1、Log4j的概念
Log4j中有三個主要的元件，它們分別是 Logger、Appender和Layout，Log4j 允許開發人員定義多個Logger，每個Logger擁有自己的名字，Logger之間通過名字來表明隸屬關係。有一個Logger稱為Root，它永遠 存在，且不能通過名字檢索或引用，可以通過Logger.getRootLogger()方法獲得，其它Logger通過 Logger.getLogger(String name)方法。
Appender則是用來指明將所有的log資訊存放到什麼地方，Log4j中支援多種appender，如 console、files、GUI components、NT Event Loggers等，一個Logger可以擁有多個Appender，也就是你既可以將Log資訊輸出到螢幕，同時儲存到一個檔案中。
Layout的作用是控制Log資訊的輸出方式，也就是格式化輸出的資訊。
Log4j中將要輸出的Log資訊定義了5種級別，依次為DEBUG、INFO、WARN、ERROR和FATAL，當輸出時，只有級別高過配置中規定的級別的資訊才能真正的輸出，這樣就很方便的來配置不同情況下要輸出的內容，而不需要更改程式碼，這點實在是方便啊。
2、Log4j的配置檔案
package dxz.log4j;
import org.apache.log4j.Logger;
public class MultiLogger {
/** * @param args */
public static void main(String[] args) {
// TODO Auto-generated method stub
/** * 此外可以指定用哪個日誌，duan或者zhang */
Logger log = Logger.getLogger("DBUpgrade");
for(int i=0;i<10;i++){
log.debug("DBUpgrade");
log.info("DBUpgrade");
log.warn("DBUpgrade");
log.error("DBUpgrade");
}
Logger log2 = Logger.getLogger("zhang");
for(int i=0;i<10;i++){
log2.debug("zhang");
log2.info("zhang");
log2.warn("zhang");
log2.error("zhang");
}
}
}
####log4j.properties###################
log4j.logger.duan=DEBUG,A
log4j.appender.A=org.apache.log4j.DailyRollingFileAppender
log4j.appender.A.File=E:/test/log/duan.log
log4j.appender.A.layout=org.apache.log4j.PatternLayout
log4j.appender.A.layout.ConversionPattern=%d%m%n
log4j.logger.zhang=DEBUG,C log4j.appender.B=org.apache.log4j.ConsoleAppender
log4j.appender.B.layout=org.apache.log4j.PatternLayout
log4j.appender.B.layout.ConversionPattern=%l%d%m%n
log4j.appender.C=org.apache.log4j.DailyRollingFileAppender
log4j.appender.C.File=E:/test/log/zhang.log
log4j.appender.C.layout=org.apache.log4j.PatternLayout
log4j.appender.C.layout.ConversionPattern=%d%m%n
log4j.logger.DBUpgrade=DEBUG,DBUpgrade
# Rolling file appender
log4j.appender.DBUpgrade=org.apache.log4j.RollingFileAppender
log4j.appender.DBUpgrade.File=e:/test/log/DBUpgradeLog.log
log4j.appender.DBUpgrade.MaxFileSize=100KB
log4j.appender.DBUpgrade.MaxBackupIndex=2
log4j.appender.DBUpgrade.layout=org.apache.log4j.PatternLayout
log4j.appender.DBUpgrade.layout.ConversionPattern=%d{MMM dd, yyyy hh:mm:ss a} %-5p [%c{1}] %m%n
log4j.appender.DBUpgrade.threshold=DEBUG
結果：
DBUpgradeLog.log
十一月 29, 2012 04:44:25 下午 DEBUG [DBUpgrade] DBUpgrade
十一月 29, 2012 04:44:25 下午 INFO [DBUpgrade] DBUpgrade
十一月 29, 2012 04:44:25 下午 WARN [DBUpgrade] DBUpgrade
十一月 29, 2012 04:44:25 下午 ERROR [DBUpgrade] DBUpgrade
十一月 29, 2012 04:44:25 下午 DEBUG [DBUpgrade] DBUpgrade
十一月 29, 2012 04:44:25 下午 INFO [DBUpgrade] DBUpgrade
十一月 29, 2012 04:44:25 下午 WARN [DBUpgrade] DBUpgrade
十一月 29, 2012 04:44:25 下午 ERROR [DBUpgrade] DBUpgrade
十一月 29, 2012 04:44:25 下午 DEBUG [DBUpgrade] DBUpgrade
duan.log
2012-11-29 16:28:57,369duan
2012-11-29 16:28:57,369duan
2012-11-29 16:28:57,369duan
2012-11-29 16:28:57,369duan
2012-11-29 16:28:57,369duan
2012-11-29 16:28:57,369duan
2012-11-29 16:28:57,370duan
2012-11-29 16:28:57,370duan
不如寫一個能夠實現以上功能的類吧。
MultiFileLoggerByLogLevel.java
package com.bjinfotech.practice.logging;
import org.apache.log4j.PropertyConfigurator;
import org.apache.log4j.Level;
import org.apache.log4j.Category;
import org.apache.log4j.FileAppender;
/**
* 使用isEnableFor方法作判斷，提高了log的效能，避免了處理低等級的資訊導致的系統浪費
* 根據日誌level建立多個不同級別的log，將日誌內容按照級別寫入不同的日誌檔案
*
*/
public class MultiFileLoggerByLogLevel {
