使用Mybatis对数据库进行单表操作的方法

<&#63;xml version="1.0" encoding="UTF-8" &#63;>
<!DOCTYPE configuration
    PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
  <environments default="e1">
    <environment id="e1">
      <transactionManager type="JDBC"></transactionManager>
      <dataSource type="POOLED">
        <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3306/bank&#63;serverTimezone=CST"/>
        <property name="username" value="root"/>
        <property name="password" value="123456"/>
      </dataSource>
    </environment>
    <environment id="e2">
      <transactionManager type=""></transactionManager>
      <dataSource type=""></dataSource>
    </environment>
  </environments>
  <mappers>
    <mapper resource="mapper/UserMapper.xml"></mapper>
  </mappers>
</configuration>

<&#63;xml version="1.0" encoding="UTF-8" &#63;>
<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="dao.UserDao">
  <insert id="insert">
    INSERT ATM VALUES(#{account}, #{password}, #{balance})
  </insert>
  <update id="update">
    update atm set account=#{account},password=#{password},balance=#{balance} where account=#{account};
  </update>
  <delete id="delete">
    DELETE FROM ATM WHERE account=#{account};
  </delete>

  <select id="selectAll" resultType="domain.User">
    SELECT *FROM atm;
  </select>

  <select id="getTotalCount" resultType="integer">
    SELECT COUNT(*) FROM atm;
  </select>
  <select id="gettotal" resultType="hashmap">
    select count(*),max(balance) from atm;
  </select>


  <select id="selectAllByAcc" resultType="domain.User">
    SELECT *FROM atm order by ${flag} ${order};
  </select>
</mapper>

public class UserDao {

  //增加一条记录，user对象是我创建的实体类
    //mapper.xml文件的sql语句如下：
    //update atm set account=#{account},password=#{password},balance=#{balance} where account=#{account};
    //#{key}中的key要和实体类user的属性名一致
    //如果传递的是基本数据类型或者String，且#{key}只有一个，那么名字可以不一致
    //如果传入的是map集合，#{key}中的key要和map集合里的key一致
  public void insert(User user){
    //MYBATIS操作流程
    //获取工厂Builder对象
    SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
    //获取configuration.xml配置文件的输入流
    InputStream is = Thread.currentThread().getContextClassLoader().getResourceAsStream("configuration.xml");
    //builder根据is获取SqlSessionFactory工厂对象
    SqlSessionFactory factory = builder.build(is);
    //获取SqlSession对象
    SqlSession sqlSession = factory.openSession();
    //执行sql语句操作
      //insert是在mapper.xml下，insert标签的id名
      //user是我要插入的数据（动态操作），替换掉sql语句的#{}
    sqlSession.insert("insert", user);

    sqlSession.commit();
  }

  //改：修改记录，user是要修改的数据
    //mapper.xml文件的sql语句如下：
    //update atm set account=#{account},password=#{password},balance=#{balance} where account=#{account};
  public void update(User user){
    //MYBATIS操作流程
    //获取工厂Builder对象
    SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
    //获取configuration.xml配置文件的输入流
    InputStream is = Thread.currentThread().getContextClassLoader().getResourceAsStream("configuration.xml");
    //builder根据is获取SqlSessionFactory工厂对象
    SqlSessionFactory factory = builder.build(is);
    //获取SqlSession对象
    SqlSession sqlSession = factory.openSession(true);
    //执行sql语句操作
    sqlSession.update("update",user);
  }
  
  //删除：根据account删除
  //mapper.xml的sql语句如下：
    // DELETE FROM ATM WHERE account=#{account};
  public void delete(String account){
    //MYBATIS操作流程
    //获取工厂Builder对象
    SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
    //获取configuration.xml配置文件的输入流
    InputStream is = Thread.currentThread().getContextClassLoader().getResourceAsStream("configuration.xml");
    //builder根据is获取SqlSessionFactory工厂对象
    SqlSessionFactory factory = builder.build(is);
    //获取SqlSession对象
    SqlSession sqlSession = factory.openSession(true);
    //执行sql语句操作
    sqlSession.update("delete",account);
  }
  
  
  //===============================查询====================================
  //查询：查找记录总条数以及balance的最大值
  //sql语句如下：select count(*),max(balance) from atm;
  //select标签上的resultType表示的是返回值，指的是一条记录的类型，最后包裹成list集合
    //我这里用的hashMap
  public List<Map<String, Object>> gettotal(){
    InputStream is = Thread.currentThread().getContextClassLoader().getResourceAsStream("configuration.xml");
    SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(is);
    SqlSession sqlSession = factory.openSession(true);
    return sqlSession.selectList("gettotal");
  }
  
  //查询：获取总记录数
  //sql语句： SELECT COUNT(*) FROM atm;
  //resultType类型：integer
  public Integer getTotalCount(){
    InputStream is = Thread.currentThread().getContextClassLoader().getResourceAsStream("configuration.xml");
    SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(is);
    SqlSession sqlSession = factory.openSession(true);
    return sqlSession.selectOne("getTotalCount");
  }
  
  //查询：获取表格的所有记录
  //sql语句：SELECT *FROM atm;
  //resultType类型：domain.User （如果是自己写的实体类，需要类名的具体路径，除非做了配置）
  public List<User> selectAll(){
    InputStream is = Thread.currentThread().getContextClassLoader().getResourceAsStream("configuration.xml");
    SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(is);
    SqlSession sqlSession = factory.openSession(true);
    return sqlSession.selectList("selectAll");
  }

  //查询：查询所有该表所有记录，并根据flag列进行order排序
      //flag不确定，order可能是升序也可能是降序(由调用这个方法的用户决定)
  //sql语句： SELECT *FROM atm order by ${flag} ${order};
    //这里用的是${}而不是#{}
    //#{}和${}的区别：
    //#{}:当我们的动态参数是用作条件的时候我们用这个，比如说account=#{key}
    //${}：当我们的动态参数表示的是一个普通字符串，比如说表名、列名或者关键字我们用这个
  //resultType：domain.User(domain包下的User类）
  public List<User> selectAllByAcc(String flag, String order){
    InputStream is = Thread.currentThread().getContextClassLoader().getResourceAsStream("configuration.xml");
    SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(is);
    SqlSession sqlSession = factory.openSession(true);
    Map<String, Object> map = new HashMap<>();
    map.put("flag", flag);
    map.put("order", order);
    return sqlSession.selectList("selectAllByAcc", map);
  }
}