动态代理示例:
public class VectorProxy implements InvocationHandler {
private Object proxyObject;
//执行方法时候调用
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
System.out.println("before");
Object o = method.invoke(proxyObject,args);
System.out.println("after");
return o;
}
public VectorProxy(Object proxyObject) {
this.proxyObject = proxyObject;
}
public Object bind(){
return Proxy.newProxyInstance(proxyObject.getClass().getClassLoader(),proxyObject.getClass().getInterfaces(),this);
}
public static void main(String[] args) throws Throwable {
Vector vector = new Vector();
VectorProxy vectorProxy = new VectorProxy(vector);
List v= (List) vectorProxy.bind();
v.add("123");
// vectorProxy.invoke(null,vector.getClass().getMethod("add",Object.class),new Object[]{2});
System.out.println(vector.size());
}
}
动态代理对象是如何生成的?invoke方法又是何时执行的?,阅读静态工厂方法的代码:
@CallerSensitive
public static Object newProxyInstance(ClassLoader loader,//被代理对象的类加载器
Class<?>[] interfaces,//被代理对象实现的接口
InvocationHandler h)//代理对象handler
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.
* 这段代码生成了动态代理对象的class对象
*/
Class<?> cl = getProxyClass0(loader, intfs);
/*
* Invoke its constructor with the designated invocation handler.
*可见,生成的代理对象包含一个参数类型是InvocationHandler的构造方法,执行方法时,就可以调用这个InvocationHandler的invoke方法,从而实现
*动态代理
*/
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());
}
}getProxyClass0(loader, intfs)方法实现如下:
/**
* 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);
}其内部是调用了proxyClassCache,这个是动态代理对象缓存,代码如下.这段代码有点麻烦,似乎是当对象不存在时创建新对象,不过最重要的是subKeyFactory的apply()方法
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);
}
}
}
}这个方法重要的是
Object subKey = Objects.requireNonNull(subKeyFactory.apply(key, parameter));
apply方法是用来生成字节码数组的:这里可以很清楚地知道生成的包名,类名是啥
/**
* 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
/*
* 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());
}
}
}生成字节码数组是通过如下代码:
byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
proxyName, interfaces);
这个方法有些复杂,就不做研究了
可以写一个程序,单独测试这个方法,让其生成字节码文件,打开class文件就知道invoke方法是如何调用的:
public class ProxyGeneratorUtils {
/**
* 把代理类的字节码写到硬盘上
* @param path 保存路径
*/
public static void writeProxyClassToHardDisk(String path) {
// 第一种方法，这种方式在刚才分析ProxyGenerator时已经知道了
// System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", true);
// 第二种方法
// 获取代理类的字节码
byte[] classFile = ProxyGenerator.generateProxyClass("$Proxy11", Vector.class.getInterfaces());
FileOutputStream out = null;
try {
out = new FileOutputStream(path);
out.write(classFile);
out.flush();
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
out.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
@Test
public void testGenerateProxyClass() {
ProxyGeneratorUtils.writeProxyClassToHardDisk("/f/classes/$Proxy11.class");
}
}打开生成的文件,可以观察到: 代理类实现了相关的接口,并重写了相关方法,在调用时实际是调用了InvocationHandler的invode方法
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//
import java.io.Serializable;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.RandomAccess;
public final class $Proxy11 extends Proxy implements List, RandomAccess, Cloneable, Serializable {
private static Method m14;
private static Method m13;
private static Method m19;
private static Method m2;
private static Method m25;
private static Method m9;
private static Method m5;
private static Method m16;
private static Method m3;
private static Method m17;
private static Method m18;
private static Method m24;
private static Method m10;
private static Method m8;
private static Method m20;
private static Method m21;
private static Method m4;
private static Method m12;
private static Method m1;
private static Method m15;
private static Method m23;
private static Method m7;
private static Method m22;
private static Method m11;
private static Method m0;
private static Method m6;
public $Proxy11(InvocationHandler var1) throws {
super(var1);
}
public final List subList(int var1, int var2) throws {
try {
return (List)super.h.invoke(this, m14, new Object[]{Integer.valueOf(var1), Integer.valueOf(var2)});
} catch (RuntimeException | Error var4) {
throw var4;
} catch (Throwable var5) {
throw new UndeclaredThrowableException(var5);
}
}
public final int size() throws {
try {
return ((Integer)super.h.invoke(this, m13, (Object[])null)).intValue();
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
public final Iterator iterator() throws {
try {
return (Iterator)super.h.invoke(this, m19, (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 boolean retainAll(Collection var1) throws {
try {
return ((Boolean)super.h.invoke(this, m25, new Object[]{var1})).booleanValue();
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
public final void clear() throws {
try {
super.h.invoke(this, m9, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
public final boolean remove(Object var1) throws {
try {
return ((Boolean)super.h.invoke(this, m5, new Object[]{var1})).booleanValue();
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
public final Object[] toArray(Object[] var1) throws {
try {
return (Object[])super.h.invoke(this, m16, new Object[]{var1});
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
public final boolean add(Object var1) throws {
try {
return ((Boolean)super.h.invoke(this, m3, new Object[]{var1})).booleanValue();
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
public final boolean addAll(int var1, Collection var2) throws {
try {
return ((Boolean)super.h.invoke(this, m17, new Object[]{Integer.valueOf(var1), var2})).booleanValue();
} catch (RuntimeException | Error var4) {
throw var4;
} catch (Throwable var5) {
throw new UndeclaredThrowableException(var5);
}
}
public final boolean addAll(Collection var1) throws {
try {
return ((Boolean)super.h.invoke(this, m18, new Object[]{var1})).booleanValue();
