一、直接使用:
//輸出到項目文件夾下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"); }} //按格式輸出到項目文件夾下output2.htmlpackage 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"); }}  //輸出到控制臺////////////////////////////////////////////////////////////////////////////////////////////////////////////Milliseconds since program start: 0Classname of caller: hunnu.sanha.test.ConsandpattDate in ISO8601 format: 2008-07-29 11:02:30,578Location of log event: hunnu.sanha.test.Consandpatt.main(Consandpatt.java:20)Message: Here is some DEBUG Milliseconds since program start: 15Classname of caller: hunnu.sanha.test.ConsandpattDate in ISO8601 format: 2008-07-29 11:02:30,593Location of log event: hunnu.sanha.test.Consandpatt.main(Consandpatt.java:21)Message: Here is some INFO Milliseconds since program start: 15Classname of caller: hunnu.sanha.test.ConsandpattDate in ISO8601 format: 2008-07-29 11:02:30,593Location of log event: hunnu.sanha.test.Consandpatt.main(Consandpatt.java:22)Message: Here is some WARN Milliseconds since program start: 15Classname of caller: hunnu.sanha.test.ConsandpattDate in ISO8601 format: 2008-07-29 11:02:30,593Location of log event: hunnu.sanha.test.Consandpatt.main(Consandpatt.java:23)Message: Here is some ERROR Milliseconds since program start: 15Classname of caller: hunnu.sanha.test.ConsandpattDate in ISO8601 format: 2008-07-29 11:02:30,593Location 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(都直接放到項目文件夾下)
//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"); }}//結果輸出到Indentify-Log.txt文件中2008-07-29 10:48:11,375 [main] DEBUG - Here is some DEBUG2008-07-29 10:48:11,375 [main] INFO - Here is some INFO2008-07-29 10:48:11,375 [main] WARN - Here is some WARN2008-07-29 10:48:11,375 [main] ERROR - Here is some ERROR2008-07-29 10:48:11,375 [main] FATAL - Here is some FATAL  // plainlog4jconfig.txt# initialise root logger with level DEBUG and call it BLAHlog4j.rootLogger=DEBUG, BLAH# add a ConsoleAppender to the logger BLAHlog4j.appender.BLAH=org.apache.log4j.ConsoleAppender# set set that layout to be SimpleLayoutlog4j.appender.BLAH.layout=org.apache.log4j.SimpleLayout //Externalplaintest.javapackage 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"); }}//結果輸出到控制臺DEBUG - Here is some DEBUGINFO - Here is some INFOWARN - Here is some WARNERROR - Here is some ERRORFATAL - Here is some FATAL附加:
2.1. 日志信息的優先級
分為OFF、FATAL、ERROR、WARN、INFO、DEBUG、ALL或者您定義的級別。 
Log4j建議只使用四個級別,優先級從高到低分別是ERROR、WARN、INFO、DEBUG。通過在這里定義的級別,您可以控制到應用程序中相應級別的日志信息的開關。 
假如在一個級別為q的Logger中發生一個級別為p的日志請求,如果p>=q,那么請求將被啟用。這是Log4j的核心原則。 
比如在這里定義了INFO級別,則應用程序中所有DEBUG級別的日志信息將不被打印出來;
2.2. 輸出源的使用
有選擇的能用或者禁用日志請求僅僅是Log4j的一部分功能。Log4j允許日志請求被輸出到多個輸出源。用Log4j的話說,一個輸出源被稱做一個Appender。 
Appender包括console(控制臺), files(文件), GUI components(圖形的組件), remote socket servers(socket 服務), JMS(java信息服務), NT Event Loggers(NT的事件日志), and remote UNIX Syslog daemons(遠程UNIX的后臺日志服務)。它也可以做到異步記錄。 
一個logger可以設置超過一個的appender。 
用addAppender 方法添加一個appender到一個給定的logger。對于一個給定的logger它每個生效的日志請求都被轉發到該logger所有的appender上和該logger的父輩logger的appender上。
2.2.1. ConsoleAppender
如果使用ConsoleAppender,那么log信息將寫到Console。效果等同于直接把信息打印到System.out上了。
2.2.2. FileAppender
使用FileAppender,那么log信息將寫到指定的文件中。這應該是比較經常使用到的情況。 
相應地,在配置文件中應該指定log輸出的文件名。如下配置指定了log文件名為dglog.txt 
log4j.appender.A2.File=dglog.txt 
注意將A2替換為具體配置中Appender的別名。
2.2.3. DailyRollingAppender
使用FileAppender可以將log信息輸出到文件中,但是如果文件太大了讀起來就不方便了。這時就可以使用DailyRollingAppender。DailyRollingAppender可以把Log信息輸出到按照日期來區分的文件中。配置文件就會每天產生一個log文件,每個log文件只記錄當天的log信息: 
log4j.appender.A2=org.apache.log4j.DailyRollingFileAppender 
log4j.appender.A2.file=dglog 
log4j.appender.A2.DatePattern='.'yyyy-MM-dd 
log4j.appender.A2.layout=org.apache.log4j.PatternLayout 
