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<Void>() {
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);
}
}