第五章手写Tomcat笔记

末蓝、 2021-11-17 12:10 232阅读 0赞

## **一、什么是Tomcat？** ##

Tomcat本质上是一款开源轻量级Web应用服务器，是一款优秀的Servlet容器实现。

核心2点，Web服务器、Servlet容器。

阿里中间件团队：[http://jm.taobao.org/about/][http_jm.taobao.org_about]

很多公司都手写或者重写Tomcat.比如aliTomcat :    https://help.aliyun.com/document\_detail/90754.html

### **1、网络基础知识：** ###

网络通讯，客户端和服务端的关系，java中建立Socket通讯，注意一般Socket是基于TCP的协议。

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### **2、还原Tomcat本质：** ###

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## **二、手写Tomcat实现代码** ##

### **1、手写第一步：完成简单的一个BIO的通讯** ###

//1、绑定端口 ---JDK 为我们提供的网络操作的API
    ServerSocket serverSocket = new ServerSocket(8080);
    System.out.println("服务器启动成功!");
    while(!serverSocket.isClosed()){//在等待请求
        //2、有请求过来了  ,使用一个socket: 代表着一个客户端--服务端的连接
       Socket socket =  serverSocket.accept();
       //3、使用一个线程来处理请求
        executorService.execute(()->{
            try{
                InputStream inputStream = socket.getInputStream();
                System.out.println("收到请求：");
                BufferedReader reader = new BufferedReader( new InputStreamReader(inputStream,"utf-8"));
                //字符串
                String msg =null;
                StringBuilder requestInfo = new StringBuilder();
                while ( (msg=reader.readLine()) !=null ){
                    if(msg.length()==0) break;
                    requestInfo.append(msg).append("\r\n");
                }
                System.out.println(requestInfo);
                //要对请求的头进行解析，获取请求的第一行
                String firstline =requestInfo.toString().split("\r\n")[0];
                System.out.println(firstline);

### **2、Tomcat如何和浏览器互动：** ###

浏览器之间通讯必须要符合HTTP协议，响应信息加入HTTP格式的响应

//要对请求的头进行解析，获取请求的第一行
        String firstline =requestInfo.toString().split("\r\n")[0];
        System.out.println(firstline);
        //防止浏览器发空过的请求过来
        if(firstline.length()<1){
            return;
        }
        String servletPath = firstline.split(" ")[1];
        //Servet映射
        Map<String,String> servletMapping=  (Map<String,String>)webAppMap.get("servlet-mapping");
        //Servlet实例
        Map<String,Object> servletInstances=  (Map<String,Object> )webAppMap.get("servlet");
        //是否有正确的url对应的Servlet
        if(servletMapping.containsKey(servletPath)){
            String servletName = servletMapping.get(servletPath);
            HttpServlet httpServlet =  (HttpServlet)servletInstances.get(servletName);
            HttpServletRequest httpServletRequest =createRequest();
            HttpServletResponse httpServletResponse = createResponse();
            httpServlet.service(httpServletRequest,httpServletResponse);
            OutputStream outputStream = socket.getOutputStream();
            byte[] response ="请求成功!".getBytes();
            outputStream.write("HTTP/1.1 200 OK \r\n".getBytes());
            outputStream.write("Content-Type:text/html;charset=utf-8 \r\n".getBytes());
            outputStream.write( ("Content-Length:"+response.length+"\r\n").getBytes());
            outputStream.write("\r\n".getBytes());
            outputStream.write(response);
            outputStream.flush();
            System.out.println("----END");
        }else{
            //要与浏览器进行“互动” ,HTTP 协议
            OutputStream outputStream = socket.getOutputStream();
            byte[] response ="对不起，没有对应的Servlet请求信息!".getBytes();
            outputStream.write("HTTP/1.1 200 OK \r\n".getBytes());
            outputStream.write("Content-Type:text/html;charset=utf-8 \r\n".getBytes());
            outputStream.write( ("Content-Length:"+response.length+"\r\n").getBytes());
            outputStream.write("\r\n".getBytes());
            outputStream.write(response);
            outputStream.flush();
            System.out.println("----END");
        }
    }catch (IOException e){

