在Java的java.lang.reflect包下提供了一个Proxy类和一个InvocationHandler接口。通过这个类和接口可以生成JDK动态代理类或动态代理对象。

JDK动态代理例子：

// 抽象主题角色public interface Sleep {    void sleep();}  // 真实主题角色public class SleepImpl implements Sleep {    @Override    public void sleep() {        System.out.println("熟睡中");    }}  //动态处理器public class DynamicProxyHandler implements InvocationHandler {       private Object obj ;    public  DynamicProxyHandler(final Object obj) {               this.obj = obj;    }    @Override    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {        System.out.println("睡觉前要刷牙");        Object result = method.invoke(obj, args);        System.out.println("睡醒后要吃早饭");        return null;    }}//测试代码public class ProxyTest {    public static void main(String[] args) {                      Sleep sleep = new SleepImpl();        DynamicProxyHandler dph = new DynamicProxyHandler(sleep);        Sleep sleepProxy = (Sleep) Proxy.newProxyInstance(sleep.getClass().getClassLoader(),                sleep.getClass().getInterfaces(), dph);        sleepProxy.sleep();    }}  结果：睡觉前要刷牙      熟睡中      睡醒后要吃早饭

JDK动态代理源码分析：

生产代理类主要是通过：Proxy.newProxyInstance方法：

@CallerSensitive    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);        }    }