老师你好

请问在本视频中，在自己创建的类中以SimpleDateFormat类名创建的对象，并使用这个时间类中的方法，这是不是组合？如果让自己建的类继承SimpleDateFormat是否可以用本类的对象来使用时间类的方法？

老师，在视频3:40的时候，那为啥之前的parent在加了mvc依赖的情况下还添加了context依赖

老师，对于v-if和v-show的理解。

v-if：当值为true的时候就进行页面渲染，fales的话就不渲染了。

v-show:基于css样式进行渲染，元素始终会被渲染并保留在 DOM 中，通过操作属性ture,fales进行显示和隐藏.

1.

do都和视频里的操作一样，为什么都报错

避坑：用qq浏览器能安装flash，完美解决Chrome不支持flash的问题！

老师，视频的2:40秒，为什么启动前还要安装一下啊

因为说的赋值的之前的，不确定之前的有没有安装Nginx的依赖，可以重新安装吗？？？？？？？？？？？？？？？？？？？？

HashMap也是假排序的吗？因为我看输出是按字典序进行排序的

老师，有个路径访问的问题，一直出错，不知道如何解决，为了能让您更好地理解我的意思，内容可能会多，望老师能看完。

问题：我的项目出现了路径访问的错误，就是不能更好处理请求转发与重定向产生的资源路径访问问题。

首先，我知道的是，请求转发是需要在请求头中添加信息需要带会给客户端的时候是用它；重定向更好是在使用表单时使用。

那么现在，我的项目就是：基于请求转发时，没操作功能时可以正常的返回主页面，但是一旦操作了一个功能后页面就会报404错误；但是若是基于重定向的话，就不会出现这个问题，不管是执行完后，还是没执行功能前都可以返回上一层。

详情如下：就以添加用户为例：

但是，这一切，若是在重定向上，就完全没有问题.。

但是这样一来，却违背了我想将数据显示在同样的页面上的，要是使用重定向，将需要显示的数据放在另一个页面上，不太方便，就像很多图书管理系统，数据就显示到了当前的页面上。

所有的servlet代码：

package com.example.servlet.UserManager;

import com.example.exception.NotSearchUserResultException;
import com.example.pojo.Users;
import com.example.service.ServiceImpl.ServiceUserManagerClass;

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("/userManager.do")
public class UserManagerServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doPost(req, resp);
    }

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

        /**
         * 我在这里面就对其用户管理进行全部操作
         */
        String flag = req.getParameter("flag");

        if ("addUser".equals(flag)) {
            /**
             * 执行添加用户函数
             */
            try {

                Users users = this.getUsersMessage(req);
                ServiceUserManagerClass serviceUserManagerClass = new ServiceUserManagerClass();
                serviceUserManagerClass.addUsers(users);
                List<Users> list = serviceUserManagerClass.allUsers();
                req.setAttribute("listAllUsers",list);
                req.setAttribute("addUserMessageSuccess","用户信息已经添加成功！");
                req.getRequestDispatcher("userManagerJsp/addUser.jsp").forward(req,resp);
                
              //resp.sendRedirect("userManagerJsp/addUser.jsp");

                /**
                 * 老师以上就是我刚才举得例子：
                 * 是基于请求转发的
                 */


            } catch (Exception e) {
                e.printStackTrace();
                resp.sendRedirect("error.jsp");
            }

        } else if ("deleteUser".equals(flag)) {
            /**
             * 执行删除用户函数
             */
            try {

                String userName = req.getParameter("userName");

                ServiceUserManagerClass serviceUserManagerClass = new ServiceUserManagerClass();
                serviceUserManagerClass.deleteUser(userName);
                List<Users> list = serviceUserManagerClass.allUsers();
                req.setAttribute("listAllUsers",list);
                req.setAttribute("deleteUserMessageSuccess","用户信息已经删除成功！");
                req.getRequestDispatcher("userManagerJsp/deleteUser.jsp").forward(req,resp);

            } catch (Exception e) {
                e.printStackTrace();
                resp.sendRedirect("error.jsp");
            }


        } else if ("updateUser".equals(flag)) {
            /**
             * 执行更新用户函数
             */
            try {

