2、MyBatis教程之第一个MyBatis程序

3、MyBatis第一个程序

1、搭建实验数据库

CREATE DATABASE `mybatis`;
USE `mybatis`;
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
`id` int(20) NOT NULL,
`name` varchar(30) DEFAULT NULL,
`pwd` varchar(30) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

insert  into `user`(`id`,`name`,`pwd`) values (1,'王五','123456'),(2,'张三','abcdef'),(3,'李四','987654');

2、导入MyBatis相关 jar 包

<dependency>
   <groupId>org.mybatis</groupId>
   <artifactId>mybatis</artifactId>
   <version>3.5.2</version>
</dependency>
<dependency>
   <groupId>mysql</groupId>
   <artifactId>mysql-connector-java</artifactId>
   <version>5.1.47</version>
</dependency>

3、编写MyBatis核心配置文件

• 查看帮助文档 resources下面创建mybatis-config.xml

<?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>
    <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=true&amp;useUnicode=true&amp;characterEncoding=utf8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="mapper/usermapper.xml"/>
    </mappers>
</configuration>

4、编写MyBatis工具类

• 查看帮助文档

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.IOException;
import java.io.InputStream;

public class MybatisUtils {

   private static SqlSessionFactory sqlSessionFactory;

   static {
       try {
           String resource = "mybatis-config.xml";
           InputStream inputStream = Resources.getResourceAsStream(resource);
           sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
      } catch (IOException e) {
           e.printStackTrace();
      }
  }

   //获取SqlSession连接
   public static SqlSession getSession(){
       return sqlSessionFactory.openSession();
  }

}

5、创建实体类

package com.feng.pojo;

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 + '\'' +
                '}';
    }
}

6、编写Mapper接口类

package com.feng.mapper;

import com.feng.pojo.User;

import java.util.List;

public interface UserMapper {
    List<User> getUserList();
}

7、编写Mapper.xml配置文件

• namespace 十分重要，不能写错！

<?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.feng.mapper.UserMapper">
    <select id="getUserList" resultType="com.feng.pojo.User">
      select * from User
  </select>
</mapper>

8、编写测试类

• Junit 包测试

import com.feng.mapper.UserMapper;
import com.feng.pojo.User;
import com.feng.utils.MyBatisUtil;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class MyTest {
    @Test
    public  void  testgetUserList()
    {
        SqlSession sqlSession = MyBatisUtil.getSession();
        //方法一
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        List<User> userList = userMapper.getUserList();
        for (User user : userList) {
            System.out.println(user);
        }

        //方法二
        List<User> userList1=sqlSession.selectList("com.feng.mapper.UserMapper.getUserList");
        for (User user : userList1) {
            System.out.println(user);
        }
        sqlSession.close();
    }
}

9、运行测试，成功的查询出来的我们的数据，ok！

10、项目目录

问题说明

可能出现问题说明：

1. Maven静态资源过滤问题

<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>

2. intellij idea连接mysql数据库时报错:Server returns invalid timezone. Go to ‘Advanced’ tab and set ‘serverTimezon’

解决方法: 在Advanced中将serverTimezone设置成Hongkong即可

此时再重新连接就可以了

3. 数据库路径

   jdbc:mysql://localhost:3306/mybatis?useSSL=true&useUnicode=true&characterEncoding=utf8

4. Idea的Maven导入包问题
   

   Idea的包导入都正常Buid的时候找不到jar包，如上图
   解决办法 File->settings->Buid……->Maven->Runner
   ->Delegate IDE build…… 勾选保存就好了