一、直接使用：
//輸出到項目檔案夾下output1.txt檔案中
//
// 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");
}
}
//按格式輸出到項目檔案夾下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");
}
}
//輸出到控制台
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、使用配置檔案（都直接放到項目檔案夾下）
//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檔案中
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");
}
}
//結果輸出到控制台
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. 日志資訊的優先級
分為OFF、FATAL、ERROR、WARN、INFO、DEBUG、ALL或者您定義的級别。
Log4j建議隻使用四個級别，優先級從高到低分别是ERROR、WARN、INFO、DEBUG。通過在這裡定義的級别，您可以控制到應用程式中相應級别的日志資訊的開關。
假如在一個級别為q的Logger中發生一個級别為p的日志請求，如果p>=q,那麼請求将被啟用。這是Log4j的核心原則。
比如在這裡定義了INFO級别，則應用程式中所有DEBUG級别的日志資訊将不被列印出來；
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（控制台）, files（檔案）, GUI components（圖形的元件）, remote socket servers（socket 服務）, JMS（java資訊服務）, NT Event Loggers（NT的事件日志）, and remote UNIX Syslog daemons（遠端UNIX的背景日志服務）。它也可以做到異步記錄。
一個logger可以設定超過一個的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，那麼log資訊将寫到Console。效果等同于直接把資訊列印到System.out上了。
2.2.2. FileAppender
使用FileAppender，那麼log資訊将寫到指定的檔案中。這應該是比較經常使用到的情況。
相應地，在配置檔案中應該指定log輸出的檔案名。如下配置指定了log檔案名為dglog.txt
log4j.appender.A2.File=dglog.txt
注意将A2替換為具體配置中Appender的别名。
2.2.3. DailyRollingAppender
使用FileAppender可以将log資訊輸出到檔案中，但是如果檔案太大了讀起來就不友善了。這時就可以使用DailyRollingAppender。DailyRollingAppender可以把Log資訊輸出到按照日期來區分的檔案中。配置檔案就會每天産生一個log檔案，每個log檔案隻記錄當天的log資訊：
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
檔案大小到達指定尺寸的時候産生一個新的檔案。
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
這個配置檔案指定了輸出源R，是一個輪轉日志檔案。最大的檔案是100KB，當一個日志檔案達到最大尺寸時，Log4J會自動把example.log重命名為dglog.log.1，然後重建一個新的dglog.log檔案，依次輪轉。
2.2.5. org.apache.log4j.WriterAppender
将日志資訊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資訊輸出的樣式。
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（包含日志資訊的級别和資訊字元串），
org.apache.log4j.TTCCLayout（包含日志産生的時間、線程、類别等等資訊）
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資訊耗費的毫秒數
%c 輸出所屬的類目，通常就是所在類的全名
%t 輸出産生該日志事件的線程名
%n 輸出一個回車換行符，Windows平台為"rn"，Unix平台為"n"
%d 輸出日志時間點的日期或時間，預設格式為ISO8601，也可以在其後指定格式，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資訊
log4j.appender.A2.layout=org.apache.log4j.PatternLayout
log4j.appender.A2.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss,SSS} %m%n
列印的資訊是：
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資訊
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級别,時間,調用方法,log資訊
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資訊:
[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. 配置檔案的例子:
log4j.rootLogger=DEBUG
#将DAO層log記錄到DAOLog,allLog中
log4j.logger.DAO=DEBUG,A2,A4
#将邏輯層log記錄到BusinessLog,allLog中
log4j.logger.Businesslog=DEBUG,A3,A4
#A1--列印到螢幕上
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--列印到檔案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--列印到檔案BusinessLog中--專門記錄邏輯處理層服務log資訊
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--列印到檔案alllog中--記錄所有log資訊
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
![Java小案例——随機數猜測随機數猜測[圖]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)