                /**
                 * 是从表单里面提取的新的数据，但是我还需要旧的，咋办？？？
                 */
                Users newUser = this.getUsersMessage(req);
                String oldUserID = req.getParameter("oldUserID");

                ServiceUserManagerClass serviceUserManagerClass = new ServiceUserManagerClass();
                serviceUserManagerClass.updateUsers(oldUserID, newUser);

                List<Users> list = serviceUserManagerClass.allUsers();
                req.setAttribute("listAllUsers",list);
                req.setAttribute("deleteUserMessageSuccess","用户信息已经修改成功！");
                req.getRequestDispatcher("userManagerJsp/userUpdate.jsp").forward(req,resp);

            } catch (Exception e) {
                e.printStackTrace();
                resp.sendRedirect("error.jsp");
            }

        } else if ("searchUser".equals(flag)){
            /**
             * 执行查找用户函数
             */
            try {
                String userName = req.getParameter("userName");
                ServiceUserManagerClass serviceUserManagerClass = new ServiceUserManagerClass();
                Users usersTemp = serviceUserManagerClass.searchUsers(userName);
                List<Users> list = serviceUserManagerClass.allUsers();
                if (usersTemp != null) {

                    req.setAttribute("userIdMsg",usersTemp.getUserID());
                    req.setAttribute("userNameMsg",usersTemp.getUserName());
                    req.setAttribute("userEmailMsg",usersTemp.getUserEmial());
                    req.setAttribute("listAllUsers",list);
                    req.setAttribute("searchUserResultMsgSuccess","成功查询结果信息");
                    req.getRequestDispatcher("userManagerJsp/findUser.jsp").forward(req,resp);

                } else {
                    throw new NotSearchUserResultException("查询结果信息不存在，请重新输入...");
                }
            } catch (NotSearchUserResultException e) {
                e.printStackTrace();
                req.setAttribute("searchUserResultMsg",e.getMessage());
                req.getRequestDispatcher("userManagerJsp/findUser.jsp").forward(req,resp);
            }
        }
    }

    /**
     * 获取来自前端的用户的数据
     */
    private Users getUsersMessage(HttpServletRequest req) {
        Users users = new Users();

        String userID = req.getParameter("userName");
        String userPwd = req.getParameter("userPwd");
        String userEmail = req.getParameter("userEmail");
        users.setUserID(userID);
        users.setUserName(userPwd);
        users.setUserEmial(userEmail);

        return users;
    }
}

老师，如果需要项目的话，我全部上传。

Error parsing Mapper XML. The XML location is 'com/bjsxt/mapper/UsersMapper.xml'. Cause: java.lang.IllegalArgumentException: Result Maps collection already contains value for com.bjsxt.mapper.UsersMapper.BaseResultMap

