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动态代理源码分析

Proxy.newProxyInstance实现

  1.  public static Object newProxyInstance(ClassLoader loader,Class<?>[] interfaces,
  2.                                           InvocationHandler h)
  3.         throws IllegalArgumentException
  4.     {
  5.         //检验h不为空，h为空抛异常
  6.         Objects.requireNonNull(h);
  7.         //接口的类对象拷贝一份
  8.         final Class<?>[] intfs = interfaces.clone();
  9.         //进行一些安全性检查
  10.         final SecurityManager sm = System.getSecurityManager();
  11.         if (sm != null) {
  12.             checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
  13.         }
  15.         /*
  16.          * Look up or generate the designated proxy class.
  17.          *  查询（在缓存中已经有）或生成指定的代理类的class对象。
  18.          */
  19.         Class<?> cl = getProxyClass0(loader, intfs);
  21.         /*
  22.          * Invoke its constructor with the designated invocation handler.
  23.          */
  24.         try {
  25.             if (sm != null) {
  26.                 checkNewProxyPermission(Reflection.getCallerClass(), cl);
  27.             }
  28.             //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
  29.             //参数constructorParames为常量值：
  30.             //private static final Class<?>[] constructorParams = 
  31.             //{ InvocationHandler.class };
  32.             final Constructor<?> cons = cl.getConstructor(constructorParams);
  33.             final InvocationHandler ih = h;
  34.             if (!Modifier.isPublic(cl.getModifiers())) {
  35.                 AccessController.doPrivileged(new PrivilegedAction<Void>() {
  36.                     public Void run() {
  37.                         cons.setAccessible(true);
  38.                         return null;
  39.                     }
  40.                 });
  41.             }
  42.             //这里生成代理对象，传入的参数new Object[]{h}后面讲
  43.             return cons.newInstance(new Object[]{h});
  44.         } catch (IllegalAccessException|InstantiationException e) {
  45.             throw new InternalError(e.toString(), e);
  46.         } catch (InvocationTargetException e) {
  47.             Throwable t = e.getCause();
  48.             if (t instanceof RuntimeException) {
  49.                 throw (RuntimeException) t;
  50.             } else {
  51.                 throw new InternalError(t.toString(), t);
  52.             }
  53.         } catch (NoSuchMethodException e) {
  54.             throw new InternalError(e.toString(), e);
  55.         }
  56.     }

getProxyClass0实现

  1.    //此方法也是Proxy类下的方法
  2.     private static Class<?> getProxyClass0(ClassLoader loader,
  3.                                            Class<?>... interfaces) {
  4.         if (interfaces.length > 65535) {
  5.             throw new IllegalArgumentException("interface limit exceeded");
  6.         }
  8.         // If the proxy class defined by the given loader implementing
  9.         // the given interfaces exists, this will simply return the cached copy;
  10.         // otherwise, it will create the proxy class via the ProxyClassFactory
  11.         //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，
  12.         //那么就返回缓存的代理类对象，否则使用ProxyClassFactory创建代理类。
  13.         return proxyClassCache.get(loader, interfaces);
  14.     }

proxyClassCache 实现

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

WeakCache 类的成员变量和构造方法

  1. //K代表key的类型，P代表参数的类型，V代表value的类型。
  2. // WeakCache<ClassLoader, Class<?>[], Class<?>>  proxyClassCache  
  3. //说明proxyClassCache存的值是Class<?>对象，正是我们需要的代理类对象。
  4. final class WeakCache<K, P, V> {
  6.     private final ReferenceQueue<K> refQueue
  7.         = new ReferenceQueue<>();
  8.     // the key type is Object for supporting null key
  9.     private final ConcurrentMap<Object, ConcurrentMap<Object, Supplier<V>>> map
  10.         = new ConcurrentHashMap<>();
  11.     private final ConcurrentMap<Supplier<V>, Boolean> reverseMap
  12.         = new ConcurrentHashMap<>();
  13.     private final BiFunction<K, P, ?> subKeyFactory;
  14.     private final BiFunction<K, P, V> valueFactory;
  17.     public WeakCache(BiFunction<K, P, ?> subKeyFactory,
  18.                      BiFunction<K, P, V> valueFactory) {
  19.         this.subKeyFactory = Objects.requireNonNull(subKeyFactory);
  20.         this.valueFactory = Objects.requireNonNull(valueFactory);
  21.     }

