mybaits入门笔记

其他 2021-03-25 18:59:37 阅读次数: 0

MyBatis入门及使用

  • MyBatis 是一款优秀的持久层框架
  • MyBatis 支持定制化 SQL、存储过程以及高级映射。
  • MyBatis 避免了几乎所有的 JDBC 代码和手动设置参数以及获取结果集。
  • MyBatis 可以使用简单的 XML 或注解来配置和映射原生信息，将接口和 Java 的 POJOs(Plain Ordinary Java Object,普通的 Java对象)映射成数据库中的记录。

第一个Mybaits程序

思路：搭建环境->导入Mbaits–>编写代码–>测试

搭建数据库

CREATE DATABASE `Mybaits`
USE Mybaits
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,'张三','123456'),
(2,'李四','123456'),
(3,'王五','123456');

1.新建项目

1.1新建一个普通的maven项目

1.2.删除src目录

1.3.pom.xml导入maven依赖

 <!--导入依赖-->
    <dependencies>
        <!--数据库-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
    </dependencies>

2.创建一个模块(Module)

2.1编写mybaits的核心配置文件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">
<!--核心配置文件-->
<configuration>
    <environments default="development">
        <environment id="development">
            <!--事务管理-->
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybaits?characterEncoding=utf8&amp;useSSL=false&amp;serverTimezone=UTC"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
</configuration>

2.2编写mybaits工具类

package com.wu.utils;

public class MybatisUtils {
    
    
    private  static  SqlSessionFactory sqlSessionFactory = null;
    static{
    
    
        try {
    
    
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            // 使用Mybatis第一步，获取sqlSessionFactory
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
    
    
            e.printStackTrace();
        }
    }

    // 从 SqlSessionFactory 中获取 SqlSession
    public static SqlSession getSqlSession(){
    
    
        return sqlSessionFactory.openSession();
    }
}

2.3编写代码

  1. 实体类
package com.wu.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 String getName() {
    
    
        return name;
    }

    public String getPwd() {
    
    
        return pwd;
    }

    public void setId(int id) {
    
    
        this.id = id;
    }

    public void setName(String name) {
    
    
        this.name = name;
    }

    public void setPwd(String pwd) {
    
    
        this.pwd = pwd;
    }
}
  1. Dao接口(Mapper)
package com.wu.dao;

public interface UserDAO {
    
    
    List<User> getUserList();
}
  1. 接口实现类由UserDaoImpl转变为一个Mapper配置文件UserMapper.xml
<?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">
<!--命名空间绑定一个对应的Dao或Mapper接口-->
<mapper namespace="com.wu.dao.UserDAO">
    <!-- 查询   -->
    <select id="getUserList" resultType="com.wu.pojo.User">
        select * from mybaits.user
    </select>
</mapper>

3.测试

在test创建的包目录和main下的包目录是一样的

3.1junit测试

public class UserDAOTest {
    
    
    @Test
    public void test(){
    
    
        //第一步：获得 SqlSession对象
       SqlSession sqlSession =  MybatisUtils.getSqlSession();
       //方式一：getMapper
       UserDAO mapper = sqlSession.getMapper(UserDAO.class);

       List<User> userList = mapper.getUserList();
        for (User user:userList) {
    
    
            System.out.println(user.getName());
        }
        // 关闭连接
        sqlSession.close();
    }
}

3.2在mybatis-config.xml注册mapper文件

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

注意 maven约定大于配置，（默认是在resources目录下，但我定义在dao目录下）我们之后可以能遇到编写的配置文件无法被导出或者不生效的问题。解决方案如下（适用于所有maven项目）:

在pom.xml，添加bulid

    <build>
        <resources>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.xml</include>
                    <include>**/*.properties</include>
                </includes>
            </resource>

            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.xml</include>
                    <include>**/*.properties</include>
                </includes>
            </resource>
        </resources>
    </build>

CRUD

1.namespace

注意：命名空间中的包名要和接口中的包名一致

2.编写接口

public interface UserMapper {
    
    
    //查询全部用户
    List<User> getUserList();

    //根据id查询用户
    User getUserById(int id);

    // 插入用户
    int addUser(User user);

    // 修改用户
    int updateUser(User user);

