前几个设计模式主要解决对象的创建问题，封装复杂的创建过程，解耦对象的创建代码和使用代码。
结构型模式。结构型模式主要总结了一些类或者对象组合在一起的经典结构。这些经典结构可以解决特定应用场景的问题。
public class UserController { //...省略其他属性和方法... private MetricsCollector metricsCollector; // 依赖注入 public UserVo login(String telephone, String password) { long startTimestamp = System.currentTimeMillis(); // ... 省略login逻辑... long endTimeStamp = System.currentTimeMillis(); long responseTime = endTimeStamp - startTimestamp; RequestInfo requestInfo = new RequestInfo("login", responseTime, startTimestamp); metricsCollector.recordRequest(requestInfo); //...返回UserVo数据... } public UserVo register(String telephone, String password) { long startTimestamp = System.currentTimeMillis(); // ... 省略register逻辑... long endTimeStamp = System.currentTimeMillis(); long responseTime = endTimeStamp - startTimestamp; RequestInfo requestInfo = new RequestInfo("register", responseTime, startTimestamp); metricsCollector.recordRequest(requestInfo); //...返回UserVo数据... } }
public interface IUserController { UserVo login(String telephone, String password); UserVo register(String telephone, String password); } public class UserController implements IUserController { //...省略其他属性和方法... @Override public UserVo login(String telephone, String password) { //...省略login逻辑... //...返回UserVo数据... } @Override public UserVo register(String telephone, String password) { //...省略register逻辑... //...返回UserVo数据... } } public class UserControllerProxy implements IUserController { private MetricsCollector metricsCollector; private UserController userController; public UserControllerProxy(UserController userController) { this.userController = userController; this.metricsCollector = new MetricsCollector(); } @Override public UserVo login(String telephone, String password) { long startTimestamp = System.currentTimeMillis(); // 委托 UserVo userVo = userController.login(telephone, password); long endTimeStamp = System.currentTimeMillis(); long responseTime = endTimeStamp - startTimestamp; RequestInfo requestInfo = new RequestInfo("login", responseTime, startTimestamp); metricsCollector.recordRequest(requestInfo); return userVo; } @Override public UserVo register(String telephone, String password) { long startTimestamp = System.currentTimeMillis(); UserVo userVo = userController.register(telephone, password); long endTimeStamp = System.currentTimeMillis(); long responseTime = endTimeStamp - startTimestamp; RequestInfo requestInfo = new RequestInfo("register", responseTime, startTimestamp); metricsCollector.recordRequest(requestInfo); return userVo; } } //UserControllerProxy使用举例 //因为原始类和代理类实现相同的接口，是基于接口而非实现编程 //将UserController类对象替换为UserControllerProxy类对象，不需要改动太多代码 IUserController userController = new UserControllerProxy(new UserController());
public class UserControllerProxy extends UserController { private MetricsCollector metricsCollector; public UserControllerProxy() { this.metricsCollector = new MetricsCollector(); } public UserVo login(String telephone, String password) { long startTimestamp = System.currentTimeMillis(); UserVo userVo = super.login(telephone, password); long endTimeStamp = System.currentTimeMillis(); long responseTime = endTimeStamp - startTimestamp; RequestInfo requestInfo = new RequestInfo("login", responseTime, startTimestamp); metricsCollector.recordRequest(requestInfo); return userVo; } public UserVo register(String telephone, String password) { long startTimestamp = System.currentTimeMillis(); UserVo userVo = super.register(telephone, password); long endTimeStamp = System.currentTimeMillis(); long responseTime = endTimeStamp - startTimestamp; RequestInfo requestInfo = new RequestInfo("register", responseTime, startTimestamp); metricsCollector.recordRequest(requestInfo); return userVo; } } //UserControllerProxy使用举例 UserController userController = new UserControllerProxy();
刚才的实现还是有点问题：
动态代理：不事先为每个原始类编写代理类，而是运行的时候动态创建原始类对应的代理类。
public class MetricsCollectorProxy { private MetricsCollector metricsCollector; public MetricsCollectorProxy() { this.metricsCollector = new MetricsCollector(); } public Object createProxy(Object proxiedObject) { Class<?>[] interfaces = proxiedObject.getClass().getInterfaces(); DynamicProxyHandler handler = new DynamicProxyHandler(proxiedObject); return Proxy.newProxyInstance(proxiedObject.getClass().getClassLoader(), interfaces, handler); } private class DynamicProxyHandler implements InvocationHandler { private Object proxiedObject; public DynamicProxyHandler(Object proxiedObject) { this.proxiedObject = proxiedObject; } @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { long startTimestamp = System.currentTimeMillis(); Object result = method.invoke(proxiedObject, args); long endTimeStamp = System.currentTimeMillis(); long responseTime = endTimeStamp - startTimestamp; String apiName = proxiedObject.getClass().getName() + ":" + method.getName(); RequestInfo requestInfo = new RequestInfo(apiName, responseTime, startTimestamp); metricsCollector.recordRequest(requestInfo); return result; } } } //MetricsCollectorProxy使用举例 MetricsCollectorProxy proxy = new MetricsCollectorProxy(); IUserController userController = (IUserController) proxy.createProxy(new UserController());
比如监控、日志、统计、鉴权、限流、事务、幂等。Spring AOP完成的东西。
GoF 的《设计模式》一书中把它称作远程代理。通过远程代理，将网络通信、数据编解码等细节隐藏起来。客户端在使用 RPC 服务的时候，就像使用本地函数一样，无需了解跟服务器交互的细节。除此之外，RPC 服务的开发者也只需要开发业务逻辑，就像开发本地使用的函数一样，不需要关注跟客户端的交互细节。