☕️【Java 技术之旅】深入分析 JDK 动态代理的分析（源码深入）

    ProxyObject proxyObject = new ProxyObject();    InvocationHandler invocationHandler = new DynamicProxy(proxyObject);    ClassLoader classLoader = proxyObject.getClass().getClassLoader();    ProxyObjectInterface proxy = (IRoom) Proxy.newProxyInstance(classLoader,new Class[]  {ProxyObjectInterface.class},invocationHandler);    proxy.execute();
    public class DynamicProxy implements InvocationHandler {    private Object object;
    public DynamicProxy(Object object){        this.object = object;    }
    @Override    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {        Object result = method.invoke(object,args);        return result;    }}

    public static Object newProxyInstance(ClassLoader loader,                                          Class<?>[] interfaces,                                          InvocationHandler h)        throws IllegalArgumentException    {        //检验h不为空，h为空抛异常        Objects.requireNonNull(h);        //接口的类对象拷贝一份        final Class<?>[] intfs = interfaces.clone();        //进行一些安全性检查        final SecurityManager sm = System.getSecurityManager();        if (sm != null) {            checkProxyAccess(Reflection.getCallerClass(), loader, intfs);        }        /*         * Look up or generate the designated proxy class.         *  查询（在缓存中已经有）或生成指定的代理类的class对象。         */        Class<?> cl = getProxyClass0(loader, intfs);        /*         * Invoke its constructor with the designated invocation handler.         */        try {            if (sm != null) {                checkNewProxyPermission(Reflection.getCallerClass(), cl);            }            //得到代理类对象的构造函数，这个构造函数的参数由constructorParams指定            //参数constructorParames为常量值：      private static final Class<?>[] constructorParams = { InvocationHandler.class };            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;                    }                });            }            //这里生成代理对象，传入的参数new Object[]{h}后面讲            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);        }    }

    //此方法也是Proxy类下的方法    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        //意思是：如果代理类被指定的类加载器loader定义了，并实现了给定的接口interfaces，        //那么就返回缓存的代理类对象，否则使用ProxyClassFactory创建代理类。        return proxyClassCache.get(loader, interfaces);    }

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

//K代表key的类型，P代表参数的类型，V代表value的类型。// WeakCache<ClassLoader, Class<?>[], Class<?>>  proxyClassCache  说明proxyClassCache存的值是Class<?>对象，正是我们需要的代理类对象。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);    }

//K和P就是WeakCache定义中的泛型，key是类加载器，parameter是接口类数组public V get(K key, P parameter) {        //检查parameter不为空        Objects.requireNonNull(parameter);         //清除无效的缓存        expungeStaleEntries();        // cacheKey就是(key, sub-key) -> value里的一级key，        Object cacheKey = CacheKey.valueOf(key, refQueue);        // lazily install the 2nd level valuesMap for the particular cacheKey        //根据一级key得到 ConcurrentMap<Object, Supplier<V>>对象。如果之前不存在，则新建一个ConcurrentMap<Object, Supplier<V>>和cacheKey（一级key）一起放到map中。        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        //这部分就是调用生成sub-key的代码，上面我们已经看过怎么生成的了        Object subKey = Objects.requireNonNull(subKeyFactory.apply(key, parameter));        //通过sub-key得到supplier        Supplier<V> supplier = valuesMap.get(subKey);        //supplier实际上就是这个factory        Factory factory = null;
        while (true) {            //如果缓存里有supplier ，那就直接通过get方法，得到代理类对象，返回，就结束了，一会儿分析get方法。            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            //下面的所有代码目的就是：如果缓存中没有supplier，则创建一个Factory对象，把factory对象在多线程的环境下安全的赋给supplier。            //因为是在while（true）中，赋值成功后又回到上面去调get方法，返回才结束。            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 synchronized V get() { // serialize access            // re-check            Supplier<V> supplier = valuesMap.get(subKey);            //重新检查得到的supplier是不是当前对象            if (supplier != this) {                // something changed while we were waiting:                // might be that we were replaced by a CacheValue                // or were removed because of failure ->                // return null to signal WeakCache.get() to retry                // the loop                return null;            }            // else still us (supplier == this)            // create new value            V value = null;            try {                 //代理类就是在这个位置调用valueFactory生成的                 //valueFactory就是我们传入的 new ProxyClassFactory()                //一会我们分析ProxyClassFactory()的apply方法                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)            //把value包装成弱引用            CacheValue<V> cacheValue = new CacheValue<>(value);
            // put into reverseMap            // reverseMap是用来实现缓存的有效性            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;        }    }