使用这个插件 org.mybatis.generator 生成的xml文件，里面有多个id，相同

是什么回事

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.bjsxt.mapper.UsersMapper">
  <resultMap id="BaseResultMap" type="com.bjsxt.pojo.Users">
    <result column="USER" jdbcType="CHAR" property="user" />
    <result column="CURRENT_CONNECTIONS" jdbcType="BIGINT" property="currentConnections" />
    <result column="TOTAL_CONNECTIONS" jdbcType="BIGINT" property="totalConnections" />
  </resultMap>
  <sql id="Example_Where_Clause">
    <where>
      <foreach collection="oredCriteria" item="criteria" separator="or">
        <if test="criteria.valid">
          <trim prefix="(" prefixOverrides="and" suffix=")">
            <foreach collection="criteria.criteria" item="criterion">
              <choose>
                <when test="criterion.noValue">
                  and ${criterion.condition}
                </when>
                <when test="criterion.singleValue">
                  and ${criterion.condition} #{criterion.value}
                </when>
                <when test="criterion.betweenValue">
                  and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
                </when>
                <when test="criterion.listValue">
                  and ${criterion.condition}
                  <foreach close=")" collection="criterion.value" item="listItem" open="(" separator=",">
                    #{listItem}
                  </foreach>
                </when>
              </choose>
            </foreach>
          </trim>
        </if>
      </foreach>
    </where>
  </sql>
  <sql id="Update_By_Example_Where_Clause">
    <where>
      <foreach collection="example.oredCriteria" item="criteria" separator="or">
        <if test="criteria.valid">
          <trim prefix="(" prefixOverrides="and" suffix=")">
            <foreach collection="criteria.criteria" item="criterion">
              <choose>
                <when test="criterion.noValue">
                  and ${criterion.condition}
                </when>
                <when test="criterion.singleValue">
                  and ${criterion.condition} #{criterion.value}
                </when>
                <when test="criterion.betweenValue">
                  and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
                </when>
                <when test="criterion.listValue">
                  and ${criterion.condition}
                  <foreach close=")" collection="criterion.value" item="listItem" open="(" separator=",">
                    #{listItem}
                  </foreach>
                </when>
              </choose>
            </foreach>
          </trim>
        </if>
      </foreach>
    </where>
  </sql>
  <sql id="Base_Column_List">
    USER, CURRENT_CONNECTIONS, TOTAL_CONNECTIONS
  </sql>
  <select id="selectByExample" parameterType="com.bjsxt.pojo.UsersExample" resultMap="BaseResultMap">
    select
    <if test="distinct">
      distinct
    </if>
    <include refid="Base_Column_List" />
    from users
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
    <if test="orderByClause != null">
      order by ${orderByClause}
    </if>
  </select>
  <delete id="deleteByExample" parameterType="com.bjsxt.pojo.UsersExample">
    delete from users
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
  </delete>
  <insert id="insert" parameterType="com.bjsxt.pojo.Users">
    insert into users (USER, CURRENT_CONNECTIONS, TOTAL_CONNECTIONS
      )
    values (#{user,jdbcType=CHAR}, #{currentConnections,jdbcType=BIGINT}, #{totalConnections,jdbcType=BIGINT}
      )
  </insert>
  <insert id="insertSelective" parameterType="com.bjsxt.pojo.Users">
    insert into users
    <trim prefix="(" suffix=")" suffixOverrides=",">
      <if test="user != null">
        USER,
      </if>
      <if test="currentConnections != null">
        CURRENT_CONNECTIONS,
      </if>
      <if test="totalConnections != null">
        TOTAL_CONNECTIONS,
      </if>
    </trim>
    <trim prefix="values (" suffix=")" suffixOverrides=",">
      <if test="user != null">
        #{user,jdbcType=CHAR},
      </if>
      <if test="currentConnections != null">
        #{currentConnections,jdbcType=BIGINT},
      </if>
      <if test="totalConnections != null">
        #{totalConnections,jdbcType=BIGINT},
      </if>
    </trim>
  </insert>
  <select id="countByExample" parameterType="com.bjsxt.pojo.UsersExample" resultType="java.lang.Long">
    select count(*) from users
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
  </select>
  <update id="updateByExampleSelective" parameterType="map">
    update users
    <set>
      <if test="record.user != null">
        USER = #{record.user,jdbcType=CHAR},
      </if>
      <if test="record.currentConnections != null">
        CURRENT_CONNECTIONS = #{record.currentConnections,jdbcType=BIGINT},
      </if>
      <if test="record.totalConnections != null">
        TOTAL_CONNECTIONS = #{record.totalConnections,jdbcType=BIGINT},
      </if>
    </set>
    <if test="_parameter != null">
      <include refid="Update_By_Example_Where_Clause" />
    </if>
  </update>
  <update id="updateByExample" parameterType="map">
    update users
    set USER = #{record.user,jdbcType=CHAR},
      CURRENT_CONNECTIONS = #{record.currentConnections,jdbcType=BIGINT},
      TOTAL_CONNECTIONS = #{record.totalConnections,jdbcType=BIGINT}
    <if test="_parameter != null">
      <include refid="Update_By_Example_Where_Clause" />
    </if>
