2.第一个Mybatis程序

技术文章 1年前 (2020) 完美者
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标签:values   jdbc   insert   type   util   private   工具   nts   password   

2、第一个Mybatis程序

思路:搭建环境-->导入Mybatis-->编写代码-->测试!

2.1、搭建环境

搭建数据库

CREATE DATABASE `mybatis`;

USE `mybatis`;

CREATE TABLE `user`(
  `id` INT(20) NOT NULL PRIMARY KEY,
  `name` VARCHAR(30) DEFAULT NULL,
  `pwd` VARCHAR(30) DEFAULT NULL
)ENGINE=INNODB DEFAULT CHARSET=utf8;

INSERT INTO `user`(`id`,`name`,`pwd`) VALUES 
(1,‘狂神‘,‘123456‘),
(2,‘张三‘,‘123456‘),
(3,‘李四‘,‘123890‘)

新建项目

  1. 新建一个普通的maven项目

  2. 删除src目录

  3. 导入maven依赖

        <!--导入依赖-->
        <dependencies>
            <!--mysql驱动-->
            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
                <version>5.1.47</version>
            </dependency>
            <!--mybatis-->
            <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
            <dependency>
                <groupId>org.mybatis</groupId>
                <artifactId>mybatis</artifactId>
                <version>3.5.2</version>
            </dependency>
            <!--junit-->
            <dependency>
                <groupId>junit</groupId>
                <artifactId>junit</artifactId>
                <version>4.12</version>
            </dependency>
        </dependencies>
    

2.2、创建一个模块

  • 编写mybatis的核心配置文件

    <?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE configuration
            PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
            "http://mybatis.org/dtd/mybatis-3-config.dtd">
    <!--configuration核心配置文件-->
    <configuration>
    
        <environments default="development">
            <environment id="development">
                <transactionManager type="JDBC"/>
                <dataSource type="POOLED">
                    <property name="driver" value="com.mysql.jdbc.Driver"/>
                    <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=false&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                    <property name="username" value="root"/>
                    <property name="password" value="123456"/>
                </dataSource>
            </environment>
        </environments>
    
    </configuration>
    
  • 编写mybatis工具类

    //sqlSessionFactory --> sqlSession
    public class MybatisUtils {
    
        private static SqlSessionFactory sqlSessionFactory;
    
        static{
            try {
                //使用Mybatis第一步:获取sqlSessionFactory对象
                String resource = "mybatis-config.xml";
                InputStream inputStream = Resources.getResourceAsStream(resource);
                sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
            } catch (IOException e) {
                e.printStackTrace();
            }
    
        }
    
        //既然有了 SqlSessionFactory,顾名思义,我们就可以从中获得 SqlSession 的实例了。
        // SqlSession 完全包含了面向数据库执行 SQL 命令所需的所有方法。
        public static SqlSession  getSqlSession(){
            return sqlSessionFactory.openSession();
        }
    
    }
    
    

2.3、编写代码

  • 实体类

    package com.kuang.pojo;
    
    //实体类
    public class User {
        private int id;
        private String name;
        private String pwd;
    
        public User() {
        }
    
        public User(int id, String name, String pwd) {
            this.id = id;
            this.name = name;
            this.pwd = pwd;
        }
    
        public int getId() {
            return id;
        }
    
        public void setId(int id) {
            this.id = id;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public String getPwd() {
            return pwd;
        }
    
        public void setPwd(String pwd) {
            this.pwd = pwd;
        }
    
        @Override
        public String toString() {
            return "User{" +
                    "id=" + id +
                    ", name=‘" + name + ‘\‘‘ +
                    ", pwd=‘" + pwd + ‘\‘‘ +
                    ‘}‘;
        }
    }
    
    
  • Dao接口

    public interface UserDao {
        List<User> getUserList();
    }
    
  • 接口实现类由原来的UserDaoImpl转变为一个 Mapper配置文件.

    <?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">
            <!--namespace=绑定一个对应的Dao/Mapper接口-->
    <mapper namespace="com.kuang.dao.UserDao">
    
    <!--select查询语句-->
       <select id="getUserList" resultType="com.kuang.pojo.User">
           select * from mybatis.user
       </select>
    
    </mapper>
    

2.4、测试

注意点:

org.apache.ibatis.binding.BindingException: Type interface com.kuang.dao.UserDao is not known to the MapperRegistry.

MapperRegistry是什么?

每一个Mapper.xml 都需要在Mybatis核心配置文件中注册

<!-- 每一个Mapper.xml 都需要在Mybatis核心配置文件中注册 -->
	<mappers>
		<mapper resource="com/yhn/dao/UserMapper.xml"/>
	</mappers>

核心配置文件中注册 mappers

  • junit测试

    @Test
    public void test(){
        //第一步:获得SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
    
    
        //方式一:getMapper
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        List<User> userList = userDao.getUserList();
    
        for (User user : userList) {
            System.out.println(user);
        }
    
    
    
        //关闭SqlSession
        sqlSession.close();
    }
    
    

你们可以能会遇到的问题:

  1. 配置文件没有注册

  2. 绑定接口错误。

  3. 方法名不对

  4. 返回类型不对

  5. Maven导出资源问题

    <!--在build中配置resources,来防止我们资源导出失败的问题-->
    <build>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>
    

2.第一个Mybatis程序

标签:values   jdbc   insert   type   util   private   工具   nts   password   

原文地址:https://www.cnblogs.com/yhnCoder/p/13619931.html

版权声明:完美者 发表于 2020-09-17 15:46:51。
转载请注明:2.第一个Mybatis程序 | 完美导航

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