天天研究各种框架，一问是利用什么技术，都说是用java的动态代理。但动态代理到底怎么玩，源码是什么样？
下面我们先看看一个简单的应用
作为例子，力求简单，Tool是一个接口，有个operate方法。ConcreateInvocationHandler 实现了InvocationHandler接口，实现的invoke方法中，利用方法入参和被代理对象，用反射技术实现，对象方法调用。main方法中，Proxy.newProxyInstance 创建一个包裹被代理对象并实现Tool接口的代理对象。调用代理对象，最终调用了被代理对象的方法***
public class Main {
public static void main(String[] args) {
System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles","true");
ConcreateInvocationHandler concreateInvocationHandler = new ConcreateInvocationHandler();
Tool proxy= (Tool) Proxy.newProxyInstance(concreateInvocationHandler.getClass().getClassLoader(), new Class<?>[]{Tool.class}, concreateInvocationHandler);
proxy.operate();
}
public interface Tool{
public void operate();
}
public static class ConcreateInvocationHandler implements InvocationHandler{
Tool tool = new SawTool();
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
System.out.println("代理类的方法将被调用");
method.invoke(tool,args);
System.out.println("代理类的方法调用完毕");
return null;
}
}
public static class SawTool implements Tool{
@Override
public void operate() {
System.out.println("开始据木头");
}
}
}
打印结果
代理类的方法将被调用
开始据木头
代理类的方法调用完毕
Process finished with exit code 0
特意在main方法中加了这一行代码，这样Proxy的生成类看到在项目中看到
System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles","true");
这个$Proxy0类继承于Proxy，实现我们创建的接口Tool.内部依次命名四个方法m0-m3。其中m0-m2已经被Object的三个方法：hashCode，equals，toString内定了。m3开始就是我们写的接口里的方法，依次m4,m5,m6… static静态代码段在加载类的时候完成，类中静态成员变量Method系列的赋值。在该类的方法被调用时，都是通过super.h（其实就是我们的ConcreateInvocationHandler）来调用他的invoke方法来调用我们的实现.
public final class $Proxy0 extends Proxy implements Tool {
private static Method m1;
private static Method m2;
private static Method m0;
private static Method m3;
public $Proxy0(InvocationHandler var1) throws {
super(var1);
}
public final boolean equals(Object var1) throws {
try {
return (Boolean)super.h.invoke(this, m1, new Object[]{var1});
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
public final String toString() throws {
try {
return (String)super.h.invoke(this, m2, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
public final int hashCode() throws {
try {
return (Integer)super.h.invoke(this, m0, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
public final void operate() throws {
try {
super.h.invoke(this, m3, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
static {
try {
m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
m2 = Class.forName("java.lang.Object").getMethod("toString");
m0 = Class.forName("java.lang.Object").getMethod("hashCode");
m3 = Class.forName("Main$Tool").getMethod("operate");
} catch (NoSuchMethodException var2) {
throw new NoSuchMethodError(var2.getMessage());
} catch (ClassNotFoundException var3) {
throw new NoClassDefFoundError(var3.getMessage());
}
}
}
从例子来看，Proxy完成了具体实现和接口的绑定，并对用户程序员无感的调用。一般的框架都是保证了稳定的接口，然后对具体实现扩展态度，你可以自己依照接口实现各种协议，由框架帮你应用到内部，供其他模块调用。在运行时中生成对应字节码，对比编译时注解生成器，aspectj，可能来说，在运行时的初次性能有点损耗，但不影响利用该技术实现强大的框架。下面着重分析下内部源码，并理性的止步于native 字节码生成的调用。jni,c++的代码有时间后续再做分析
首先是InvocationHandler接口源码，他充当一个中间人的角色存在于proxy的成员变量。最后活还是委托实际的实现类负责干
public interface InvocationHandler {
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable;
}
public class Proxy implements java.io.Serializable {
private static final long serialVersionUID = -2222568056686623797L;
/** parameter types of a proxy class constructor */
private static final Class<?>[] constructorParams =
{ InvocationHandler.class };
/**
* a cache of proxy classes
*/
private static final WeakCache<ClassLoader, Class<?>[], Class<?>>
proxyClassCache = new WeakCache<>(new KeyFactory(), new ProxyClassFactory());
/**
* the invocation handler for this proxy instance.
* @serial
*/
protected InvocationHandler h;
/**
* Prohibits instantiation.
