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

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 {
<span class="hljs-keyword">private</span> <span class="hljs-type">EatRunner</span> eatRunner = <span class="hljs-keyword">new</span> <span class="hljs-type">EatRunner</span>();

<span class="hljs-meta">@Override</span>
public void service(<span class="hljs-type">HttpServletRequest</span> req, <span class="hljs-type">HttpServletResponse</span> resp)
        <span class="hljs-keyword">throws</span> <span class="hljs-type">ServletException</span>, <span class="hljs-type">IOException</span> {
    <span class="hljs-comment">//将request，和response放入上下文对象中</span>
    eatRunner.init(req, resp);
    <span class="hljs-keyword">try</span> {
        <span class="hljs-comment">//执行前置过滤</span>
        eatRunner.preRoute();
        <span class="hljs-comment">//执行过滤</span>
        eatRunner.route();
        <span class="hljs-comment">//执行后置过滤</span>
        eatRunner.postRoute();
    } <span class="hljs-keyword">catch</span> (<span class="hljs-type">Throwable</span> e) {
        <span class="hljs-type">RequestContext</span>.getCurrentContext().getResponse()
                      .sendError(<span class="hljs-type">HttpServletResponse</span>.<span class="hljs-type">SC_NOT_FOUND</span>, e.getMessage());
    } <span class="hljs-keyword">finally</span> {
        <span class="hljs-comment">//清除变量</span>
        <span class="hljs-type">RequestContext</span>.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());

}});

}};
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">init</span><span class="hljs-params">(HttpServletRequest req, HttpServletResponse resp)</span> </span>{
    RequestContext ctx = RequestContext.getCurrentContext();
    ctx.setRequest(req);
    ctx.setResponse(resp);
}

<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">preRoute</span><span class="hljs-params">()</span> <span class="hljs-keyword">throws</span> Throwable </span>{
    runFilters(<span class="hljs-string">"pre"</span>);  
}

<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">route</span><span class="hljs-params">()</span> <span class="hljs-keyword">throws</span> Throwable</span>{
    runFilters(<span class="hljs-string">"route"</span>);    
}

<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">postRoute</span><span class="hljs-params">()</span> <span class="hljs-keyword">throws</span> Throwable</span>{
    runFilters(<span class="hljs-string">"post"</span>);
}

 <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">runFilters</span><span class="hljs-params">(String sType)</span> <span class="hljs-keyword">throws</span> Throwable </span>{
        List&lt;EatuulFilter&gt; list = <span class="hljs-keyword">this</span>.hashFiltersByType.get(sType);
        <span class="hljs-keyword">if</span> (list != <span class="hljs-keyword">null</span>) {
            <span class="hljs-keyword">for</span> (<span class="hljs-keyword">int</span> i = <span class="hljs-number">0</span>; i &lt; 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 {
<span class="hljs-function"><span class="hljs-keyword">abstract</span> <span class="hljs-keyword">public</span> String <span class="hljs-title">filterType</span><span class="hljs-params">()</span></span>;

<span class="hljs-function"><span class="hljs-keyword">abstract</span> <span class="hljs-keyword">public</span> <span class="hljs-keyword">int</span> <span class="hljs-title">filterOrder</span><span class="hljs-params">()</span></span>;

<span class="hljs-function"><span class="hljs-keyword">abstract</span> <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">run</span><span class="hljs-params">()</span></span>;

}

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{
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> String <span class="hljs-title">filterType</span><span class="hljs-params">()</span> </span>{
    <span class="hljs-comment">// TODO Auto-generated method stub</span>
    <span class="hljs-keyword">return</span> <span class="hljs-string">"pre"</span>;
}

<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">int</span> <span class="hljs-title">filterOrder</span><span class="hljs-params">()</span> </span>{
    <span class="hljs-comment">// TODO Auto-generated method stub</span>
    <span class="hljs-keyword">return</span> -<span class="hljs-number">1</span>;
}

<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">run</span><span class="hljs-params">()</span> </span>{
    String rootURL = <span class="hljs-string">"http://localhost:9090"</span>;
    RequestContext ctx =RequestContext.getCurrentContext();
    HttpServletRequest servletRequest = ctx.getRequest();
    String targetURL = rootURL + servletRequest.getRequestURI();
    RequestEntity&lt;<span class="hljs-keyword">byte</span>[]&gt; requestEntity = <span class="hljs-keyword">null</span>;
    <span class="hljs-keyword">try</span> {
        requestEntity = createRequestEntity(servletRequest, targetURL);
    } <span class="hljs-keyword">catch</span> (Exception e) {
        e.printStackTrace();
    }
    <span class="hljs-comment">//4、将requestEntity放入全局threadlocal之中</span>
    ctx.setRequestEntity(requestEntity);
}

