MyBatis 实例

• MyBatis简介

MyBatis 是一款优秀的持久层框架，它支持自定义 SQL、存储过程以及高级映射。MyBatis 免除了几乎所有的 JDBC 代码以及设置参数和获取结果集的工作。MyBatis 可以通过简单的 XML 或注解来配置和映射原始类型、接口和 Java POJO（Plain Old Java Objects，普通老式 Java 对象）为数据库中的记录。

• 项目实例

1.创建一个普通的maven项目

2.在pom.xml中导入依赖

<!-- 导入依赖 -->
<dependencies>
    <!--mysql驱动-->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.47</version>
    </dependency>
    <!--mybatis-->
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.2</version>
    </dependency>
    <!--junit 这个使用来测试的 @Test 注解-->
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
    </dependency>
</dependencies>

注意在pom.xml配置如下，防止资源导入不成功问题

<!-- 在maven中，约定大于配置，在pom中添加此文件可以解决 -->
    <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>

在resources目录下编写MyBatis核心配置文件mybatis-config.xml,自定义填写数据库信息

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-config.dtd">
<!--这是数据库的配置文件，负责存储连接数据库的信息-->
<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/test?autoReconnect=true&amp;useUnicode=true&amp;characterEncoding=utf8&amp;serverTimezone=GMT%2B8"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
<!--这里注册Mapper信息-->
    <mappers>
        <mapper resource="com/mao/dao/UserDaoMapper.xml" />
    </mappers>
</configuration>

3.测试数据库建立表结构

CREATE DATABASE `mybatis`;
USE `mybatis`;
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
  `id` int(20) NOT NULL,
  `name` varchar(30) DEFAULT NULL,
  `password` varchar(30) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
insert  into `user`(`id`,`name`,`password`) values (1,'王二','123456'),(2,'张三','abcdef'),(3,'李四','987654');

4.创建如下的包结构

5.编写工具类utils下MybatisUtils

public class MybatisUtils {

    private static SqlSessionFactory sqlSessionFactory; //提升作用域
    //获取工厂，固定代码
    static {
        try {

            // 获取MyBatis核心配置文件mybatis-config.xml，连接数据库，（创建）映射到sqlSessionFactory.openSession()的SqlSession对象
            String resource="mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    //获取sqlSession
    //SqlSession完全包含了面向对象数据库执行SQL命令所需的方法
    public static SqlSession getSqlSession(){ return sqlSessionFactory.openSession();}
}

6.在pojo包下创建User实体类

package com.mao.pojo;

// 实体类User，对应User表

public class User {
    private int id;
    private String name;
    private String password;

    public User() {
    }

    public User(int id, String name, String password) {
        this.id = id;
        this.name = name;
        this.password = password;
    }

    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 getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}

7.在dao包下创建编写Mapper接口类UserDao.java,并创建Mapper.xml（可以理解为像UserDao接口的实现类的配置）

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

<?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：命名空间，绑定mapper/Dao接口-->
<mapper namespace="com.mao.dao.UserDao">
    <!--id:接口的方法，resultType：接口的返回值类型,test为数据库名称-->
    <select id="getUserList" resultType="com.mao.pojo.User">
        select * from test.user
    </select>
</mapper>

然后记得在MyBatis核心配置文件mybatis-config.xml中注册Mapper

<!--这里注册Mapper信息-->
<mappers>
	<mapper resource="com/mao/dao/UserDaoMapper.xml" />
</mappers>

8.测试

public class UserDaoTest {
    @Test
    public void test(){
        //获取SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        try{
            //获取mapper
            UserDao mapper = sqlSession.getMapper(UserDao.class);
            List<User> list = mapper.getUserList();
            for (User u:list){
                System.out.println(u);
            }
            //不推荐使用
//        List<User> list = sqlSession.selectList("com.qian.dao.UserDao.getUserList");
//        for (User user : list) {
//            System.out.println(user);
//        }
        }finally {
            //关闭SqlSession
            sqlSession.close();
        }
    }
}