1.内存版表白墙

1.创建servlet项目
2.创建必要的目录src
3.调整pom.xml
引入servlet和jackson依赖：
在这里插入图片描述
4.message-wall.html：

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>表白墙</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        .container {
            width: 400px;
            margin: 0 auto;
        }

        h1 {
            text-align: center;
            padding: 20px 0;
        }

        p {
            color: #666;
            text-align: center;
            font-size: 14px;
            padding: 10px 0;
        }

        .row {
            height: 40px;
            display: flex;
            justify-content: center;
            align-items: center;
        }

        span {
            width: 100px;
            line-height: 40px;
        }

        .edit {
            width: 200px;
            height: 30px;
        }

        .submit {
            width: 304px;
            height: 40px;
            color: white;
            background-color: orange;
            border: none;
        }

        .submit:active {
            background-color: #666;
        }



    </style>
    <script src="js/jquery-1.9.1.min.js"></script>
</head>

<body>
<div id="container" class="container">
    <h1>表白墙</h1>
    <p>输入后点击提交, 会将信息显示在表格中</p>
    <div class="row">
        <span>谁: </span>
        <input id="from" class="edit" type="text">
    </div>
    <div class="row">
        <span>对谁: </span>
        <input id="to" class="edit" type="text">
    </div>
    <div class="row">
        <span>说什么: </span>
        <input id="message" class="edit" type="text">
    </div>
    <div class="row">
        <input type="button" value="提交" class="submit" onclick="mySubmit()">
    </div>
    <div id="allMsg">
        <div class="row">
            猫猫对狗狗说: 喵喵喵
        </div>
        <div class="row">
            小赵对小张说: 你好
        </div>
    </div>
</div>
<script>
    // 添加表白信息
    function mySubmit(){
       var from = jQuery("#from");
       var to = jQuery("#to");
       var msg = jQuery("#message");
       // todo:1.非空效验
       // 2.ajax 提交数据给后端
       jQuery.ajax({
         url:"message/add",   // 提交到后端的地址
         type:"POST", // 提交类型
         data:{
            from:from.val(),
            to:to.val(),
            msg:msg.val()
         }, // 参数
         success:function(result){ // 后端返回给前端的数据
            if(result!=null && result>0){
                alert("恭喜：添加成功！");
                // 刷新表白列表
                getAllMsg();
            }else{
              alert("抱歉：添加失败，请重试！");
            }
         }
       });
    }

    // 查询所有的表白信息
    function getAllMsg(){
        jQuery.ajax({
            url:"message/list",
            type:"GET",
            data:{},
            success:function(result){
                if(result!=null && result.length>0){
                    // 表示有表白数据
                    var msgHtml = "";
                    for(var i=0;i<result.length;i++){
                        msgHtml +='<div class="row">'+
                            result[i].from +'对'+
                            result[i].to+'说: '+
                            result[i].message+'</div>';
                    }
                    jQuery("#allMsg").html(msgHtml);
                }else if(result!=null && result.length==0){
                    // 没有表白数据
                    console.log("没有表白信息");
                }else{
                    alert("访问出错！");
                }
            }
        });
    }
    getAllMsg(); // 执行方法
</script>
</body>

</html>

5.AddMeaageServlet.java:
在这里插入图片描述

import lombok.Getter;
import lombok.Setter;
import utils.StringUtils;

import javax.servlet.ServletException;
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.util.ArrayList;
import java.util.List;

@WebServlet("/message/add")
public class AddMessageServlet  extends HttpServlet {
    public static List<Message> msgList = new ArrayList<>();

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        int result = -1;
        //1.得到前端参数并效验
        String from = req.getParameter("from");
        String to = req.getParameter("to");
        String msg = req.getParameter("msg");
        if (StringUtils.hasLength(from) && StringUtils.hasLength(to) && StringUtils.hasLength(msg)) {
            //2.将表白对象加入到集合(内存)
            AddMessageServlet.msgList.add(new Message(from, to, msg));
            result = 1;
            //
        }
            resp.setContentType("text/html;charset=utf-8");
            resp.getWriter().println(result);

