Java动态代理Proxy类的解析

使用过代理的，对Proxy不会感到陌生，主要分析Proxy类的内部结构。

一、Proxy类的结构

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

/**
 * the invocation handler for this proxy instance.
 * @serial
 */
protected InvocationHandler h;

/**
 * Prohibits instantiation.
 */
private Proxy() {
    }

二、Proxy类的方法
(1)public static Object newProxyInstance(ClassLoader loader,Class<?>[] interfaces,InvocationHandler h)方法

      public static Object newProxyInstance(ClassLoader loader,
                                          Class<?>[] interfaces,
                                          InvocationHandler h)
throws IllegalArgumentException
    {
if (h == null) {
throw new NullPointerException();
        }
//复制接口
final Class<?>[] intfs = interfaces.clone();
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
//检查访问权限
            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 {
//通过class获得constructor
final Constructor<?> cons = cl.getConstructor(constructorParams);
            ...
            ...
//创建代理实例
return newInstance(cons, ih);
        } catch (NoSuchMethodException e) {
throw new InternalError(e.toString());
        }
    }

(2) private static Class<?> getProxyClass0(ClassLoader loader,
Class<?>... interfaces)方法

private static Class<?> getProxyClass0(ClassLoader loader,
                                           Class<?>... interfaces) {
//接口的数量限制 
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
//从缓存中获取，如果没有就通过ProxyClassFactory创建
return proxyClassCache.get(loader, interfaces);
    }

(3)proxyClassCache.get(loader,interface) 方法

public V get(K key, P parameter) {
//省略中间的代码
    ...
    ...
    ...
// create subKey and retrieve the possible Supplier<V> stored by that
// subKey from valuesMap
        Object subKey = Objects.requireNonNull(subKeyFactory.apply(key, parameter));
      ...
      ...
    }

(4)subKeyFactory.apply(key, parameter) 方法调用的是ProxyClassFactory@apply(ClassLoader loader, Class<?>[] interfaces) 方法

 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());
                }
            }
           ...
           ...
/*
 * 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);
try {
//根据字节码文件，类加载器，代理类名，定义代理类
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());
            }
        }
    }

以上调用过程生成代理类的过程。
更多代理相关的资料：
http://rejoy.iteye.com/blog/1627405
http://www.jianshu.com/p/6f6bb2f0ece9