<dependency>
  <groupId>org.mybatis</groupId>
  <artifactId>mybatis</artifactId>
  <version>x.x.x</version>
</dependency>

String resource = "org/mybatis/example/mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

<?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>
  <environments default="development">
    <environment id="development">
      <transactionManager type="JDBC"/>
      <dataSource type="POOLED">
        <property name="driver" value="${driver}"/>
        <property name="url" value="${url}"/>
        <property name="username" value="${username}"/>
        <property name="password" value="${password}"/>
      </dataSource>
    </environment>
  </environments>
  <mappers>
    <mapper resource="org/mybatis/example/BlogMapper.xml"/>
  </mappers>
</configuration>

try (SqlSession session = sqlSessionFactory.openSession()) {
  Blog blog = (Blog) session.selectOne("org.mybatis.example.BlogMapper.selectBlog", 101);
}

try (SqlSession session = sqlSessionFactory.openSession()) {
  BlogMapper mapper = session.getMapper(BlogMapper.class);
  Blog blog = mapper.selectBlog(101);
}

<?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.mybatis.example.BlogMapper">
  <select id="selectBlog" resultType="Blog">
    select * from Blog where id = #{id}
  </select>
</mapper>

Blog blog = (Blog) session.selectOne("org.mybatis.example.BlogMapper.selectBlog", 101);

BlogMapper mapper = session.getMapper(BlogMapper.class);
Blog blog = mapper.selectBlog(101);

<properties resource="org/mybatis/example/config.properties">
  <property name="username" value="dev_user"/>
  <property name="password" value="F2Fa3!33TYyg"/>
</properties>

<dataSource type="POOLED">
  <property name="driver" value="${driver}"/>
  <property name="url" value="${url}"/>
  <property name="username" value="${username}"/>
  <property name="password" value="${password}"/>
</dataSource>

<typeAliases>
  <typeAlias alias="Author" type="domain.blog.Author"/>
  <typeAlias alias="Blog" type="domain.blog.Blog"/>
  <typeAlias alias="Comment" type="domain.blog.Comment"/>
  <typeAlias alias="Post" type="domain.blog.Post"/>
  <typeAlias alias="Section" type="domain.blog.Section"/>
  <typeAlias alias="Tag" type="domain.blog.Tag"/>
</typeAliases>

<typeAliases>
  <package name="domain.blog"/>
</typeAliases>

@Alias("author")
public class Author {
    ...
}

mybatis-plus:
  type-aliases-package: fun.maluyao.pojo #别名扫描包
  mapper-locations: "classpath*:/mapper/**/*.xml" #Mapper.xml文件地址，默认值 configuration:
  configuration:
    map-underscore-to-camel-case: true #是否开启下划线和驼峰的映射
    cache-enabled: false #是否开启二级缓存
  global-config:
    db-config:
      id-type: assign_id #id为雪花算法生成
      update-strategy: not_null #更新策略：只更新非空字段

new QueryWrapper<Main>();
new UpdateWrapper<Main>();
new LambdaQueryWrapper<>();
new LambdaUpdateWrapper<>();

List<Long> ids = List.of(1L,2L, 4L):
int amount=200;
//1.构建条件
LambdaQuerywrapper<User> wrapper=new LambdaQuerywrapper<User>().in(User::getId，ids); //2.自定义SQL方法调用
userMapper.updateBalanceByIds(wrapper，amount);

void updateBalanceByIds(@Param("ew")LambdaQuerywrapper<User>wrapper，@Param("amount")int amount);

<update id="updateBalanceByIds">
	UPDATE tb_user sET balance=balance-#{amount} ${ew.customSqlSegment}
</update>

public class MainServiceImpl extends ServiceImpl<MainMapper,Main> implements MainService{
}

mybatis-plus:
  global-config:
    db-config:
      logic-delete-field:flag#全局逻辑删除的实体字段名，字段类型可以是boolean、integer
      logic-delete-value:#逻辑已删除值（默认为1）
      logic-not-delete-value: #逻辑未删除值（默认为0）

@Getter
@AllArgsConstructor
@NoArgsConstructor
public enum Season {
    SPRING(100,"春天"),
    SUMMER(200,"夏天"),
    AUTUMN(300,"秋天"),
    WINTER(400,"冬天")
    ;
    @EnumValue
    Integer code;
    String desc;
}

mybatis-plus:
  configuration:
    default-enum-type-handler: com.baomidou.mybatisplus.core.handlers.MybatisEnumTypeHandler

@JsonValue
String desc;

@TableField(typeHandler =JacksonTypeHandler.class) 
privaate UserInfo info;

