【原创】自己动手写一个服务网关

引言什么是网关？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，再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

(1)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。

(2)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

(3)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

代码语言：javascript代码运行次数：0运行复制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(); @Override

public 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

代码语言：javascript代码运行次数：0运行复制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> hashFiltersByType = new ConcurrentHashMap>(){{

put("pre",new ArrayList(){{

add(new RequestWrapperFilter());

}});

put("route",new ArrayList(){{

add(new RoutingFilter());

}});

put("post",new ArrayList(){{

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 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

代码语言：javascript代码运行次数：0运行复制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

代码语言：javascript代码运行次数：0运行复制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{ @Override

public String filterType() { // TODO Auto-generated method stub

return "pre";

} @Override

public int filterOrder() { // TODO Auto-generated method stub

return -1;

} @Override

public void run() {

String rootURL = "http://localhost:9090";

RequestContext ctx =RequestContext.getCurrentContext();

HttpServletRequest servletRequest = ctx.getRequest();

String targetURL = rootURL + servletRequest.getRequestURI();

RequestEntity 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 headers =createRequestHeaders(request); //2、封装请求体

byte[] body = createRequestBody(request); //3、构造出RestTemplate能识别的RequestEntity

RequestEntity requestEntity = new RequestEntity(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 createRequestHeaders(HttpServletRequest request) {

HttpHeaders headers = new HttpHeaders();

List headerNames = Collections.list(request.getHeaderNames()); for(String headerName:headerNames) {

List 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

代码语言：javascript代码运行次数：0运行复制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{ @Override

public String filterType() { // TODO Auto-generated method stub

return "route";

} @Override

public int filterOrder() { // TODO Auto-generated method stub

return 0;

}

@Override

public 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

代码语言：javascript代码运行次数：0运行复制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{ @Override

public String filterType() { return "post";

} @Override

public int filterOrder() { return 1000;

} @Override

public 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> entry:httpHeaders.entrySet()) {

String headerName = entry.getKey();

List 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 set

servletResponse.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

代码语言：javascript代码运行次数：0运行复制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 { protected static Class contextClass = RequestContext.class; protected static final ThreadLocal threadLocal = new ThreadLocal() { @Override

protected 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); else

remove(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

代码语言：javascript代码运行次数：0运行复制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

代码语言：javascript代码运行次数：0运行复制package com.rjzheng.eatservice.controller;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RestController;

@RestControllerpublic 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

作者：孤独烟 出处： http://rjzheng.cnblogs.com/

本文版权归作者和博客园共有，欢迎转载，但未经作者同意必须保留此段声明，且在文章页面明显位置给出原文连接，否则保留追究法律责任的权利。