*/
private Proxy() {
}
protected Proxy(InvocationHandler h) {
Objects.requireNonNull(h);
this.h = h;
}
@CallerSensitive
public static Class<?> getProxyClass(ClassLoader loader,
Class<?>... interfaces)
throws IllegalArgumentException
{
final Class<?>[] intfs = interfaces.clone();
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
}
return getProxyClass0(loader, intfs);
}
private static void checkProxyAccess(Class<?> caller,
ClassLoader loader,
Class<?>... interfaces)
{
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
ClassLoader ccl = caller.getClassLoader();
if (VM.isSystemDomainLoader(loader) && !VM.isSystemDomainLoader(ccl)) {
sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
}
ReflectUtil.checkProxyPackageAccess(ccl, interfaces);
}
}
/**
* Generate a proxy class. Must call the checkProxyAccess method
* to perform permission checks before calling this.
*/
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);
}
/*
* a key used for proxy class with 0 implemented interfaces
*/
private static final Object key0 = new Object();
private static final class Key1 extends WeakReference<Class<?>> {
private final int hash;
Key1(Class<?> intf) {
super(intf);
this.hash = intf.hashCode();
}
@Override
public int hashCode() {
return hash;
}
@Override
public boolean equals(Object obj) {
Class<?> intf;
return this == obj ||
obj != null &&
obj.getClass() == Key1.class &&
(intf = get()) != null &&
intf == ((Key1) obj).get();
}
}
/*
* a key used for proxy class with 2 implemented interfaces
*/
private static final class Key2 extends WeakReference<Class<?>> {
private final int hash;
private final WeakReference<Class<?>> ref2;
Key2(Class<?> intf1, Class<?> intf2) {
super(intf1);
hash = 31 * intf1.hashCode() + intf2.hashCode();
ref2 = new WeakReference<Class<?>>(intf2);
}
@Override
public int hashCode() {
return hash;
}
@Override
public boolean equals(Object obj) {
Class<?> intf1, intf2;
return this == obj ||
obj != null &&
obj.getClass() == Key2.class &&
(intf1 = get()) != null &&
intf1 == ((Key2) obj).get() &&
(intf2 = ref2.get()) != null &&
intf2 == ((Key2) obj).ref2.get();
}
}
/*
* a key used for proxy class with any number of implemented interfaces
* (used here for 3 or more only)
*/
private static final class KeyX {
private final int hash;
private final WeakReference<Class<?>>[] refs;
@SuppressWarnings("unchecked")
KeyX(Class<?>[] interfaces) {
hash = Arrays.hashCode(interfaces);
refs = (WeakReference<Class<?>>[])new WeakReference<?>[interfaces.length];
for (int i = 0; i < interfaces.length; i++) {
refs[i] = new WeakReference<>(interfaces[i]);
}
}
@Override
public int hashCode() {
return hash;
}
@Override
public boolean equals(Object obj) {
return this == obj ||
obj != null &&
obj.getClass() == KeyX.class &&
equals(refs, ((KeyX) obj).refs);
}
private static boolean equals(WeakReference<Class<?>>[] refs1,
WeakReference<Class<?>>[] refs2) {
if (refs1.length != refs2.length) {
return false;
}
for (int i = 0; i < refs1.length; i++) {
Class<?> intf = refs1[i].get();
if (intf == null || intf != refs2[i].get()) {
return false;
}
}
return true;
}
}
/**
* A function that maps an array of interfaces to an optimal key where
* Class objects representing interfaces are weakly referenced.
*/
private static final class KeyFactory
implements BiFunction<ClassLoader, Class<?>[], Object>
{
@Override
public Object apply(ClassLoader classLoader, Class<?>[] interfaces) {
switch (interfaces.length) {
case 1: return new Key1(interfaces[0]); // the most frequent
case 2: return new Key2(interfaces[0], interfaces[1]);
case 0: return key0;
default: return new KeyX(interfaces);
}
}
}
/**
* A factory function that generates, defines and returns the proxy class given
* the ClassLoader and array of interfaces.