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
public final boolean removeAll(Collection var1) throws {
try {
return ((Boolean)super.h.invoke(this, m24, new Object[]{var1})).booleanValue();
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
public final boolean contains(Object var1) throws {
try {
return ((Boolean)super.h.invoke(this, m10, new Object[]{var1})).booleanValue();
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
public final int indexOf(Object var1) throws {
try {
return ((Integer)super.h.invoke(this, m8, new Object[]{var1})).intValue();
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
public final Object set(int var1, Object var2) throws {
try {
return (Object)super.h.invoke(this, m20, new Object[]{Integer.valueOf(var1), var2});
} catch (RuntimeException | Error var4) {
throw var4;
} catch (Throwable var5) {
throw new UndeclaredThrowableException(var5);
}
}
public final boolean containsAll(Collection var1) throws {
try {
return ((Boolean)super.h.invoke(this, m21, new Object[]{var1})).booleanValue();
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
public final void add(int var1, Object var2) throws {
try {
super.h.invoke(this, m4, new Object[]{Integer.valueOf(var1), var2});
} catch (RuntimeException | Error var4) {
throw var4;
} catch (Throwable var5) {
throw new UndeclaredThrowableException(var5);
}
}
public final int lastIndexOf(Object var1) throws {
try {
return ((Integer)super.h.invoke(this, m12, new Object[]{var1})).intValue();
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
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 Object[] toArray() throws {
try {
return (Object[])super.h.invoke(this, m15, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
public final ListIterator listIterator(int var1) throws {
try {
return (ListIterator)super.h.invoke(this, m23, new Object[]{Integer.valueOf(var1)});
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
public final Object get(int var1) throws {
try {
return (Object)super.h.invoke(this, m7, new Object[]{Integer.valueOf(var1)});
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
public final ListIterator listIterator() throws {
try {
return (ListIterator)super.h.invoke(this, m22, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
public final boolean isEmpty() throws {
try {
return ((Boolean)super.h.invoke(this, m11, (Object[])null)).booleanValue();
} 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);
}
}
public final Object remove(int var1) throws {
try {
return (Object)super.h.invoke(this, m6, new Object[]{Integer.valueOf(var1)});
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
static {
try {
m14 = Class.forName("java.util.List").getMethod("subList", new Class[]{Integer.TYPE, Integer.TYPE});
m13 = Class.forName("java.util.List").getMethod("size", new Class[0]);
m19 = Class.forName("java.util.List").getMethod("iterator", new Class[0]);
m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
m25 = Class.forName("java.util.List").getMethod("retainAll", new Class[]{Class.forName("java.util.Collection")});
m9 = Class.forName("java.util.List").getMethod("clear", new Class[0]);
m5 = Class.forName("java.util.List").getMethod("remove", new Class[]{Class.forName("java.lang.Object")});
m16 = Class.forName("java.util.List").getMethod("toArray", new Class[]{Class.forName("[Ljava.lang.Object;")});
m3 = Class.forName("java.util.List").getMethod("add", new Class[]{Class.forName("java.lang.Object")});
m17 = Class.forName("java.util.List").getMethod("addAll", new Class[]{Integer.TYPE, Class.forName("java.util.Collection")});
m18 = Class.forName("java.util.List").getMethod("addAll", new Class[]{Class.forName("java.util.Collection")});
m24 = Class.forName("java.util.List").getMethod("removeAll", new Class[]{Class.forName("java.util.Collection")});
m10 = Class.forName("java.util.List").getMethod("contains", new Class[]{Class.forName("java.lang.Object")});
m8 = Class.forName("java.util.List").getMethod("indexOf", new Class[]{Class.forName("java.lang.Object")});
m20 = Class.forName("java.util.List").getMethod("set", new Class[]{Integer.TYPE, Class.forName("java.lang.Object")});
m21 = Class.forName("java.util.List").getMethod("containsAll", new Class[]{Class.forName("java.util.Collection")});
m4 = Class.forName("java.util.List").getMethod("add", new Class[]{Integer.TYPE, Class.forName("java.lang.Object")});
m12 = Class.forName("java.util.List").getMethod("lastIndexOf", new Class[]{Class.forName("java.lang.Object")});
m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[]{Class.forName("java.lang.Object")});
m15 = Class.forName("java.util.List").getMethod("toArray", new Class[0]);
m23 = Class.forName("java.util.List").getMethod("listIterator", new Class[]{Integer.TYPE});
m7 = Class.forName("java.util.List").getMethod("get", new Class[]{Integer.TYPE});
m22 = Class.forName("java.util.List").getMethod("listIterator", new Class[0]);
m11 = Class.forName("java.util.List").getMethod("isEmpty", new Class[0]);
m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
m6 = Class.forName("java.util.List").getMethod("remove", new Class[]{Integer.TYPE});
} catch (NoSuchMethodException var2) {
throw new NoSuchMethodError(var2.getMessage());
} catch (ClassNotFoundException var3) {
throw new NoClassDefFoundError(var3.getMessage());
}
}
}
总结
JDK实现动态代理的过程如下：
克隆传入的接口Class数组(通过clone()方法)
查找或者生成实现了接口数组中所有接口的动态代理类的Class
利用动态代理类的Class获取Constructor对象,利用我们传入的InvocationHandler实现类对象作为输入参数，生成动态代理类的对象动态代理类对象的性质:
实现了传入的接口Class数组中所有的接口
这些接口中如果含有非public的接口，非public接口必须在同一个包下面,而且代理类也必须和他们在同一包下,要不代理类必然访问
不了部分接口
父类(Proxy)有一个InvocationHandler的成员变量，它的值是我们在Proxy.newInstance()方法中传入的,子类的所有方法都是围绕InvocationHandler进行.