### **3、让代码在Tomcat上跑** ###

类加载

public static void main(String[] args) throws  Exception{
        //0、加载项目（类加载）、容器、HashMap
        Map<String,Object> webAppMap = ProjectLoader.load();
    
    
    
    public class ProjectLoader {
        public static Map load() throws Exception{
            //定义一个Map,存储项目信息
            Map<String,Object> webapp = new HashMap<>();
            Map<String, Servlet> servletInstances = new HashMap<>(); //servlet
            Map<String, String> servletMapping = new HashMap<>(); //servlet-mapping
            //项目路径
            String webappPath ="D:\\work_public\\servletdemo\\out\\artifacts\\servletdemo_war_exploded\\WEB-INF";
            //JDK提供类加载器 URL
            URL classFile = new URL("file:"+webappPath+"\\classes\\");
            URLClassLoader urlClassLoader = new URLClassLoader(new URL[]{classFile});
            //解析xml文件
            //1.获取解析器
            SAXReader reader = new SAXReader();
            //2.获取文档对象(xml)
            Document document = reader.read(new File(webappPath+"\\web.xml"));
            //3.获取根元素
            Element root = document.getRootElement();
            //4.获取根元素中下的子元素
            List<Element> childElements = root.elements();
            //5.遍历子元素
            for (Element element:childElements) {
                //6.判断元素名称为servlet的元素
                if ("servlet".equals(element.getName())) {
                    //获取servlet-name元素
                    Element servletName = element.element("servlet-name");
                    //获取servlet-class元素
                    Element servletClass = element.element("servlet-class");
                    String strServletName = servletName.getText();
                    String strServletClass = servletClass.getText();
                    System.out.println("servlet:"+strServletName+"="+strServletClass);
                    //1.加载到JVM
                    Class<?> classzz= urlClassLoader.loadClass(strServletClass);
                    //2 创建对象实例(反射) -servlet;
                    Servlet servlet  = (Servlet)classzz.newInstance();
                    //web.xml的servlet实例化放入hashmap
                    servletInstances.put(strServletName, servlet);
                }
                //7.判断元素名称为servlet-mapping的元素
                if ("servlet-mapping".equals(element.getName())) {
                    //获取servlet-name元素
                    Element servletName = element.element("servlet-name");
                    //获取url-pattern元素
                    Element urlPattern = element.element("url-pattern");
                    String strServletName = servletName.getText();
                    String strUrlPattern = urlPattern.getText();
                    //web.xml的servlet的Mapping放入hashmap
                    System.out.println("servlet-mapping:"+strUrlPattern+"="+strServletName);
                    servletMapping.put(strUrlPattern,strServletName);
                }
            }
            webapp.put("servlet",servletInstances);
            webapp.put("servlet-mapping",servletMapping);
            return  webapp;
        }
    }

解析请求地址，找到对应的Servlet

### **4、构造参数，执行Servlet的service方法** ###

//是否有正确的url对应的Servlet
    if(servletMapping.containsKey(servletPath)){
        String servletName = servletMapping.get(servletPath);
        HttpServlet httpServlet =  (HttpServlet)servletInstances.get(servletName);
        HttpServletRequest httpServletRequest =createRequest();
        HttpServletResponse httpServletResponse = createResponse();
        httpServlet.service(httpServletRequest,httpServletResponse);
        OutputStream outputStream = socket.getOutputStream();
        byte[] response ="请求成功!".getBytes();
        outputStream.write("HTTP/1.1 200 OK \r\n".getBytes());
        outputStream.write("Content-Type:text/html;charset=utf-8 \r\n".getBytes());
        outputStream.write( ("Content-Length:"+response.length+"\r\n").getBytes());
        outputStream.write("\r\n".getBytes());
        outputStream.write(response);
        outputStream.flush();
        System.out.println("----END");

构建简单的参数

HttpServletRequest httpServletRequest =*createRequest*();  
HttpServletResponse httpServletResponse = *createResponse*();

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