log4j.appender.A2.layout.ConversionPattern= %5r %-5p %c{2} - %m%n
2.2.4. org.apache.log4j.RollingFileAppender
文件大小到達指定尺寸的時候產生一個新的文件。 
log4j.appender.R=org.apache.log4j.RollingFileAppender 
log4j.appender.R.File= ../logs/dglog.log 
# Control the maximum log file size 
log4j.appender.R.MaxFileSize=100KB 
# Archive log files (one backup file here) 
log4j.appender.R.MaxBackupIndex=1 
log4j.appender.R.layout=org.apache.log4j.PatternLayout 
log4j.appender.R.layout.ConversionPattern=%p %t %c - %m%n 
這個配置文件指定了輸出源R,是一個輪轉日志文件。最大的文件是100KB,當一個日志文件達到最大尺寸時,Log4J會自動把example.log重命名為dglog.log.1,然后重建一個新的dglog.log文件,依次輪轉。
2.2.5. org.apache.log4j.WriterAppender
將日志信息以流格式發送到任意指定的地方。
2.3. Layout的配置
Layout指定了log信息輸出的樣式。
2.3.1. 布局樣式
org.apache.log4j.HTMLLayout(以HTML表格形式布局), 
org.apache.log4j.PatternLayout(可以靈活地指定布局模式), 
org.apache.log4j.SimpleLayout(包含日志信息的級別和信息字符串), 
org.apache.log4j.TTCCLayout(包含日志產生的時間、線程、類別等等信息)
2.3.2. 格式
%m 輸出代碼中指定的消息 
%p 輸出優先級,即DEBUG,INFO,WARN,ERROR,FATAL 
%r 輸出自應用啟動到輸出該log信息耗費的毫秒數 
%c 輸出所屬的類目,通常就是所在類的全名 
%t 輸出產生該日志事件的線程名 
%n 輸出一個回車換行符,Windows平臺為"rn",Unix平臺為"n" 
%d 輸出日志時間點的日期或時間,默認格式為ISO8601,也可以在其后指定格式,比如:%d{yyy MMM dd HH:mm:ss,SSS},輸出類似:2002年10月18日 22:10:28,921 
%l 輸出日志事件的發生位置,包括類目名、發生的線程,以及在代碼中的行數。舉例:Testlog4.main(Test Log4.java:10)
2.3.3. 例子
例子1:顯示日期和log信息 
log4j.appender.A2.layout=org.apache.log4j.PatternLayout 
log4j.appender.A2.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss,SSS} %m%n 
打印的信息是: 
2002-11-12 11:49:42,866 SELECT * FROM Role WHERE 1=1 order by createDate desc
例子2:顯示日期,log發生地方和log信息 
log4j.appender.A2.layout=org.apache.log4j.PatternLayout 
log4j.appender.A2.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss,SSS} %l "#" %m%n 
2002-11-12 11:51:46,313 cn.net.unet.weboa.system.dao.RoleDAO.select(RoleDAO.java:409) "#" 
SELECT * FROM Role WHERE 1=1 order by createDate desc 
  
例子3:顯示log級別,時間,調用方法,log信息 
log4j.appender.A2.layout=org.apache.log4j.PatternLayout 
log4j.appender.A2.layout.ConversionPattern=[%-5p] %d{yyyy-MM-dd HH:mm:ss,SSS} 
method:%l%n%m%n 
log信息: 
[DEBUG] 2002-11-12 12:00:57,376 
method:cn.net.unet.weboa.system.dao.RoleDAO.select(RoleDAO.java:409) 
SELECT * FROM Role WHERE 1=1 order by createDate desc
2.4. 配置文件的例子:
log4j.rootLogger=DEBUG 
#將DAO層log記錄到DAOLog,allLog中 
log4j.logger.DAO=DEBUG,A2,A4 
#將邏輯層log記錄到BusinessLog,allLog中 
log4j.logger.Businesslog=DEBUG,A3,A4
#A1--打印到屏幕上 
log4j.appender.A1=org.apache.log4j.ConsoleAppender 
log4j.appender.A1.layout=org.apache.log4j.PatternLayout 
log4j.appender.A1.layout.ConversionPattern=%-5p [%t] %37c %3x - %m%n
#A2--打印到文件DAOLog中--專門為DAO層服務 
log4j.appender.A2=org.apache.log4j.DailyRollingFileAppender 
log4j.appender.A2.file=DAOLog 
log4j.appender.A2.DatePattern='.'yyyy-MM-dd 
log4j.appender.A2.layout=org.apache.log4j.PatternLayout 
log4j.appender.A2.layout.ConversionPattern=[%-5p] %d{yyyy-MM-dd HH:mm:ss,SSS} 
method:%l%n%m%n
#A3--打印到文件BusinessLog中--專門記錄邏輯處理層服務log信息 
log4j.appender.A3=org.apache.log4j.DailyRollingFileAppender 
log4j.appender.A3.file=BusinessLog 
log4j.appender.A3.DatePattern='.'yyyy-MM-dd 
log4j.appender.A3.layout=org.apache.log4j.PatternLayout 
log4j.appender.A3.layout.ConversionPattern=[%-5p] %d{yyyy-MM-dd HH:mm:ss,SSS} 
method:%l%n%m%n
#A4--打印到文件alllog中--記錄所有log信息 
log4j.appender.A4=org.apache.log4j.DailyRollingFileAppender 
log4j.appender.A4.file=alllog 
log4j.appender.A4.DatePattern='.'yyyy-MM-dd 
log4j.appender.A4.layout=org.apache.log4j.PatternLayout 
log4j.appender.A4.layout.ConversionPattern=[%-5p] %d{yyyy-MM-dd HH:mm:ss,SSS} 
method:%l%n%m%n
以上這篇淺談在JAVA項目中LOG4J的使用就是小編分享給大家的全部內容了,希望能給大家一個參考,也希望大家多多支持武林網。
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