什么是網(wǎng)關(guān)？為什么需要使用網(wǎng)關(guān)？

如圖所示，在不使用網(wǎng)關(guān)的情況下，我們的服務(wù)是直接暴露給服務(wù)調(diào)用方。當調(diào)用方增多，勢必需要添加定制化訪問權(quán)限、校驗等邏輯。當添加API網(wǎng)關(guān)后，在第三方調(diào)用端和服務(wù)提供方之間就創(chuàng)建了一面墻，這面墻直接與調(diào)用方通信進行權(quán)限控制。
本文所實現(xiàn)的網(wǎng)關(guān)源碼抄襲了---Oh,不對，是借鑒。借鑒了Zuul網(wǎng)關(guān)的源碼，提煉出其核心思路，實現(xiàn)了一套簡單的網(wǎng)關(guān)源碼，博主將其改名為Eatuul。

題外話

本文是業(yè)內(nèi)能搜到的第一篇自己動手實現(xiàn)網(wǎng)關(guān)的文章。博主寫的手把手系列的文章，目的是在以最簡單的方式，揭露出中間件的核心原理，讓讀者能夠迅速了解實現(xiàn)的核心。需要說明的是，這不是源碼分析系列的文章，因此寫出來的代碼，省去了一些復(fù)雜的內(nèi)容，畢竟大家能理解到該中間件的核心原理即可。如果想看源碼分析系列的，請關(guān)注博主，后期會將spring、spring boot、dubbo、mybatis等開源框架一一揭示。

正文設(shè)計思路

先大致說一下，就是定義一個Servlet接收請求。然后經(jīng)過preFilter(封裝請求參數(shù)),routeFilter(轉(zhuǎn)發(fā)請求)，postFilter(輸出內(nèi)容)。三個過濾器之間，共享request、response以及其他的一些全局變量。如下圖所示

和真正的Zuul的區(qū)別?主要區(qū)別有如下幾點

Zuul中在異常處理模塊，有一個ErrorFilter來處理，博主在實現(xiàn)的時候偷懶了，略去。

Zuul中PreFilters,RoutingFilters,PostFilters默認都實現(xiàn)了一組，具體如下表所示

博主總不可能每一個都給你們實現(xiàn)一遍吧。所以偷懶了，每種只實現(xiàn)一個。但是調(diào)用順序還是不變，按照PreFilters->RoutingFilters->PostFilters的順序調(diào)用

在routeFilters確實有轉(zhuǎn)發(fā)請求的Filter,然而博主偷天換日了，改用RestTemplate實現(xiàn).

代碼結(jié)構(gòu)

大家去spring官網(wǎng)上搭建一套springboot的項目，博主就不展示pom的代碼了。直接將項目結(jié)構(gòu)展示一下，如下圖所示

EatuulServlet.java

這個是網(wǎng)關(guān)的入口，邏輯也十分簡單，分為三步
(1)將request,response放入threadlocal中
(2)執(zhí)行三組過濾器
(3)清除threadlocal中的的環(huán)境變量

源碼如下

package?com.rjzheng.eatuul.http;import?java.io.IOException;import?javax.servlet.ServletException; import?javax.servlet.annotation.WebServlet; import?javax.servlet.http.HttpServlet; import?javax.servlet.http.HttpServletRequest; import?javax.servlet.http.HttpServletResponse;@WebServlet(name =?"eatuul", urlPatterns =?"/*") public?class?EatuulServlet?extends?HttpServlet?{private?EatRunner eatRunner =?new?EatRunner();@Overridepublic?void?service(HttpServletRequest req, HttpServletResponse resp)throws?ServletException, IOException?{//將request，和response放入上下文對象中eatRunner.init(req, resp);try?{//執(zhí)行前置過濾eatRunner.preRoute();//執(zhí)行過濾eatRunner.route();//執(zhí)行后置過濾eatRunner.postRoute();}?catch?(Throwable e) {RequestContext.getCurrentContext().getResponse().sendError(HttpServletResponse.SC_NOT_FOUND, e.getMessage());}?finally?{//清除變量RequestContext.getCurrentContext().unset();}}}