proxyClassCache.get(loader, interfaces); 源码

  1. //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
  2. public V get(K key, P parameter) {
  3.         //检查parameter不为空
  4.         Objects.requireNonNull(parameter);
  5.          //清除无效的缓存
  6.         expungeStaleEntries();
  7.         // cacheKey就是(key, sub-key) -> value里的一级key，
  8.         Object cacheKey = CacheKey.valueOf(key, refQueue);
  10.         // lazily install the 2nd level valuesMap for the particular cacheKey
  11.         //根据一级key得到 ConcurrentMap<Object, Supplier<V>>对象。如果之前不存在，
  12.         //则新建一个ConcurrentMap<Object, Supplier<V>>和cacheKey（一级key）一起放到map中。
  13.        /**
  14.         *  reference 懒加载
  15.         */
  16.         ConcurrentMap<Object, Supplier<V>> valuesMap = map.get(cacheKey);
  17.         if (valuesMap == null) {
  18.             ConcurrentMap<Object, Supplier<V>> oldValuesMap
  19.                 = map.putIfAbsent(cacheKey,
  20.                                   valuesMap = new ConcurrentHashMap<>());
  21.             if (oldValuesMap != null) {
  22.                 valuesMap = oldValuesMap;
  23.             }
  24.         }
  26.         // create subKey and retrieve the possible Supplier<V> stored by that
  27.         // subKey from valuesMap
  28.         //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
  29.         Object subKey = Objects.requireNonNull(subKeyFactory.apply(key, parameter));
  30.         //通过sub-key得到supplier
  31.         Supplier<V> supplier = valuesMap.get(subKey);
  32.         //supplier实际上就是这个factory
  33.         Factory factory = null;
  35.         while (true) {
  36.             //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，
  37.             //一会儿分析get方法。
  38.             if (supplier != null) {
  39.                 // supplier might be a Factory or a CacheValue<V> instance
  40.                 V value = supplier.get();
  41.                 if (value != null) {
  42.                     return value;
  43.                 }
  44.             }
  45.             // else no supplier in cache
  46.             // or a supplier that returned null (could be a cleared CacheValue
  47.             // or a Factory that wasn't successful in installing the CacheValue)
  48.             // lazily construct a Factory
  49.             //下面的所有代码目的就是：如果缓存中没有supplier，
  50.             //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。
  51.             //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。
  52.             if (factory == null) {
  53.                 factory = new Factory(key, parameter, subKey, valuesMap);
  54.             }
  56.             if (supplier == null) {
  57.                 supplier = valuesMap.putIfAbsent(subKey, factory);
  58.                 if (supplier == null) {
  59.                     // successfully installed Factory
  60.                     supplier = factory;
  61.                 }
  62.                 // else retry with winning supplier
  63.             } else {
  64.                 if (valuesMap.replace(subKey, supplier, factory)) {
  65.                     // successfully replaced
  66.                     // cleared CacheEntry / unsuccessful Factory
  67.                     // with our Factory
  68.                     supplier = factory;
  69.                 } else {
  70.                     // retry with current supplier
  71.                     supplier = valuesMap.get(subKey);
  72.                 }
  73.             }
  74.         }
  75.     }

