【原創】自己動手寫一個服務網關

阿新 • • 發佈：2018-06-25

exception 負責 lis world 前置 create ble ddr load

引言

什麽是網關？為什麽需要使用網關？

技術分享圖片
如圖所示，在不使用網關的情況下，我們的服務是直接暴露給服務調用方。當調用方增多，勢必需要添加定制化訪問權限、校驗等邏輯。當添加API網關後，再第三方調用端和服務提供方之間就創建了一面墻，這面墻直接與調用方通信進行權限控制。
本文所實現的網關源碼抄襲了---Oh,不對，是借鑒。借鑒了Zuul網關的源碼，提煉出其核心思路，實現了一套簡單的網關源碼，博主將其改名為Eatuul。

題外話

本文是業內能搜到的第一篇自己動手實現網關的文章。博主寫的手把手系列的文章，目的是在以最簡單的方式，揭露出中間件的核心原理，讓讀者能夠迅速了解實現的核心。需要說明的是，這不是源碼分析系列的文章，因此寫出來的代碼，省去了一些復雜的內容，畢竟大家能理解到該中間件的核心原理即可。如果想看源碼分析系列的，請關註博主，後期會將spring、spring boot、dubbo、mybatis等開源框架一一揭示。

正文

設計思路

先大致說一下，就是定義一個Servlet接收請求。然後經過preFilter(封裝請求參數),routeFilter(轉發請求)，postFilter(輸出內容)。三個過濾器之間，共享request、response以及其他的一些全局變量。如下圖所示
技術分享圖片
和真正的Zuul的區別?
主要區別有如下幾點
(1)Zuul中在異常處理模塊，有一個ErrorFilter來處理，博主在實現的時候偷懶了，略去。
(2)Zuul中PreFilters,RoutingFilters,PostFilters默認都實現了一組，具體如下表所示

博主總不可能每一個都給你們實現一遍吧。所以偷懶了，每種只實現一個。但是調用順序還是不變，按照PreFilters->RoutingFilters->PostFilters的順序調用

(3)在routeFilters確實有轉發請求的Filter,然而博主偷天換日了，改用RestTemplate實現.

代碼結構

大家去spring官網上搭建一套springboot的項目，博主就不展示pom的代碼了。直接將項目結構展示一下，如下圖所示
技術分享圖片
EatuulServlet.java
這個是網關的入口，邏輯也十分簡單，分為三步
(1)將request,response放入threadlocal中
(2)執行三組過濾器
(3)清除threadlocal中的的環境變量
源碼如下

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 {
        //將request，和response放入上下文對象中
        eatRunner.init(req, resp);
        try {
            //執行前置過濾
            eatRunner.preRoute();
            //執行過濾
            eatRunner.route();
            //執行後置過濾
            eatRunner.postRoute();
        } catch (Throwable e) {
            RequestContext.getCurrentContext().getResponse()
                          .sendError(HttpServletResponse.SC_NOT_FOUND, e.getMessage());
        } finally {
            //清除變量
            RequestContext.getCurrentContext().unset();
        }
    }

}

EatuulRunner.java
這個是具體的執行器。需要說明一下，在Zuul中，ZuulRunner在獲取具體有哪些過濾器的時候，有一個FileLoader可以動態讀取配置加載。博主在實現我們自己的EatuulRunner時候，略去動態讀取的過程，直接靜態寫死。
源碼如下

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 {
    //靜態寫死過濾器
    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
接下來就是一系列Filter的代碼了，先上父類EatuulFilter的源碼

package com.rjzheng.eatuul.filter;

public abstract class EatuulFilter {

    abstract public String filterType();

    abstract public int filterOrder();

    abstract public void run();
}

RequestWrapperFilter.java
這個是PreFilter,前置執行過濾器，負責封裝請求。步驟如下所示
(1)封裝請求頭
(2)封裝請求體
(3)構造出RestTemplate能識別的RequestEntity
(4)將RequestEntity放入全局threadlocal之中
代碼如下所示

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、將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、封裝請求頭
        MultiValueMap<String, String> headers =createRequestHeaders(request);
        //2、封裝請求體
        byte[] body = createRequestBody(request);
        //3、構造出RestTemplate能識別的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
這個是routeFilter,這裏我偷懶了，直接做轉發請求，並且將返回值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
這個是postFilters,將ResponseEntity輸出即可

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
最後是一直在說的全局threadlocal變量

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();
    }

}

如何測試？

自己另外起一個server端口為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);
    }
}

再來一個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";
    }
}

然後，你就發現可以從localhost:8080/index進行跳轉訪問了

結論

本文模擬了一下zuul網關的源碼，借鑒了一下其精髓的部分。希望大家能有所收獲

【原創】自己動手寫一個服務網關

exception 負責 lis world 前置 create ble ddr load 引言什麽是網關？為什麽需要使用網關？如圖所示，在不使用網關的情況下，我們的服務是直接暴露給服務調用方。當調用方增多，勢必需要添加定制化訪問權限、校驗等邏輯。當添加API網關後，

【原創】自己動手寫一個服務網關

引言

什麽是網關？為什麽需要使用網關？

題外話

正文

設計思路

代碼結構

如何測試？

結論

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【原創】自己動手寫一個服務網關

引言

什麽是網關？為什麽需要使用網關？

題外話

正文

設計思路

代碼結構

如何測試？

結論

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