  </update>
  <resultMap id="BaseResultMap" type="com.bjsxt.pojo.Users">
    <result column="username" jdbcType="VARCHAR" property="username" />
    <result column="password" jdbcType="VARCHAR" property="password" />
    <result column="salting" jdbcType="VARCHAR" property="salting" />
  </resultMap>
  <sql id="Example_Where_Clause">
    <where>
      <foreach collection="oredCriteria" item="criteria" separator="or">
        <if test="criteria.valid">
          <trim prefix="(" prefixOverrides="and" suffix=")">
            <foreach collection="criteria.criteria" item="criterion">
              <choose>
                <when test="criterion.noValue">
                  and ${criterion.condition}
                </when>
                <when test="criterion.singleValue">
                  and ${criterion.condition} #{criterion.value}
                </when>
                <when test="criterion.betweenValue">
                  and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
                </when>
                <when test="criterion.listValue">
                  and ${criterion.condition}
                  <foreach close=")" collection="criterion.value" item="listItem" open="(" separator=",">
                    #{listItem}
                  </foreach>
                </when>
              </choose>
            </foreach>
          </trim>
        </if>
      </foreach>
    </where>
  </sql>
  <sql id="Update_By_Example_Where_Clause">
    <where>
      <foreach collection="example.oredCriteria" item="criteria" separator="or">
        <if test="criteria.valid">
          <trim prefix="(" prefixOverrides="and" suffix=")">
            <foreach collection="criteria.criteria" item="criterion">
              <choose>
                <when test="criterion.noValue">
                  and ${criterion.condition}
                </when>
                <when test="criterion.singleValue">
                  and ${criterion.condition} #{criterion.value}
                </when>
                <when test="criterion.betweenValue">
                  and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
                </when>
                <when test="criterion.listValue">
                  and ${criterion.condition}
                  <foreach close=")" collection="criterion.value" item="listItem" open="(" separator=",">
                    #{listItem}
                  </foreach>
                </when>
              </choose>
            </foreach>
          </trim>
        </if>
      </foreach>
    </where>
  </sql>
  <sql id="Base_Column_List">
    username, password, salting
  </sql>
  <select id="selectByExample" parameterType="com.bjsxt.pojo.UsersExample" resultMap="BaseResultMap">
    select
    <if test="distinct">
      distinct
    </if>
    <include refid="Base_Column_List" />
    from users
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
    <if test="orderByClause != null">
      order by ${orderByClause}
    </if>
  </select>
  <delete id="deleteByExample" parameterType="com.bjsxt.pojo.UsersExample">
    delete from users
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
  </delete>
  <insert id="insert" parameterType="com.bjsxt.pojo.Users">
    insert into users (username, password, salting
      )
    values (#{username,jdbcType=VARCHAR}, #{password,jdbcType=VARCHAR}, #{salting,jdbcType=VARCHAR}
      )
  </insert>
  <insert id="insertSelective" parameterType="com.bjsxt.pojo.Users">
    insert into users
    <trim prefix="(" suffix=")" suffixOverrides=",">
      <if test="username != null">
        username,
      </if>
      <if test="password != null">
        password,
      </if>
      <if test="salting != null">
        salting,
      </if>
    </trim>
    <trim prefix="values (" suffix=")" suffixOverrides=",">
      <if test="username != null">
        #{username,jdbcType=VARCHAR},
      </if>
      <if test="password != null">
        #{password,jdbcType=VARCHAR},
      </if>
      <if test="salting != null">
        #{salting,jdbcType=VARCHAR},
      </if>
    </trim>
  </insert>
  <select id="countByExample" parameterType="com.bjsxt.pojo.UsersExample" resultType="java.lang.Long">
    select count(*) from users
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
  </select>
  <update id="updateByExampleSelective" parameterType="map">
    update users
    <set>
      <if test="record.username != null">
        username = #{record.username,jdbcType=VARCHAR},
      </if>
      <if test="record.password != null">
        password = #{record.password,jdbcType=VARCHAR},
      </if>
      <if test="record.salting != null">
        salting = #{record.salting,jdbcType=VARCHAR},
      </if>
    </set>
    <if test="_parameter != null">
      <include refid="Update_By_Example_Where_Clause" />
    </if>
  </update>
  <update id="updateByExample" parameterType="map">
    update users
    set username = #{record.username,jdbcType=VARCHAR},
      password = #{record.password,jdbcType=VARCHAR},
      salting = #{record.salting,jdbcType=VARCHAR}
    <if test="_parameter != null">
      <include refid="Update_By_Example_Where_Clause" />
    </if>
  </update>
  <resultMap id="BaseResultMap" type="com.bjsxt.pojo.Users">
    <id column="userid" jdbcType="INTEGER" property="userid" />
    <result column="username" jdbcType="VARCHAR" property="username" />
    <result column="userage" jdbcType="INTEGER" property="userage" />
  </resultMap>
  <sql id="Example_Where_Clause">
