自己动手写一个服务网关

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孤独烟 java进阶架构师

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

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
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{

   @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<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RequestEntity
       RequestEntity 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{

   @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

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<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 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

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>() {
       @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

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