最近在用Netty做开发，需要提供一个http web server，供调用方调用。采用Netty本身提供的HttpServerCodec handler进行Http协议的解析，但是需要自己提供路由。
最开始是通过对Http method及uri 采用多层if else 嵌套判断的方法路由到真正的controller类：
String uri = request.uri();HttpMethod method = request.method();if (method == HttpMethod.POST) { ???if (uri.startsWith("/login")) { ???????//url参数解析，调用controller的方法 ???} else if (uri.startsWith("/logout")) { ???????//同上 ???}} else if (method == HttpMethod.GET) { ???if (uri.startsWith("/")) { ???} else if (uri.startsWith("/status")) { ???}}在只需提供login及logoutAPI时，代码可以完成功能，可是随着API的数量越来越多，需要支持的方法及uri越来越多，else if 越来越多，代码越来越复杂。
在阿里开发手册中也提到过：
因此首先考虑采用状态设计模式及策略设计模式重构。
状态模式
状态模式的角色：
- state状态
表示状态，定义了根据不同状态进行不同处理的接口，该接口是那些处理内容依赖于状态的方法集合，对应实例的state类 - 具体的状态
实现了state接口，对应daystate和nightstate - context
context持有当前状态的具体状态的实例，此外，他还定义了供外部调用者使用的状态模式的接口。
首先我们知道每个http请求都是由method及uri来唯一标识的，所谓路由就是通过这个唯一标识定位到controller类的中的某个方法。
因此把HttpLabel作为状态
@Data@AllArgsConstructorpublic class HttpLabel { ???private String uri; ???private HttpMethod method;}状态接口：
public interface Route { ???/** ????* 路由 ????* ????* @param request ????* @return ????*/ ???GeneralResponse call(FullHttpRequest request);}为每个状态添加状态实现：
public void route() { ???//单例controller类 ???final DemoController demoController = DemoController.getInstance(); ???Map<HttpLabel, Route> map = new HashMap<>(); ???map.put(new HttpLabel("/login", HttpMethod.POST), demoController::login); ???map.put(new HttpLabel("/logout", HttpMethod.POST), demoController::login);}接到请求，判断状态，调用不同接口：
public class ServerHandler extends SimpleChannelInboundHandler<FullHttpRequest> { ???@Override ???public void channelRead0(ChannelHandlerContext ctx, FullHttpRequest request) { ???????String uri = request.uri(); ???????GeneralResponse generalResponse; ???????if (uri.contains("?")) { ???????????uri = uri.substring(0, uri.indexOf("?")); ???????} ???????Route route = map.get(new HttpLabel(uri, request.method())); ???????if (route != null) { ???????????ResponseUtil.response(ctx, request, route.call(request)); ???????} else { ???????????generalResponse = new GeneralResponse(HttpResponseStatus.BAD_REQUEST, "请检查你的请求方法及url", null); ???????????ResponseUtil.response(ctx, request, generalResponse); ???????} ???}}使用状态设计模式重构代码，在增加url时只需要网map里面put一个值就行了。
类似SpringMVC路由功能
后来看了 JAVA反射+运行时注解实现URL路由 发现反射+注解的方式很优雅，代码也不复杂。
下面介绍Netty使用反射实现URL路由。
路由注解：
@Target(ElementType.METHOD)@Retention(RetentionPolicy.RUNTIME)public @interface RequestMapping { ???/** ????* 路由的uri ????* ????* @return ????*/ ???String uri(); ???/** ????* 路由的方法 ????* ????* @return ????*/ ???String method();}扫描classpath下带有@RequestMapping注解的方法，将这个方法放进一个路由Map：Map<HttpLabel, Action<GeneralResponse>> httpRouterAction，key为上面提到过的Http唯一标识 HttpLabel，value为通过反射调用的方法：
@Slf4jpublic class HttpRouter extends ClassLoader { ???private Map<HttpLabel, Action<GeneralResponse>> httpRouterAction = new HashMap<>(); ???private String classpath = this.getClass().getResource("").getPath(); ???private Map<String, Object> controllerBeans = new HashMap<>(); ???@Override ???protected Class<?