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Mybatis初体验

news 来源：原创 2024/4/25 20:34:49

MyBatis 是支持普通 SQL查询，存储过程和高级映射的优秀持久层框架。MyBatis 消除了几乎所有的JDBC代码和参数的手工设置以及结果集的检索。MyBatis 使用简单的 XML或注解用于配置和原始映射，将接口和 Java 的POJOs（Plain Old Java Objects，普通的 Java对象）映射成数据库中的记录。

以前都是用Hibernate比较多，项目中使用到的Mybatis封装的Dao也是别人封装好的。今天第一次看Mybatis文档，写一个简单的demo加深印象。

Mybatis入门

开发环境配置

新建一个maven项目：

加入mysql-connector-java和mybatis，还有Lombok（Lombok不是必须的）的依赖:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.fengyuan</groupId>
    <artifactId>mybatis-demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>

    <dependencies>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.14.4</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.38</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.2.8</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

建表

在mysql中新建数据库mybatisdemo，并创建student表:

表中有两条记录：

创建实体类

创建表对应的Model，Student类:

package com.fengyuan.domain;

import lombok.Data;

public @Data class Student {
    private int id;
    private String name;
    private int age;
}

添加配置文件

在项目中新建mybatis文件夹，在其中添加Mybatis的配置文件mybatis-conf.xml，在其中配置数据源。

<?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>
    <typeAliases>
        <typeAlias alias="Student" type="com.fengyuan.domain.Student" />
    </typeAliases>
    
    <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/mybatisdemo" />
                <property name="username" value="root" />
                <property name="password" value="123456" />
            </dataSource>
        </environment>
    </environments>
</configuration>

其中，<typeAliases>标签内指定的是你定义的实体类的别名，方便之后使用。

定义映射文件

在mybatis文件夹底下新建一个mapper文件夹，存放映射文件，在其中新建student表对应的映射文件studentMapper.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">
<mapper namespace="com.fengyuan.domain.StudentMapper">
    <select id="getStudentById" parameterType="int" resultType="Student">
        select * from student where id=#{id}
    </select>
</mapper>

namespace是唯一的，namespace有点像包名+类名，id像是方法名。parameterType是方法的参数类型，resultType中的"Student"就是前面定义的别名，是方法的返回类型。
定义完映射文件，将其注册到配置文件中：

<?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>
    <typeAliases>
        <typeAlias alias="Student" type="com.fengyuan.domain.Student" />
    </typeAliases>
    
    <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/mybatisdemo" />
                <property name="username" value="root" />
                <property name="password" value="123456" />
            </dataSource>
        </environment>
    </environments>

    <!--注册映射文件-->
    <mappers>
        <mapper resource="mybatis/mapper/studentMapper.xml" />
    </mappers>
</configuration>

测试

完成以上步骤，就可以开始测试了。
测试类：

package com.fengyuan.client;

import java.io.IOException;
import java.io.Reader;

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 com.fengyuan.domain.Student;

public class Main {
    public static void main(String[] args) {
        Reader reader = null;
        try {
            // 加载配置文件
            reader = Resources.getResourceAsReader("mybatis/mybatis-conf.xml");
        } catch (IOException e) {
            e.printStackTrace();
        }
        // 构建SqlSession工厂，并从工厂里打开一个SqlSession
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        
        try {
             // 找到对应的sql
            String statement = "com.fengyuan.domain.StudentMapper.getStudentById";
            // 传入参数id=1，执行sql，返回查询结果
            Student student = sqlSession.selectOne(statement, 1);
            System.out.println(student);
        } finally {
            sqlSession.close();
        }
    }
}

执行结果：

Student(id=1, name=Can Liu, age=40)

表中id为1的记录已经取出来了。

项目结构：

另一种映射方式

前面的这种映射方式，虽然可以用，但是要用字符串来找对应的sql很不方便，还有可能出错。mybatis提供了注解的方式，更简单也更直观。

定义接口

在项目中创建一个Dao接口StudentDao.java

package com.fengyuan.dao;

import org.apache.ibatis.annotations.Select;

import com.fengyuan.domain.Student;

public interface StudentDao {
    @Select("select * from student where id = #{id}")
    public Student getStudentById(int id);
}

