自己动手写一个服务网关

什么是网关？为什么需要使用网关？

如图所示，在不使用网关的情况下，我们的服务是直接暴露给服务调用方。当调用方增多，势必需要添加定制化访问权限、校验等逻辑。当添加API网关后，在第三方调用端和服务提供方之间就创建了一面墙，这面墙直接与调用方通信进行权限控制。
本文所实现的网关源码抄袭了---Oh,不对，是借鉴。借鉴了Zuul网关的源码，提炼出其核心思路，实现了一套简单的网关源码，博主将其改名为Eatuul。

题外话

本文是业内能搜到的第一篇自己动手实现网关的文章。博主写的手把手系列的文章，目的是在以最简单的方式，揭露出中间件的核心原理，让读者能够迅速了解实现的核心。需要说明的是，这不是源码分析系列的文章，因此写出来的代码，省去了一些复杂的内容，毕竟大家能理解到该中间件的核心原理即可。如果想看源码分析系列的，请关注博主，后期会将spring、spring boot、dubbo、mybatis等开源框架一一揭示。

正文设计思路

先大致说一下，就是定义一个Servlet接收请求。然后经过preFilter(封装请求参数),routeFilter(转发请求)，postFilter(输出内容)。三个过滤器之间，共享request、response以及其他的一些全局变量。如下图所示

和真正的Zuul的区别?主要区别有如下几点

Zuul中在异常处理模块，有一个ErrorFilter来处理，博主在实现的时候偷懒了，略去。
Zuul中PreFilters,RoutingFilters,PostFilters默认都实现了一组，具体如下表所示

博主总不可能每一个都给你们实现一遍吧。所以偷懒了，每种只实现一个。但是调用顺序还是不变，按照PreFilters->RoutingFilters->PostFilters的顺序调用

在routeFilters确实有转发请求的Filter,然而博主偷天换日了，改用RestTemplate实现.

代码结构

大家去spring官网上搭建一套springboot的项目，博主就不展示pom的代码了。直接将项目结构展示一下，如下图所示

EatuulServlet.java

这个是网关的入口，逻辑也十分简单，分为三步
(1)将request,response放入threadlocal中
(2)执行三组过滤器
(3)清除threadlocal中的的环境变量

源码如下

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 {//将request，和response放入上下文对象中eatRunner.init(req, resp);try {//执行前置过滤eatRunner.preRoute();//执行过滤eatRunner.route();//执行后置过滤eatRunner.postRoute();} catch (Throwable e) {RequestContext.getCurrentContext().getResponse().sendError(HttpServletResponse.SC_NOT_FOUND, e.getMessage());} finally {//清除变量RequestContext.getCurrentContext().unset();}}}

EatuulRunner.java

这个是具体的执行器。需要说明一下，在Zuul中，ZuulRunner在获取具体有哪些过滤器的时候，有一个FileLoader可以动态读取配置加载。博主在实现我们自己的EatuulRunner时候，略去动态读取的过程，直接静态写死。

源码如下

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 {//静态写死过滤器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

接下来就是一系列Filter的代码了，先上父类EatuulFilter的源码

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

RequestWrapperFilter.java

这个是PreFilter,前置执行过滤器，负责封装请求。步骤如下所示

(1)封装请求头

(2)封装请求体

(3)构造出RestTemplate能识别的RequestEntity

(4)将RequestEntity放入全局threadlocal之中

代码如下所示

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、将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、封装请求头MultiValueMap<String, String> headers =createRequestHeaders(request);//2、封装请求体byte[] body = createRequestBody(request);//3、构造出RestTemplate能识别的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

这个是routeFilter,这里我偷懒了，直接做转发请求，并且将返回值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

这个是postFilters,将ResponseEntity输出即可

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

最后是一直在说的全局threadlocal变量

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();}}

如何测试？

自己另外起一个server端口为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);}
}

再来一个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，你就发现可以从localhost:8080/index进行跳转访问了

结论

本文模拟了一下zuul网关的源码，借鉴了一下其精髓的部分。希望大家能有所收获

出处： http://rjzheng.cnblogs.com/

作者：孤独烟，作者公号，可以关注一波