servlet

在这里插入图片描述

上面就是一个web项目的典型目录，servlet处理request和response的逻辑
web.xml管理路由信息
index.jsp作为首页访问的页面，jsp是java server page可以认为用java和html混合写前端

源码：servlet01

web.xml

<?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="false">
    <!--注册Servlet-->
    <servlet>
        <servlet-name>hello</servlet-name>
        <servlet-class>com.zty.servlet.HelloServlet</servlet-class>
    </servlet>
    <!--Servlet的请求路径-->
    <servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>

    <!--404-->
    <servlet>
        <servlet-name>error</servlet-name>
        <servlet-class>com.zty.servlet.ErrorServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>error</servlet-name>
        <url-pattern>/*</url-pattern>
    </servlet-mapping>
</web-app>

他的意思是除了hello页（输出hello），其他都是error页（输出404）
hello页会用HelloServlet做处理
error页会用ErrorServlet做处理
metadata-complete需要注意，如果是True则不支持@WebServlet注解，如果是false表示web.xml路由不完全，支持注解

ErrorServlet.java

package com.zty.servlet;

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;
import java.io.PrintWriter;

public class ErrorServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");
        response.setCharacterEncoding("utf-8");
        PrintWriter writer = response.getWriter();
        writer.print("<h1>404</h1>");
    }

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

get中设置了一下resp的输出类型，编码格式，来了一个PrintWriter把输出打印到html上，writer.print写的是html内容
doPost不处理先

HelloServlet.java

package com.zty.servlet;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet(urlPatterns = "/helloanno")
public class HelloServlet extends HttpServlet {
    //由于get或者post只是请求实现的方式不同，可以相互调用，业务逻辑都一样！
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("进入了doGet方法！");
        //ServletOutputStream outputStream = response.getOutputStream();
        PrintWriter writer = response.getWriter();//响应流
        writer.println("Hello Servlet");
    }

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