JDK8动态代理源码分析

class proxyed implements pro{    @Override    public void text() {        System.err.println("本方法");    }}interface pro {    void text();}public class JavaProxy implements InvocationHandler {        private Object source;        public JavaProxy(Object source) {            super();            this.source = source;        }        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {            System.out.println("before");            Object invoke = method.invoke(source, args);            System.out.println("after");            return invoke;        }        public Object getProxy(){            return Proxy.newProxyInstance(getClass().getClassLoader(), source.getClass().getInterfaces(), this);        }        public static void main(String[] args) throws IllegalAccessException, InvocationTargetException, InstantiationException, NoSuchMethodException {            //第一种，自己写            //1.设置saveGeneratedFiles值为true则生成 class字节码文件方便分析            System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");            //2.获取动态代理类            Class proxyClazz = Proxy.getProxyClass(pro.class.getClassLoader(),pro.class);            //3.获得代理类的构造函数，并传入参数类型InvocationHandler.class            Constructor constructor = proxyClazz.getConstructor(InvocationHandler.class);            //4.通过构造函数来创建动态代理对象，将自定义的InvocationHandler实例传入            pro iHello = (pro) constructor.newInstance(new JavaProxy(new proxyed()));            //5.通过代理对象调用目标方法            iHello.text();            //第二种，调用JDK提供的方法，实现了2~4步            Proxy.newProxyInstance(JavaProxy.class.getClassLoader(),proxyed.class.getInterfaces(),new JavaProxy(new proxyed()));        }}

public static Object newProxyInstance(ClassLoader loader, Class<?>[] interfaces, InvocationHandler h) throws IllegalArgumentException {        //Objects.requireNonNull 判空方法，之后所有的单纯的判断null并抛异常，都是此方法        Objects.requireNonNull(h);        //clone 类实现的所有接口        final Class<?>[] intfs = interfaces.clone();        //获取当前系统安全接口        final SecurityManager sm = System.getSecurityManager();        if (sm != null) {            //Reflection.getCallerClass返回调用该方法的方法的调用类;loader：接口的类加载器            //进行包访问权限、类加载器权限等检查            checkProxyAccess(Reflection.getCallerClass(), loader, intfs);        }        /*         * Look up or generate the designated proxy class.         *  查找或生成代理类         */        Class<?> cl = getProxyClass0(loader, intfs);        /*         * Invoke its constructor with the designated invocation handler.         * 使用指定的调用处理程序调用它的构造函数         */        try {            if (sm != null) {                checkNewProxyPermission(Reflection.getCallerClass(), cl);            }            //获取构造            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;                    }                });            }            //返回 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);        }    }

　　/**     * a cache of proxy classes：动态代理类的弱缓存容器     * KeyFactory:根据接口的数量，映射一个最佳的key生成函数,其中表示接口的类对象被弱引用；也就是key对象被弱引用继承自WeakReference（key0、key1、key2、keyX），保存接口密钥(hash值)     * ProxyClassFactory：生成动态类的工厂     * 注意，两个都实现了BiFunction<ClassLoader, Class<?>[], Object>接口     */    private static final WeakCache<ClassLoader, Class<?>[], Class<?>> proxyClassCache = new WeakCache<>(new KeyFactory(), new ProxyClassFactory());    /**     * Generate a proxy class.  Must call the checkProxyAccess method     * to perform permission checks before calling this.     * 生成代理类，调用前必须进行 checkProxyAccess权限检查，所以newProxyInstance进行了权限检查     */    private static Class<?> getProxyClass0(ClassLoader loader, Class<?>... interfaces) {        //实现接口的最大数量<65535;谁写的类能实现这么多接口        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        // 如果缓存中有，就直接返回，否则会生成        return proxyClassCache.get(loader, interfaces);    }

public V get(K key, P parameter) {        //key：类加载器；parameter：接口数组        Objects.requireNonNull(parameter);        //清除已经被GC回收的弱引用        expungeStaleEntries();        //CacheKey弱引用类，refQueue已经被回收的弱引用队列；构建一个CacheKey        Object cacheKey = CacheKey.valueOf(key, refQueue);                //map一级缓存，获取valuesMap二级缓存        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;            }        }        // subKeyFactory类型是KeyFactory，apply返回表示接口的key        Object subKey = Objects.requireNonNull(subKeyFactory.apply(key, parameter));        //Factory 实现了supplier，我们实际是获取缓存中的Factory，调用其get方法        Supplier<V> supplier = valuesMap.get(subKey);        Factory factory = null;                //下面用到了 CAS+重试 实现的多线程安全的 非阻塞算法        while (true) {            if (supplier != null) {                // 只需要知道，最终会调用get方法，此supplier可能是缓存中取出来的，也可能是Factory新new出来的                V value =http://www.mamicode.com/ 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);                }            }        }    }

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.                 * 类加载器和接口名解析出的是同一个                 */            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.                 * 确保是一个接口                 */            if (!interfaceClass.isInterface()) {                throw new IllegalArgumentException( interfaceClass.getName() + " is not an interface");            }                /*                 * Verify that this interface is not a duplicate.                 * 确保接口没重复                 */            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.             * 验证所有非公共的接口在同一个包内；公共的就无需处理             */        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.             * proxyClassNamePrefix = $Proxy             * nextUniqueNumber 是一个原子类，确保多线程安全，防止类名重复，类似于：$Proxy0，$Proxy1......             */        long num = nextUniqueNumber.getAndIncrement();        String proxyName = proxyPkg + proxyClassNamePrefix + num;            /*             * Generate the specified proxy class.             * 生成类字节码的方法:重点             */        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());        }    }