    <where>
      <foreach collection="oredCriteria" item="criteria" separator="or">
        <if test="criteria.valid">
          <trim prefix="(" prefixOverrides="and" suffix=")">
            <foreach collection="criteria.criteria" item="criterion">
              <choose>
                <when test="criterion.noValue">
                  and ${criterion.condition}
                </when>
                <when test="criterion.singleValue">
                  and ${criterion.condition} #{criterion.value}
                </when>
                <when test="criterion.betweenValue">
                  and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
                </when>
                <when test="criterion.listValue">
                  and ${criterion.condition}
                  <foreach close=")" collection="criterion.value" item="listItem" open="(" separator=",">
                    #{listItem}
                  </foreach>
                </when>
              </choose>
            </foreach>
          </trim>
        </if>
      </foreach>
    </where>
  </sql>
  <sql id="Update_By_Example_Where_Clause">
    <where>
      <foreach collection="example.oredCriteria" item="criteria" separator="or">
        <if test="criteria.valid">
          <trim prefix="(" prefixOverrides="and" suffix=")">
            <foreach collection="criteria.criteria" item="criterion">
              <choose>
                <when test="criterion.noValue">
                  and ${criterion.condition}
                </when>
                <when test="criterion.singleValue">
                  and ${criterion.condition} #{criterion.value}
                </when>
                <when test="criterion.betweenValue">
                  and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
                </when>
                <when test="criterion.listValue">
                  and ${criterion.condition}
                  <foreach close=")" collection="criterion.value" item="listItem" open="(" separator=",">
                    #{listItem}
                  </foreach>
                </when>
              </choose>
            </foreach>
          </trim>
        </if>
      </foreach>
    </where>
  </sql>
  <sql id="Base_Column_List">
    userid, username, userage
  </sql>
  <select id="selectByExample" parameterType="com.bjsxt.pojo.UsersExample" resultMap="BaseResultMap">
    select
    <if test="distinct">
      distinct
    </if>
    <include refid="Base_Column_List" />
    from users
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
    <if test="orderByClause != null">
      order by ${orderByClause}
    </if>
  </select>
  <select id="selectByPrimaryKey" parameterType="java.lang.Integer" resultMap="BaseResultMap">
    select 
    <include refid="Base_Column_List" />
    from users
    where userid = #{userid,jdbcType=INTEGER}
  </select>
  <delete id="deleteByPrimaryKey" parameterType="java.lang.Integer">
    delete from users
    where userid = #{userid,jdbcType=INTEGER}
  </delete>
  <delete id="deleteByExample" parameterType="com.bjsxt.pojo.UsersExample">
    delete from users
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
  </delete>
  <insert id="insert" parameterType="com.bjsxt.pojo.Users">
    insert into users (userid, username, userage
      )
    values (#{userid,jdbcType=INTEGER}, #{username,jdbcType=VARCHAR}, #{userage,jdbcType=INTEGER}
      )
  </insert>
  <insert id="insertSelective" parameterType="com.bjsxt.pojo.Users">
    insert into users
    <trim prefix="(" suffix=")" suffixOverrides=",">
      <if test="userid != null">
        userid,
      </if>
      <if test="username != null">
        username,
      </if>
      <if test="userage != null">
        userage,
      </if>
    </trim>
    <trim prefix="values (" suffix=")" suffixOverrides=",">
      <if test="userid != null">
        #{userid,jdbcType=INTEGER},
      </if>
      <if test="username != null">
        #{username,jdbcType=VARCHAR},
      </if>
      <if test="userage != null">
        #{userage,jdbcType=INTEGER},
      </if>
    </trim>
  </insert>
  <select id="countByExample" parameterType="com.bjsxt.pojo.UsersExample" resultType="java.lang.Long">
    select count(*) from users
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
  </select>
  <update id="updateByExampleSelective" parameterType="map">
    update users
    <set>
      <if test="record.userid != null">
        userid = #{record.userid,jdbcType=INTEGER},
      </if>
      <if test="record.username != null">
        username = #{record.username,jdbcType=VARCHAR},
      </if>
      <if test="record.userage != null">
        userage = #{record.userage,jdbcType=INTEGER},
      </if>
    </set>
    <if test="_parameter != null">
      <include refid="Update_By_Example_Where_Clause" />
    </if>
  </update>
  <update id="updateByExample" parameterType="map">
    update users
    set userid = #{record.userid,jdbcType=INTEGER},
      username = #{record.username,jdbcType=VARCHAR},
      userage = #{record.userage,jdbcType=INTEGER}
    <if test="_parameter != null">
      <include refid="Update_By_Example_Where_Clause" />
    </if>
  </update>
  <update id="updateByPrimaryKeySelective" parameterType="com.bjsxt.pojo.Users">
    update users
    <set>
      <if test="username != null">
        username = #{username,jdbcType=VARCHAR},
      </if>
      <if test="userage != null">
        userage = #{userage,jdbcType=INTEGER},
      </if>
