前言：

本文内容：日志工程、Log4j讲解、Limit实现分页

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日志工程

日志工厂

如果一个数据库操作出现了异常，我们日志帮助我们排错

日志工厂

loglmpl 指定MyBatis所用日志的具体实现，未指定时自动查找 SLF4J / LOG4J / LOG4J2 / JDK_LOGGING / COMMONS_LOGGING / STDOUT_LOGGING / NO_LOGGING 未设置
  • LOG4j(掌握)
  • STDOUT_LOGGING(掌握)
  • …

使用那个配置即可

STDOUT_LOGGING标准日志输出

配置

mybatis-config.xml

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<!--    配置日志工厂-->
    <settings>
        <setting name="logImpl" value="STDOUT_LOGGING"/>
    </settings>

配置后运行结果

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Logging initialized using 'class org.apache.ibatis.logging.stdout.StdOutImpl' adapter.
PooledDataSource forcefully closed/removed all connections.
PooledDataSource forcefully closed/removed all connections.
PooledDataSource forcefully closed/removed all connections.
PooledDataSource forcefully closed/removed all connections.
Opening JDBC Connection
Created connection 1840976765.
Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@6dbb137d]
==>  Preparing: select * from user where id=?
==> Parameters: 1(Integer)
<==    Columns: id, name, pwd
<==        Row: 1, admin, 123
<==      Total: 1
User{id=1, username='admin', password='123'}
Resetting autocommit to true on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@6dbb137d]
Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@6dbb137d]
Returned connection 1840976765 to pool.

Process finished with exit code 0

Log4j讲解

注意Log4j被爆出存在漏洞，建议使用最新版本或者1.x版本

最后：实际开发已经弃用log4j了，这里仅作了解(时间2022/4/28)

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组件等

我们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，我们能够更加细致的控制日志的生成过程

通过配置文件灵活的进行配置，而不需要修改应用的代码。

先导包

父工程的pom.xml

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<!--        log4j-->
<!--        注意：log4j目前存在高危漏洞，不建议在正式项目中使用-->
<dependency>
    <groupId>log4j</groupId>
    <artifactId>log4j</artifactId>
    <version>1.2.12</version>
</dependency>

新建

在resources下新建log4j.properties

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#将等级为DEBUG的日志信息输出到console和file这两个目的地，console和file的定义在下面的代码
log4j.rootLogger=DEBUG,console,file

#控制台输出的相关设置
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

#文件输出的相关设置
log4j.appender.file = org.apache.log4j.RollingFileAppender
log4j.appender.file.File=./log/jokerdig.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

#日志输出级别
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

配置

mybatis-config.xml

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<settings>
    <setting name="logImpl" value="LOG4j"/>
</settings>

运行结果

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[org.apache.ibatis.logging.LogFactory]-Logging initialized using 'class org.apache.ibatis.logging.log4j.Log4jImpl' adapter.
[org.apache.ibatis.logging.LogFactory]-Logging initialized using 'class org.apache.ibatis.logging.log4j.Log4jImpl' adapter.
[org.apache.ibatis.datasource.pooled.PooledDataSource]-PooledDataSource forcefully closed/removed all connections.
[org.apache.ibatis.datasource.pooled.PooledDataSource]-PooledDataSource forcefully closed/removed all connections.
[org.apache.ibatis.datasource.pooled.PooledDataSource]-PooledDataSource forcefully closed/removed all connections.
[org.apache.ibatis.datasource.pooled.PooledDataSource]-PooledDataSource forcefully closed/removed all connections.
[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Opening JDBC Connection
[org.apache.ibatis.datasource.pooled.PooledDataSource]-Created connection 1782580546.
[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@6a400542]
[com.jokerdig.mapper.UserMapper.getUserById]-==>  Preparing: select * from user where id=?
[com.jokerdig.mapper.UserMapper.getUserById]-==> Parameters: 1(Integer)
[com.jokerdig.mapper.UserMapper.getUserById]-<==      Total: 1
User{id=1, username='admin', password='123'}
[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Resetting autocommit to true on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@6a400542]
[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@6a400542]
[org.apache.ibatis.datasource.pooled.PooledDataSource]-Returned connection 1782580546 to pool.

Process finished with exit code 0

简单使用

测试代码

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package com.jokerdig.test;

import com.jokerdig.mapper.UserMapper;
import com.jokerdig.pojo.User;
import com.jokerdig.util.MyBatisUtil;
import org.apache.ibatis.session.SqlSession;
import org.apache.log4j.Logger;
import org.junit.Test;

/**
 * @author Joker大雄
 * @data 2022/4/28 - 14:08
 **/
public class Log4jTest {
    static Logger logger =Logger.getLogger(MapperTest.class);
    @Test
    public void log4j(){
        logger.info("info:进入了log4j");
        logger.debug("debug:进入了log4j");
        logger.error("error:进入了log4j");
    }
}

运行结果

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[com.jokerdig.test.MapperTest]-info:进入了log4j
[com.jokerdig.test.MapperTest]-debug:进入了log4j
[com.jokerdig.test.MapperTest]-error:进入了log4j
    
Process finished with exit code 0

Limit实现分页

为什么分页？

  • 减少数据处理量
  • 优化用户体验

使用Limit分页

语法

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select * from user limit startIndex.pageSize;

使用myBatis分页

  1. 接口

    UserMapper.java

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

  2. Mapper.xml

    UserMapper.xml

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    <!--    分页查询-->
    <select id="getUserByList" parameterType="map" resultMap="userMap">
        select * from user limit #{startIndex},#{pageSize}
    </select>

  3. 测试

    MapperTest.java

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    // 分页
        @Test
        public void getUserByLimit(){
            SqlSession sqlSession = MyBatisUtil.getSqlSession();

            UserMapper mapper = sqlSession.getMapper(UserMapper.class);

            Map<String,Integer> userMap = new HashMap<String, Integer>();

            userMap.put("startIndex",0);
            userMap.put("pageSize",2);

            List<User> userByList = mapper.getUserByList(userMap);

            for (User user : userByList) {
                System.out.println(user);
            }
            sqlSession.close();
        }

  4. 运行结果

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    .......
    Opening JDBC Connection
    Created connection 1702940637.
    Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@6580cfdd]
    ==>  Preparing: select * from user limit ?,?
    ==> Parameters: 0(Integer), 2(Integer)
    <==    Columns: id, name, pwd
    <==        Row: 1, admin, 123
    <==        Row: 2, abc, 123
    <==      Total: 2
    User{id=1, username='admin', password='123'}
    User{id=2, username='abc', password='123'}
    Resetting autocommit to true on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@6580cfdd]
    Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@6580cfdd]
    Returned connection 1702940637 to pool.

    Process finished with exit code 0