 //这里的BiFunction<T, U, R>是个函数式接口，可以理解为用T，U两种类型做参数，得到R类型的返回值private static final class ProxyClassFactory        implements BiFunction<ClassLoader, Class<?>[], Class<?>>    {        // prefix for all proxy class names        //所有代理类名字的前缀        private static final String proxyClassNamePrefix = "$Proxy";        // next number to use for generation of unique proxy class names        //用于生成代理类名字的计数器        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，可不看            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;     // package to define proxy class in            //代理类访问控制符: public ,final            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.             */            //验证所有非公共的接口在同一个包内；公共的就无需处理            //生成包名和类名的逻辑，包名默认是com.sun.proxy，      // 类名默认是$Proxy 加上一个自增的整数值            //如果被代理类是 non-public proxy interface ，则用和被代理类接口一样的包名            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();            //代理类的完全限定名，如com.sun.proxy.$Proxy0.calss            String proxyName = proxyPkg + proxyClassNamePrefix + num;
            /*             * Generate the specified proxy class.             */            //核心部分，生成代理类的字节码            byte[] proxyClassFile = ProxyGenerator.generateProxyClass(                proxyName, interfaces, accessFlags);            try {                //把代理类加载到JVM中，至此动态代理过程基本结束了                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 List<Method> getMethods(Class<?>[] interfaces) {        List<Method> result = new ArrayList<Method>();        try {            result.add(Object.class.getMethod("equals", Object.class));            result.add(Object.class.getMethod("hashCode", EmptyArray.CLASS));            result.add(Object.class.getMethod("toString", EmptyArray.CLASS));        } catch (NoSuchMethodException e) {            throw new AssertionError();        }
        getMethodsRecursive(interfaces, result);        return result;    }private static void getMethodsRecursive(Class<?>[] interfaces, List<Method> methods) {        for (Class<?> i : interfaces) {            getMethodsRecursive(i.getInterfaces(), methods);            Collections.addAll(methods, i.getDeclaredMethods());        }    }

package com.zhb.jdk.proxy;import java.io.FileOutputStream;import java.io.IOException;import java.lang.reflect.Proxy;
import com.zhb.jdk.dynamicProxy.HelloworldImpl;
import sun.misc.ProxyGenerator;
/** * @author ZHB * @date 2018年8月31日下午11:35:07 * @todo TODO */public class DynamicProxyTest {
    public static void main(String[] args) {
        IUserService target = new UserServiceImpl();        MyInvocationHandler handler = new MyInvocationHandler(target);        //第一个参数是指定代理类的类加载器（我们传入当前测试类的类加载器）        //第二个参数是代理类需要实现的接口（我们传入被代理类实现的接口，这样生成的代理类和被代理类就实现了相同的接口）        //第三个参数是invocation handler，用来处理方法的调用。这里传入我们自己实现的handler        IUserService proxyObject = (IUserService) Proxy.newProxyInstance(DynamicProxyTest.class.getClassLoader(),                target.getClass().getInterfaces(), handler);        proxyObject.add("陈粒");
        String path = "D:/$Proxy0.class";        byte[] classFile = ProxyGenerator.generateProxyClass("$Proxy0", HelloworldImpl.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();            }        }
    }}

// Decompiled by Jad v1.5.8e2. Copyright 2001 Pavel Kouznetsov.// Jad home page: http://kpdus.tripod.com/jad.html// Decompiler options: packimports(3) fieldsfirst ansi space 
import com.zhb.jdk.proxy.IUserService;import java.lang.reflect.*;
public final class $Proxy0 extends Proxy    implements IUserService{
    private static Method m1;    private static Method m2;    private static Method m3;    private static Method m0;    //代理类的构造函数，其参数正是是InvocationHandler实例，    //Proxy.newInstance方法就是通过通过这个构造函数来创建代理实例的    public $Proxy0(InvocationHandler invocationhandler)    {        super(invocationhandler);    }     // Object类中的三个方法，equals，toString， hashCode    public final boolean equals(Object obj)    {        try        {            return ((Boolean)super.h.invoke(this, m1, new Object[] {                obj            })).booleanValue();        }        catch (Error ) { }        catch (Throwable throwable)        {            throw new UndeclaredThrowableException(throwable);        }    }
    public final String toString()    {        try        {            return (String)super.h.invoke(this, m2, null);        }        catch (Error ) { }        catch (Throwable throwable)        {            throw new UndeclaredThrowableException(throwable);        }    }    //接口代理方法    public final void add(String s)    {        try        {            // invocation handler的 invoke方法在这里被调用            super.h.invoke(this, m3, new Object[] {                s            });            return;        }        catch (Error ) { }        catch (Throwable throwable)        {            throw new UndeclaredThrowableException(throwable);        }    }
    public final int hashCode()    {        try        {            // 在这里调用了invoke方法。            return ((Integer)super.h.invoke(this, m0, null)).intValue();        }        catch (Error ) { }        catch (Throwable throwable)        {            throw new UndeclaredThrowableException(throwable);        }    }
    // 静态代码块对变量进行一些初始化工作    static     {        try        {            m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] {                Class.forName("java.lang.Object")            });            m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);            m3 = Class.forName("com.zhb.jdk.proxy.IUserService").getMethod("add", new Class[] {                Class.forName("java.lang.String")            });            m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);        }        catch (NoSuchMethodException nosuchmethodexception)        {            throw new NoSuchMethodError(nosuchmethodexception.getMessage());        }        catch (ClassNotFoundException classnotfoundexception)        {            throw new NoClassDefFoundError(classnotfoundexception.getMessage());        }    }}