*/
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
int accessFlags = Modifier.PUBLIC | Modifier.FINAL;
/*
* 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)) {
accessFlags = Modifier.FINAL;
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, accessFlags);
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());
}
}
}
@CallerSensitive
public static Object newProxyInstance(ClassLoader loader,
Class<?>[] interfaces,
InvocationHandler h)
throws IllegalArgumentException
{
Objects.requireNonNull(h);
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 {
if (sm != null) {
checkNewProxyPermission(Reflection.getCallerClass(), cl);
}
final Constructor<?> cons = cl.getConstructor(constructorParams);
final InvocationHandler ih = h;
if (!Modifier.isPublic(cl.getModifiers())) {
AccessController.doPrivileged(new PrivilegedAction<Void>() {
public Void run() {
cons.setAccessible(true);
return null;
}
});
}
return cons.newInstance(new Object[]{h});
} catch (IllegalAccessException|InstantiationException e) {
throw new InternalError(e.toString(), e);
} catch (InvocationTargetException e) {
Throwable t = e.getCause();
if (t instanceof RuntimeException) {
throw (RuntimeException) t;
} else {
throw new InternalError(t.toString(), t);
}
} catch (NoSuchMethodException e) {
throw new InternalError(e.toString(), e);
}
}
private static void checkNewProxyPermission(Class<?> caller, Class<?> proxyClass) {
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
if (ReflectUtil.isNonPublicProxyClass(proxyClass)) {
ClassLoader ccl = caller.getClassLoader();
ClassLoader pcl = proxyClass.getClassLoader();
// do permission check if the caller is in a different runtime package
// of the proxy class
int n = proxyClass.getName().lastIndexOf('.');
String pkg = (n == -1) ? "" : proxyClass.getName().substring(0, n);
n = caller.getName().lastIndexOf('.');
String callerPkg = (n == -1) ? "" : caller.getName().substring(0, n);
if (pcl != ccl || !pkg.equals(callerPkg)) {
sm.checkPermission(new ReflectPermission("newProxyInPackage." + pkg));
}
}
}
}
public static boolean isProxyClass(Class<?> cl) {
return Proxy.class.isAssignableFrom(cl) && proxyClassCache.containsValue(cl);
}
@CallerSensitive
public static InvocationHandler getInvocationHandler(Object proxy)
throws IllegalArgumentException
{
/*
* Verify that the object is actually a proxy instance.
*/
if (!isProxyClass(proxy.getClass())) {
throw new IllegalArgumentException("not a proxy instance");
}
final Proxy p = (Proxy) proxy;
final InvocationHandler ih = p.h;
if (System.getSecurityManager() != null) {
Class<?> ihClass = ih.getClass();
Class<?> caller = Reflection.getCallerClass();
if (ReflectUtil.needsPackageAccessCheck(caller.getClassLoader(),
ihClass.getClassLoader()))
{
ReflectUtil.checkPackageAccess(ihClass);
}
}
return ih;
}
private static native Class<?> defineClass0(ClassLoader loader, String name,
byte[] b, int off, int len);
}
Proxy是所有生成代理类的父类，他支持序列化
public class Proxy implements java.io.Serializable
Proxy有个单参构造方法。这个静态常量数组用于反射创建代理类实例
private static final Class<?>[] constructorParams =
{ InvocationHandler.class };
只支持单入参的构造函数创建
protected InvocationHandler h;
private Proxy() {
}
protected Proxy(InvocationHandler h) {
Objects.requireNonNull(h);
this.h = h;
}
其实动态代理对象有两种方式，本文的例子使用的是比较简单的一种
@CallerSensitive
public static Class<?> getProxyClass(ClassLoader loader,
Class<?>... interfaces)
throws IllegalArgumentException
{
final Class<?>[] intfs = interfaces.clone();
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
}
return getProxyClass0(loader, intfs);
}
//eg：：：：：：：：：：：：
InvocationHandler handler = new MyInvocationHandler(...);
proxyClass = Proxy.getProxyClass(Foo.class.getClassLoader(), Foo.class);
Foo f = (Foo) proxyClass.getConstructor(InvocationHandler.class).
