Java动态代理

最近在看spring的aop源码时，用到了动态代理模式，仅记录用于方便理解动态代理。

先上代码

1.接口类

package com.cx.proxy;/** * Created by cumt_cx on 2017/1/3. */public interface HelloWorld {    void SaySomeThing(String someThing);}

2.实现类

package com.cx.proxy;/** * Created by cumt_cx on 2017/1/3. */public class HelloWorldImpl implements HelloWorld {    @Override public void SaySomeThing(String someThing) {        System.out.println("Yes You Do ["+someThing+"]");    }}

3.增强的横切逻辑：增强类，实现InvocationHandle接口

package com.cx.proxy;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;/** * Created by cumt_cx on 2017/1/3. */public class MyInvocationHandler implements InvocationHandler {    private Object target;    public MyInvocationHandler(Object obj) {        this.target = obj;    }    @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {        System.out.println("method :"+method.getName()+" is invoked");            return method.invoke(target,args);    }}

4.调用

package com.cx.proxy;import java.lang.reflect.Constructor;import java.lang.reflect.InvocationHandler;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Proxy;/** * Created by cumt_cx on 2017/1/3. */public class ProxyDemo {    public static void main(String args[]) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {        //one way        Class<?> proxyClass = Proxy.getProxyClass(ProxyDemo.class.getClassLoader(), HelloWorld.class);        final Constructor<?> cons = proxyClass.getConstructor(InvocationHandler.class);        final InvocationHandler ih = new MyInvocationHandler(new HelloWorldImpl());        HelloWorld helloWorld = (HelloWorld) cons.newInstance(ih);        helloWorld.SaySomeThing("This is invoke,I am Coding");        //other way        HelloWorld helloWorld1 = (HelloWorld) Proxy                .newProxyInstance(ProxyDemo.class.getClassLoader(), new Class<?>[] { HelloWorld.class }, new MyInvocationHandler                        (new HelloWorldImpl()));        helloWorld1.SaySomeThing("This is invoke,Another Way ，I am Coding Too ");    }}

JDK中具体的动态代理类是怎么产生

   代理生成过程主要分为2步

• • 代理类字节码生成
  • 把字节码通过传入的类加载器加载到虚拟机中

     具体细分则如下

 获取动态代理类通过Proxy类的getProxyClass方法

@CallerSensitivepublic 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);

     代码直观的看到通过调用getProxyClass0方法

/** * 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);}

proxyClassCache的定义如下

     

/** * a cache of proxy classes */private static final WeakCache<ClassLoader, Class<?>[], Class<?>>    proxyClassCache = new WeakCache<>(new KeyFactory(), new ProxyClassFactory());

实际是在ProxyClassFactory的apply方法中实现的

/** * 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());        }    }}

最后把字节码通过传入的类加载器加载到JVM中: defineClass0(loader, proxyName,proxyClassFile, 0, proxyClassFile.length);

 

    至此，已经生成了动态代理类，具体每个代理方法：逻辑都差不多就是 h.invoke，主要是调用我们定义好的invocatinoHandler逻辑,触发目标对象target上对应的方法;