@TableName(autoResultMap = true)

@SpringBootConfiguration
public class ApplicationConfig {
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptorFactory()  {
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        PaginationInnerInterceptor paginationInnerInterceptor = new PaginationInnerInterceptor();
        paginationInnerInterceptor.setMaxLimit(200L);
        interceptor.addInnerInterceptor(paginationInnerInterceptor);
        return interceptor;
    }
}

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class);
        Page<Main> page = new Page<>(1,2);
        IPage<Main> paged = Db.page(page, Main.class);
        paged.getRecords().forEach(System.out::println);
    }
}

mybatis-plus:  
  configuration:    
    cache-enabled: true

package com.xxx.myProject.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import org.apache.ibatis.annotations.CacheNamespace;

@CacheNamespace
public interface SysUserMapper extends BaseMapper<SysUser> {
	// 省略
}

// 其它省略
public class SysUser implements Serializable {
	// 省略
}

<cache-ref namespace="com.xxx.myProject.mapper.SysUserMapper"   />

@SpringBootApplication(exclude = { DataSourceAutoConfiguration.class })
@EnableCaching
//不加也能运行
public class AmsConfigApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext run = SpringApplication.run(AmsConfigApplication.class, args);
    }
}

若没有得到，再去一级缓存，如果仍没有，再去数据库

@Test //一级缓存
    public void firstLevelCacheTest(){
        //查询所有时 可以缓存数据 但是一旦发生增加 或者删除 修改 就要清空
        iStudentDao.findAllStudentWithScoreLazy();

        //查询第一次 有执行sql select * from student_tb where id = ?
        Student student1 = iStudentDao.findStudentById(2);
        System.out.println("student:" + student1);

        //查询第二次 没有执行sql 没有去数据库查数据 从一级缓存sqlSession获取数据
        Student student2 = iStudentDao.findStudentById(2);
        System.out.println("student:" + student2);

        student2.setAge(22);
        int num = iStudentDao.upateStudent(student2);
        System.out.println("num:"+num);

        //再次查询数据 需要去数据库查数据 为什么？？
        //应为 当前sqlSession 发生 修改、删除、增加动作时，就会把当前缓存的所有数据清空
        Student student3 = iStudentDao.findStudentById(2);
        System.out.println("student3:"+student3);

        iStudentDao.findAllStudentWithScoreLazy();
    }

<settings>
        <!--开启二级缓存-->
        <setting name="cacheEnabled" value="true"/>
    </settings>

<!--配置缓存
        1.开启<cache></cache>
        2.配置参数
        - flushinterval` 缓存刷新间隔，缓存多长时间刷新一次，默认不清空，设置一个毫秒值
- `readOnly`: 是否只读；**true 只读**，MyBatis 认为所有从缓存中获取数据的操作都是只读操作，不会修改数据。MyBatis 为了加快获取数据，直接就会将数据在缓存中的引用交给用户。不安全，速度快。**读写(默认)**：MyBatis 觉得数据可能会被修改
- `size` : 缓存存放多少个元素
- `type`: 指定自定义缓存的全类名(实现Cache 接口即可)
- `blocking`： 若缓存中找不到对应的key，是否会一直blocking，直到有对应的数据进入缓存。
    -->
   <cache flushInterval="10000" eviction="LRU" size="1000" readOnly="false" blocking="false"></cache>

<!--
        useCache="true" 使用缓存 一般不需要配置 默认就开启true        
    -->
    <select id="findStudentById" resultType="Student" useCache="true" >
        select * from  student_tb where id = #{id}
    </select>

@Test  //二级缓存
    public void secondLevelCacheTest(){
        //查询第一次  执行sql语句select * from student_tb where id = ?
        Student student1 = iStudentDao.findStudentById(2);
        System.out.println("student:" + student1);

        //查询第二次，没有执行sql 从一级缓存sqlSession中获取，因为二级缓存中没有
        Student student2 = iStudentDao.findStudentById(2);
        System.out.println("student2:"+student2);

        //如果不执行这句话  下面的代码仍会执行sql
        //调用close(),commit()方法 才会将数据提交到二级缓存，其他的sqlsession才能拿到
        //sqlSession.close();
        sqlSession.commit();

        // studentDao2   studentDao 来自于不同的sqlSession
        iStudentDao2 = sqlSessionFactory.openSession(true).getMapper(IStudentDao.class);
        Student student3 = iStudentDao2.findStudentById(2);
        System.out.println("student3:"+student3);

    }

logging:
  level:
    top.maluyao.mapper: DEBUG