• Servlet环境搭建，生命周期

    Servlet

    是运行在服务器(tomcat)的java组件

    Servlet组件主要完成两个部分工作

    ​ 1.接受客户端请求

    ​ 2.返回服务器响应

    环境搭建

    UserServlet.java

    package com.javakc.web1.user;

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

public class UserServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("UserServlet doGet method!");
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("UserServlet doPost method!");

        //响应类型
        response.setContentType("text/html;charset=utf-8");
        java.io.Writer writer = response.getWriter();
        writer.write("");
        writer.write("");
        writer.close();
    }
}

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    web.xml

    
<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">


    
    <servlet>
        <servlet-name>UserServletservlet-name>
        <servlet-class>com.javakc.web1.user.UserServletservlet-class>
    servlet>

    
    <servlet-mapping>
        <servlet-name>UserServletservlet-name>
        <url-pattern>/user.dourl-pattern>
    servlet-mapping>
web-app>

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    index.html

    DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Titletitle>
head>
<body>
<a href="/web1/user.do">Helloa>  

<form action="/web1/user.do" method="post">  
    <table>
        <tr>
            <td>姓名:<input type="text" name="username" value="">td>
        tr>
        <tr>
            <td>年龄:<input type="number" name="userage" value="">td>
        tr>
        <tr>
            <td>日期:<input type="date" name="birthday" value="">td>
        tr>
        <tr>
            <td>爱好:
                <input type="checkbox" name="hobby" value="1">爱好1
                <input type="checkbox" name="hobby" value="2">爱好2
                <input type="checkbox" name="hobby" value="3">爱好3
                <input type="checkbox" name="hobby" value="4">爱好4
            td>
        tr>
        <tr>
            <td><input type="submit" value="提交">td>
        tr>
    table>
form>
body>
html>

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    Servlet生命周期

    Servlet是由服务器来负责实例化, 服务器默认管理的方式(单例模式)懒汉模式, 在客户端第一次访问服务器资源时, 由服务器负责对象的实例化过程.

    ​只有在第一次实例化时调用, 且只会调用一次!

    实例化

    package com.javakc.web1.user;

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

public class UserServlet1 extends HttpServlet {
    public UserServlet1() {
        System.out.println("实例化");
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("UserServlet doGet method!");
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("UserServlet doPost method!");

        //响应类型
        response.setContentType("text/html;charset=utf-8");
        java.io.Writer writer = response.getWriter();
        writer.write("");
        writer.write("");
        writer.close();
    }
}

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    <servlet>
        <servlet-name>UserServlet1servlet-name>
        <servlet-class>com.javakc.web1.user.UserServlet1servlet-class>
        
        <load-on-startup>0load-on-startup>
    servlet>

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    初始化方法

    package com.javakc.web1.user;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.Enumeration;

//初始化方法
public class UserServlet2 extends HttpServlet {
    @Override
    public void init(ServletConfig config) throws ServletException {
        //ServletName
        System.out.println(config.getServletName());

        //应用作用域
        System.out.println(config.getServletContext());

        //获取初始化参数
        String username = config.getInitParameter("username");
        System.out.println("username:" + username);

        //获得初始化参数名称
        Enumeration<String> enumerations = config.getInitParameterNames();
        while (enumerations.hasMoreElements()) {
            String name = enumerations.nextElement();
            System.out.println(name + ":" + config.getInitParameter(name));
        }
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("UserServlet doGet method!");
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("UserServlet doPost method!");

        //响应类型
        response.setContentType("text/html;charset=utf-8");
        java.io.Writer writer = response.getWriter();
        writer.write("");
        writer.write("");
        writer.close();
    }
}

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    <servlet>
        <servlet-name>UserServletservlet-name>
        <servlet-class>com.javakc.web1.user.UserServlet2servlet-class>
        
        <init-param>
            <param-name>usernameparam-name>
            <param-value>adminparam-value>
        init-param>
        <init-param>
            <param-name>passwordparam-name>
            <param-value>123456param-value>
        init-param>

        
        <load-on-startup>0load-on-startup>
    servlet>

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    运行

    ​ Servlet组件中运行方法是用来接收客户端请求, 返回服务器响应的方法!

    ​ 客户端发送一次请求, 运行方法便会调用一次!

    1.重写service

    public class UserServlet extends HttpServlet {
	
    void service(HttpServletRequest request, HttpServletResponse response)
    {
        
    }    
}

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    2.重写doGet + doPost

    public class UserServlet extends HttpServlet {
	
    void doGet(HttpServletRequest request, HttpServletResponse response)
    {
        
    }
    
    void doPost(HttpServletRequest request, HttpServletResponse response)
    {
        
    }    
}

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    销毁

    在服务器关闭阶段时完成方法调用, 释放资源

    package com.javakc.web1.user;

import javax.servlet.http.HttpServlet;

//销毁
public class UserServlet4 extends HttpServlet {
    @Override
    public void destroy() {
        System.out.println("destroy");
    }
}

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    Servlet生命周期用法

    package com.javakc.web1.user;

import com.javakc.web1.db.Utils;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.sql.*;

//生命周期用法
public class UserServlet5 extends HttpServlet {
    int sum = 0;

    //初始化方法
    @Override
    public void init() throws ServletException {
        Connection connection = null;
        Statement statement = null;
        ResultSet resultSet = null;
        try {
            connection = Utils.getConnection();
            statement = connection.createStatement();
            String sql = "select total from sumTotal";
            resultSet = statement.executeQuery(sql);
            while (resultSet.next()) {
                sum = resultSet.getInt(1);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                resultSet.close();
                statement.close();
                connection.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
    }

    //运行方法
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("当前访问量:" + (++sum));
    }

    //销毁方法
    @Override
    public void destroy() {
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        try {
            connection = Utils.getConnection();
            String sql = "update sumTotal set total =? where id =? ";
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setInt(1, sum);
            preparedStatement.setInt(2, 1);
            preparedStatement.executeUpdate();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                preparedStatement.close();
                connection.close();
            } catch (Exception throwables) {
                throwables.printStackTrace();
            }
        }
    }
}

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    <servlet>
        <servlet-name>UserServlet5servlet-name>
        <servlet-class>com.javakc.web1.user.UserServlet5servlet-class>
        
        <load-on-startup>0load-on-startup>
    servlet>

    
    <servlet-mapping>
        <servlet-name>UserServlet5servlet-name>
        <url-pattern>/user5.dourl-pattern>
    servlet-mapping>

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    访问路径:http://localhost:8080/web1/user5.do

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  • 原文地址：https://blog.csdn.net/qq_45939736/article/details/126795918