Servlet原理

Mapping问题 

package com.kuang.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class ErrorServlet extends HttpServlet{
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
                    resp.setContentType("text/html");
                    resp.setCharacterEncoding("utf-8");

        PrintWriter writer = resp.getWriter();
        writer.print("<h5>Not Found</h5>");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
      doGet(req, resp);
    }
}

package com.kuang.servlet;

import javax.servlet.ServletException;
import javax.servlet.ServletInputStream;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class HttpServlet extends javax.servlet.http.HttpServlet {

    //由于post 和 get 只是请求实现的不同的方式，可以相互调用，业务逻辑都一样。
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        // ServletInputStream inputStream = req.getInputStream();
        // ServletOutputStream outputStream = resp.getOutputStream();
        PrintWriter writer = resp.getWriter();//响应流
        writer.print("Hello Servlet");



    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         doGet(req, resp);
    }
}

​
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                      http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">

<!--  注册Servlet  -->
<servlet>
    <servlet-name>hello</servlet-name>
    <servlet-class>com.kuang.servlet.HttpServlet</servlet-class>
</servlet>
<!-- Servlet的请求路径   -->
    <servlet-mapping>
        <servlet-name>hello</servlet-name>
       <url-pattern>/hello</url-pattern>
    </servlet-mapping>
    <servlet>
        <servlet-name>Error</servlet-name>
        <servlet-class>com.kuang.servlet.ErrorServlet</servlet-class>
    </servlet>
    <!-- Servlet的请求路径   -->
    <servlet-mapping>
        <servlet-name>Error</servlet-name>
        <url-pattern>/*</url-pattern>
    </servlet-mapping>
</web-app>

​