newInstance(handler);
创建之前，要做权限检查
final Class<?>[] intfs = interfaces.clone();
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
}
存在一种情况，接口本身不是公有的，那个依据接口造出的动态代理对象类也要是同样的ClassLoader并具有包访问权限。checkProxyPackageAccess这个检查包权限写法真“牛逼”，var0-var7.你是要把我绕死嘛
private static void checkProxyAccess(Class<?> caller,
ClassLoader loader,
Class<?>... interfaces)
{
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
ClassLoader ccl = caller.getClassLoader();
if (VM.isSystemDomainLoader(loader) && !VM.isSystemDomainLoader(ccl)) {
sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
}
ReflectUtil.checkProxyPackageAccess(ccl, interfaces);
}
}
public static void checkProxyPackageAccess(ClassLoader var0, Class... var1) {
SecurityManager var2 = System.getSecurityManager();
if (var2 != null) {
Class[] var3 = var1;
int var4 = var1.length;
for(int var5 = 0; var5 < var4; ++var5) {
Class var6 = var3[var5];
ClassLoader var7 = var6.getClassLoader();
if (needsPackageAccessCheck(var0, var7)) {
checkPackageAccess(var6);
}
}
}
}
65535做安卓的都很熟悉啊，只不过这里是虚拟机限制实现的interfaces不能超过这个数字。
private static Class<?> getProxyClass0(ClassLoader loader,
Class<?>... interfaces) {
if (interfaces.length > 65535) {
throw new IllegalArgumentException("interface limit exceeded");
}
return proxyClassCache.get(loader, interfaces);
}
暂时我们先介绍这个WeakCache是个缓存的作用，主要有key ,sub-key， value。 之所以Weak打头，是因为，key, value 都是弱引用但sub-key是强引用。
private static final WeakCache<ClassLoader, Class<?>[], Class<?>>
proxyClassCache = new WeakCache<>(new KeyFactory(), new ProxyClassFactory());
检查一个类是不是动态代理类
public static boolean isProxyClass(Class<?> cl) {
return Proxy.class.isAssignableFrom(cl) && proxyClassCache.containsValue(cl);
}
获取动态代理类的InvocationHandler实例，首先判断是不是动态代理类，接着，取出InvocationHandler实例，下面还是对包访问权限的检查工作，通过了就返回，否则抛出异常
@CallerSensitive
public static InvocationHandler getInvocationHandler(Object proxy)
throws IllegalArgumentException
{
/*
* Verify that the object is actually a proxy instance.
*/
if (!isProxyClass(proxy.getClass())) {
throw new IllegalArgumentException("not a proxy instance");
}
final Proxy p = (Proxy) proxy;
final InvocationHandler ih = p.h;
if (System.getSecurityManager() != null) {
Class<?> ihClass = ih.getClass();
Class<?> caller = Reflection.getCallerClass();
if (ReflectUtil.needsPackageAccessCheck(caller.getClassLoader(),
ihClass.getClassLoader()))
{
ReflectUtil.checkPackageAccess(ihClass);
}
}
return ih;
}
再看看我们例子中使用的创建方法。入参ClassLoader， Class<?>[]，InvocationHandler. 第一行非空检查,接着访问权限检查，又见getProxyClass0方法，取出创建的动态代理类的Class.
public static Object newProxyInstance(ClassLoader loader,
Class<?>[] interfaces,
InvocationHandler h)
throws IllegalArgumentException
{
Objects.requireNonNull(h);
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 {
if (sm != null) {
checkNewProxyPermission(Reflection.getCallerClass(), cl);
}
final Constructor<?> cons = cl.getConstructor(constructorParams);
final InvocationHandler ih = h;
if (!Modifier.isPublic(cl.getModifiers())) {
AccessController.doPrivileged(new PrivilegedAction<Void>() {
public Void run() {
cons.setAccessible(true);
return null;
}
});
}
return cons.newInstance(new Object[]{h});
} catch (IllegalAccessException|InstantiationException e) {
throw new InternalError(e.toString(), e);
} catch (InvocationTargetException e) {
Throwable t = e.getCause();
if (t instanceof RuntimeException) {
throw (RuntimeException) t;
} else {
throw new InternalError(t.toString(), t);
}
} catch (NoSuchMethodException e) {
throw new InternalError(e.toString(), e);
}
}
不是sun.
private static void checkNewProxyPermission(Class<?> caller, Class<?> proxyClass) {
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
if (ReflectUtil.isNonPublicProxyClass(proxyClass)) {
ClassLoader ccl = caller.getClassLoader();
ClassLoader pcl = proxyClass.getClassLoader();
// do permission check if the caller is in a different runtime package
// of the proxy class
int n = proxyClass.getName().lastIndexOf('.');
String pkg = (n == -1) ? "" : proxyClass.getName().substring(0, n);
n = caller.getName().lastIndexOf('.');
String callerPkg = (n == -1) ? "" : caller.getName().substring(0, n);
if (pcl != ccl || !pkg.equals(callerPkg)) {
sm.checkPermission(new ReflectPermission("newProxyInPackage." + pkg));
}
}
}
}
大家都记得Proxy创建的类会在com.sun.proxy包下面，那个46就是 ‘.’的ascii码，对不在该包下的创建要做权限检查。
public static boolean isNonPublicProxyClass(Class<?> var0) {
String var1 = var0.getName();
int var2 = var1.lastIndexOf(46);
String var3 = var2 != -1 ? var1.substring(0, var2) : "";
return Proxy.isProxyClass(var0) && !var3.equals("com.sun.proxy");
}
有了动态代理类的class ,下面的反射创建实例大家就很熟悉了，首先取构造方法，判断开放性，突破，最后cons.newInstance(new Object[]{h})返回一个实例，外面就可以开心的调用了
final Constructor<?> cons = cl.getConstructor(constructorParams);
final InvocationHandler ih = h;
if (!Modifier.isPublic(cl.getModifiers())) {
AccessController.doPrivileged(new PrivilegedAction<Void>() {
public Void run() {
cons.setAccessible(true);
return null;
}
});
}
return cons.newInstance(new Object[]{h});
KeyFactory 工厂类。BiFunction 是java8中函数编程引入的，三个范型，apply方法使用他们，前两个入参，后一个返回值。switch函数分别根据动态代理类要实现的接口数量返回key0,Key1,Key2,KeyX.