Factory类中的get方法

  1.    public synchronized V get() { // serialize access
  2.             // re-check
  3.             Supplier<V> supplier = valuesMap.get(subKey);
  4.             //重新检查得到的supplier是不是当前对象
  5.             if (supplier != this) {
  6.                 // something changed while we were waiting:
  7.                 // might be that we were replaced by a CacheValue
  8.                 // or were removed because of failure ->
  9.                 // return null to signal WeakCache.get() to retry
  10.                 // the loop
  11.                 return null;
  12.             }
  13.             // else still us (supplier == this)
  15.             // create new value
  16.             V value = null;
  17.             try {
  18.                  //代理类就是在这个位置调用valueFactory生成的
  19.                  //valueFactory就是我们传入的 new ProxyClassFactory()
  20.                 //一会我们分析ProxyClassFactory()的apply方法
  21.                 value = Objects.requireNonNull(valueFactory.apply(key, parameter));
  22.             } finally {
  23.                 if (value == null) { // remove us on failure
  24.                     valuesMap.remove(subKey, this);
  25.                 }
  26.             }
  27.             // the only path to reach here is with non-null value
  28.             assert value != null;
  30.             // wrap value with CacheValue (WeakReference)
  31.             //把value包装成弱引用
  32.             CacheValue<V> cacheValue = new CacheValue<>(value);
  34.             // put into reverseMap
  35.             // reverseMap是用来实现缓存的有效性
  36.             reverseMap.put(cacheValue, Boolean.TRUE);
  38.             // try replacing us with CacheValue (this should always succeed)
  39.             if (!valuesMap.replace(subKey, this, cacheValue)) {
  40.                 throw new AssertionError("Should not reach here");
  41.             }
  43.             // successfully replaced us with new CacheValue -> return the value
  44.             // wrapped by it
  45.             return value;
  46.         }
  47.     }

ProxyClassFactory

  1.  //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
  3. private static final class ProxyClassFactory
  4.         implements BiFunction<ClassLoader, Class<?>[], Class<?>>
  5.     {
  6.         // prefix for all proxy class names
  7.         private static final String proxyClassNamePrefix = "$Proxy";
  9.         // next number to use for generation of unique proxy class names
  10.         private static final AtomicLong nextUniqueNumber = new AtomicLong();
  12.         @Override
  13.         public Class<?> apply(ClassLoader loader, Class<?>[] interfaces) {
  15.             Map<Class<?>, Boolean> interfaceSet = new IdentityHashMap<>(interfaces.length);
  16.             for (Class<?> intf : interfaces) {
  17.                 /*
  18.                  * Verify that the class loader resolves the name of this
  19.                  * interface to the same Class object.
  20.                  */
  21.                 Class<?> interfaceClass = null;
  22.                 try {
  23.                     interfaceClass = Class.forName(intf.getName(), false, loader);
  24.                 } catch (ClassNotFoundException e) {
  25.                 }
  26.                 if (interfaceClass != intf) {
  27.                     throw new IllegalArgumentException(
  28.                         intf + " is not visible from class loader");
  29.                 }
  30.                 /*
  31.                  * Verify that the Class object actually represents an
  32.                  * interface.
  33.                  */
  34.                 if (!interfaceClass.isInterface()) {
  35.                     throw new IllegalArgumentException(
  36.                         interfaceClass.getName() + " is not an interface");
  37.                 }
  38.                 /*
  39.                  * Verify that this interface is not a duplicate.
  40.                  */
  41.                 if (interfaceSet.put(interfaceClass, Boolean.TRUE) != null) {
  42.                     throw new IllegalArgumentException(
  43.                         "repeated interface: " + interfaceClass.getName());
  44.                 }
  45.             }
  47.             String proxyPkg = null;     // package to define proxy class in
  48.             int accessFlags = Modifier.PUBLIC | Modifier.FINAL;
  50.             /*
  51.              * Record the package of a non-public proxy interface so that the
  52.              * proxy class will be defined in the same package.  Verify that
  53.              * all non-public proxy interfaces are in the same package.
  54.              */
  55.             for (Class<?> intf : interfaces) {
  56.                 int flags = intf.getModifiers();
  57.                 if (!Modifier.isPublic(flags)) {
  58.                     accessFlags = Modifier.FINAL;
  59.                     String name = intf.getName();
  60.                     int n = name.lastIndexOf('.');
  61.                     String pkg = ((n == -1) ? "" : name.substring(0, n + 1));
  62.                     if (proxyPkg == null) {
  63.                         proxyPkg = pkg;
  64.                     } else if (!pkg.equals(proxyPkg)) {
  65.                         throw new IllegalArgumentException(
  66.                             "non-public interfaces from different packages");
  67.                     }
  68.                 }
  69.             }
  71.             if (proxyPkg == null) {
  72.                 // if no non-public proxy interfaces, use com.sun.proxy package
  73.                 proxyPkg = ReflectUtil.PROXY_PACKAGE + ".";
  74.             }
  76.             /*
  77.              * Choose a name for the proxy class to generate.
  78.              */
  79.             long num = nextUniqueNumber.getAndIncrement();
  80.             String proxyName = proxyPkg + proxyClassNamePrefix + num;
  82.             /*
  83.              * Generate the specified proxy class.
  84.              */
  85.             byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
  86.                 proxyName, interfaces, accessFlags);
  87.             try {
  88.                 return defineClass0(loader, proxyName,
  89.                                     proxyClassFile, 0, proxyClassFile.length);
  90.             } catch (ClassFormatError e) {
  91.                 /*
  92.                  * A ClassFormatError here means that (barring bugs in the
  93.                  * proxy class generation code) there was some other
  94.                  * invalid aspect of the arguments supplied to the proxy
  95.                  * class creation (such as virtual machine limitations
  96.                  * exceeded).
  97.                  */
  98.                 throw new IllegalArgumentException(e.toString());
  99.             }
  100.         }
  101.     }

