什么是网关？为什么需要使用网关？
![6674fe9b3183380413e2f56817f12b1bb2adb092]()
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
![9a6452cacce44e4f2f301fb710d6a0d7afe53090]()
# 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
![d46f5605628dd35fde4f9e224f91cfc9f252d5e1]()
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
![e3903213a87a5433431b958ac7b33c544cca8d91]()
# 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