把刚才写在映射文件中的sql语句写在@Select注解中即可，这样一来映射文件studentMappper.xml就不用了。

当然，如果要用xml来映射也是可以的，接口中只写方法，不要加注解。此时要求namespace必须与对应的接口全类名一致，id必须与对应接口的某个对应的方法名一致，如下：

<?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.fengyuan.dao.StudentDao">
    <select id="getStudentById" parameterType="int" resultType="Student">
        select * from student where id=#{id}
    </select>
</mapper>

注册接口

<?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>
    <!-- 别名 -->
    <typeAliases>
        <typeAlias alias="Student" type="com.fengyuan.domain.Student" />
    </typeAliases>
    
    <!-- 数据源 -->
    <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/mybatisdemo" />
                <property name="username" value="root" />
                <property name="password" value="123456" />
            </dataSource>
        </environment>
    </environments>

    <!-- 注册映射文件 -->
    <!-- <mappers>
        <mapper resource="mybatis/mapper/studentMapper.xml" />
    </mappers> -->
    
    <!-- 注册接口 -->
    <mappers>
        <mapper class="com.fengyuan.dao.StudentDao" />
    </mappers>
    
</configuration>

测试

package com.fengyuan.client;

import java.io.IOException;
import java.io.Reader;

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 com.fengyuan.dao.StudentDao;
import com.fengyuan.domain.Student;

public class Main {
    public static void main(String[] args) {
        Reader reader = null;
        try {
            // 加载配置文件
            reader = Resources.getResourceAsReader("mybatis/mybatis-conf.xml");
        } catch (IOException e) {
            e.printStackTrace();
        }
        // 构建SqlSession工厂，并从工厂里打开一个SqlSession
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        // 如果配置文件中没有注册接口，可以在代码里注册
        //sqlSession.getConfiguration().addMapper(StudentDao.class);
        
        try {
            // 获取映射类
            StudentDao studentDao = sqlSession.getMapper(StudentDao.class);
            // 直接调用接口的方法，传入参数id=1，返回Student对象
            Student student = studentDao.getStudentById(1);
            System.out.println(student);
        } finally {
            sqlSession.close();
        }
    }
}

如代码中的注释，除了在配置文件中注册接口，也可以在代码中用
sqlSession.getConfiguration().addMapper(StudentDao.class);来注册。
然后就可以直接调用接口的方法来执行对应的sql语句，比第一种方式要直观、而且“面向对象”了很多。

此时的项目结构：

CURD

除了前面演示的select语句，这边补充一下其他的示例。

使用注解映射

在接口studentDao.java中定义相应的方法，并在注解中写上对应的sql：

package com.fengyuan.dao;

import java.util.List;

import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;

import com.fengyuan.domain.Student;

public interface StudentDao {
    @Select("select * from student where id= #{id}")
    public Student getStudentById(int id);
    
    @Insert("insert into student(name, age) values(#{name}, #{age})")
    public int addStudent(Student student);
    
    @Delete("delete from student where name = #{name}")
    public int removeStudentByName(String name);
    
    @Update("update student set age = #{age} where id = #{id}")
    public int updateStudent(Student student);
    
    @Select("select * from student")
    public List<Student> listAllStudents();
}

使用XML文件映射

如果是用XML文件，接口中只要定义好方法：

package com.fengyuan.dao;

import java.util.List;

import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;

import com.fengyuan.domain.Student;

public interface StudentDao {
    public Student getStudentById(int id);
    
    public int addStudent(Student student);
    
    public int removeStudentByName(String name);
    
    public int updateStudent(Student student);
    
    public List<Student> listAllStudents();
}

然后，在XML文件中，定义好对应的sql：

<?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.fengyuan.dao.StudentDao">
    <select id="getStudentById" parameterType="int" resultType="Student">
        select * from student where id=#{id}
    </select>
    
    <insert id="addStudent" parameterType="Student">
        insert into student(name, age) values(#{name}, #{age})
    </insert>
    
    <delete id="removeStudentByName" parameterType="String">
        delete from student where name = #{name}
    </delete>
    
    <update id="updateStudent" parameterType="Student">
        update student set age = #{age} where id = #{id}
    </update>
    
    <select id="listAllStudents" resultType="Student">
        select * from student
    </select>
</mapper>

注意namespace与id要与接口中一一对应。

注册到配置文件中

<mappers>
    <mapper class="com.fengyuan.dao.StudentDao" />
</mappers>

或者

<mappers>
    <mapper resource="mybatis/mapper/studentMapper.xml" />
</mappers>

测试

package com.fengyuan.client;

import java.io.Reader;
import java.util.List;