    </set>
    where userid = #{userid,jdbcType=INTEGER}
  </update>
  <update id="updateByPrimaryKey" parameterType="com.bjsxt.pojo.Users">
    update users
    set username = #{username,jdbcType=VARCHAR},
      userage = #{userage,jdbcType=INTEGER}
    where userid = #{userid,jdbcType=INTEGER}
  </update>
  <resultMap id="BaseResultMap" type="com.bjsxt.pojo.Users">
    <result column="username" jdbcType="VARCHAR" property="username" />
    <result column="password" jdbcType="VARCHAR" property="password" />
    <result column="salting" jdbcType="VARCHAR" property="salting" />
  </resultMap>
  <sql id="Example_Where_Clause">
    <where>
      <foreach collection="oredCriteria" item="criteria" separator="or">
        <if test="criteria.valid">
          <trim prefix="(" prefixOverrides="and" suffix=")">
            <foreach collection="criteria.criteria" item="criterion">
              <choose>
                <when test="criterion.noValue">
                  and ${criterion.condition}
                </when>
                <when test="criterion.singleValue">
                  and ${criterion.condition} #{criterion.value}
                </when>
                <when test="criterion.betweenValue">
                  and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
                </when>
                <when test="criterion.listValue">
                  and ${criterion.condition}
                  <foreach close=")" collection="criterion.value" item="listItem" open="(" separator=",">
                    #{listItem}
                  </foreach>
                </when>
              </choose>
            </foreach>
          </trim>
        </if>
      </foreach>
    </where>
  </sql>
  <sql id="Update_By_Example_Where_Clause">
    <where>
      <foreach collection="example.oredCriteria" item="criteria" separator="or">
        <if test="criteria.valid">
          <trim prefix="(" prefixOverrides="and" suffix=")">
            <foreach collection="criteria.criteria" item="criterion">
              <choose>
                <when test="criterion.noValue">
                  and ${criterion.condition}
                </when>
                <when test="criterion.singleValue">
                  and ${criterion.condition} #{criterion.value}
                </when>
                <when test="criterion.betweenValue">
                  and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
                </when>
                <when test="criterion.listValue">
                  and ${criterion.condition}
                  <foreach close=")" collection="criterion.value" item="listItem" open="(" separator=",">
                    #{listItem}
                  </foreach>
                </when>
              </choose>
            </foreach>
          </trim>
        </if>
      </foreach>
    </where>
  </sql>
  <sql id="Base_Column_List">
    username, password, salting
  </sql>
  <select id="selectByExample" parameterType="com.bjsxt.pojo.UsersExample" resultMap="BaseResultMap">
    select
    <if test="distinct">
      distinct
    </if>
    <include refid="Base_Column_List" />
    from users
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
    <if test="orderByClause != null">
      order by ${orderByClause}
    </if>
  </select>
  <delete id="deleteByExample" parameterType="com.bjsxt.pojo.UsersExample">
    delete from users
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
  </delete>
  <insert id="insert" parameterType="com.bjsxt.pojo.Users">
    insert into users (username, password, salting
      )
    values (#{username,jdbcType=VARCHAR}, #{password,jdbcType=VARCHAR}, #{salting,jdbcType=VARCHAR}
      )
  </insert>
  <insert id="insertSelective" parameterType="com.bjsxt.pojo.Users">
    insert into users
    <trim prefix="(" suffix=")" suffixOverrides=",">
      <if test="username != null">
        username,
      </if>
      <if test="password != null">
        password,
      </if>
      <if test="salting != null">
        salting,
      </if>
    </trim>
    <trim prefix="values (" suffix=")" suffixOverrides=",">
      <if test="username != null">
        #{username,jdbcType=VARCHAR},
      </if>
      <if test="password != null">
        #{password,jdbcType=VARCHAR},
      </if>
      <if test="salting != null">
        #{salting,jdbcType=VARCHAR},
      </if>
    </trim>
  </insert>
  <select id="countByExample" parameterType="com.bjsxt.pojo.UsersExample" resultType="java.lang.Long">
    select count(*) from users
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
  </select>
  <update id="updateByExampleSelective" parameterType="map">
    update users
    <set>
      <if test="record.username != null">
        username = #{record.username,jdbcType=VARCHAR},
      </if>
      <if test="record.password != null">
        password = #{record.password,jdbcType=VARCHAR},
      </if>
      <if test="record.salting != null">
        salting = #{record.salting,jdbcType=VARCHAR},
      </if>
    </set>
    <if test="_parameter != null">
      <include refid="Update_By_Example_Where_Clause" />
    </if>
  </update>
  <update id="updateByExample" parameterType="map">
    update users
    set username = #{record.username,jdbcType=VARCHAR},
      password = #{record.password,jdbcType=VARCHAR},
      salting = #{record.salting,jdbcType=VARCHAR}
    <if test="_parameter != null">
      <include refid="Update_By_Example_Where_Clause" />
    </if>
  </update>
</mapper>

