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 继上一篇文章什么，这年头还有人不知道404_cow__sky的博客-CSDN博客后，有些同学发现，学了之后有啥用，有什么实际场景可以用到吗？程序员就是这样，不习惯于纸上谈兵，给一个场景show me code才是最实在的，好了，不扯淡了，回归正文吧！

一、场景

有这么一个场景，大家看看怎么来实现，在咱们使用sentinel（熔断限流器）alibaba/Sentinel: A powerful flow control component enabling reliability, resilience and monitoring for microservices. (面向云原生微服务的高可用流控防护组件) (github.com)时，需要在dashboard展示和编辑各种各样的数据，比如展示某个应用下集群机器列表、展示实时监控数据、规则展示、规则编辑等等。

dashboard展示图如下：

二、需求拆解

看到这个场景后，我们能想到的就是这些数据从哪里来？又流向哪里？清楚这个后，才能制定具体的事实施方案。

1. 这些需要展示的数据从哪里来？

   客户端

2. 在dashboard上编辑规则后，这些数据流向哪里？

   客户端

三、需求实现

那么在清楚需求之后，总结起来就是一句话，客户端有数据需要传到dashborad，同样dashborad也有数据需要传到客户端。那么如何实现呢？

1. dashboard 如何知道某个app下某个接口的通讯 ip + port

2. dashboard 如何接受客户端的请求

3. 同样，客户端如何接受dashboard的请求（这是本文讲解的重点）

sentinel 的实现逻辑如下：

根据上图，如果换做我们，那估计就是分别在客户端和dashboard上开几个接口就ok了，那么sentinel 是这么做的吗？是，也不是。我们拿dashboard从客户端读/写数据为例，在早期的sentinel版本中，并没有在客户端使用web容器开启http接口，因为它觉得使用web容器的方式太重了。不信，你看sentinel官方给出的解释

使用web容器太过于重要级我理解有两层含义，第一就是web框架本身就比较重，其次就是有些客户端并不是使用的spring或者spring mvc 框架，为了减小依赖，sentinel提供了比较原生的实现方式。从图中可以看出，sentinel 专门写了一个transport模块用来通信，早期的transport中包含sentinel-transport-simple-http 和 sentinel-transport-netty-http两个模块，sentinel-transport-simple-http 使用的是jdk原生的socket 而sentinel-transport-netty-http采用的netty来实现http server。那么怎么实现的呢？可以简单看看，以 sentinel-transport-simple-http 模块为例，其大概得执行过程是：

可以简单看看代码：

// HttpEventTask 类public void run() {if (socket == null) {return;}PrintWriter printWriter = null;InputStream inputStream = null;try {long start = System.currentTimeMillis();inputStream = new BufferedInputStream(socket.getInputStream());OutputStream outputStream = socket.getOutputStream();printWriter = new PrintWriter(new OutputStreamWriter(outputStream, Charset.forName(SentinelConfig.charset())));String firstLine = readLine(inputStream);CommandCenterLog.info("[SimpleHttpCommandCenter] Socket income: " + firstLine+ ", addr: " + socket.getInetAddress());CommandRequest request = processQueryString(firstLine);if (firstLine.length() > 4 && StringUtil.equalsIgnoreCase("POST", firstLine.substring(0, 4))) {// Deal with post methodprocessPostRequest(inputStream, request);}// Validate the target command.String commandName = HttpCommandUtils.getTarget(request);if (StringUtil.isBlank(commandName)) {writeResponse(printWriter, StatusCode.BAD_REQUEST, INVALID_COMMAND_MESSAGE);return;}// Find the matching command handler.CommandHandler<?> commandHandler = SimpleHttpCommandCenter.getHandler(commandName);if (commandHandler != null) {CommandResponse<?> response = commandHandler.handle(request);handleResponse(response, printWriter);} else {// No matching command handler.writeResponse(printWriter, StatusCode.BAD_REQUEST, "Unknown command `" + commandName + '`');}long cost = System.currentTimeMillis() - start;CommandCenterLog.info("[SimpleHttpCommandCenter] Deal a socket task: " + firstLine+ ", address: " + socket.getInetAddress() + ", time cost: " + cost + " ms");} catch (RequestException e) {writeResponse(printWriter, e.getStatusCode(), e.getMessage());} catch (Throwable e) {CommandCenterLog.warn("[SimpleHttpCommandCenter] CommandCenter error", e);try {if (printWriter != null) {String errorMessage = SERVER_ERROR_MESSAGE;e.printStackTrace();if (!writtenHead) {writeResponse(printWriter, StatusCode.INTERNAL_SERVER_ERROR, errorMessage);} else {printWriter.println(errorMessage);}printWriter.flush();}} catch (Exception e1) {CommandCenterLog.warn("Failed to write error response", e1);}} finally {closeResource(inputStream);closeResource(printWriter);closeResource(socket);}}