private static final class KeyFactory
implements BiFunction<ClassLoader, Class<?>[], Object>
{
@Override
public Object apply(ClassLoader classLoader, Class<?>[] interfaces) {
switch (interfaces.length) {
case 1: return new Key1(interfaces[0]); // the most frequent
case 2: return new Key2(interfaces[0], interfaces[1]);
case 0: return key0;
default: return new KeyX(interfaces);
}
}
}
key0是一个常量，key1,key2,keyx分别是继承WeakReference 包含一到多键。实现了hashCode,equals方法
private static final Object key0 = new Object();
private static final class Key1 extends WeakReference<Class<?>> {
private final int hash;
Key1(Class<?> intf) {
super(intf);
this.hash = intf.hashCode();
}
@Override
public int hashCode() {
return hash;
}
@Override
public boolean equals(Object obj) {
Class<?> intf;
return this == obj ||
obj != null &&
obj.getClass() == Key1.class &&
(intf = get()) != null &&
intf == ((Key1) obj).get();
}
}
/*
* a key used for proxy class with 2 implemented interfaces
*/
private static final class Key2 extends WeakReference<Class<?>> {
private final int hash;
private final WeakReference<Class<?>> ref2;
Key2(Class<?> intf1, Class<?> intf2) {
super(intf1);
hash = 31 * intf1.hashCode() + intf2.hashCode();
ref2 = new WeakReference<Class<?>>(intf2);
}
@Override
public int hashCode() {
return hash;
}
@Override
public boolean equals(Object obj) {
Class<?> intf1, intf2;
return this == obj ||
obj != null &&
obj.getClass() == Key2.class &&
(intf1 = get()) != null &&
intf1 == ((Key2) obj).get() &&
(intf2 = ref2.get()) != null &&
intf2 == ((Key2) obj).ref2.get();
}
}
/*
* a key used for proxy class with any number of implemented interfaces
* (used here for 3 or more only)
*/
private static final class KeyX {
private final int hash;
private final WeakReference<Class<?>>[] refs;
@SuppressWarnings("unchecked")
KeyX(Class<?>[] interfaces) {
hash = Arrays.hashCode(interfaces);
refs = (WeakReference<Class<?>>[])new WeakReference<?>[interfaces.length];
for (int i = 0; i < interfaces.length; i++) {
refs[i] = new WeakReference<>(interfaces[i]);
}
}
@Override
public int hashCode() {
return hash;
}
@Override
public boolean equals(Object obj) {
return this == obj ||
obj != null &&
obj.getClass() == KeyX.class &&
equals(refs, ((KeyX) obj).refs);
}
private static boolean equals(WeakReference<Class<?>>[] refs1,
WeakReference<Class<?>>[] refs2) {
if (refs1.length != refs2.length) {
return false;
}
for (int i = 0; i < refs1.length; i++) {
Class<?> intf = refs1[i].get();
if (intf == null || intf != refs2[i].get()) {
return false;
}
}
return true;
}
}
ProxyClassFactory工厂类是动态代理类class的生成类。
/**
* A factory function that generates, defines and returns the proxy class given
* the ClassLoader and array of interfaces.