得到动态代理字节码

  1.   byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
  2.                 proxyName, interfaces, accessFlags);
  1. public class DynamicProxyTest {
  3.     public static void main(String[] args) {
  5.         //动态代理使用代码见掘金
  7.         String path = "D:/$Proxy0.class";
  8.         byte[] classFile = ProxyGenerator.generateProxyClass("$Proxy0", ServiceImpl.class.getInterfaces());
  9.         FileOutputStream out = null;
  11.         try {
  12.             out = new FileOutputStream(path);
  13.             out.write(classFile);
  14.             out.flush();
  15.         } catch (Exception e) {
  16.             e.printStackTrace();
  17.         } finally {
  18.             try {
  19.                 out.close();
  20.             } catch (IOException e) {
  21.                 e.printStackTrace();
  22.             }
  23.         }
  25.     }
  26. }

JDK动态代理和CGLIB字节码生成的区别

  1. JDK动态代理只能对实现了接口的类生成代理，而不能针对类。
  2. CGLIB是针对类实现代理，主要是对指定的类生成一个子类，覆盖其中的方法，并覆盖其中方法实现增强，但是因为采用的是继承，所以该类或方法最好不要声明成final，对于final类或方法，是无法继承的。

CGLIB示例代码

  2. public class CGLibProxy implements MethodInterceptor {
  3.     /** CGLib需要代理的目标对象 */
  4.     private Object targetObject;
  6.     public Object createProxyObject(Object obj) {
  7.         this.targetObject = obj;
  8.         Enhancer enhancer = new Enhancer();
  9.         enhancer.setSuperclass(obj.getClass());
  10.         enhancer.setCallback(this);
  11.         Object proxyObj = enhancer.create();
  12.         // 返回代理对象
  13.         return proxyObj;
  14.     }
  16.     @Override
  17.     public Object intercept(Object proxy, Method method, Object[] args,
  18.                             MethodProxy methodProxy) throws Throwable {
  19.         Object obj = null;
  20.         // 过滤方法
  21.         if ("addUser".equals(method.getName())) {
  22.             // 检查权限
  23.             checkPopedom();
  24.         }
  25.         obj = method.invoke(targetObject, args);
  26.         return obj;
  27.     }
  29.     private void checkPopedom() {
  30.         System.out.println("======检查权限checkPopedom()======");
  31.     }
  32. }

客户端测试类

  2. public class Client {
  3.     public static void main(String[] args) {
  4.         System.out.println("**********************CGLibProxy**********************");
  5.         CGLibProxy cgLibProxy = new CGLibProxy();
  6.         IUserManager userManager = (IUserManager) cgLibProxy.createProxyObject
  7.             (new UserManagerImpl());
  8.         //执行的是增强的add方法
  9.         userManager.addUser("jpeony", "123456");
  10.     }