mybatis一级缓存在SSM项目中的范围问题

Question

mybatis的一级缓存是同一个sqlSession对象，但是在SSM整个中sqlSession对象属于自动生成，那么mybatis的一级缓存范围是多少

Answer 1

不知道你这个问题是否已经解决, 如果还没有解决的话:

• 你可以参考下这个问题的回答, 看看是否对你有帮助, 链接: https://ask.csdn.net/questions/7641654
• 这篇博客你也可以参考下：SSM基础-MyBatis缓存
• 这篇博客也不错, 你可以看下SSM基础-MyBatis缓存
• 除此之外, 这篇博客: SSM基础-MyBatis缓存中的 一级缓存 部分也许能够解决你的问题, 你可以仔细阅读以下内容或者直接跳转源博客中阅读:
  

  1.一级缓存也叫本地缓存:与数据库同一次会话期间查询到的数据会放入的本地缓存当中，如果以后需要获取相同的数据直接去缓存当中拿，没必要再去查询数据库。

  2.测试一级缓存

  创建maven项目，在src\main\resource目录下创建SqlMapConfig.xml文件，配置数据库信息

  <?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>
      <settings>
          <!--设置mybatis输出日志-->
          <!--logImpl：表示对日志的控制-->
          <!--STDOUT_LOGGING:将日志输出到控制台上-->
          <setting name="logImpl" value="STDOUT_LOGGING" />
  
      </settings>
      <environments default="mysql">
          <environment id="mysql">
              <!--配置事务的类型，使用本地事务策略-->
              <transactionManager type="JDBC"></transactionManager>
              <!--是否使用连接池 POOLED表示使用链接池，UNPOOLED表示不使用连接池-->
              <dataSource type="POOLED">
                  <property name="driver" value="com.mysql.jdbc.Driver"/>
                  <property name="url" value="jdbc:mysql://localhost:3306/mybatis_demo"/>
                  <property name="username" value="root"/>
                  <property name="password" value="20220101"/>
              </dataSource>
          </environment>
      </environments>
      <mappers>
          
      </mappers>
  </configuration>

  编写数据库中的user表

  create database mybatis_demo;
   
  use mybatis_demo;
   
  CREATE TABLE `user` (
  `id` int(11) NOT NULL auto_increment,
  `username` varchar(32) NOT NULL COMMENT '用户名称',
  `birthday` datetime default NULL COMMENT '生日',
  `sex` char(1) default NULL COMMENT '性别',
  `address` varchar(256) default NULL COMMENT '地址',
  PRIMARY KEY (`id`)
  ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
   
  insert into `user`(`id`,`username`,`birthday`,`sex`,`address`) 
  values (1,'老王','2018-02-27 17:47:08','男','北京'),
  (2,'熊大','2018-03-02 15:09:37','女','上海'),
  (3,'熊二','2018-03-04 11:34:34','女','深圳'),
  (4,'光头强','2018-03-04 12:04:06','男','广州');

  在src\main\java目录下创建com.qcby.entity包，在包下创建User类以及get,set,toString方法

  public class User {
      private Integer user_id;
      private String username;
      private Date birthday;
      private String sex;
      private String address;
      //...
  }

  在src\main\java目录下创建com.qcby.dao包，在包下创建UserDao接口

  public interface UserDao {
  
  }

  在src\main\resource目录下创建mapper文件夹，在文件夹里面创建UserMapper.xml文件

  <?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.qcby.dao.UserDao">
      <select id="findAll" resultType="com.qcby.entity.User">
          select * from user where id=1
      </select>
  </mapper>

  在UserDao中创建新方法

  public interface UserDao {
      public User findAll();
  }

  在SqlMapConfig.xml文件的mapper标签里添加下面内容

  <mapper resource="mapper/UserMapper.xml"></mapper>

  在src\test\java目录下创建UserTest测试类

  public class UserTest {
      private InputStream in = null;
      private SqlSession session = null;
      private UserDao mapper = null;
  
