前言
Java中代理有静态代理、动态代理，动态代理中又分JDK动态代理和CGLib动态代理
本文讲一下JDK动态代理的使用和源码实现
基于jdk1.8.0_161
附上其他两种代理的博文
Java静态代理
使用
步骤
1.新建接口
2.新建被代理类
3.新建InvocationHandler接口的实现类，Override invoke方法
4.使用Proxy生成动态代理
代码
为了方便，上述步骤的接口、类都写到一个类下面
package com.jaylin.jaylin.proxy;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
public class JDKProxyTest {
//接口
public interface ITestClass {
void testMethod();
}
//被代理类
static class TestClass implements ITestClass {
@Override
public void testMethod() {
System.out.println("TestClass");
}
}
//InvocationHandler实现类
static class Ih implements InvocationHandler {
//目标对象
private Object target;
public Ih(Object target) {
this.target = target;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
Object obj = method.invoke(target, args);
return obj;
}
}
public static void main(String[] args) {
//生成$Proxy0的class文件
System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");
//参数分别为1.加载接口的类加载器 2.接口 3.InvocationHandler实现类
ITestClass iTestClass = (ITestClass) Proxy.newProxyInstance(
ITestClass.class.getClassLoader(),
new Class[]{
ITestClass.class},
new Ih(new TestClass())
);
iTestClass .testMethod();
}
}
源码解读
动态代理入口
ITestClass iTestClass = (ITestClass) Proxy.newProxyInstance(
ITestClass.class.getClassLoader(),
new Class[]{
ITestClass.class},
new Ih(new TestClass())
);
新建代理实例 Proxy.newProxyInstance
/**
* 返回指定接口的代理类的实例，该实例将方法调用分派到指定的调用处理程序
*
* @param loader 定义代理类的类加载器
* @param interfaces 代理类要实现的接口列表
* @param h 分发方法调用的调用处理器
* @return 一个代理实例，具有代理类的具体调用处理器，由指定的类加载器定义，实现了指定的接口
* @throws IllegalArgumentException 非法参数异常
* @throws SecurityException 安全异常
* @throws NullPointerException 空指针异常
*/
@CallerSensitive
public static Object newProxyInstance(ClassLoader loader,
Class<?>[] interfaces,
InvocationHandler h)
throws IllegalArgumentException
{
//空校验
Objects.requireNonNull(h);
//复制一份接口对象数组为常量，防止后续改变导致不一致
final Class<?>[] intfs = interfaces.clone();
//安全检查
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
}
//查找或生成指定的代理类
Class<?> cl = getProxyClass0(loader, intfs);
//用指定的调用处理器调用其构造函数
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;
}
});
}
//通过反射构造代理对象
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);
}
}
获取代理对象 Proxy.getProxyClass0;
/**
* 生成代理类
* 在调用此方法之前，必须调用checkProxyAccess方法执行权限检查
*/
private static Class<?> getProxyClass0(ClassLoader loader,
Class<?>... interfaces) {
if (interfaces.length > 65535) {
throw new IllegalArgumentException("interface limit exceeded");
}
// 如果存在由 实现了给定接口的 给定加载器 定义的代理类
// 将返回缓存的副本
// 否则，将通过ProxyClassFactory创建代理类
return proxyClassCache.get(loader, interfaces);
}
看一下proxyClassCache，第二个参数为ProxyClassFactory
/**
* 代理类的缓存
*/
private static final WeakCache<ClassLoader, Class<?>[], Class<?>>
proxyClassCache = new WeakCache<>(new KeyFactory(), new ProxyClassFactory());
可以先忽略WeakCache的实现，先考虑ProxyClassFactory的作用
调用链
Proxy.getProxyClass0
return proxyClassCache.get(loader, interfaces);
↓
WeakCache.get
V value = supplier.get();
↓
WeakCache$Factory.get
value = Objects.requireNonNull(valueFactory.apply(key, parameter));
↓
Proxy$ProxyClassFactory.apply
走到aplly方法中
产生代理对象 ProxyClassFactory.apply
private static final class ProxyClassFactory
implements BiFunction<ClassLoader, Class<?>[], Class<?>>
{
// 所有代理类名称的前缀
private static final String proxyClassNamePrefix = "$Proxy";
// 下一个用于生成唯一代理类名称的数字
private static final AtomicLong nextUniqueNumber = new AtomicLong();
@Override
public Class<?> apply(ClassLoader loader, Class<?>[] interfaces) {
Map<Class<?>, Boolean> interfaceSet = new IdentityHashMap<>(interfaces.length);
//验证代理接口