> findClass(String name) throws ClassNotFoundException { ???????String path = classpath + name.replaceAll("\\.", "/"); ???????byte[] bytes; ???????try (InputStream ins = new FileInputStream(path)) { ???????????try (ByteArrayOutputStream out = new ByteArrayOutputStream()) { ???????????????byte[] buffer = new byte[1024 * 5]; ???????????????int b = 0; ???????????????while ((b = ins.read(buffer)) != -1) { ???????????????????out.write(buffer, 0, b); ???????????????} ???????????????bytes = out.toByteArray(); ???????????} ???????} catch (Exception e) { ???????????throw new ClassNotFoundException(); ???????} ???????return defineClass(name, bytes, 0, bytes.length); ???} ???public void addRouter(String controllerClass) { ???????try { ???????????Class<?> cls = loadClass(controllerClass); ???????????Method[] methods = cls.getDeclaredMethods(); ???????????for (Method invokeMethod : methods) { ???????????????Annotation[] annotations = invokeMethod.getAnnotations(); ???????????????for (Annotation annotation : annotations) { ???????????????????if (annotation.annotationType() == RequestMapping.class) { ???????????????????????RequestMapping requestMapping = (RequestMapping) annotation; ???????????????????????String uri = requestMapping.uri(); ???????????????????????String httpMethod = requestMapping.method().toUpperCase(); ???????????????????????// 保存Bean单例 ???????????????????????if (!controllerBeans.containsKey(cls.getName())) { ???????????????????????????controllerBeans.put(cls.getName(), cls.newInstance()); ???????????????????????} ???????????????????????Action action = new Action(controllerBeans.get(cls.getName()), invokeMethod); ???????????????????????//如果需要FullHttpRequest，就注入FullHttpRequest对象 ???????????????????????Class[] params = invokeMethod.getParameterTypes(); ???????????????????????if (params.length == 1 && params[0] == FullHttpRequest.class) { ???????????????????????????action.setInjectionFullhttprequest(true); ???????????????????????} ???????????????????????// 保存映射关系 ???????????????????????httpRouterAction.put(new HttpLabel(uri, new HttpMethod(httpMethod)), action); ???????????????????} ???????????????} ???????????} ???????} catch (Exception e) { ???????????log.warn("{}", e); ???????} ???} ???public Action getRoute(HttpLabel httpLabel) { ???????return httpRouterAction.get(httpLabel); ???}}通过反射调用controller 类中的方法：
@Data@RequiredArgsConstructor@Slf4jpublic class Action<T> { ???@NonNull ???private Object object; ???@NonNull ???private Method method; ???private boolean injectionFullhttprequest; ???public T call(Object... args) { ???????try { ???????????return (T) method.invoke(object, args); ???????} catch (IllegalAccessException | InvocationTargetException e) { ???????????log.warn("{}", e); ???????} ???????return null; ???}ServerHandler.java处理如下：
//根据不同的请求API做不同的处理(路由分发)Action<GeneralResponse> action = httpRouter.getRoute(new HttpLabel(uri, request.method()));if (action != null) { ???if (action.isInjectionFullhttprequest()) { ???????ResponseUtil.response(ctx, request, action.call(request)); ???} else { ???????ResponseUtil.response(ctx, request, action.call()); ???}} else { ???//错误处理 ???generalResponse = new GeneralResponse(HttpResponseStatus.BAD_REQUEST, "请检查你的请求方法及url", null); ???ResponseUtil.response(ctx, request, generalResponse);}测试结果如下：
完整代码在 https://github.com/morethink/Netty-Route
Netty URL路由方案探讨
原文地址：https://www.cnblogs.com/morethink/p/9710918.html