JAVA —— 最基础日志

深碍√TFBOYSˉ_ 2024-02-19 15:24 12阅读 0赞

日志的基本要素:以上面为例：\[ 时间 \] \[ 日志级别 \] \[ 调用的类和方法第几行 \] - 日志内容

例：\[2019-01-04 17:43:20,936\] \[INFO\] \[TestMain.checkFile:40\] - 日志内容

#### 写日志步骤： ####

1：导入日志包：log4j-1.2.14.jar

2：添加日志配置文件：log4j.xml (里面有日志的具体配置，如输出格式，日志文件路径等等)

log4j.xml ：

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE log4j:configuration PUBLIC "-//log4j/log4j Configuration//EN" "log4j.dtd">
    
    <log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
    
    	<appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">
    		<layout class="org.apache.log4j.PatternLayout">
    			<param name="ConversionPattern" value="[%d{yyyy-MM-dd HH:mm:ss,SSS\}] [%p] [%c.%M:%L] - %m%n" />
    		</layout>
    	</appender>
    
    	<appender name="INFO_FILE" class="org.apache.log4j.RollingFileAppender">
    		<param name="File" value="logs/gjj.log" />
    		<param name="encoding" value="UTF-8" />
    		<param name="Append" value="true" />
    		<param name="MaxBackupIndex" value="50" />
    		<param name="MaxFileSize" value="10MB" />
    		<layout class="org.apache.log4j.PatternLayout">
    			<param name="ConversionPattern" value="[%d{yyyy-MM-dd HH:mm:ss\}] [%p] [%c.%M:%L] - %m%n" />
    		</layout>
    	</appender>
    
    	<appender name="ERROR_FILE" class="org.apache.log4j.RollingFileAppender">
    		<param name="File" value="logs/gjj.error.log" />
    		<param name="encoding" value="UTF-8" />
    		<param name="Append" value="true" />
    		<param name="MaxBackupIndex" value="50" />
    		<param name="MaxFileSize" value="10MB" />
    		<layout class="org.apache.log4j.PatternLayout">
    			<param name="ConversionPattern" value="[%d{yyyy-MM-dd HH:mm:ss\}] [%p] [%c.%M:%L] - %m%n" />
    		</layout>
    		<filter class="org.apache.log4j.varia.LevelRangeFilter">
    		    <param name="LevelMax" value="ERROR"/>
    		    <param name="LevelMin" value="ERROR"/>
    		</filter>
    	</appender>
    	<appender name="WARN_FILE" class="org.apache.log4j.RollingFileAppender">
    		<param name="File" value="logs/gjj.warn.log" />
    		<param name="encoding" value="UTF-8" />
    		<param name="Append" value="true" />
    		<param name="MaxBackupIndex" value="50" />
    		<param name="MaxFileSize" value="10MB" />
    		<layout class="org.apache.log4j.PatternLayout">
    			<param name="ConversionPattern" value="[%d{yyyy-MM-dd HH:mm:ss\}] [%p] [%c.%M:%L] - %m%n" />
    		</layout>
    		<filter class="org.apache.log4j.varia.LevelRangeFilter">
    		    <param name="LevelMax" value="WARN"/>
    		    <param name="LevelMin" value="WARN"/>
    		</filter>
    	</appender>
    
    	<logger name="warn.log">
    		<level value="WARN" />
    		<appender-ref ref="WARN_FILE" />
    	</logger>
    	<logger name="error.log" additivity="false">
    		<level value="ERROR" />
    		<appender-ref ref="ERROR_FILE" />
    	</logger>
    	<logger name="info.log" additivity="false">
    		<level value="INFO" />
    		<appender-ref ref="INFO_FILE" />
    	</logger>
    	<root>
    		<priority value="INFO" />
    		<appender-ref ref="STDOUT" />
    		<appender-ref ref="WARN_FILE" />
    		<appender-ref ref="ERROR_FILE" />
    		<appender-ref ref="INFO_FILE" />
    	</root>
    
    </log4j:configuration>

3：建立日志工具类：LoggerUtil.java

import org.apache.log4j.Logger;
    import org.apache.log4j.spi.LoggerFactory;
    import org.apache.log4j.xml.DOMConfigurator;
    
    public class LoggerUtil {
    	static {
    		DOMConfigurator.configure(LoggerUtil.class.getResource(
    				"/").getFile() + "log4j.xml");
    	}
    
    	public static Logger getLogger(Class<?> clazz) {
    		return Logger.getLogger(clazz);
    	}
    
    	public static Logger getLogger(String name) {
    		return Logger.getLogger(name);
    	}
    
    	public static Logger getLogger(String name, LoggerFactory factory) {
    		return Logger.getLogger(name, factory);
    	}
    
    	public static Logger getRootLogger() {
    		return Logger.getRootLogger();
    	}
    }

4：在每个要打印日志的类前面放一句(基本每个类都要打日志)：

**private** **static** Logger *log* = LoggerUtil.*getLogger*(TestMain.**class**);

例：![20190105000248910.png][]

注：TestMain.**class****要根据不同的类进行变化**

**类中要打日志时就可以：**

![20190105000357999.png][]

总结：以后，上述日志都会打印到日志文件中，如下：

![20190105000445656.png][]

当项目上线后，我们就可以通过查看日志来监控项目的情况，和项目出问题的位置（因为上线后项目都是class文件，它也不可能给你用eclipse跑在控制台看错误位置）

要养成良好的写日志习惯，日志一定要慢慢变完整，宁可多谢也不要节约，这样以后项目出问题就可以很快找到位置，减少痛苦（过来人警告！！）

![20190105000459643.png][]

[20190105000248910.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/29/03a451acd19c4229a07289fa90e151c6.png
[20190105000357999.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/29/eccf3eb1f22647178cccc296ee207704.png
[20190105000445656.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/29/5bcce4f441f047b0806606b1966bbce1.png
[20190105000459643.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/29/5eeef2c0b7984763b2393e9195342a7d.png