手写tomcat透彻理解Servlet实现原理

电玩女神 2022-02-20 14:06 219阅读 0赞

### 疑问： ###

1.  ### 为什么要配置一个web.xml文件？ ###
2.  ### 为什么一定要继承Servlet，不继承不行吗？ ###
3.  ### 为什么一定要重写doPost/doGet方法？ ###
4.  ### HttpRequest和HttpResponse是哪里冒出来的，自己从来没有new过？ ###
5.  ### 在浏览器输入url是如何被转换为调用java方法的？ ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L09ubHlvbmVGcmlzdA_size_16_color_FFFFFF_t_70][]

代码结构如下：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L09ubHlvbmVGcmlzdA_size_16_color_FFFFFF_t_70 1][]

### http包中的代码 ###

package com.zuojie.http;
    
    import java.io.OutputStream;
    
    public class ZuojieReponse {
    
        private OutputStream os;
    
        public ZuojieReponse(OutputStream os){
            this.os=os;
        }
    
        public void write(String outString)throws Exception{
            os.write(outString.getBytes());
    
        }
    
    }

package com.zuojie.http;
    
    import java.io.IOException;
    import java.io.InputStream;
    import java.io.OutputStream;
    import java.util.Map;
    
    public class ZuojieRequest {
        private String method;
        private String url;
        //构造方法
        public ZuojieRequest(InputStream is){
            //http协议，就是一串字符串
          //  System.out.println();
            try {
                String content="";
                byte [] buff= new byte[1024];
                int len=0;
                if((len = is.read(buff))>  0){
                    content= new String (buff,0,len);
                    System.out.println(content);
                }
                String line=content.split("\\n")[0];
                String [] arr= line.split("\\s");
                this.method=arr[0];
                this.url=arr[0].split("\\?")[0];//这里目前有点问题。希望可以在评论分享
    
    
    
            } catch (IOException e) {
                e.printStackTrace();
            }
    
        }
    
        public String getMethod(){
            return this.method;
        }
    
        public  String getUrl(){
            return  this.url;
        }
    
        public Map <String,String > getParmenter(){
            return null;
        }
    }

package com.zuojie.servlet;
    
    import com.zuojie.http.ZuojieReponse;
    import com.zuojie.http.ZuojieRequest;
    import com.zuojie.http.ZuojieServlet;
    
    public class MiniServlet extends ZuojieServlet {
        @Override
        public void doGet(ZuojieRequest request, ZuojieReponse reponse) throws Exception {
            this.doPost(request,reponse);
        }
    
        @Override
        public void doPost(ZuojieRequest request, ZuojieReponse reponse) throws Exception {
            reponse.write("this is MiniTomcat");
    
        }
    }

package com.zuojie.servlet;
    
    import com.zuojie.http.ZuojieReponse;
    import com.zuojie.http.ZuojieRequest;
    import com.zuojie.http.ZuojieServlet;
    
    public class MiniTwoServlet extends ZuojieServlet{
        @Override
        public void doGet(ZuojieRequest request, ZuojieReponse reponse) throws Exception {
            this.doPost(request,reponse);
        }
    
        @Override
        public void doPost(ZuojieRequest request, ZuojieReponse reponse) throws Exception {
            reponse.write("this is MiniTwoServlet");
        }
    }

### tomcat中的代码  ###

package com.zuojie.tomcat;
    
    
    import com.zuojie.http.ZuojieReponse;
    import com.zuojie.http.ZuojieRequest;
    import com.zuojie.http.ZuojieServlet;
    
    import java.io.FileInputStream;
    import java.io.IOException;
    import java.io.InputStream;
    import java.io.OutputStream;
    import java.net.ServerSocket;
    import java.net.Socket;
    import java.util.HashMap;
    import java.util.Map;
    import java.util.Properties;
    
    /**
     * author:佐杰
     */
    
    public class ZuojieTomcat {
        private int port=9090;//定义一个默认的端口
        private ServerSocket server;
        private Map<String,ZuojieServlet> servletMappping=new HashMap<String,ZuojieServlet>();
        private Properties webxml=new Properties();
    
        //1.加载配置文件，初始化ServletMaping
        private void init(){
            //1.加载web.xml,同是初始化servletmaping对象
            try {
                String WEB_INF=this.getClass().getResource("/").getPath();
                FileInputStream fis=new FileInputStream(WEB_INF+"web.properties");
                webxml.load(fis);
    
                for (Object key:webxml.keySet()) {
                    String k=key.toString();
                    if(k.endsWith(".url")){
                      String servletName=  k.replaceAll("\\.url$","");
    
                      String url=webxml.getProperty("k");
    
                      String className=webxml.getProperty(servletName+".className");
    
                      ZuojieServlet obj= (ZuojieServlet) Class.forName(className).newInstance();
    
                      servletMappping.put(url,obj);
                    }
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    
        private void process(Socket client) throws  Exception{
            //3.获取到Socket对象，将socket getInputStream()封装成request
            //                    将socket getInputStream()封装成response
    
            InputStream is= client.getInputStream();
            OutputStream out=client.getOutputStream();
    
            ZuojieRequest request=new ZuojieRequest(is);
            ZuojieReponse reponse=new ZuojieReponse(out);
    
            //想办法拿到用户请求的url才行
    
            System.out.println("===="+request.getMethod());
            String url=request.getUrl();
            if(servletMappping.containsKey(url)) {
                servletMappping.get(request.getMethod()).service(request, reponse);
            }else {
                reponse.write("404-NOT-FOUND");
            }
    
            out.flush();//刷新
            out.close();
            //为什么要关闭client,因为HTTP请求都是采用短链接
            client.close();
        }
    
        //4.实现动态调用doGet/doPost方法，并且能够自定义返回结果
        public void start(){
            init();
            try {
                server=new ServerSocket(this.port);
                System.out.println("Zuojie Tomcat 已启动，监听的端口是"+this.port);
               // Socket socket = server.accept();
              //  System.out.println(socket);
                //2.等待用户请求，用一个死循环来等待用户请求
                while(true){
                    try {
                        Socket client = server.accept();
                        process(client);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
    
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        public static void main(String[] args) {
            new ZuojieTomcat().start();
    
        }
    
    }

### web.properties ###

servlet.one.url=/MiniServlet.do
    servlet.one.className=com.zuojie.servlet.MiniServlet
    
    servlet.two.url=/MiniTwoServlet.do
    servlet.two.className=com.zuojie.servlet.MiniTwoServlet

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