CommandHandler<?> commandHandler = SimpleHttpCommandCenter.getHandler(commandName); 这行代码就是根据commandName 获取 CommandHandler，CommandHandler 是一个顶层接口，其实现类上定义了一个@CommandMapping，该注解中有个name字段，用来定义command路径，这里有点类似 @RequestMapping的味道，具体代码如下：

@CommandMapping(name = "tree", desc = "get metrics in tree mode, use id to specify detailed tree root")
public class FetchTreeCommandHandler implements CommandHandler<String> {@Overridepublic CommandResponse<String> handle(CommandRequest request) {String id = request.getParam("id");StringBuilder sb = new StringBuilder();DefaultNode start = Constants.ROOT;if (id == null) {visitTree(0, start, sb);} else {boolean exactly = false;for (Node n : start.getChildList()) {DefaultNode dn = (DefaultNode)n;if (dn.getId().getName().equals(id)) {visitTree(0, dn, sb);exactly = true;break;}}if (!exactly) {for (Node n : start.getChildList()) {DefaultNode dn = (DefaultNode)n;if (dn.getId().getName().contains(id)) {visitTree(0, dn, sb);}}}}sb.append("\r\n\r\n");sb.append("t:threadNum  pq:passQps  bq:blockQps  tq:totalQps  rt:averageRt  prq: passRequestQps 1mp:1m-pass "+ "1mb:1m-block 1mt:1m-total").append("\r\n");return CommandResponse.ofSuccess(sb.toString());}private void visitTree(int level, DefaultNode node, /*@NonNull*/ StringBuilder sb) {for (int i = 0; i < level; ++i) {sb.append("-");}if (!(node instanceof EntranceNode)) {sb.append(String.format("%s(t:%s pq:%s bq:%s tq:%s rt:%s prq:%s 1mp:%s 1mb:%s 1mt:%s)",node.getId().getShowName(), node.curThreadNum(), node.passQps(),node.blockQps(), node.totalQps(), node.avgRt(), node.successQps(),node.totalRequest() - node.blockRequest(), node.blockRequest(),node.totalRequest())).append("\n");} else {sb.append(String.format("EntranceNode: %s(t:%s pq:%s bq:%s tq:%s rt:%s prq:%s 1mp:%s 1mb:%s 1mt:%s)",node.getId().getShowName(), node.curThreadNum(), node.passQps(),node.blockQps(), node.totalQps(), node.avgRt(), node.successQps(),node.totalRequest() - node.blockRequest(), node.blockRequest(),node.totalRequest())).append("\n");}for (Node n : node.getChildList()) {DefaultNode dn = (DefaultNode)n;visitTree(level + 1, dn, sb);}}
}

这样我们请求接口http://localhost:10000/tree?type=root时，其返回结果如下：

同样，sentinel-transport-netty-http 也是类似的逻辑！这样看来一切安好。

四、spring-mvc 模式通信兼容

直到有一天有人提出以下问题：

总的来看就是现在和dashboard交互的端口需要和sprinboot web 应用共用一个端口。那现在有个难题。由于已经存在 sentinel-transport-simple-http和sentinel-transport-netty-http 模块，底层设计采用的是 CommandHandler 来适配各类请求，那么如果是以web容器来执行mvc模式的请求该如何兼容呢？