*/
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
int accessFlags = Modifier.PUBLIC | Modifier.FINAL;
/*
* 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)) {
accessFlags = Modifier.FINAL;
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, accessFlags);
try {
return defineClass0(loader, proxyName,
proxyClassFile, 0, proxyClassFile.length);
} catch (ClassFormatError e) {
throw new IllegalArgumentException(e.toString());
}
}
}
生成类名的前缀+index ,就是 Proxy1，…,$ProxyN
// prefix for all proxy class names
private static final String proxyClassNamePrefix = "$Proxy";
// next number to use for generation of unique proxy class names
private static final AtomicLong nextUniqueNumber = new AtomicLong();
接着是接口验证，class能加载，是否是接口，去重。
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());
}
}
默认情况Class被定义成public final。但假如接口不是公共的，那个动态代理类只能是final. 且后续要验证在同一包下。
String proxyPkg = null; // package to define proxy class in
int accessFlags = Modifier.PUBLIC | Modifier.FINAL;
/*
* 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)) {
accessFlags = Modifier.FINAL;
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");
}
}
}
*一般情况下，接口都是公共的，就是com.sun.proxy做为包名，类名前缀固定，后面加递增索引。
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;
剩下的就是class字节码的生成工作。
byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
proxyName, interfaces, accessFlags);
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());
}
private static native Class<?> defineClass0(ClassLoader loader, String name,
byte[] b, int off, int len);
最后我们来看WeakCache这个部分，分key ，subkey , value 。key 和value是弱引用，subkey 是强引用。
final class WeakCache<K, P, V> {
private final ReferenceQueue<K> refQueue
= new ReferenceQueue<>();
// the key type is Object for supporting null key
private final ConcurrentMap<Object, ConcurrentMap<Object, Supplier<V>>> map
= new ConcurrentHashMap<>();
private final ConcurrentMap<Supplier<V>, Boolean> reverseMap
= new ConcurrentHashMap<>();
private final BiFunction<K, P, ?> subKeyFactory;
private final BiFunction<K, P, V> valueFactory;
public WeakCache(BiFunction<K, P, ?> subKeyFactory,
BiFunction<K, P, V> valueFactory) {
this.subKeyFactory = Objects.requireNonNull(subKeyFactory);
this.valueFactory = Objects.requireNonNull(valueFactory);
}
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;
}
}
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);
}
}
}
}
public boolean containsValue(V value) {
Objects.requireNonNull(value);
expungeStaleEntries();
return reverseMap.containsKey(new LookupValue<>(value));
}
public int size() {
expungeStaleEntries();
return reverseMap.size();
}
private void expungeStaleEntries() {
CacheKey<K> cacheKey;
while ((cacheKey = (CacheKey<K>)refQueue.poll()) != null) {
cacheKey.expungeFrom(map, reverseMap);
}
}
private final class Factory implements Supplier<V> {
private final K key;
private final P parameter;
private final Object subKey;
private final ConcurrentMap<Object, Supplier<V>> valuesMap;
Factory(K key, P parameter, Object subKey,
ConcurrentMap<Object, Supplier<V>> valuesMap) {
this.key = key;
this.parameter = parameter;
this.subKey = subKey;
this.valuesMap = valuesMap;
}
@Override
public synchronized V get() { // serialize access
// re-check
Supplier<V> supplier = valuesMap.get(subKey);
if (supplier != this) {
return null;
}
// else still us (supplier == this)
// create new value
V value = null;
try {
value = Objects.requireNonNull(valueFactory.apply(key, parameter));
} finally {
if (value == null) { // remove us on failure
valuesMap.remove(subKey, this);
}
}
// the only path to reach here is with non-null value
assert value != null;
// wrap value with CacheValue (WeakReference)
CacheValue<V> cacheValue = new CacheValue<>(value);
// put into reverseMap
reverseMap.put(cacheValue, Boolean.TRUE);
// try replacing us with CacheValue (this should always succeed)
if (!valuesMap.replace(subKey, this, cacheValue)) {
throw new AssertionError("Should not reach here");
}
// successfully replaced us with new CacheValue -> return the value
// wrapped by it
return value;
}
}
private interface Value<V> extends Supplier<V> {}
private static final class LookupValue<V> implements Value<V> {
private final V value;
LookupValue(V value) {
this.value = value;
}
@Override
public V get() {
return value;
}
@Override
public int hashCode() {
return System.identityHashCode(value); // compare by identity
}
@Override
public boolean equals(Object obj) {
return obj == this ||
obj instanceof Value &&
this.value == ((Value<?>) obj).get(); // compare by identity
}
}
/**
* A {@link Value} that weakly references the referent.