插件配置

<build>
    <plugins>
        <!-- generator  -->
        <plugin>
            <groupId>org.mybatis.generator</groupId>
            <artifactId>mybatis-generator-maven-plugin</artifactId>
            <dependencies>
                <!-- 插件中引入依赖，只会去本地仓库中查找 -->
                <dependency>
                    <groupId>mysql</groupId>
                    <artifactId>mysql-connector-java</artifactId>
                    <version>8.0.22</version>
                </dependency>
            </dependencies>
            <configuration>
                <configurationFile>
                    ${project.basedir}/src/main/resources/generatorConfig.xml
                </configurationFile>
                <verbose>true</verbose>
                <overwrite>true</overwrite>
            </configuration>
        </plugin>
    </plugins>
    <resources>
        <resource>
            <directory>src/main/java</directory>
            <includes>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
            </includes>
            <filtering>false</filtering>
        </resource>
        <resource>
            <directory>src/main/resources</directory>
            <includes>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
            </includes>
            <filtering>false</filtering>
        </resource>
    </resources>
</build>

解决方法是，将相同的id删除，我就是想问一下，这个插件为什么会出现这种情况

为什么c='dd#'与d='dd#'不是一个对象不同id，而a='abd_33'与b='abd33'却是同一个对象同一个id， #特殊？

class car:
    def __init__(self,motor,chassis,seat,shell):
        self.motor = motor
        self.chassis = chassis
        self.seat = seat
        self.shell = shell

    def run(self):
        self.motor.work()
        self.seat.work()
        self.shell.work()
        self.chassis.work()


class Motor:
    def work(self):
        return "发动机要开始工作啦"

class Chassis:
    def work(self):
        return "底盘开始工作啦"

class Seat:
    def work(self):
        return "座椅开始工作啦"

class Shell:
    def work(self):
        return "车辆外壳开始工作啦"

a = car(Motor(),Chassis(),Seat(),Shell())

老师为什么这里我的return的值没有办法在结果中呈现呢

老师，比较器可以定义在Person类吗?那样好像Person对象就能自动排序

老师，我返回值是2，但是里面删除成功了。。。。。。

这是为啥？

老师，请问这里的UserMapper是我们自定义的类吗