仓库源文，用日志来调试程序.md)，站点原文

<!--more--> <p>java调试代码不再用system.out.println();，用完再删除，想用了再添加。</p><p>用日志直接打印。</p><p>两对好基友：Commons Logging加Log4j，SLF4J加Logback。</p><p>两对好基友看不起java内置的JDK Logging</p><p>JDK Logging</p>

{% code %} package _22javacoreclass;

import java.util.logging.Logger;

public class Main5{ public static void main(String[] args) { Logger logger = Logger.getGlobal(); /*JDK Logging / //默认info，info以下不打印信息 //不常用 //严重 logger.severe("process will be terminated..."); //警告 logger.warning("memory is running out..."); //信息 logger.info("start process..."); //config logger.config("ignored."); //fine logger.fine("ignored."); //finer logger.finer("ignored."); //finest logger.finest("ignored."); } } {% endcode %}

<p>Commons Logging加Log4j，需要增加log4j2.xml</p>

{% code %} package _22javacoreclass;

import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory;

public class Main5{ public static void main(String[] args) { /*Commons Logging / Log log = LogFactory.getLog(Main5.class); log.fatal("fatal..."); log.error("error."); log.warn("warn..."); log.info("info."); log.debug("debug..."); log.trace("trace.");

    /**Log4j */ 
    // Commons Logging自动发现并调用|好基友

}

} {% endcode %}

<p> log4j2.xml</p>

{% code %} <?xml version="1.0" encoding="UTF-8"?>

<Configuration> <Properties> <!-- 定义日志格式 --> <Property name="log.pattern">%d{MM-dd HH:mm:ss.SSS} [%t] %-5level %logger{36}%n%msg%n%n</Property> <!-- 定义文件名变量 --> <Property name="file.err.filename">log/err.log</Property> <Property name="file.err.pattern">log/err.%i.log.gz</Property> </Properties> <!-- 定义Appender，即目的地 --> <Appenders> <!-- 定义输出到屏幕 --> <Console name="console" target="SYSTEM_OUT"> <!-- 日志格式引用上面定义的log.pattern --> <PatternLayout pattern="${log.pattern}" /> </Console> <!-- 定义输出到文件,文件名引用上面定义的file.err.filename --> <RollingFile name="err" bufferedIO="true" fileName="${file.err.filename}" filePattern="${file.err.pattern}"> <PatternLayout pattern="${log.pattern}" /> <Policies> <!-- 根据文件大小自动切割日志 --> <SizeBasedTriggeringPolicy size="1 MB" /> </Policies> <!-- 保留最近10份 --> <DefaultRolloverStrategy max="10" /> </RollingFile> </Appenders> <Loggers> <Root level="info"> <!-- 对info级别的日志，输出到console --> <AppenderRef ref="console" level="info" /> <!-- 对error级别的日志，输出到err，即上面定义的RollingFile --> <AppenderRef ref="err" level="error" /> </Root> </Loggers> </Configuration> {% endcode %}

<p>SLF4J加Logback，需要增加logback.xml</p>

{% code %} package _22javacoreclass;

import org.slf4j.Logger; import org.slf4j.LoggerFactory;

//SLF4J和Logback好基友 public class Main51 { public static void main(String[] args) { Logger logger = LoggerFactory.getLogger(Main51.class); logger.error("error."); logger.warn("warn..."); logger.info("info."); logger.debug("debug..."); logger.trace("trace."); } } {% endcode %}

<p>logback.xml</p>

{% code %} <?xml version="1.0" encoding="UTF-8"?>

<configuration> 
<appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
    <encoder>
        <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
    </encoder>
</appender>

<appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
    <encoder>
        <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
        <charset>utf-8</charset>
    </encoder>
    <file>log/output.log</file>
    <rollingPolicy class="ch.qos.logback.core.rolling.FixedWindowRollingPolicy">
        <fileNamePattern>log/output.log.%i</fileNamePattern>
    </rollingPolicy>
    <triggeringPolicy class="ch.qos.logback.core.rolling.SizeBasedTriggeringPolicy">
        <MaxFileSize>1MB</MaxFileSize>
    </triggeringPolicy>
</appender>

<root level="INFO">
    <appender-ref ref="CONSOLE" />
    <appender-ref ref="FILE" />
</root>

</configuration> {% endcode %}