    // 删除用户
    int deleteUser(int id);
}

3.编写UserMapper.xml

<!--命名空间绑定一个对应的Dao或Mapper接口-->
<mapper namespace="com.wu.dao.UserMapper">
    <!-- 查询-->
    <select id="getUserList" resultType="com.wu.pojo.User">
        select * from mybaits.user
    </select>

    <select id="getUserById" parameterType="int" resultType="com.wu.pojo.User">
        select * from mybaits.user where id = #{id};
    </select>

     <!--插入-->
    <insert id="addUser" parameterType="com.wu.pojo.User">
        insert into mybaits.user(id,name,pwd) values (#{id},#{name},#{pwd});
    </insert>

    <!-- 修改-->
    <update id="updateUser" parameterType="com.wu.pojo.User">
        update mybaits.user set name= #{name},pwd = #{pwd} where id = #{id};
    </update>

    <!--删除-->
    <delete id="deleteUser" parameterType="int">
        delete from mybaits.user where id = #{id};
    </delete>
</mapper>

4.进行测试

public class UserMapperTest {
    
    
    @Test
    public void test(){
    
    
        //第一步：获得 SqlSession对象
       SqlSession sqlSession =  MybatisUtils.getSqlSession();
       //方式一：getMapper
       UserMapper mapper = sqlSession.getMapper(UserMapper.class);

       List<User> userList = mapper.getUserList();
        for (User user:userList) {
    
    
            System.out.println(user.getName());
        }
        // 关闭连接
        sqlSession.close();
    }

    @Test
    public void getUserByIdTest(){
    
    
        SqlSession sqlSession =  MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        // 查询id为1的用户名
        User user = mapper.getUserById(1);
        System.out.println(user.getName());
        sqlSession.close();
    }

    //注意：增删改需要提交事务
    @Test
    public void addUserTest(){
    
    
        SqlSession sqlSession =  MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        // 插入id为4的用户，并查询
        mapper.addUser(new User(4, "赵六", "123456"));
        //注意：增删改需要提交事务
        sqlSession.commit();
        User user = mapper.getUserById(4);
        System.out.println(user.getName());
        sqlSession.close();
    }

@Test
    public void updateUserTest(){
    
    
        SqlSession sqlSession =  MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        // 修改4号用户的姓名为 赵liu 密码为13456
        mapper.updateUser(new User(4,"赵liu","123456"));
        sqlSession.commit();
        User user = mapper.getUserById(4);
        System.out.println(user.getName());
        sqlSession.close();
    }

    @Test
    public void deleteUserTest(){
    
    
        SqlSession sqlSession =  MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        // 删除4号用户的姓名
        mapper.deleteUser(4);
        sqlSession.commit();
        sqlSession.close();
    }
}

Map和模糊查询

Map

使用map比较灵活，可随意传递参数，假设实体类属性过多时，而开发人员并不想传递这么多参数，这时map就很有优势。

UserMapper.java

 int addUser2(Map<String,Object> map);

userMapper.xml

<!-- 此时values后面可以起任意的名字，只要和map里的key相同即可-->
<insert id="addUser2" parameterType="map">
        insert into mybaits.user(id,name,pwd) values (#{userId},#{userName},#{Password});
 </insert>

测试

    @Test
    public void addUser2Test(){
    
    
        SqlSession sqlSession =  MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        // 插入id为4的用户，并查询
        Map map = new HashMap<String,Object>();
        map.put("userId",1111);
        map.put("userName","赵六");
        map.put("Password","1223456");
        mapper.addUser2(map);
        //注意：增删改需要提交事务
        sqlSession.commit();
        sqlSession.close();
    }

可以看到map里的key要和userMapper.xml配置的值要相同。

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模糊查询

1.UserMapper.java

    //模糊查询
    List<User> getUserLike(String value);

2.userMapper.xml

    <select id="getUserLike" parameterType="string" resultType="com.wu.pojo.User">
        select * from mybaits.user where name like #{value};
    </select>

3.测试UserMapperTest.java


@Test
    public void getUserLikeTest(){
    
    
        SqlSession sqlSession =  MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
 //方式一:在参数里面添加通配符 % 或 _,%匹配多个任意字符，_匹配单个任意字符，方式二是在UserMapper.xml里的sql语句用字符串拼接使用通配符select * from mybaits.user where name like "%"#{value}"%";
        List<User> userList = mapper.getUserLike("%李%");

        for (User user:userList) {
    
    
            System.out.println(user.getName());
        }
        sqlSession.commit();
        sqlSession.close();
    }

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