      @Test
      public void findAll() throws IOException {
          //加载主配置文件，目的是为了构建SqlSessionFactory对象
          in = Resources.getResourceAsStream("SqlMapConfig.xml");
          //创建SqlSessionFactory对象
          SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
          //通过SqlSessionFactory工厂对象创建SqlSesssion对象
          session = factory.openSession();
          //通过Session创建UserDao接口代理对象
          mapper = session.getMapper(UserDao.class);
  
          User user1 = mapper.findAll();
          System.out.println(user1.toString());
          
  
          User user2 = mapper.findAll();
          System.out.println(user2.toString());
  
          System.out.println(user1 == user2);
  
          //释放资源
          session.close();
          in.close();
      }
  }

  测试结果

  

   3.缓存失效的情况

  编写UserMapper.xml

  <select id="findID" parameterType="java.lang.Integer" resultType="com.qcby.entity.User">
          select * from user where id=#{id}
      </select>

  编写UserDao接口，添加新方法

  public interface UserDao {
      public User findID(Integer id);
  }

  • sqlSession不同

  public class UserTest {
      private InputStream in = null;
      private SqlSession session = null;
      private UserDao mapper = null;
      private SqlSession session2 = null;
      private UserDao mapper2 = null;
      @Test
      public void findAll1() throws IOException {
          in = Resources.getResourceAsStream("SqlMapConfig.xml");
          SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
          session = factory.openSession();
          session2 = factory.openSession();
  
          mapper = session.getMapper(UserDao.class);
          mapper2 = session2.getMapper(UserDao.class);
          User user1 = mapper.findID(1);
          System.out.println(user1.toString());
          User user2 = mapper2.findID(1);
          System.out.println(user2.toString());
          System.out.println(user1 == user2);
          //释放资源
          session.close();
          session2.close();
          in.close();
      }
  }

  

  • sqlSession相同，查询条件不同

  public void findAll1() throws IOException {
          in = Resources.getResourceAsStream("SqlMapConfig.xml");
          SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
          session = factory.openSession();
          mapper = session.getMapper(UserDao.class);
          User user1 = mapper.findID(1);
          System.out.println(user1.toString());
          User user2 = mapper.findID(2);
          System.out.println(user2.toString());
          System.out.println(user1 == user2);
          //释放资源
          session.close();
          in.close();
      }

  

  • sqlSession相同，两次查询之间执行了增删改操作！

  编写UserMapper.xml文件，添加以下删除语句

  <delete id="delete" parameterType="java.lang.Integer">
          delete from user where id=#{id}
      </delete>

  编写UserDao接口，新增delete方法

  public interface UserDao {
      //删除
      public int delete(Integer id);
  }

   编写UserTest

  public void findAll1() throws IOException {
          in = Resources.getResourceAsStream("SqlMapConfig.xml");
          SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
          session = factory.openSession();
          mapper = session.getMapper(UserDao.class);
          User user1 = mapper.findID(1);
          System.out.println(user1.toString());
          //删除操作
          mapper.delete(3);
          User user2 = mapper.findID(1);
          System.out.println(user2.toString());
          System.out.println(user1 == user2);
          //释放资源
          session.close();
          in.close();
      }

  

  • sqlSession相同，手动清除一级缓存

  public void findAll1() throws IOException {
          in = Resources.getResourceAsStream("SqlMapConfig.xml");
          SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
          session = factory.openSession();
          mapper = session.getMapper(UserDao.class);
          User user1 = mapper.findID(1);
          System.out.println(user1.toString());
          //清除缓存
          session.clearCache();
          User user2 = mapper.findID(1);
          System.out.println(user2.toString());
          System.out.println(user1 == user2);
          //释放资源
          session.close();
          in.close();
      }

  

如果你已经解决了该问题, 非常希望你能够分享一下解决方案, 写成博客, 将相关链接放在评论区, 以帮助更多的人 ^-^