<span class="hljs-function"><span class="hljs-keyword">private</span> RequestEntity <span class="hljs-title">createRequestEntity</span><span class="hljs-params">(HttpServletRequest request,String url)</span> <span class="hljs-keyword">throws</span> URISyntaxException, IOException </span>{
    String method = request.getMethod();
    HttpMethod httpMethod = HttpMethod.resolve(method);
    <span class="hljs-comment">//1、封装请求头</span>
    MultiValueMap&lt;String, String&gt; headers =createRequestHeaders(request);
    <span class="hljs-comment">//2、封装请求体</span>
    <span class="hljs-keyword">byte</span>[] body = createRequestBody(request);
    <span class="hljs-comment">//3、构造出RestTemplate能识别的RequestEntity</span>
    RequestEntity requestEntity = <span class="hljs-keyword">new</span> RequestEntity&lt;<span class="hljs-keyword">byte</span>[]&gt;(body,headers,httpMethod, <span class="hljs-keyword">new</span> URI(url));
    <span class="hljs-keyword">return</span> requestEntity;
}


<span class="hljs-keyword">private</span> <span class="hljs-keyword">byte</span>[] createRequestBody(HttpServletRequest request) <span class="hljs-keyword">throws</span> IOException {
    InputStream inputStream = request.getInputStream();
    <span class="hljs-keyword">return</span> StreamUtils.copyToByteArray(inputStream);
}

<span class="hljs-function"><span class="hljs-keyword">private</span> MultiValueMap&lt;String, String&gt; <span class="hljs-title">createRequestHeaders</span><span class="hljs-params">(HttpServletRequest request)</span> </span>{
    HttpHeaders headers = <span class="hljs-keyword">new</span> HttpHeaders();
    List&lt;String&gt; headerNames = Collections.list(request.getHeaderNames());
    <span class="hljs-keyword">for</span>(String headerName:headerNames) {
        List&lt;String&gt; headerValues = Collections.list(request.getHeaders(headerName));
        <span class="hljs-keyword">for</span>(String headerValue:headerValues) {
            headers.add(headerName, headerValue);
        }
    }
    <span class="hljs-keyword">return</span> 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{
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> String <span class="hljs-title">filterType</span><span class="hljs-params">()</span> </span>{
    <span class="hljs-comment">// TODO Auto-generated method stub</span>
    <span class="hljs-keyword">return</span> <span class="hljs-string">"route"</span>;
}

<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">int</span> <span class="hljs-title">filterOrder</span><span class="hljs-params">()</span> </span>{
    <span class="hljs-comment">// TODO Auto-generated method stub</span>
    <span class="hljs-keyword">return</span> <span class="hljs-number">0</span>;
}

<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">run</span><span class="hljs-params">()</span></span>{
    RequestContext ctx = RequestContext.getCurrentContext();
    RequestEntity requestEntity = ctx.getRequestEntity();
    RestTemplate restTemplate = <span class="hljs-keyword">new</span> RestTemplate();
    ResponseEntity responseEntity = restTemplate.exchange(requestEntity,<span class="hljs-keyword">byte</span>[].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{
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> String <span class="hljs-title">filterType</span><span class="hljs-params">()</span> </span>{
    <span class="hljs-keyword">return</span> <span class="hljs-string">"post"</span>;
}

<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">int</span> <span class="hljs-title">filterOrder</span><span class="hljs-params">()</span> </span>{
    <span class="hljs-keyword">return</span> <span class="hljs-number">1000</span>;
}

<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">run</span><span class="hljs-params">()</span> </span>{
    <span class="hljs-keyword">try</span> {
        addResponseHeaders();
        writeResponse();
    } <span class="hljs-keyword">catch</span> (Exception e) {
        e.printStackTrace();
    }
}

