浅谈在JAVA项目中LOG4J的使用

一、直接使用：

//输出到项目文件夹下output1.txt文件中

//////////////////////////////

// DEBUG - Here is some DEBUG

// INFO - Here is some INFO

// WARN - Here is some WARN

// ERROR - Here is some ERROR

// FATAL - Here is some FATAL

//////////////////////////////

package hunnu.sanha.test;

import org.apache.log4j.Level;

import org.apache.log4j.Logger;

import org.apache.log4j.SimpleLayout;

import org.apache.log4j.FileAppender;

public class Simpandfile {

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

 public static void main(String args[]) {

  SimpleLayout layout = new SimpleLayout();

  FileAppender appender = null;

  try {

   appender = new FileAppender(layout,"output1.txt",false);

  } catch(Exception e) {}

  logger.addAppender(appender);

  logger.setLevel((Level) Level.);

  logger.debug("Here is some DEBUG");

  logger.info("Here is some INFO");

  logger.warn("Here is some WARN");

  logger.error("Here is some ERROR");

  logger.fatal("Here is some FATAL");

 }

}

 

//按格式输出到项目文件夹下output2.html

package hunnu.sanha.test;

import java.io.*;

import org.apache.log4j.Level;

import org.apache.log4j.Logger;

import org.apache.log4j.HTMLLayout;

import org.apache.log4j.WriterAppender;

public class Htmlandwrite {

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

 public static void main(String args[]) {

  HTMLLayout layout = new HTMLLayout();

  WriterAppender appender = null;

  try {

   FileOutputStream output = new FileOutputStream("output2.html");

   appender = new WriterAppender(layout,output);

  } catch(Exception e) {}

  logger.addAppender(appender);

  logger.setLevel((Level) Level.);

  logger.debug("Here is some DEBUG");

  logger.info("Here is some INFO");

  logger.warn("Here is some WARN");

  logger.error("Here is some ERROR");

  logger.fatal("Here is some FATAL");

 }

}

 

 

//输出到控制台

////////////////////////////////////////////////////////////////////////////////////////////////////////////

Milliseconds since program start: 0

Classname of caller: hunnu.sanha.test.Consandpatt

Date in ISO8601 format: 2008-07-29 11:02:30,578

Location of log event: hunnu.sanha.test.Consandpatt.main(Consandpatt.java:20)

Message: Here is some DEBUG

 

Milliseconds since program start: 15

Classname of caller: hunnu.sanha.test.Consandpatt

Date in ISO8601 format: 2008-07-29 11:02:30,593

Location of log event: hunnu.sanha.test.Consandpatt.main(Consandpatt.java:21)

Message: Here is some INFO

 

Milliseconds since program start: 15

Classname of caller: hunnu.sanha.test.Consandpatt

Date in ISO8601 format: 2008-07-29 11:02:30,593

Location of log event: hunnu.sanha.test.Consandpatt.main(Consandpatt.java:22)

Message: Here is some WARN

 

Milliseconds since program start: 15

Classname of caller: hunnu.sanha.test.Consandpatt

Date in ISO8601 format: 2008-07-29 11:02:30,593

Location of log event: hunnu.sanha.test.Consandpatt.main(Consandpatt.java:23)

Message: Here is some ERROR

 

Milliseconds since program start: 15

Classname of caller: hunnu.sanha.test.Consandpatt

Date in ISO8601 format: 2008-07-29 11:02:30,593

Location of log event: hunnu.sanha.test.Consandpatt.main(Consandpatt.java:24)

Message: Here is some FATAL

///////////////////////////////////////////////////////

package hunnu.sanha.test;

import org.apache.log4j.Level;

import org.apache.log4j.Logger;

import org.apache.log4j.PatternLayout;

import org.apache.log4j.ConsoleAppender;

public class Consandpatt {

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

 public static void main(String args[]) {

  // Note,%n is newline

  String pattern = "Milliseconds since program start: %r %n";

    pattern += "Classname of caller: %C %n";

    pattern += "Date in ISO8601 format: %d{ISO8601} %n";

    pattern += "Location of log event: %l %n";

    pattern += "Message: %m %n %n";

  

  PatternLayout layout = new PatternLayout(pattern);

  ConsoleAppender appender = new ConsoleAppender(layout);

  logger.addAppender(appender);

  logger.setLevel((Level) Level.);

  logger.debug("Here is some DEBUG");

  logger.info("Here is some INFO");

  logger.warn("Here is some WARN");

  logger.error("Here is some ERROR");

  logger.fatal("Here is some FATAL");