*/
private static final class CacheValue<V>
extends WeakReference<V> implements Value<V>
{
private final int hash;
CacheValue(V value) {
super(value);
this.hash = System.identityHashCode(value); // compare by identity
}
@Override
public int hashCode() {
return hash;
}
@Override
public boolean equals(Object obj) {
V value;
return obj == this ||
obj instanceof Value &&
// cleared CacheValue is only equal to itself
(value = get()) != null &&
value == ((Value<?>) obj).get(); // compare by identity
}
}
private static final class CacheKey<K> extends WeakReference<K> {
// a replacement for null keys
private static final Object NULL_KEY = new Object();
static <K> Object valueOf(K key, ReferenceQueue<K> refQueue) {
return key == null
// null key means we can't weakly reference it,
// so we use a NULL_KEY singleton as cache key
? NULL_KEY
// non-null key requires wrapping with a WeakReference
: new CacheKey<>(key, refQueue);
}
private final int hash;
private CacheKey(K key, ReferenceQueue<K> refQueue) {
super(key, refQueue);
this.hash = System.identityHashCode(key); // compare by identity
}
@Override
public int hashCode() {
return hash;
}
@Override
public boolean equals(Object obj) {
K key;
return obj == this ||
obj != null &&
obj.getClass() == this.getClass() &&
// cleared CacheKey is only equal to itself
(key = this.get()) != null &&
// compare key by identity
key == ((CacheKey<K>) obj).get();
}
void expungeFrom(ConcurrentMap<?, ? extends ConcurrentMap<?, ?>> map,
ConcurrentMap<?, Boolean> reverseMap) {
// removing just by key is always safe here because after a CacheKey
// is cleared and enqueue-ed it is only equal to itself
// (see equals method)...
ConcurrentMap<?, ?> valuesMap = map.remove(this);
// remove also from reverseMap if needed
if (valuesMap != null) {
for (Object cacheValue : valuesMap.values()) {
reverseMap.remove(cacheValue);
}
}
}
}
}
既然用到软引用肯定是会用到ReferenceQueue， map是个二级缓存，一级的CacheKey是类加载器为核心的key,二级subkey是接口类数组组成的key0，key1,key2…keyX。二级对应的supplier可能是CacheValue或者Factory。reverseMap用于包含查询，数量查询。subKeyFactory，valueFactory就是new WeakCache<>(new KeyFactory(), new ProxyClassFactory())
private final ReferenceQueue<K> refQueue
= new ReferenceQueue<>();
// the key type is Object for supporting null key
private final ConcurrentMap<Object, ConcurrentMap<Object, Supplier<V>>> map
= new ConcurrentHashMap<>();
private final ConcurrentMap<Supplier<V>, Boolean> reverseMap
= new ConcurrentHashMap<>();
private final BiFunction<K, P, ?> subKeyFactory;
private final BiFunction<K, P, V> valueFactory;
public WeakCache(BiFunction<K, P, ?> subKeyFactory,
BiFunction<K, P, V> valueFactory) {
this.subKeyFactory = Objects.requireNonNull(subKeyFactory);
this.valueFactory = Objects.requireNonNull(valueFactory);
}
java8的函数编程范型接口，一个get方法
@FunctionalInterface
public interface Supplier<T> {
T get();
}
定义一个通用类型
private interface Value<V> extends Supplier<V> {}
CacheValue 继承于WeakReference
private static final class CacheValue<V>
extends WeakReference<V> implements Value<V>
{
private final int hash;
CacheValue(V value) {
super(value);
this.hash = System.identityHashCode(value); // compare by identity
}
@Override
public int hashCode() {
return hash;
}
@Override
public boolean equals(Object obj) {
V value;
return obj == this ||
obj instanceof Value &&
// cleared CacheValue is only equal to itself
(value = get()) != null &&
value == ((Value<?>) obj).get(); // compare by identity
}
}
一个用于快速查找CacheValue
private static final class LookupValue<V> implements Value<V> {
private final V value;
LookupValue(V value) {
this.value = value;
}
@Override
public V get() {
return value;
}
@Override
public int hashCode() {
return System.identityHashCode(value); // compare by identity
}
@Override
public boolean equals(Object obj) {
return obj == this ||
obj instanceof Value &&
this.value == ((Value<?>) obj).get(); // compare by identity
}
}
CacheKey也继承软引用，静态创建方法valueOf，key为空，返回NULL_KEY，否则创建一个关联ReferenceQueue的自身对象。expungeFrom把自己key对应的数据从WeakCache 的map与reverseMap中清除。
private static final class CacheKey<K> extends WeakReference<K> {
// a replacement for null keys
private static final Object NULL_KEY = new Object();
static <K> Object valueOf(K key, ReferenceQueue<K> refQueue) {
return key == null
// null key means we can't weakly reference it,
// so we use a NULL_KEY singleton as cache key
? NULL_KEY
// non-null key requires wrapping with a WeakReference
: new CacheKey<>(key, refQueue);
}
private final int hash;
private CacheKey(K key, ReferenceQueue<K> refQueue) {
super(key, refQueue);
this.hash = System.identityHashCode(key); // compare by identity
}
@Override
public int hashCode() {
return hash;
}
@Override
public boolean equals(Object obj) {
K key;
return obj == this ||
obj != null &&
obj.getClass() == this.getClass() &&
// cleared CacheKey is only equal to itself
(key = this.get()) != null &&
// compare key by identity
key == ((CacheKey<K>) obj).get();
}
void expungeFrom(ConcurrentMap<?, ? extends ConcurrentMap<?, ?>> map,
ConcurrentMap<?, Boolean> reverseMap) {
// removing just by key is always safe here because after a CacheKey
// is cleared and enqueue-ed it is only equal to itself
// (see equals method)...
