory.apply(key, parameter));

这行代码核心。

点进去，发现是一个接口

interface BiFunction<T, U, R> {

/**
* Applies this function to the given arguments.
*
* @param t the first function argument
* @param u the second function argument
* @return the function result
*/
R apply(T t, U u);
}

实现类



用到了

ProxyClassFactory

类

详见：

private static final WeakCache<ClassLoader, Class<?>[], Class<?>>
proxyClassCache = new WeakCache<>(new KeyFactory(), new ProxyClassFactory());

ProxyClassFactory

源码

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) {

Map<Class<?>, Boolean> interfaceSet = new IdentityHashMap<>(interfaces.length);
for (Class<?> intf : interfaces) {
/*
* Verify that the class loader resolves the name of this
* interface to the same Class object.
*/
Class<?> interfaceClass = null;
try {
interfaceClass = Class.forName(intf.getName(), false, loader);
} catch (ClassNotFoundException e) {
}
if (interfaceClass != intf) {
throw new IllegalArgumentException(
intf + " is not visible from class loader");
}
/*
* Verify that the Class object actually represents an
* interface.
*/
if (!interfaceClass.isInterface()) {
throw new IllegalArgumentException(
interfaceClass.getName() + " is not an interface");
}
/*
* Verify that this interface is not a duplicate.
*/
if (interfaceSet.put(interfaceClass, Boolean.TRUE) != null) {
throw new IllegalArgumentException(
"repeated interface: " + interfaceClass.getName());
}
}

String proxyPkg = null;     // package to define proxy class in

/*
* Record the package of a non-public proxy interface so that the
* proxy class will be defined in the same package.  Verify that
* all non-public proxy interfaces are in the same package.
*/
for (Class<?> intf : interfaces) {
int flags = intf.getModifiers();
if (!Modifier.isPublic(flags)) {
String name = intf.getName();
int n = name.lastIndexOf('.');
String pkg = ((n == -1) ? "" : name.substring(0, n + 1));
if (proxyPkg == null) {
proxyPkg = pkg;
} else if (!pkg.equals(proxyPkg)) {
throw new IllegalArgumentException(
"non-public interfaces from different packages");
}
}
}

if (proxyPkg == null) {
// if no non-public proxy interfaces, use com.sun.proxy package
proxyPkg = ReflectUtil.PROXY_PACKAGE + ".";
}

/*
* Choose a name for the proxy class to generate.
*/
long num = nextUniqueNumber.getAndIncrement();
String proxyName = proxyPkg + proxyClassNamePrefix + num;

/*
* Generate the specified proxy class.
*/
byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
proxyName, interfaces);
try {
return defineClass0(loader, proxyName,
proxyClassFile, 0, proxyClassFile.length);
} catch (ClassFormatError e) {
/*
* A ClassFormatError here means that (barring bugs in the
* proxy class generation code) there was some other
* invalid aspect of the arguments supplied to the proxy
* class creation (such as virtual machine limitations
* exceeded).
*/
throw new IllegalArgumentException(e.toString());
}
}
}

关键代码

byte[] proxyClassFile = ProxyGenerator.generateProxyClass(

proxyName, interfaces);

源码

下面这段源码属于sun包下的，oracle并没有开放源码，我在下面网址收到的源码：http://www.docjar.com/html/api/sun/misc/ProxyGenerator.java.html，生成代理类的class文件

public static byte[] generateProxyClass(final String name,
Class[] interfaces)
{
ProxyGenerator gen = new ProxyGenerator(name, interfaces);
final byte[] classFile = gen.generateClassFile();

if (saveGeneratedFiles) {
java.security.AccessController.doPrivileged(
new java.security.PrivilegedAction<Void>() {
public Void run() {
try {
FileOutputStream file =
new FileOutputStream(dotToSlash(name) + ".class");
file.write(classFile);
file.close();
return null;
} catch (IOException e) {
throw new InternalError(
"I/O exception saving generated file: " + e);
}
}
});
}

return classFile;
}

private static native Class defineClass0(ClassLoader loader, String name,
byte[] b, int off, int len);

这块代码使用native修饰，具体实现不是使用java编写，应该是在jvm中使用c编写的。

所有的代码生成的工作都由神秘的ProxyGenerator所完成了，当你尝试去探索这个类时，你所能获得的信息仅仅是它位于并未公开的sun.misc包，有若干常量、变量和方法以完成这个神奇的代码生成的过程，但是sun并没有提供源代码以供研读。至于动态类的定义，则由Proxy的native静态方法defineClass0执行。

网上找到一块代码，使用C++实现的defineClass0方法

/*
* Clasbs:     com_test_start_CommonClassLoader
* Method:    defineClass0
* Signature: (Ljava/lang/String;[BII)Ljava/lang/Class;
*/
JNIEXPORT jclass JNICALL Java_com_test_start_CommonClassLoader_defineClass0
(JNIEnv *env, jobject loader, jstring  name, jbyteArray buffer, jint start, jint len)
{
jbyteArray temp=env->NewByteArray(len);//new一个数组，并申请一块内存
arraycopy(env,buffer,start,temp,start,len);//数组的复制相当于System.copy()方法
jbyteArray byte0=encrypt(env,temp,len);//进行class文件的解密操作
if(byte0==NULL)
{
env->DeleteLocalRef(temp);//释放内存
return NULL;
}
jsize size=env->GetArrayLength(byte0);//技术数组的长度相当于Array的length属性
jclass classLoader=env->GetSuperclass(env->GetSuperclass(env->GetSuperclass(env->GetObjectClass(loader))));//获取父类装载器
jmethodID mid=env->GetMethodID(classLoader,"defineClass","(Ljava/lang/String;[BII)Ljava/lang/Class;");//获取defineClass方法
defineClass jclass cls=(jclass)env->CallObjectMethod(loader,mid,name,byte0,start,size);//调用Classloader的defineClass定义一个类到jvm中
env->DeleteLocalRef(byte0);//释放内存
return cls;
}