 }

}

二、使用配置文件（都直接放到项目文件夹下）

//xmllog4jconfig.xml

<?xml version="1.0" encoding="UTF-8" ?>

<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">

 <appender name="appender" class="org.apache.log4j.FileAppender">

  <param name="File" value="Indentify-Log.txt"/>

  <param name="Append" value="false"/>

  <layout class="org.apache.log4j.PatternLayout">

  <param name="ConversionPattern" value="%d [%t] %p - %m%n"/>

  </layout>

 </appender>

 <root>

  <priority value ="debug"/>

  <appender-ref ref="appender"/>

 </root>

</log4j:configuration>

 

//Externalxmltest.java

 package hunnu.sanha.external;

import org.apache.log4j.Logger;

import org.apache.log4j.xml.DOMConfigurator;

public class Externalxmltest {

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

 public static void main(String args[]) {

  DOMConfigurator.configure("xmllog4jconfig.xml");

  logger.debug("Here is some DEBUG");

  logger.info("Here is some INFO");

  logger.warn("Here is some WARN");

  logger.error("Here is some ERROR");

  logger.fatal("Here is some FATAL");

 }

}

//结果输出到Indentify-Log.txt文件中

2008-07-29 10:48:11,375 [main] DEBUG - Here is some DEBUG

2008-07-29 10:48:11,375 [main] INFO - Here is some INFO

2008-07-29 10:48:11,375 [main] WARN - Here is some WARN

2008-07-29 10:48:11,375 [main] ERROR - Here is some ERROR

2008-07-29 10:48:11,375 [main] FATAL - Here is some FATAL

 

 

// plainlog4jconfig.txt

# initialise root logger with level DEBUG and call it BLAH

log4j.rootLogger=DEBUG,BLAH

# add a ConsoleAppender to the logger BLAH

log4j.appender.BLAH=org.apache.log4j.ConsoleAppender

# set set that layout to be SimpleLayout

log4j.appender.BLAH.layout=org.apache.log4j.SimpleLayout

 

//Externalplaintest.java

package hunnu.sanha.external;

import org.apache.log4j.Logger;

import org.apache.log4j.PropertyConfigurator;

public class Externalplaintest {

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

 public static void main(String args[]) {

  PropertyConfigurator.configure("plainlog4jconfig.txt");

  logger.debug("Here is some DEBUG");

  logger.info("Here is some INFO");

  logger.warn("Here is some WARN");

  logger.error("Here is some ERROR");

  logger.fatal("Here is some FATAL");

 }

}

//结果输出到控制台

DEBUG - Here is some DEBUG

INFO - Here is some INFO

WARN - Here is some WARN

ERROR - Here is some ERROR

FATAL - Here is some FATAL

附加：

2.1.   日志信息的优先级

分为OFF、FATAL、ERROR、WARN、INFO、DEBUG、ALL或者您定义的级别。
Log4j建议只使用四个级别，优先级从高到低分别是ERROR、WARN、INFO、DEBUG。通过在这里定义的级别，您可以控制到应用程序中相应级别的日志信息的开关。
假如在一个级别为q的Logger中发生一个级别为p的日志请求，如果p>=q,那么请求将被启用。这是Log4j的核心原则。
比如在这里定义了INFO级别，则应用程序中所有DEBUG级别的日志信息将不被打印出来；

2.2.   输出源的使用

有选择的能用或者禁用日志请求仅仅是Log4j的一部分功能。Log4j允许日志请求被输出到多个输出源。用Log4j的话说，一个输出源被称做一个Appender。
Appender包括console（控制台）,files（文件）,GUI components（图形的组件）,remote socket servers（socket 服务）,JMS（java信息服务）,NT Event Loggers（NT的事件日志）,and remote UNIX Syslog daemons（远程UNIX的后台日志服务）。它也可以做到异步记录。
一个logger可以设置超过一个的appender。
用addAppender 方法添加一个appender到一个给定的logger。对于一个给定的logger它每个生效的日志请求都被转发到该logger所有的appender上和该logger的父辈logger的appender上。

2.2.1.  ConsoleAppender

如果使用ConsoleAppender，那么log信息将写到Console。效果等同于直接把信息打印到System.out上了。

2.2.2.  FileAppender

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