ConcurrentMap<?, ?> valuesMap = map.remove(this);
// remove also from reverseMap if needed
if (valuesMap != null) {
for (Object cacheValue : valuesMap.values()) {
reverseMap.remove(cacheValue);
}
}
}
}
containsValue 和size之前都做expungeStaleEntries操作，因为软引用被GC了，会放入关联的ReferenceQueue，所以每次要循环遍历清除干净。
public boolean containsValue(V value) {
Objects.requireNonNull(value);
expungeStaleEntries();
return reverseMap.containsKey(new LookupValue<>(value));
}
/**
* Returns the current number of cached entries that
* can decrease over time when keys/values are GC-ed.
*/
public int size() {
expungeStaleEntries();
return reverseMap.size();
}
private void expungeStaleEntries() {
CacheKey<K> cacheKey;
while ((cacheKey = (CacheKey<K>)refQueue.poll()) != null) {
cacheKey.expungeFrom(map, reverseMap);
}
}
四个入参，key：类加载器,parameter：接口数组,subKey:刚才的key0,key1… valuesMap ：subkey为key的动态代理类映射。主要看get方法，首先valuesMap取出如果不是自身，则代表当前发生了被移除。不过不用担心，当前Factory.get操作是处于一个循环中，总归能有实例返回。后面就是根据key,parameter创建动态代理类。fi nally处理极端情况，清除自身，有异常就会终止后面的执行。 创建新CacheValue，保存刚才的动态代理类，reverseMap保存（主要用于查询），最后更新valuesMap中的老数据。可以看出valuesMap放的不是Factory就是CacheValue。如果是CacheValue会直接返回动态代理类，如果是Factory，就会创建CacheValue并替换自身。就是说如果WeakCache没有直接返回动态代理类，总会先创建Factory，再生成CacheValue再返回动态代理类，满满的高级感。
private final class Factory implements Supplier<V> {
private final K key;
private final P parameter;
private final Object subKey;
private final ConcurrentMap<Object, Supplier<V>> valuesMap;
Factory(K key, P parameter, Object subKey,
ConcurrentMap<Object, Supplier<V>> valuesMap) {
this.key = key;
this.parameter = parameter;
this.subKey = subKey;
this.valuesMap = valuesMap;
}
@Override
public synchronized V get() { // serialize access
// re-check
Supplier<V> supplier = valuesMap.get(subKey);
if (supplier != this) {
return null;
}
// else still us (supplier == this)
// create new value
V value = null;
try {
value = Objects.requireNonNull(valueFactory.apply(key, parameter));
} finally {
if (value == null) { // remove us on failure
valuesMap.remove(subKey, this);
}
}
// the only path to reach here is with non-null value
assert value != null;
// wrap value with CacheValue (WeakReference)
CacheValue<V> cacheValue = new CacheValue<>(value);
// put into reverseMap
reverseMap.put(cacheValue, Boolean.TRUE);
// try replacing us with CacheValue (this should always succeed)
if (!valuesMap.replace(subKey, this, cacheValue)) {
throw new AssertionError("Should not reach here");
}
// successfully replaced us with new CacheValue -> return the value
// wrapped by it
return value;
}
}
1.非空判断 2.数据更正，清除保持有效。创建CacheKey。3.根据CacheKey取出valuesMap. valuesMap如果为空，就创建新的。 subKeyFactory创建subKey，valuesMap根据subkey取出supplier。下面是一个while死循环，supplier如果是CacheValue，非空的话，直接get得到动态代理类，如果是Factory，get不为空直接返回（上面已经介绍过）。以上没有得到结果，就继续创建Factory.并在之后在valuesMap中替换。再下一次的循环中，不管supplier会成功返回动态代理类。
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);
}
}
}
}
一开始分析时候没想到篇幅会比较长。设计的思路还是很巧妙。后面将对一些实用场景进行分析。