java代理

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() {
                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);
    }
}

//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);
    }

　这里看到proxyClassCache，有Cache便知道是缓存的意思，正好呼应了前面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对象这段注释。

//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

public synchronized V get() { // serialize access
            // re-check
            Supplier 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 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[], 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, 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());
            }
        }
    }

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("张玉龙");
        
        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());
        }
    }
}

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
        ConcurrentMapObject, Supplier> valuesMap = map.get(cacheKey);
        if (valuesMap == null) {
            ConcurrentMapObject, Supplier> oldValuesMap
                = map.putIfAbsent(cacheKey,
                                  valuesMap = new ConcurrentHashMap());
            if (oldValuesMap != null) {
                valuesMap = oldValuesMap;
            }
        }
.......
}

private void expungeStaleEntries() {
        CacheKey cacheKey;
        while ((cacheKey = (CacheKey)refQueue.poll()) != null) {
            cacheKey.expungeFrom(map, reverseMap);
        }
    }

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);
                }
            }
        }

Object cacheKey = CacheKey.valueOf(key, refQueue);

private static final class CacheKeyK> extends WeakReferenceK> {

        // a replacement for null keys
        private static final Object NULL_KEY = new Object();

        static Object valueOf(K key, ReferenceQueue 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 refQueue) {
            super(key, refQueue);
            this.hash = System.identityHashCode(key);  // compare by identity
        }
.....
}