SqlSession sqlSession = null;
    try {
      sqlSession = DBUtils.openSqlSession();
      UserMapper mapper = sqlSession.getMapper(UserMapper.class);
      //查询同一条数据时会缓存
      User user = mapper.getUser(1l);
      User user2 = mapper.getUser(1l);
      System.out.println(user.toString());
      System.out.println(user2.toString());
      sqlSession.commit();
    } catch (Exception e) {
      System.err.println(e.getMessage());
      sqlSession.rollback();
    } finally {
      if (sqlSession != null) {
        sqlSession.close();
      }
    }

<?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="org.sang.db.UserMapper">
  <cache/>
  <select id="getUser" resultType="org.sang.bean.User" parameterType="Long">
    select * from user where id = #{id}
  </select>
  <insert id="insertUser" parameterType="org.sang.bean.User">
    INSERT INTO user(username,password,address) VALUES (#{username},#{password},#{address})
  </insert>
  <delete id="deleteUser" parameterType="Long">
    DELETE FROM user where id=#{id}
  </delete>
  <select id="getAll" resultType="u">
    SELECT * from user
  </select>
</mapper>

public class User implements Serializable{
  private Long id;
  private String username;
  private String password;
  private String address;

  ...

}

SqlSession sqlSession = null;
    SqlSession sqlSession2 = null;
    try {
      sqlSession = DBUtils.openSqlSession();
      UserMapper mapper = sqlSession.getMapper(UserMapper.class);
      User user = mapper.getUser(1l);
      System.out.println(user.toString());
      sqlSession.commit();
      sqlSession2 = DBUtils.openSqlSession();
      UserMapper mapper2 = sqlSession2.getMapper(UserMapper.class);
      User user2 = mapper2.getUser(1l);
      System.out.println(user2.toString());
      sqlSession2.commit();
    } catch (Exception e) {
      System.err.println(e.getMessage());
      sqlSession.rollback();
      sqlSession2.rollback();
    } finally {
      if (sqlSession != null) {
        sqlSession.close();
      }
      if (sqlSession2 != null) {
        sqlSession2.close();
      }
    }