        }
    }

@Setter
@Getter
class Message{
    private String from;
    private String to;
    private String message;

    public Message(String from, String to, String message) {
        this.from = from;
        this.to = to;
        this.message = message;
    }
}

6.MessageListServlet.java:

import com.fasterxml.jackson.databind.ObjectMapper;

import javax.servlet.ServletException;
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.util.List;

@WebServlet("/message/list")
public class MessageListServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        List<Message> messageList=AddMessageServlet.msgList;
        resp.setContentType("application/json;charset=utf-8");
        ObjectMapper objectMapper=new ObjectMapper();
        resp.getWriter().println(objectMapper.writeValueAsString(messageList));

    }
}

7.通过浏览器访问：http://localhost:8080/first-servlet/message-wall.html可以看到：
在这里插入图片描述
添加表白信息：
(1)成功添加表白信息：

(2)用户输入不完整时提示输入错误：
在这里插入图片描述

表白信息列表：
在这里插入图片描述
上面的程序有一个问题数据是存储在内存中的，当服务器重启之后数据就会丢失。

2.数据库版表白墙

1.创建数据库和数据表：
在这里插入图片描述
此时数据库中还没有数据：

2.连接数据库：
pom.xml中添加MYSQL JDBC依赖：

3.message-wallv2.html:

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>表白墙——连接数据库版本</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        .container {
            width: 400px;
            margin: 0 auto;
        }

        h1 {
            text-align: center;
            padding: 20px 0;
        }

        p {
            color: #666;
            text-align: center;
            font-size: 14px;
            padding: 10px 0;
        }

        .row {
            height: 40px;
            display: flex;
            justify-content: center;
            align-items: center;
        }

        span {
            width: 100px;
            line-height: 40px;
        }

        .edit {
            width: 200px;
            height: 30px;
        }

        .submit {
            width: 304px;
            height: 40px;
            color: white;
            background-color: orange;
            border: none;
        }

        .submit:active {
            background-color: #666;
        }

    </style>
    <script src="js/jquery-1.9.1.min.js"></script>
</head>

<body>
<div id="container" class="container">
    <h1>表白墙</h1>
    <p>输入后点击提交, 会将信息显示在表格中</p>
    <div class="row">
        <span>谁: </span>
        <input id="from" class="edit" type="text">
    </div>
    <div class="row">
        <span>对谁: </span>
        <input id="to" class="edit" type="text">
    </div>
    <div class="row">
        <span>说什么: </span>
        <input id="message" class="edit" type="text">
    </div>
    <div class="row">
        <input type="button" value="提交" class="submit" onclick="mySubmit()">
    </div>
    <div id="allMsg">
        <!-- <div class="row">
            小猫对小狗说: 喵
        </div>
        <div class="row">
            小黑对小白说: 拜拜。
        </div> -->
    </div>
</div>
<script>
    // 添加表白信息
    function mySubmit(){
       var from = jQuery("#from");
       var to = jQuery("#to");
       var msg = jQuery("#message");
       // todo:1.非空效验
       // 2.ajax 提交数据给后端
       jQuery.ajax({
         url:"message/add2",   // 提交到后端的地址
         type:"POST", // 提交类型
         data:{
            from:from.val(),
            to:to.val(),
            msg:msg.val()
         }, // 参数
         success:function(result){ // 后端返回给前端的数据
            if(result!=null && result>0){
                alert("恭喜：添加成功！");
                // 刷新表白列表
                getAllMsg();
            }else{
              alert("抱歉：添加失败，请重试！");
            }
         }
       });
    }

    // 查询所有的表白信息
    function getAllMsg(){
        jQuery.ajax({
            url:"message/list2",
            type:"GET",
            data:{},
            success:function(result){
                if(result!=null && result.length>0){
                    // 表示有表白数据
                    var msgHtml = "";
                    for(var i=0;i<result.length;i++){
                        msgHtml +='<div class="row">'+
                            result[i].from +'对'+
                            result[i].to+'说: '+
                            result[i].message+'</div>';
                    }
                    jQuery("#allMsg").html(msgHtml);
                }else if(result!=null && result.length==0){
                    // 没有表白数据
                    console.log("没有表白信息");
                }else{
                    alert("访问出错！");
                }
            }
        });
    }
    getAllMsg(); // 执行方法