EatuulRunner.java

這個是具體的執(zhí)行器。需要說明一下，在Zuul中，ZuulRunner在獲取具體有哪些過濾器的時候，有一個FileLoader可以動態(tài)讀取配置加載。博主在實現(xiàn)我們自己的EatuulRunner時候，略去動態(tài)讀取的過程，直接靜態(tài)寫死。

源碼如下

package?com.rjzheng.eatuul.http;import?java.util.ArrayList; import?java.util.List; import?java.util.concurrent.ConcurrentHashMap;import?javax.servlet.http.HttpServletRequest; import?javax.servlet.http.HttpServletResponse;import?com.rjzheng.eatuul.filter.EatuulFilter; import?com.rjzheng.eatuul.filter.post.SendResponseFilter; import?com.rjzheng.eatuul.filter.pre.RequestWrapperFilter; import?com.rjzheng.eatuul.filter.route.RoutingFilter;public?class?EatRunner?{//靜態(tài)寫死過濾器private?ConcurrentHashMap<String, List<EatuulFilter>> hashFiltersByType =?new?ConcurrentHashMap<String, List<EatuulFilter>>(){{ ?put("pre",new?ArrayList<EatuulFilter>(){{add(new?RequestWrapperFilter());}});put("route",new?ArrayList<EatuulFilter>(){{add(new?RoutingFilter());}});put("post",new?ArrayList<EatuulFilter>(){{add(new?SendResponseFilter());}});}};public?void?init(HttpServletRequest req, HttpServletResponse resp)?{RequestContext ctx = RequestContext.getCurrentContext();ctx.setRequest(req);ctx.setResponse(resp);}public?void?preRoute()?throws?Throwable?{runFilters("pre"); ?}public?void?route()?throws?Throwable{runFilters("route"); ? ?}public?void?postRoute()?throws?Throwable{runFilters("post");}public?void?runFilters(String sType)?throws?Throwable?{List<EatuulFilter> list =?this.hashFiltersByType.get(sType);if?(list !=?null) {for?(int?i =?0; i < list.size(); i++) {EatuulFilter zuulFilter = list.get(i);zuulFilter.run();}}} }

EatuulFilter.java

接下來就是一系列Filter的代碼了，先上父類EatuulFilter的源碼

package?com.rjzheng.eatuul.filter;public?abstract?class?EatuulFilter?{abstract?public?String?filterType();abstract?public?int?filterOrder();abstract?public?void?run(); }

