2.mybatis入门实例 连接数据库进行查询

1.新建项目，添加mybatis和mysql的jar包

2.在mysql中新建表user[id,name,age]

CREATE TABLE `users` (
   `id` int(11) NOT NULL auto_increment,
   `NAME` varchar(50) default NULL,
   `age` int(11) default NULL,
   PRIMARY KEY  (`id`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8

3.新建User类，与db的表对应

public class User {
 
    public User() {
    }
    public User(int id, String name, int age) {
        super();
        this.id = id;
        this.name = name;
        this.age = age;
    }
    private int id;
    private String name;
    private int age;
    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 int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    @Override
    public String toString() {
        return "User [id=" + id + ", name=" + name + ", age=" + age + "]";
    }
 
}

4.在src目录下面新建mybatis的配置文件conf.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>
    <!--
        development：开发模式
        work：工作模式
     -->
    <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?autoReconnect=true&amp;useUnicode=true&amp;characterEncoding=utf8" />
                <property name="username" value="root" />
                <property name="password" value="root" />
            </dataSource>
        </environment>
    </environments>
 
</configuration>

5.新建userMapper.xml，添加数据库操作语句

<?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">
<!--
    为了使用mapper的标签，在此要在Window-Preference-Xml Catalog中配置mybatis-3-mapper.dtd，
    key=-//mybatis.org//DTD Mapper 3.0//EN
 -->
<mapper namespace="com.mlxs.mybatis.test.userMapper">
 
    <select id="getUser" parameterType="int" resultType="com.mlxs.mybatis.test1.User">
        select * from users where id=#{id}
    </select>
 
    <!-- 添加，参数是一个user对象 -->
    <insert id="addUser" parameterType="com.mlxs.mybatis.test1.User">
        insert into users(name,age) values(#{name},#{age})
    </insert>
    <!-- 更新，参数是一个user对象 -->
    <insert id="updateUser" parameterType="com.mlxs.mybatis.test1.User">
        update users set name=#{name}, age=#{age} where id=#{id}
    </insert>
    <!-- 添加，参数是一个user对象 -->
    <insert id="deleteUser" parameterType="int">
        delete from users where id=#{id}
    </insert>
 
    <!-- 返回一个list，resultType="包名+类名"：必须在类中有个无参的构造函数，不然会报错：
            java.lang.NoSuchMethodException: com.mlxs.mybatis.test1.User.<init>()
            Caused by: java.lang.NoSuchMethodException: com.mlxs.mybatis.test1.User.<init>()
            at java.lang.Class.getConstructor0(Class.java:2706)
            at java.lang.Class.getDeclaredConstructor(Class.java:1985)
            at org.apache.ibatis.reflection.factory.DefaultObjectFactory.instantiateClass(DefaultObjectFactory.java:57)
    -->
    <select id="selectAllUsers" resultType="com.mlxs.mybatis.test1.User">
        select * from users
    </select>
</mapper>

将mapper配置文件添加到mybatis的配置文件conf.xml的mappers标签中：

<!-- 在conf.xml文件中注册Mapper.xml文件和Mapper类 -->
    <mappers>
        <mapper resource="com/mlxs/mybatis/test1/userMapper.xml" />
 
    </mappers>

6.添加测试类，获取一个user的信息

import java.io.IOException;
import java.io.InputStream;
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;
 
public class _Test1SelectOne {
    public static void main(String[] args) throws IOException {
        //加载mybatis的xml文件（同时加载加载关联的映射文件）
        //1.使用类加载器加载mybatis的配置文件
//        InputStream config = _Test1SelectOne.class.getClassLoader().getResourceAsStream("conf.xml");
        //2.使用mybatis的Resources类加载
        Reader config = Resources.getResourceAsReader("conf.xml");
        //创建sqlSessionFactory
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(config);
        //创建sqlSession，执行mapper.xml中的sql语句
        SqlSession sqlSession = sessionFactory.openSession();
        //执行映射文件中的sql(namespace + select的id)
        String sql = "com.mlxs.mybatis.test.userMapper.getUser";
        User user = sqlSession.selectOne(sql, "1");//查询id=1
        //关闭session
        sqlSession.close();
        System.out.println(user);
    }
}

7.结果

User [id=1, name=Tom, age=12]

8.测试 增删改查，导入junit包，添加测试类

import java.util.List;
 
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.junit.Test;
 
import com.mlxs.mybatis.util.MyBatisUtil;
 
public class _Test2UserCrud {
 
    @Test
    public void addUser(){
        SqlSessionFactory sessionFactory = MyBatisUtil.getSessionFactory();
        SqlSession sqlSession = sessionFactory.openSession();
        String statement = "com.mlxs.mybatis.test.userMapper.addUser";
        int count = sqlSession.insert(statement, new User(0, "add1", 10));
        sqlSession.commit();
        sqlSession.close();
        System.out.println("add count:"+count);
    }
    @Test
    public void updateUser(){
        SqlSessionFactory sessionFactory = MyBatisUtil.getSessionFactory();
        SqlSession sqlSession = sessionFactory.openSession();
        String statement = "com.mlxs.mybatis.test.userMapper.updateUser";
        int count = sqlSession.update(statement, new User(3, "update2", 100));
        sqlSession.commit();
        sqlSession.close();
        System.out.println("update count:"+count);
    }
    @Test
    public void delUser(){
        SqlSessionFactory sessionFactory = MyBatisUtil.getSessionFactory();
        boolean autoCommit = true;//自动提交，不需手动commit
        SqlSession sqlSession = sessionFactory.openSession(autoCommit);
        String statement = "com.mlxs.mybatis.test.userMapper.deleteUser";
        int count = sqlSession.delete(statement, 4);
        sqlSession.close();
        System.out.println("del count:"+count);
    }
    @Test
    public void selectAll(){
        SqlSessionFactory sessionFactory = MyBatisUtil.getSessionFactory();
        boolean autoCommit = true;//自动提交，不需手动commit
        SqlSession sqlSession = sessionFactory.openSession(autoCommit);
        String statement = "com.mlxs.mybatis.test.userMapper.selectAllUsers";
        List<User> userList = sqlSession.selectList(statement);
        sqlSession.close();
        System.out.println(userList);
    }
}