[log] what does a log do? What is a log factory? Configuration and use of log4j? log4j. Properties file configuration, log4j jar package coordinates

journal

1 Log factory

If a database operation , Something is wrong , We need to make a mistake , The journal is the best assistant ！

once ：sout 、 debug

Now? ： Log factory

https://mybatis.org/mybatis-3/zh/configuration.html#settings

• SLF4J simple logging facade for java Abbreviation ,java Simple appearance log

• LOG4J（3.5.9 Start and discard ） 【 master 】

• LOG4J2

• JDK_LOGGING

• COMMONS_LOGGING

• STDOUT_LOGGING 【 master 】

• NO_LOGGING

stay mybatis Try which log to use in , stay setting Set the ！

STDOUT_LOGGING Standard log output

mybaits-config.xml

<settings>
    <!-- journal -->
    <!--STDOUT_LOGGING  Standard log output -->
    <setting name="logImpl" value="STDOUT_LOGGING"/>
</settings>

2 log4j

What is? log4j?

• yes apache An open source project of
• adopt log4j, The destination where we can control the delivery of log information is the console or In the file or GUI Components
• Can pass log4j Control the output format of each log
• By defining the level of each log message , The production process of logs can be controlled more carefully
• Flexible configuration through a configuration file ,【log4j.properties 】, No code changes required

How to use log4j?

1. Import log4j jar package \

   pom.xml

   <!--log4j-->
   <dependency>
       <groupId>log4j</groupId>
       <artifactId>log4j</artifactId>
       <version>1.2.17</version>
   </dependency>
   

2. stay resources Set up under the log4j.properties

   log4j.properties

   # Rank as DEBUG Log information output to console and file These two destinations ,console and file Is defined in the following code 
   log4j.rootLogger=DEBUG,console,file
   
   # Related settings of console output 
   log4j.appender.console = org.apache.log4j.ConsoleAppender
   log4j.appender.console.Target = System.out
   log4j.appender.console.Threshold=DEBUG
   log4j.appender.console.layout = org.apache.log4j.PatternLayout
   log4j.appender.console.layout.ConversionPattern=[%c]-%m%n
   
   # File output related settings 
   log4j.appender.file = org.apache.log4j.RollingFileAppender
   log4j.appender.file.File=./log/kuang.log
   log4j.appender.file.MaxFileSize=10mb
   log4j.appender.file.Threshold=DEBUG
   log4j.appender.file.layout=org.apache.log4j.PatternLayout
   log4j.appender.file.layout.ConversionPattern=[%p][%d{yy-MM-dd}][%c]%m%n
   
   # Log output level 
   log4j.logger.org.mybatis=DEBUG
   log4j.logger.java.sql=DEBUG
   log4j.logger.java.sql.Statement=DEBUG
   log4j.logger.java.sql.ResultSet=DEBUG
   log4j.logger.java.sql.PreparedStatement=DEBUG
   

3. To configure log4j For the implementation of log

   mybatis-config.xml

   <settings>
       <!--LOG4J log4j Log output -->
       <setting name="logImpl" value="LOG4J"/>
   </settings>
   

4. Log4j Use , test run findUserById

   UserMapperTest.java

   package com.kuang.dao;
   
   import com.kuang.pojo.User;
   import com.kuang.utils.MyBatisUtils;
   import org.apache.ibatis.session.SqlSession;
   import org.junit.Test;
   
   public class UserMapperTest {
         
   
       @Test
       public void findUserByIdTest(){
         
   
           SqlSession sqlSession = MyBatisUtils.getSqlSession();
   
           UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
   
           User user = userMapper.findUserById(2);
   
           System.out.println(user);
   
           sqlSession.close();
   
       }
   }
   

   test result ：

   

   Automatically generated log file ：

​

Easy to use

1. To use log4j In the class , Import package import org.apache.log4j.Logger;

2. Log object , The parameter is of the current class class

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

3. The level of logging

   logger.info("info： Into the testLog4j Method ");
   logger.error("error： Into the testLog4j Method ");
   logger.debug("debug： Into the testLog4j Method ");
   

UserMapperTest.java

package com.kuang.dao;

import com.kuang.pojo.User;
import com.kuang.utils.MyBatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.apache.log4j.Logger;
import org.junit.Test;

public class UserMapperTest {
    


    @Test
    public void findUserByIdTest(){
    

        SqlSession sqlSession = MyBatisUtils.getSqlSession();

        // Get UserMapper Object instances 
        Logger logger = Logger.getLogger(UserMapper.class);
        logger.info(" test , go in getUserById Method success ！");

        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        User user = userMapper.findUserById(2);
        System.out.println(user);

        sqlSession.close();

    }

    @Test
    public void testLog4j(){
    
        // Get UserMapper Object instances 
        Logger logger = Logger.getLogger(UserMapper.class);

        logger.info("info： Into the testLog4j Method ");
        logger.error("error： Into the testLog4j Method ");
        logger.debug("debug： Into the testLog4j Method ");


    }
}

kuang.log