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 com.fengyuan.dao.StudentDao;
import com.fengyuan.domain.Student;

public class Main {
    private static Reader reader;
    private static SqlSessionFactory sqlSessionFactory;
    
    static {
        try {
            reader = Resources.getResourceAsReader("mybatis/mybatis-conf.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    
    /**
     * 获取sqlSession
     * @return
     */
    public static SqlSession getSqlSession() {
        return sqlSessionFactory.openSession();
    }
    
    /**
     * 查询
     */
    public static void testQuery() {
        SqlSession sqlSession = getSqlSession();
        try {
            // 获取映射类
            StudentDao studentDao = sqlSession.getMapper(StudentDao.class);
            
            // 根据id返回Student对象
            Student student = studentDao.getStudentById(1);
            System.out.println(student);
            
        } finally {
            sqlSession.close();
        }
    }
    
    /**
     * 新增
     */
    public static void testInsert() {
        SqlSession sqlSession = getSqlSession();
        try {
            // 获取映射类
            StudentDao studentDao = sqlSession.getMapper(StudentDao.class);
            
            // 新建一个student对象
            Student student = new Student();
            student.setName("Aaron");
            student.setAge(24);
            
            // 插入到表中
            studentDao.addStudent(student);
            // 提交事务
            sqlSession.commit();
        } finally {
            sqlSession.close();
        }
    }
    
    /**
     * 更新
     */
    public static void testUpdate() {
        SqlSession sqlSession = getSqlSession();
        try {
            // 获取映射类
            StudentDao studentDao = sqlSession.getMapper(StudentDao.class);
            
            // 取出student记录，修改年龄，再更新到数据库
            Student student = studentDao.getStudentById(2);
            student.setAge(44);
            studentDao.updateStudent(student);
            
            // 提交事务
            sqlSession.commit();
        } finally {
            sqlSession.close();
        }
    }
    
    /**
     * 删除
     */
    public static void testRemove() {
        SqlSession sqlSession = getSqlSession();
        try {
            // 获取映射类
            StudentDao studentDao = sqlSession.getMapper(StudentDao.class);
            
            studentDao.removeStudentByName("cly");
            
            // 提交事务
            sqlSession.commit();
        } finally {
            sqlSession.close();
        }
    }
    
    /**
     * 以List返回student表中所有记录
     */
    public static void testGetAll() {
        SqlSession sqlSession = getSqlSession();
        try {
            // 获取映射类
            StudentDao studentDao = sqlSession.getMapper(StudentDao.class);
            
            List<Student> students = studentDao.listAllStudents();
            System.out.println(students);
            
            // 提交事务
            sqlSession.commit();
        } finally {
            sqlSession.close();
        }
    }
    
    
    public static void main(String[] args) {
        
    }
}

Mybatis-Generator

手动书写Mapping映射文件不仅繁琐而且容易出错，通过Mybatis-Generator，可以帮我们自动生成相关的文件。以下内容是从这篇博客中学习的，感谢博主。

准备

建表
这边我们还是用前面的student表来作为示例。
mybatis-generator-core包
我这边用的是mybatis-generator-core-1.3.2.jar。
数据库驱动
同样，数据库用的是mysql，所以用了mysql-connector-java-5.1.25.jar。
配置文件
generatorConfig.xml:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE generatorConfiguration
  PUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN"
  "http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd">
<generatorConfiguration>
    <!--数据库驱动-->
    <classPathEntry    location="mysql-connector-java-5.1.25.jar"/>
    <context id="DB2Tables" targetRuntime="MyBatis3">
        <commentGenerator>
            <property name="suppressDate" value="true"/>
            <property name="suppressAllComments" value="true"/>
        </commentGenerator>
        <!--数据库链接地址账号密码-->
        <jdbcConnection driverClass="com.mysql.jdbc.Driver" connectionURL="jdbc:mysql://localhost:3306/mybatisdemo" userId="root" password="123456">
        </jdbcConnection>
        <javaTypeResolver>
            <property name="forceBigDecimals" value="false"/>
        </javaTypeResolver>
        <!--生成Model类存放位置-->
        <javaModelGenerator targetPackage="com.fengyuan.model" targetProject="src/main/java">
            <property name="enableSubPackages" value="true"/>
            <property name="trimStrings" value="true"/>
        </javaModelGenerator>
        <!--生成映射文件存放位置-->
        <sqlMapGenerator targetPackage="com.fengyuan.mapping" targetProject="src/main/java">
            <property name="enableSubPackages" value="true"/>
        </sqlMapGenerator>
        <!--生成Dao类存放位置-->
        <javaClientGenerator type="XMLMAPPER" targetPackage="com.fengyuan.dao" targetProject="src/main/java">
            <property name="enableSubPackages" value="true"/>
        </javaClientGenerator>
        <!--生成对应表及类名-->
        <table tableName="student" domainObjectName="Student" enableCountByExample="false" enableUpdateByExample="false" enableDeleteByExample="false" enableSelectByExample="false" selectByExampleQueryId="false"></table>
    </context>
</generatorConfiguration>