<span class="hljs-function"><span class="hljs-keyword">private</span> <span class="hljs-keyword">void</span> <span class="hljs-title">addResponseHeaders</span><span class="hljs-params">()</span> </span>{
    RequestContext ctx = RequestContext.getCurrentContext();
    HttpServletResponse servletResponse = ctx.getResponse();
    ResponseEntity responseEntity = ctx.getResponseEntity();
    HttpHeaders httpHeaders = responseEntity.getHeaders();
    <span class="hljs-keyword">for</span>(Map.Entry&lt;String, List&lt;String&gt;&gt; entry:httpHeaders.entrySet()) {
        String headerName = entry.getKey();
        List&lt;String&gt; headerValues = entry.getValue();
        <span class="hljs-keyword">for</span>(String headerValue:headerValues) {
            servletResponse.addHeader(headerName, headerValue);
        }
    }
}

<span class="hljs-function"><span class="hljs-keyword">private</span> <span class="hljs-keyword">void</span> <span class="hljs-title">writeResponse</span><span class="hljs-params">()</span><span class="hljs-keyword">throws</span> Exception </span>{
    RequestContext ctx = RequestContext.getCurrentContext();
    HttpServletResponse servletResponse = ctx.getResponse();
    <span class="hljs-keyword">if</span> (servletResponse.getCharacterEncoding() == <span class="hljs-keyword">null</span>) { <span class="hljs-comment">// only set if not set</span>
        servletResponse.setCharacterEncoding(<span class="hljs-string">"UTF-8"</span>);
    }
    ResponseEntity responseEntity = ctx.getResponseEntity();
    <span class="hljs-keyword">if</span>(responseEntity.hasBody()) {
        <span class="hljs-keyword">byte</span>[] body = (<span class="hljs-keyword">byte</span>[]) 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);

}

}

};
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> RequestContext <span class="hljs-title">getCurrentContext</span><span class="hljs-params">()</span> </span>{
    RequestContext context = threadLocal.get();
    <span class="hljs-keyword">return</span> context;
}

<span class="hljs-function"><span class="hljs-keyword">public</span> HttpServletRequest <span class="hljs-title">getRequest</span><span class="hljs-params">()</span> </span>{
    <span class="hljs-keyword">return</span> (HttpServletRequest) get(<span class="hljs-string">"request"</span>);
}

<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">setRequest</span><span class="hljs-params">(HttpServletRequest request)</span> </span>{
    put(<span class="hljs-string">"request"</span>, request);
}

<span class="hljs-function"><span class="hljs-keyword">public</span> HttpServletResponse <span class="hljs-title">getResponse</span><span class="hljs-params">()</span> </span>{
    <span class="hljs-keyword">return</span> (HttpServletResponse) get(<span class="hljs-string">"response"</span>);
}

<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">setResponse</span><span class="hljs-params">(HttpServletResponse response)</span> </span>{
    set(<span class="hljs-string">"response"</span>, response);
}


<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">setRequestEntity</span><span class="hljs-params">(RequestEntity requestEntity)</span></span>{
    set(<span class="hljs-string">"requestEntity"</span>,requestEntity);
}

<span class="hljs-function"><span class="hljs-keyword">public</span> RequestEntity <span class="hljs-title">getRequestEntity</span><span class="hljs-params">()</span> </span>{
    <span class="hljs-keyword">return</span> (RequestEntity) get(<span class="hljs-string">"requestEntity"</span>);
}

<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">setResponseEntity</span><span class="hljs-params">(ResponseEntity responseEntity)</span></span>{
    set(<span class="hljs-string">"responseEntity"</span>,responseEntity);
}

<span class="hljs-function"><span class="hljs-keyword">public</span> ResponseEntity <span class="hljs-title">getResponseEntity</span><span class="hljs-params">()</span> </span>{
    <span class="hljs-keyword">return</span> (ResponseEntity) get(<span class="hljs-string">"responseEntity"</span>);
}

<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">set</span><span class="hljs-params">(String key, Object value)</span> </span>{
    <span class="hljs-keyword">if</span> (value != <span class="hljs-keyword">null</span>)
        put(key, value);
    <span class="hljs-keyword">else</span>
        remove(key);
}

<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">unset</span><span class="hljs-params">()</span> </span>{
    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 {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> main(String[] args) {
    <span class="hljs-keyword">new</span> SpringApplicationBuilder(Application.<span class="hljs-keyword">class</span>).properties(<span class="hljs-string">"server.port=9090"</span>).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 {
@<span class="hljs-keyword">RequestMapping</span>("/<span class="hljs-keyword">index</span>")
public String index() {
    <span class="hljs-selector-tag">return</span> "<span class="hljs-selector-tag">hello</span>!<span class="hljs-selector-tag">world</span>";
}

}

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

原文地址：https://www.cnblogs.com/rjzheng/p/9220437.html