</script>
</body>
</html>

4.DBUtils.java:

package utils;

import com.mysql.jdbc.Connection;
import com.mysql.jdbc.jdbc2.optional.MysqlDataSource;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class DBUtils {
    private DBUtils() {
    }
    private static volatile MysqlDataSource mysqlDataSource;
    private static volatile Connection connection;

    private static MysqlDataSource getMysqlDataSource() {
        if (mysqlDataSource == null) {
            synchronized (DBUtils.class) {
                if (mysqlDataSource == null) {
                    mysqlDataSource = new MysqlDataSource();
                    mysqlDataSource.setURL("jdbc:mysql://127.0.0.1:3306/messagewall?character=utf8&useSSL=true");
                    mysqlDataSource.setUser("root");
                    mysqlDataSource.setPassword("123456");
                }
            }
        }
        return mysqlDataSource;
    }

    // 1.get connect
    public static Connection getConnection() {
        if (connection == null) { // 首次访问
            synchronized (DBUtils.class) {
                if (connection == null) {
                    try {
                        MysqlDataSource dataSource = getMysqlDataSource();
                        connection = (Connection) dataSource.getConnection();
                    } catch (SQLException throwables) {
                        throwables.printStackTrace();
                    }
                }
            }
        }
        return connection;
    }
    // 2.提供关闭资源的方法
    public static void close(ResultSet resultSet, PreparedStatement statement, Connection connection) throws SQLException {
        if (resultSet != null) {
            resultSet.close();
        }
        if (statement != null) {
            statement.close();
        }
        if (connection != null) {
            connection.close();
        }
    }
}

5.AddMessageServletV2.java:

import com.mysql.jdbc.Connection;
import lombok.SneakyThrows;
import utils.DBUtils;
import utils.StringUtils;

import javax.servlet.ServletException;
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.PreparedStatement;

@WebServlet("/message/add2")
public class AddMessageServletV2 extends HttpServlet {
    @SneakyThrows
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        int result = -1;
        // 1.得到前端参数并效验
        String from = req.getParameter("from");
        String to = req.getParameter("to");
        String msg = req.getParameter("msg");
        if (StringUtils.hasLength(from) && StringUtils.hasLength(to)
                && StringUtils.hasLength(msg)) {
            // 2.将表白对象加入到集合
            // 2.1 得到 Connection
            Connection connection = DBUtils.getConnection();
            // 2.2 拼接 sql，创建执行器
            String sql = "insert into messages(`from`,`to`,`message`) values(?,?,?)";
            PreparedStatement statement = connection.prepareStatement(sql);
            statement.setString(1, from);
            statement.setString(2, to);
            statement.setString(3, msg);
            // 2.3 执行执行器，并返回结果
            result = statement.executeUpdate();
            // 2.4 关闭资源
            DBUtils.close(null, statement, connection);
        }
        resp.setContentType("text/html; charset=utf-8");
        resp.getWriter().println(result);
    }
}

6.MessageListServletV2.java:

import com.fasterxml.jackson.databind.ObjectMapper;
import com.mysql.jdbc.Connection;
import lombok.SneakyThrows;
import utils.DBUtils;

import javax.servlet.ServletException;
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.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

@WebServlet("/message/list2")
public class MessageListServletV2 extends HttpServlet {
    @SneakyThrows
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //查询数据库中的表白列表
        List<Message> list=new ArrayList<>();
        //1.得到connection
        Connection connection= DBUtils.getConnection();
        //2.拼接sql,创建执行器
        String sql="select * from messages";
        PreparedStatement statement=connection.prepareStatement(sql);
        //3.执行sql,返回resultSet并循环将数据添加到List
        ResultSet resultSet=statement.executeQuery();
        while(resultSet.next ()){
            String from=resultSet.getString("from");
            String to=resultSet.getString("to");
            String message=resultSet.getString("message");
            list.add(new Message(from,to,message));
        }
        //4.关闭资源
        DBUtils.close(resultSet,statement,connection);
        resp.setContentType("application/json;charset=utf-8");
        ObjectMapper objectMapper=new ObjectMapper();
        resp.getWriter().println(objectMapper.writeValueAsString(list));

    }
}