RequestWrapperFilter.java

這個是PreFilter,前置執(zhí)行過濾器，負責封裝請求。步驟如下所示

(1)封裝請求頭

(2)封裝請求體

(3)構(gòu)造出RestTemplate能識別的RequestEntity

(4)將RequestEntity放入全局threadlocal之中

代碼如下所示

package?com.rjzheng.eatuul.filter.pre;import?java.io.IOException; import?java.io.InputStream; import?java.net.URI; import?java.net.URISyntaxException; import?java.util.Collections; import?java.util.List;import?javax.servlet.http.HttpServletRequest;import?org.springframework.http.HttpHeaders; import?org.springframework.http.HttpMethod; import?org.springframework.http.RequestEntity; import?org.springframework.util.MultiValueMap; import?org.springframework.util.StreamUtils;import?com.rjzheng.eatuul.filter.EatuulFilter; import?com.rjzheng.eatuul.http.RequestContext;public?class?RequestWrapperFilter?extends?EatuulFilter{@Overridepublic?String?filterType()?{// TODO Auto-generated method stubreturn?"pre";}@Overridepublic?int?filterOrder()?{// TODO Auto-generated method stubreturn?-1;}@Overridepublic?void?run()?{String rootURL =?"http://localhost:9090";RequestContext ctx =RequestContext.getCurrentContext();HttpServletRequest servletRequest = ctx.getRequest();String targetURL = rootURL + servletRequest.getRequestURI();RequestEntity<byte[]> requestEntity =?null;try?{requestEntity = createRequestEntity(servletRequest, targetURL);}?catch?(Exception e) {e.printStackTrace();}//4、將requestEntity放入全局threadlocal之中ctx.setRequestEntity(requestEntity);}private?RequestEntity?createRequestEntity(HttpServletRequest request,String url)?throws?URISyntaxException, IOException?{String method = request.getMethod();HttpMethod httpMethod = HttpMethod.resolve(method);//1、封裝請求頭MultiValueMap<String, String> headers =createRequestHeaders(request);//2、封裝請求體byte[] body = createRequestBody(request);//3、構(gòu)造出RestTemplate能識別的RequestEntityRequestEntity requestEntity =?new?RequestEntity<byte[]>(body,headers,httpMethod,?new?URI(url));return?requestEntity;}private?byte[] createRequestBody(HttpServletRequest request)?throws?IOException {InputStream inputStream = request.getInputStream();return?StreamUtils.copyToByteArray(inputStream);}private?MultiValueMap<String, String>?createRequestHeaders(HttpServletRequest request)?{HttpHeaders headers =?new?HttpHeaders();List<String> headerNames = Collections.list(request.getHeaderNames());for(String headerName:headerNames) {List<String> headerValues = Collections.list(request.getHeaders(headerName));for(String headerValue:headerValues) {headers.add(headerName, headerValue);}}return?headers;} }

RoutingFilter.java

這個是routeFilter,這里我偷懶了，直接做轉(zhuǎn)發(fā)請求，并且將返回值ResponseEntity放入全局threadlocal中

package?com.rjzheng.eatuul.filter.route;import?org.springframework.http.RequestEntity; import?org.springframework.http.ResponseEntity; import?org.springframework.web.client.RestTemplate;import?com.rjzheng.eatuul.filter.EatuulFilter; import?com.rjzheng.eatuul.http.RequestContext;public?class?RoutingFilter?extends?EatuulFilter{@Overridepublic?String?filterType()?{// TODO Auto-generated method stubreturn?"route";}@Overridepublic?int?filterOrder()?{// TODO Auto-generated method stubreturn?0;}@Overridepublic?void?run(){RequestContext ctx = RequestContext.getCurrentContext();RequestEntity requestEntity = ctx.getRequestEntity();RestTemplate restTemplate =?new?RestTemplate();ResponseEntity responseEntity = restTemplate.exchange(requestEntity,byte[].class);ctx.setResponseEntity(responseEntity);}}

SendResponseFilter.java

這個是postFilters,將ResponseEntity輸出即可

package?com.rjzheng.eatuul.filter.post;import?java.util.List; import?java.util.Map;import?javax.servlet.ServletOutputStream; import?javax.servlet.http.HttpServletResponse;import?org.springframework.http.HttpHeaders; import?org.springframework.http.ResponseEntity;import?com.rjzheng.eatuul.filter.EatuulFilter; import?com.rjzheng.eatuul.http.RequestContext;public?class?SendResponseFilter?extends?EatuulFilter{@Overridepublic?String?filterType()?{return?"post";}@Overridepublic?int?filterOrder()?{return?1000;}@Overridepublic?void?run()?{try?{addResponseHeaders();writeResponse();}?catch?(Exception e) {e.printStackTrace();}}private?void?addResponseHeaders()?{RequestContext ctx = RequestContext.getCurrentContext();HttpServletResponse servletResponse = ctx.getResponse();ResponseEntity responseEntity = ctx.getResponseEntity();HttpHeaders httpHeaders = responseEntity.getHeaders();for(Map.Entry<String, List<String>> entry:httpHeaders.entrySet()) {String headerName = entry.getKey();List<String> headerValues = entry.getValue();for(String headerValue:headerValues) {servletResponse.addHeader(headerName, headerValue);}}}private?void?writeResponse()throws?Exception?{RequestContext ctx = RequestContext.getCurrentContext();HttpServletResponse servletResponse = ctx.getResponse();if?(servletResponse.getCharacterEncoding() ==?null) {?// only set if not setservletResponse.setCharacterEncoding("UTF-8");}ResponseEntity responseEntity = ctx.getResponseEntity();if(responseEntity.hasBody()) {byte[] body = (byte[]) responseEntity.getBody();ServletOutputStream outputStream = servletResponse.getOutputStream();outputStream.write(body);outputStream.flush();}}}

