Mybatis之第一个程序

今天开始学习mybatis的知识，编写一个小程序，实现的是查询数据库。

1、首先导入依赖

    <!--导入依赖-->
    <dependencies>
        <!--mysql依赖-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.18</version>
        </dependency>
        <!-- mybatis依赖-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>
        <!-- junit依赖-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
    </dependencies>

2、编写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.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8&amp;serverTimezone=UTC"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/lizheng/dao/UserMapper.xml"/>
    </mappers>
</configuration>

3、编写工具类MybatisUtils，实现获得sqlSession 对象功能

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();
        }
        //既然有了 SqlSessionFactory，顾名思义，我们可以从中获得 SqlSession 的实例。SqlSession 提供了在数据库执行 SQL 命令所需的所有方法。
        // 你可以通过 SqlSession 实例来直接执行已映射的 SQL 语句。
    }
    public static SqlSession getSqlSession() {
        return sqlSessionFactory.openSession();
    }
}

4、编写实体类User，与数据库绑定

package com.lizheng.pojo;

/**
 * User实体类：数据库连接对象
 * @author 李争
 */
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 + '\'' +
                '}';
    }
}

5、创建UserMapper，操作数据库对象实体

import com.lizheng.pojo.User;

import java.util.List;

/**
 * 操作对象数据库的实体
 */
public interface UserMapper {
    //只写方法名，不写方法体，花括号也不行
    public List<User> getUserList();
}

 6、编写UserMapper.xml 执行SQL语句

<?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对应全路径下的mapper-->
<mapper namespace="com.lizheng.dao.UserMapper">
<!--  id 对应 重写方法名称-->
<!-- resultType 对应返回类型，list 只写范型-->
    <select id="getUserList" resultType="com.lizheng.pojo.User">
    select * from mybatis.user
  </select>
</mapper>

7、编写测试类UserMapperTest

import java.util.List;

//测试
public class UserMapperTest {

    @Test
    public void test(){
        //第一步：获取sqlsession对象
        SqlSession session = MybatisUtils.getSqlSession();
        //执行SQL语句
        UserMapper mapper = session.getMapper(UserMapper.class);
        List<User> userList = mapper.getUserList();
        for (User user : userList) {
            System.out.println(user);
        }
        //关闭sqlSession
        session.close();

    }
}

8、运行结果

注意点：

1、 mybatis-config.xml中要又mapper标签，每一个mapper绑定一个mapper.xml

2、pom.xml文件中设置资源过滤，防止出现资源导不出的问题

3、mapper.xml中namespace、id等要编写正确

 

 

 

 

 

 

 

本文地址：https://blog.csdn.net/qq_38723455/article/details/112212119