public static final int DEBUG=0;
public static final int INFO=1;
public static final int WARN=2;
public static final int ERROR=3;
public static final int CATEGORY_MAXNUM=4;
private String[] categoryNameArray={"DEBUG","INFO","WARN","ERROR"};
private Category[] categoryArray=new Category[CATEGORY_MAXNUM];
/**
* 構造方法
* @param propertyFilePath 配置檔案路徑
*/
public MultiFileLoggerByLogLevel(String propertyFilePath){
init(propertyFilePath);
}
/**
* 初始化，建立category陣列
* @param propertyFilePath 配置檔案路徑
*/
private void init(String propertyFilePath ){
PropertyConfigurator.configure(propertyFilePath);
for(int i=0;i<CATEGORY_MAXNUM;i++){
categoryArray[i]=Category.getInstance(categoryNameArray[i]);
FileAppender fileAppender=(FileAppender)categoryArray[i].getAppender("R_"+categoryNameArray[i]);
categoryArray[i].addAppender(fileAppender);
}
}
public void debug(String msg){
if (categoryArray[DEBUG].isEnabledFor(Level.DEBUG)){
categoryArray[DEBUG].debug(msg);
}
}
public void info(String msg){
if (categoryArray[INFO].isEnabledFor(Level.INFO)){
categoryArray[INFO].info(msg);
}
}
public void warn(String msg){
if (categoryArray[WARN].isEnabledFor(Level.WARN)){
categoryArray[WARN].warn(msg);
}
}
public void error(String msg){
if (categoryArray[ERROR].isEnabledFor(Level.ERROR)){
categoryArray[ERROR].error(msg);
}
}
public static void main(String[] args) {
String propertyFilePath="./src/com/bjinfotech/practice/logging/multiFileLoggerConfig.properties";
MultiFileLoggerByLogLevel mflogger=new MultiFileLoggerByLogLevel(propertyFilePath);
mflogger.debug("test");
mflogger.info("test");
mflogger.warn("test");
mflogger.error("test");
}
}
log4j的屬性檔案如下：
multiFileLoggerConfig.properties
log4j.rootCategory=DEBUG,stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] (%F:%L) - %m%n
log4j.category.ERROR=ERROR,stdout,R_ERROR
log4j.additivity.ERROR=false
log4j.appender.R_ERROR=org.apache.log4j.RollingFileAppender
log4j.appender.R_ERROR.file=example_ERROR.log
log4j.appender.R_ERROR.MaxFileSize=100KB
log4j.appender.R_ERROR.MaxBackupIndex=1
log4j.appender.R_ERROR.layout=org.apache.log4j.PatternLayout
log4j.appender.R_ERROR.layout.ConversionPattern=%p %t %c - %m%n
log4j.category.WARN=WARN,stdout,R_WARN
log4j.additivity.WARN=false
log4j.appender.R_WARN=org.apache.log4j.RollingFileAppender
log4j.appender.R_WARN.file=example_WARN.log
log4j.appender.R_WARN.MaxFileSize=100KB
log4j.appender.R_WARN.MaxBackupIndex=1
log4j.appender.R_WARN.layout=org.apache.log4j.PatternLayout
log4j.appender.R_WARN.layout.ConversionPattern=%p %t %c - %m%n
log4j.category.INFO=INFO,stdout,R_INFO
log4j.additivity.INFO=false
log4j.appender.R_INFO=org.apache.log4j.RollingFileAppender
log4j.appender.R_INFO.File=example_INFO.log
log4j.appender.R_INFO.MaxFileSize=100KB
log4j.appender.R_INFO.MaxBackupIndex=1
log4j.appender.R_INFO.layout=org.apache.log4j.PatternLayout
log4j.appender.R_INFO.layout.ConversionPattern=%p %t %c - %m%n
log4j.category.DEBUG=DEBUG,stdout,R_DEBUG
log4j.additivity.DEBUG=false
log4j.appender.R_DEBUG=org.apache.log4j.RollingFileAppender
log4j.appender.R_DEBUG.File=example_DEBUG.log
log4j.appender.R_DEBUG.MaxFileSize=100KB
log4j.appender.R_DEBUG.MaxBackupIndex=1
log4j.appender.R_DEBUG.layout=org.apache.log4j.PatternLayout
log4j.appender.R_DEBUG.layout.ConversionPattern=%p %t %c - %m%n