RequestContext.java

最后是一直在說的全局threadlocal變量

package?com.rjzheng.eatuul.http;import?java.util.HashMap; import?java.util.Map; import?java.util.concurrent.ConcurrentHashMap;import?javax.servlet.http.HttpServletRequest; import?javax.servlet.http.HttpServletResponse;import?org.springframework.http.RequestEntity; import?org.springframework.http.ResponseEntity;public?class?RequestContext?extends?ConcurrentHashMap<String,?Object>?{protected?static?Class<? extends RequestContext> contextClass = RequestContext.class;protected?static?final?ThreadLocal<? extends RequestContext> threadLocal =?new?ThreadLocal<RequestContext>() {@Overrideprotected?RequestContext?initialValue()?{try?{return?contextClass.newInstance();}?catch?(Throwable e) {throw?new?RuntimeException(e);}}};public?static?RequestContext?getCurrentContext()?{RequestContext context = threadLocal.get();return?context;}public?HttpServletRequest?getRequest()?{return?(HttpServletRequest) get("request");}public?void?setRequest(HttpServletRequest request)?{put("request", request);}public?HttpServletResponse?getResponse()?{return?(HttpServletResponse) get("response");}public?void?setResponse(HttpServletResponse response)?{set("response", response);}public?void?setRequestEntity(RequestEntity requestEntity){set("requestEntity",requestEntity);}public?RequestEntity?getRequestEntity()?{return?(RequestEntity) get("requestEntity");}public?void?setResponseEntity(ResponseEntity responseEntity){set("responseEntity",responseEntity);}public?ResponseEntity?getResponseEntity()?{return?(ResponseEntity) get("responseEntity");}public?void?set(String key, Object value)?{if?(value !=?null)put(key, value);elseremove(key);}public?void?unset()?{threadLocal.remove();}}

如何測試？

自己另外起一個server端口為9090如下所示

package?com.rjzheng.eatservice;import?org.springframework.boot.autoconfigure.SpringBootApplication; import?org.springframework.boot.builder.SpringApplicationBuilder; import?org.springframework.boot.web.servlet.ServletComponentScan;import?com.rjzheng.eatservice.controller.IndexController;@SpringBootApplication @ServletComponentScan(basePackageClasses = IndexController.class) public?class?Application?{public?static?void?main(String[] args)?{new?SpringApplicationBuilder(Application.class).properties("server.port=9090").run(args);} }

再來一個controller

package?com.rjzheng.eatservice.controller;import?org.springframework.web.bind.annotation.RequestMapping; import?org.springframework.web.bind.annotation.RestController;@RestController public class IndexController {@RequestMapping("/index")public String index() {return?"hello!world";} }

然后，你就發(fā)現(xiàn)可以從localhost:8080/index進行跳轉(zhuǎn)訪問了

結(jié)論

本文模擬了一下zuul網(wǎng)關(guān)的源碼，借鑒了一下其精髓的部分。希望大家能有所收獲

?

出處：?http://rjzheng.cnblogs.com/

作者：孤獨煙，作者公號，可以關(guān)注一波

《新程序員》：云原生和全面數(shù)字化實踐50位技術(shù)專家共同創(chuàng)作，文字、視頻、音頻交互閱讀

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