江湖中不缺好手，时隔半年后，有人提出，在不改变底层设计的情况下，只需要实现HandlerAdapter 和 HandlerMapping 即可，看到这里是不是觉得很熟悉，HandlerAdapter 和 HandlerMapping不就是大名鼎鼎的处理器适配器和处理器映射器吗？咱们回顾下，用大白话说HandlerMapping的作用就是根据url路径找handler， HandlerAdapter就是对handler进行装饰，忽略底层细节，对上层提供统一的调用方法来进行handler处理。那么sentinel是怎么做的呢？我们看看

public class SentinelApiHandlerAdapter implements HandlerAdapter, Ordered {private int order = Ordered.LOWEST_PRECEDENCE;public void setOrder(int order) {this.order = order;}@Overridepublic int getOrder() {return order;}@Overridepublic boolean supports(Object handler) {return handler instanceof SentinelApiHandler;}@Overridepublic ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {SentinelApiHandler sentinelApiHandler = (SentinelApiHandler) handler;// 调用底层的CommandHandler接口sentinelApiHandler.handle(request, response);return null;}@Overridepublic long getLastModified(HttpServletRequest request, Object handler) {return -1;}
}

public class SentinelApiHandlerMapping extends AbstractHandlerMapping implements ApplicationListener {private static final String SPRING_BOOT_WEB_SERVER_INITIALIZED_EVENT_CLASS = "org.springframework.boot.web.context.WebServerInitializedEvent";private static Class webServerInitializedEventClass;static {try {webServerInitializedEventClass = ClassUtils.forName(SPRING_BOOT_WEB_SERVER_INITIALIZED_EVENT_CLASS, null);RecordLog.info("[SentinelApiHandlerMapping] class {} is present, this is a spring-boot app, we can auto detect port", SPRING_BOOT_WEB_SERVER_INITIALIZED_EVENT_CLASS);} catch (ClassNotFoundException e) {RecordLog.info("[SentinelApiHandlerMapping] class {} is not present, this is not a spring-boot app, we can not auto detect port", SPRING_BOOT_WEB_SERVER_INITIALIZED_EVENT_CLASS);}}final static Map<String, CommandHandler> handlerMap = new ConcurrentHashMap<>();private boolean ignoreInterceptor = true;public SentinelApiHandlerMapping() {setOrder(Ordered.LOWEST_PRECEDENCE - 10);}@Overrideprotected Object getHandlerInternal(HttpServletRequest request) throws Exception {String commandName = request.getRequestURI();if (commandName.startsWith("/")) {commandName = commandName.substring(1);}// 获取底层CommandHandlerCommandHandler commandHandler = handlerMap.get(commandName);return commandHandler != null ? new SentinelApiHandler(commandHandler) : null;}@Overrideprotected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {return ignoreInterceptor ? new HandlerExecutionChain(handler) : super.getHandlerExecutionChain(handler, request);}public void setIgnoreInterceptor(boolean ignoreInterceptor) {this.ignoreInterceptor = ignoreInterceptor;}public static void registerCommand(String commandName, CommandHandler handler) {if (StringUtil.isEmpty(commandName) || handler == null) {return;}if (handlerMap.containsKey(commandName)) {CommandCenterLog.warn("[SentinelApiHandlerMapping] Register failed (duplicate command): " + commandName);return;}handlerMap.put(commandName, handler);}public static void registerCommands(Map<String, CommandHandler> handlerMap) {if (handlerMap != null) {for (Map.Entry<String, CommandHandler> e : handlerMap.entrySet()) {registerCommand(e.getKey(), e.getValue());}}}@Overridepublic void onApplicationEvent(ApplicationEvent applicationEvent) {if (webServerInitializedEventClass != null && webServerInitializedEventClass.isAssignableFrom(applicationEvent.getClass())) {Integer port = null;try {BeanWrapper beanWrapper = new BeanWrapperImpl(applicationEvent);port = (Integer) beanWrapper.getPropertyValue("webServer.port");} catch (Exception e) {RecordLog.warn("[SentinelApiHandlerMapping] resolve port from event " + applicationEvent + " fail", e);}if (port != null && TransportConfig.getPort() == null) {RecordLog.info("[SentinelApiHandlerMapping] resolve port {} from event {}", port, applicationEvent);TransportConfig.setRuntimePort(port);}}}
}

后来sentinel官方也采用了这种方法做了升级，sentinel 1.8.2 升级说明如下：

好了，看到这里，你是否对spring mvc web容器下的http请求过程有了更深的理解呢？