MyBatis——日志、分页

春天有微风。微风徐徐，温不及你。夏天有烈日。烈日炎炎，灼灼思你。秋天有寒雨。寒雨泽泽，暖自于你。冬天有白雪。白雪皑皑，纯心给你。

一、日志

1、日志工厂

如果一个数据库操作，出现了异常，我们需要排除。日志就是最好的助手

曾经：sout、debug

现在：日志工厂

• SLF4J
• LOG4J
• LOG4J2
• JDK_LOGGING
• COMMONS_LOGGING
• STDOUT_LOGGING
• NO_LOGGING

在MyBatis中具体使用那个日志实现，在设置中设定

STDOUT_LOGGING标准日志输出

在mybatis核心配置文件中，配置我们的日志！

<settings>
        <setting name="logImpl" value="STDOUT_LOGGING"/>
</settings>

2、Log4j

什么是Log4j

• Log4j是Apache的一个开源项目，通过使用Log4j，我们可以控制日志信息输送的目的地是控制台、文件、GUI组件
• 我们也可以控制每一条日志的输出格式
• 通过定义每一条日志信息的级别，我们能够更加细致地控制日志的生成过程
• 通过一个配置文件来灵活地进行配置，而不需要修改应用的代码

1. 先导入log4j的包

   <dependencies>
       <!-- https://mvnrepository.com/artifact/log4j/log4j -->
       <dependency>
           <groupId>log4j</groupId>
           <artifactId>log4j</artifactId>
           <version>1.2.17</version>
       </dependency>
   </dependencies>
   
   

2. log4j.properties

   log4j.rootLogger=debug, stdout, R
   log4j.appender.stdout=org.apache.log4j.ConsoleAppender
   log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
   # Pattern to output the caller's file name and line number.
   log4j.appender.stdout.layout.ConversionPattern=%5p [%t] (%F:%L) - %m%n
   log4j.appender.R=org.apache.log4j.RollingFileAppender
   log4j.appender.R.File=example.log
   log4j.appender.R.MaxFileSize=100KB
   # Keep one backup file
   log4j.appender.R.MaxBackupIndex=5
   log4j.appender.R.layout=org.apache.log4j.PatternLayout
   log4j.appender.R.layout.ConversionPattern=%p %t %c - %m%n
   

3. 配置log4j为日志实现

   <settings>
       <setting name="logImpl" value="LOG4J"/>
   </settings>
   

4. log4j的使用，直接测试预先刚才的查询

   DEBUG [main] (LogFactory.java:105) - Logging initialized using 'class org.apache.ibatis.logging.log4j.Log4jImpl' adapter.
   DEBUG [main] (LogFactory.java:105) - Logging initialized using 'class org.apache.ibatis.logging.log4j.Log4jImpl' adapter.
   DEBUG [main] (PooledDataSource.java:353) - PooledDataSource forcefully closed/removed all connections.
   DEBUG [main] (PooledDataSource.java:353) - PooledDataSource forcefully closed/removed all connections.
   DEBUG [main] (PooledDataSource.java:353) - PooledDataSource forcefully closed/removed all connections.
   DEBUG [main] (PooledDataSource.java:353) - PooledDataSource forcefully closed/removed all connections.
   DEBUG [main] (JdbcTransaction.java:136) - Opening JDBC Connection
   Loading class `com.mysql.jdbc.Driver'. This is deprecated. The new driver class is `com.mysql.cj.jdbc.Driver'. The driver is automatically registered via the SPI and manual loading of the driver class is generally unnecessary.
   DEBUG [main] (PooledDataSource.java:424) - Created connection 2049051802.
   DEBUG [main] (JdbcTransaction.java:100) - Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@7a220c9a]
   DEBUG [main] (BaseJdbcLogger.java:143) - ==>  Preparing: /*定义sql*/ select * from mybatis.user where id = ?; 
   DEBUG [main] (BaseJdbcLogger.java:143) - ==> Parameters: 1(Integer)
   DEBUG [main] (BaseJdbcLogger.java:143) - <==      Total: 1
   User{id=1, name='狂神', password='123456'}
   DEBUG [main] (JdbcTransaction.java:122) - Resetting autocommit to true on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@7a220c9a]
   DEBUG [main] (JdbcTransaction.java:90) - Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@7a220c9a]
   DEBUG [main] (PooledDataSource.java:381) - Returned connection 2049051802 to pool.
   
   
   Disconnected from the target VM, address: '127.0.0.1:58296', transport: 'socket'
   
   Process finished with exit code 0
   
   

简单使用

1. 在要使用log4j的类中，导入org.apache.log4j.Logger

2. 日志对象，加载参数为当前类的class

   static Logger logger = Logger.getLogger(UserDaoTest.class);
   

3. 日志级别

   logger.info("info:进入了testLog4j方法");
   logger.debug("debug:进入了testLog4j");
   logger.error("error:进入了testLog4j");
   

二、分页

为什么要分页

• 减少数据的处理量

1、使用Limit分页

select * from user limit startIndex,pageSize

使用MyBatis实现分页，核心SQL

1. 接口

   //分页
   List<User> getUserByLimit(Map<String,Integer> map);
   

2. Mapper.xml

   <!--分页-->
   <select id="getUserByLimit" parameterType="map" resultMap="UserMap">
       select * from mybatis.user limit #{startIndex},#{pageSize}
   </select>
   

3. 测试

   @Test
       public void getUserByLimit(){
           SqlSession sqlSession = MyBatisUtils.getSqlSession();
           UserMapper mapper = sqlSession.getMapper(UserMapper.class);
           HashMap<String, Integer> map = new HashMap<>();
           map.put("startIndex",0);
           map.put("pageSize",2);
   
   
           List<User> userList = mapper.getUserByLimit(map);
           for (User user : userList) {
               System.out.println(user);
           }
           sqlSession.close();
       }
   

2、RowBounds分页

不再使用SQL实现分页

1. 接口

   List<User> getUserByRowBounds();
   

2. mapper.xml

   <!--分页2-->
   <select id="getUserByRowBounds" resultMap="UserMap">
       select * from mybatis.user
   </select>
   

3. 测试

   @Test
   public void getUserByRowBounds(){
       SqlSession sqlSession = MyBatisUtils.getSqlSession();
       //RowBounds实现
       RowBounds rowBounds = new RowBounds(1, 2);
   
       //通过java代码层面实现分页
       List<User> userList = sqlSession.selectList("com.rui.dao.UserMapper.getUserByRowBounds",null,rowBounds);
   
       for (User user : userList) {
           System.out.println(user);
       }
       sqlSession.close();
   }
   

3、分页插件