Mybatis基于注解开启使用二级缓存

　　关于Mybatis的一级缓存和二级缓存的概念以及理解可以参照前面文章的介绍。前文连接：https://www.cnblogs.com/hopeofthevillage/p/11427438.html，上文中二级缓存使用的是xml方式的实现，本文主要是补充一下Mybatis中基于注解的二级缓存的开启使用方法。

　　1.在Mybatis的配置文件中开启二级缓存

<?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>
        <!--开启全局的懒加载-->
        <setting name="lazyLoadingEnabled" value="true"/>
        <!--&lt;!&ndash;关闭立即加载，其实不用配置，默认为false&ndash;&gt;-->
        <!--<setting name="aggressiveLazyLoading" value="false"/>-->
        <!--开启Mybatis的sql执行相关信息打印-->
        <setting name="logImpl" value="STDOUT_LOGGING" />
        <!--默认是开启的，为了加强记忆，还是手动加上这个配置-->
        <setting name="cacheEnabled" value="true"/>
    </settings>
    <typeAliases>
        <typeAlias type="com.example.domain.User" alias="user"/>
        <package name="com.example.domain"/>
    </typeAliases>
    <environments default="test">
        <environment id="test">
            <!--配置事务-->
            <transactionManager type="jdbc"></transactionManager>
            <!--配置连接池-->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/test1"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <package name="com.example.dao"/>
    </mappers>
</configuration>

　　开启缓存 <setting name="cacheEnabled" value="true"/>，为了查看Mybatis中查询的日志，添加 <setting name="logImpl" value="STDOUT_LOGGING" />开启日志的配置。

　　2.领域类以及Dao

public class User implements Serializable{
    private Integer userId;
    private String userName;
    private Date userBirthday;
    private String userSex;
    private String userAddress;
    private List<Account> accounts;
   省略get和set方法......
}

import com.example.domain.User;
import org.apache.ibatis.annotations.*;
import org.apache.ibatis.mapping.FetchType;

import java.util.List;
@CacheNamespace(blocking = true)
public interface UserDao {
    /**
     * 查找所有用户
     * @return
     */
    @Select("select * from User")
    @Results(id = "userMap",value = {@Result(id = true,column = "id",property = "userId"),
            @Result(column = "username",property = "userName"),
            @Result(column = "birthday",property = "userBirthday"),
            @Result(column = "sex",property = "userSex"),
            @Result(column = "address",property = "userAddress"),
            @Result(column = "id",property = "accounts",many = @Many(select = "com.example.dao.AccountDao.findAccountByUid",fetchType = FetchType.LAZY))
    })
    List<User> findAll();

    /**
     * 保存用户
     * @param user
     */
    @Insert("insert into user(username,birthday,sex,address) values(#{username},#{birthday},#{sex},#{address})")
    void saveUser(User user);

    /**
     * 更新用户
     * @param user
     */
    @Update("update user set username=#{username},birthday=#{birthday},sex=#{sex},address=#{address} where id=#{id}")
    void updateUser(User user);

    /**
     * 删除用户
     * @param id
     */
    @Delete("delete from user where id=#{id}")
    void  deleteUser(Integer id);

    /**
     * 查询用户根据ID
     * @param id
     * @return
     */
    @Select("select * from user where id=#{id}")
    @ResultMap(value = {"userMap"})
    User findById(Integer id);

    /**
     * 根据用户名称查询用户
     * @param name
     * @return
     */
//    @Select("select * from user where username like #{name}")
    @Select("select * from user where username like '%${value}%'")
    List<User> findByUserName(String name);

    /**
     * 查询用户数量
     * @return
     */
    @Select("select count(*) from user")
    int findTotalUser();
}

　　3.在对应的Dao类上面增加注释以开启二级缓存　

　　@CacheNamespace(blocking = true)

　　4.测试

public class UserCacheTest {

    private InputStream in;
    private SqlSessionFactory sqlSessionFactory;

    @Before
    public void init()throws Exception{
        in = Resources.getResourceAsStream("SqlMapConfig.xml");
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);

    }
    @After
    public void destory()throws Exception{
        in.close();
    }
    @Test
    public void testFindById(){
        //第一查询
        SqlSession sqlSession1 = sqlSessionFactory.openSession();
        UserDao userDao1 = sqlSession1.getMapper(UserDao.class);
        User user1 = userDao1.findById(41);
        System.out.println(user1);
        //关闭一级缓存
        sqlSession1.close();
        //第二次查询
        SqlSession sqlSession2 = sqlSessionFactory.openSession();
        UserDao userDao2 = sqlSession2.getMapper(UserDao.class);
        User user2 = userDao2.findById(41);
        System.out.println(user2);
        sqlSession1.close();

        System.out.println(user1 == user2);
    }

}

（1）未开启二级缓存时

（2）开启二级缓存时