public static byte[] generateProxyClass(final String name, Class<?>[] interfaces, int accessFlags) {        ProxyGenerator gen = new ProxyGenerator(name, interfaces, accessFlags);        //真正生成字节码的方法        final byte[] classFile = gen.generateClassFile();        //如果saveGeneratedFiles为true 则生成字节码文件，所以在开始我们要设置这个参数        //当然，也可以通过返回的bytes自己输出        if (saveGeneratedFiles) {            java.security.AccessController.doPrivileged( new java.security.PrivilegedAction<Void>() {                        public Void run() {                            try {                                int i = name.lastIndexOf(‘.‘);                                Path path;                                if (i > 0) {                                    Path dir = Paths.get(name.substring(0, i).replace(‘.‘, File.separatorChar));                                    Files.createDirectories(dir);                                    path = dir.resolve(name.substring(i+1, name.length()) + ".class");                                } else {                                    path = Paths.get(name + ".class");                                }                                Files.write(path, classFile);                                return null;                            } catch (IOException e) {                                throw new InternalError( "I/O exception saving generated file: " + e);                            }                        }                    });        }        return classFile;    }

private byte[] generateClassFile() {        /* ============================================================         * Step 1: Assemble ProxyMethod objects for all methods to generate proxy dispatching code for.         * 步骤1：为所有方法生成代理调度代码，将代理方法对象集合起来。         */        //增加 hashcode、equals、toString方法        addProxyMethod(hashCodeMethod, Object.class);        addProxyMethod(equalsMethod, Object.class);        addProxyMethod(toStringMethod, Object.class);        //增加接口方法        for (Class<?> intf : interfaces) {            for (Method m : intf.getMethods()) {                addProxyMethod(m, intf);            }        }        /*         * 验证方法签名相同的一组方法，返回值类型是否相同；意思就是重写方法要方法签名和返回值一样         */        for (List<ProxyMethod> sigmethods : proxyMethods.values()) {            checkReturnTypes(sigmethods);        }        /* ============================================================         * Step 2: Assemble FieldInfo and MethodInfo structs for all of fields and methods in the class we are generating.         * 为类中的方法生成字段信息和方法信息         */        try {            //增加构造方法            methods.add(generateConstructor());            for (List<ProxyMethod> sigmethods : proxyMethods.values()) {                for (ProxyMethod pm : sigmethods) {                    // add static field for method‘s Method object                    fields.add(new FieldInfo(pm.methodFieldName,                            "Ljava/lang/reflect/Method;",                            ACC_PRIVATE | ACC_STATIC));                    // generate code for proxy method and add it                    methods.add(pm.generateMethod());                }            }            //增加静态初始化信息            methods.add(generateStaticInitializer());        } catch (IOException e) {            throw new InternalError("unexpected I/O Exception", e);        }        if (methods.size() > 65535) {            throw new IllegalArgumentException("method limit exceeded");        }        if (fields.size() > 65535) {            throw new IllegalArgumentException("field limit exceeded");        }        /* ============================================================         * Step 3: Write the final class file.         * 步骤3：编写最终类文件         */        /*         * Make sure that constant pool indexes are reserved for the following items before starting to write the final class file.         * 在开始编写最终类文件之前，确保为下面的项目保留常量池索引。         */        cp.getClass(dotToSlash(className));        cp.getClass(superclassName);        for (Class<?> intf: interfaces) {            cp.getClass(dotToSlash(intf.getName()));        }        /*         * Disallow new constant pool additions beyond this point, since we are about to write the final constant pool table.         * 设置只读，在这之前不允许在常量池中增加信息，因为要写常量池表         */        cp.setReadOnly();        ByteArrayOutputStream bout = new ByteArrayOutputStream();        DataOutputStream dout = new DataOutputStream(bout);        try {            // u4 magic;            dout.writeInt(0xCAFEBABE);            // u2 次要版本;            dout.writeShort(CLASSFILE_MINOR_VERSION);            // u2 主版本            dout.writeShort(CLASSFILE_MAJOR_VERSION);            cp.write(dout);             // (write constant pool)            // u2 访问标识;            dout.writeShort(accessFlags);            // u2 本类名;            dout.writeShort(cp.getClass(dotToSlash(className)));            // u2 父类名;            dout.writeShort(cp.getClass(superclassName));            // u2 接口;            dout.writeShort(interfaces.length);            // u2 interfaces[interfaces_count];            for (Class<?> intf : interfaces) {                dout.writeShort(cp.getClass(                        dotToSlash(intf.getName())));            }            // u2 字段;            dout.writeShort(fields.size());            // field_info fields[fields_count];            for (FieldInfo f : fields) {                f.write(dout);            }            // u2 方法;            dout.writeShort(methods.size());            // method_info methods[methods_count];            for (MethodInfo m : methods) {                m.write(dout);            }            // u2 类文件属性：对于代理类来说没有类文件属性;            dout.writeShort(0); // (no ClassFile attributes for proxy classes)        } catch (IOException e) {            throw new InternalError("unexpected I/O Exception", e);        }        return bout.toByteArray();    }

final class $Proxy0 extends Proxy implements pro {        //fields            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})).booleanValue();            } 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 text() throws  {            try {                //实际就是调用代理类的invoke方法                 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)).intValue();            } catch (RuntimeException | Error var2) {                throw var2;            } catch (Throwable var3) {                throw new UndeclaredThrowableException(var3);            }        }        static {            try {                //这里每个方法对象 和类的实际方法绑定                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("spring.commons.api.study.CreateModel.pro").getMethod("text", new Class[0]);                m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);            } catch (NoSuchMethodException var2) {                throw new NoSuchMethodError(var2.getMessage());            } catch (ClassNotFoundException var3) {                throw new NoClassDefFoundError(var3.getMessage());            }        }    }