执行

在命令行执行命令：

java -jar mybatis-generator-core-1.3.2.jar -configfile generatorConfig.xml -overwrite

输出Mybatis Generator finished successfully.，表示执行成功，在指定的路径生成了相应文件。如果有问题会输出相应的提示。

结果

根据配置，我们生成了三个文件。

在src/main/java中com.fengyuan.model中生成了Student.java:

package com.fengyuan.model;

public class Student {
    private Integer id;

    private String name;

    private Integer age;

    public Integer getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name == null ? null : name.trim();
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }
}

在src/main/java中com.fengyuan.mapping中生成了StudentMapper.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" >
<mapper namespace="com.fengyuan.dao.StudentMapper" >
  <resultMap id="BaseResultMap" type="com.fengyuan.model.Student" >
<id column="id" property="id" jdbcType="INTEGER" />
<result column="name" property="name" jdbcType="VARCHAR" />
<result column="age" property="age" jdbcType="INTEGER" />
  </resultMap>
  <sql id="Base_Column_List" >
id, name, age
  </sql>
  <select id="selectByPrimaryKey" resultMap="BaseResultMap" parameterType="java.lang.Integer" >
select 
<include refid="Base_Column_List" />
from student
where id = #{id,jdbcType=INTEGER}
  </select>
  <delete id="deleteByPrimaryKey" parameterType="java.lang.Integer" >
delete from student
where id = #{id,jdbcType=INTEGER}
  </delete>
  <insert id="insert" parameterType="com.fengyuan.model.Student" >
insert into student (id, name, age
  )
values (#{id,jdbcType=INTEGER}, #{name,jdbcType=VARCHAR}, #{age,jdbcType=INTEGER}
  )
  </insert>
  <insert id="insertSelective" parameterType="com.fengyuan.model.Student" >
insert into student
<trim prefix="(" suffix=")" suffixOverrides="," >
  <if test="id != null" >
    id,
  </if>
  <if test="name != null" >
    name,
  </if>
  <if test="age != null" >
    age,
  </if>
</trim>
<trim prefix="values (" suffix=")" suffixOverrides="," >
  <if test="id != null" >
    #{id,jdbcType=INTEGER},
  </if>
  <if test="name != null" >
    #{name,jdbcType=VARCHAR},
  </if>
  <if test="age != null" >
    #{age,jdbcType=INTEGER},
  </if>
</trim>
  </insert>
  <update id="updateByPrimaryKeySelective" parameterType="com.fengyuan.model.Student" >
update student
<set >
  <if test="name != null" >
    name = #{name,jdbcType=VARCHAR},
  </if>
  <if test="age != null" >
    age = #{age,jdbcType=INTEGER},
  </if>
</set>
where id = #{id,jdbcType=INTEGER}
  </update>
  <update id="updateByPrimaryKey" parameterType="com.fengyuan.model.Student" >
update student
set name = #{name,jdbcType=VARCHAR},
  age = #{age,jdbcType=INTEGER}
where id = #{id,jdbcType=INTEGER}
  </update>
</mapper>

在src/main/java中com.fengyuan.dao中生成了StudentMapper.java:

package com.fengyuan.dao;

import com.fengyuan.model.Student;

public interface StudentMapper {
    int deleteByPrimaryKey(Integer id);

    int insert(Student record);

    int insertSelective(Student record);

    Student selectByPrimaryKey(Integer id);

    int updateByPrimaryKeySelective(Student record);

    int updateByPrimaryKey(Student record);
}

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