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());
}
}
//生成的代理类的包名
String proxyPkg = null;
//代理类访问控制符: public ,final
int accessFlags = Modifier.PUBLIC | Modifier.FINAL;
/*
* 记录非公共代理接口的包，以便在同一包中定义代理类
* 验证所有非公共代理接口都在同一程序包中
*/
for (Class<?> intf : interfaces) {
int flags = intf.getModifiers();
//处理非公共的接口
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) {
// 如果没有非公共代理接口，使用com.sun.proxy
proxyPkg = ReflectUtil.PROXY_PACKAGE + ".";
}
/*
* 选择要生成的代理类的名称
* 代理类全限定名，如com.sun.proxy.$Proxy0.calss
*/
long num = nextUniqueNumber.getAndIncrement();
String proxyName = proxyPkg + proxyClassNamePrefix + num;
/*
* 生成指定的代理类字节码
*/
byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
proxyName, interfaces, accessFlags);
try {
// 将代理类加载到JVM中
return defineClass0(loader, proxyName,
proxyClassFile, 0, proxyClassFile.length);
} catch (ClassFormatError e) {
throw new IllegalArgumentException(e.toString());
}
}
}
生成字节码文件 ProxyGenerator.generateProxyClass
public static byte[] generateProxyClass(final String var0, Class<?>[] var1, int var2) {
ProxyGenerator var3 = new ProxyGenerator(var0, var1, var2);
final byte[] var4 = var3.generateClassFile();
// 是否要将生成代理类的字节码文件保存到磁盘中
if (saveGeneratedFiles) {
AccessController.doPrivileged(new PrivilegedAction<Void>() {
public Void run() {
try {
int var1 = var0.lastIndexOf(46);
Path var2;
if (var1 > 0) {
Path var3 = Paths.get(var0.substring(0, var1).replace('.', File.separatorChar));
Files.createDirectories(var3);
var2 = var3.resolve(var0.substring(var1 + 1, var0.length()) + ".class");
} else {
var2 = Paths.get(var0 + ".class");
}
Files.write(var2, var4, new OpenOption[0]);
return null;
} catch (IOException var4x) {
throw new InternalError("I/O exception saving generated file: " + var4x);
}
}
});
}
return var4;
}
saveGeneratedFiles定义如下
private static final boolean saveGeneratedFiles = (Boolean)AccessController.doPrivileged(new GetBooleanAction("sun.misc.ProxyGenerator.saveGeneratedFiles"));
所以我们在创建动态代理时，可以加这句
System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");
查看生成的代理类
在com.sun.proxy.$Proxy0.class，
可以看到，除了equals、toString、hashCode方法，还有被代理类的testMethod方法
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//
package com.sun.proxy;
import com.jaylin.jaylin.Test.ITestClass;
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 ITestClass {
private static Method m1;
private static Method m2;
private static Method m3;
private static Method m0;
public $Proxy0(InvocationHandler var1) throws {
super(var1);
}
public final boolean equals(Object var1) throws {
try {
return (Boolean)super.h.invoke(this, m1, new Object[]{
var1});
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
public final String toString() throws {
try {
return (String)super.h.invoke(this, m2, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
public final void testMethod() throws {
try {
super.h.invoke(this, m3, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
public final int hashCode() throws {
try {
return (Integer)super.h.invoke(this, m0, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
static {
try {
m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
m2 = Class.forName("java.lang.Object").getMethod("toString");
m3 = Class.forName("com.jaylin.jaylin.Test$ITestClass").getMethod("testMethod");
m0 = Class.forName("java.lang.Object").getMethod("hashCode");
} catch (NoSuchMethodException var2) {
throw new NoSuchMethodError(var2.getMessage());
} catch (ClassNotFoundException var3) {
throw new NoClassDefFoundError(var3.getMessage());
}
}
}
参考：