今天看到log4j裏的一個工具類，用來監控文件，如有變動就執行特定的操作，簡單且有用，只需要實現一個doOnChange()方法即可。
從這個文件可以看出，其實log4j.properties或者log4j.xml是可以實現在線修改的，不用重啓服務，只需在web.xml里加一個org.springframework.web.util.Log4jConfigListener，再用<context-param>配置一個初始屬性log4jRefreshInterval，即刷新log4j配置信息的間隔時間，單位是毫秒，如下：
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<context-param> <param-name>log4jConfigLocation</param-name> <param-value>log4j.properties</param-value> </context-param> <context-param> <param-name>log4jRefreshInterval</param-name> <param-value>60000</param-value> </context-param> <listener> <listener-class>org.springframework.web.util.Log4jConfigListener</listener-class> </listener>
非web應用的話需要寫一個類Foo繼承org.apache.log4j.varia.ReloadingPropertyConfigurator，重寫doConfigure方法，直接調用org.apache.log4j.PropertyConfigurator.configureAndWatch(String, long)；
FileWatchdog源碼如下： /* *
Licensed to the Apache Software Foundation (ASF) under one or more *
contributor license agreements. See the NOTICE file distributed with *
this work for additional information regarding copyright ownership. *
The ASF licenses this file to You under the Apache License, Version 2.0 *
(the "License"); you may not use this file except in compliance with *
the License. You may obtain a copy of the License at * *
http://www.apache.org/licenses/LICENSE-2.0 * *
Unless required by applicable law or agreed to in writing, software *
distributed under the License is distributed on an "AS IS" BASIS, *
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. *
See the License for the specific language governing permissions and *
limitations under the License. *///
Contributors: Mathias Bogaertpackageorg.apache.log4j.helpers;importjava.io.File;importorg.apache.log4j.helpers.LogLog;/** Check
every now and then that a certain file has not changed. If it has,
then call the {<a href="http://my.oschina.net/link1212" target="_blank" rel="nofollow">@link</a> #doOnChange} method. <a
href="http://my.oschina.net/arthor" target="_blank" rel="nofollow">@author</a> Ceki Gülcü <a
href="http://my.oschina.net/u/266547" target="_blank" rel="nofollow">@since</a> version 0.9.1 */publicabstract
class
FileWatchdog extendsThread
{ /** The
default delay between every file modification check, set to 60 seconds.
*/ staticfinal
public
long
DEFAULT_DELAY = 60000; /** The
name of the file to observe for changes. */ protectedString
filename; /** The
delay to observe between every check. By default set {<a href="http://my.oschina.net/link1212" target="_blank" rel="nofollow">@link</a> #DEFAULT_DELAY}.
*/ protectedlong
delay = DEFAULT_DELAY; File
file; longlastModif
= 0; booleanwarnedAlready
= false; booleaninterrupted
= false; protected FileWatchdog(String
filename) { this.filename
= filename; file
= newFile(filename); setDaemon(true); checkAndConfigure(); } /** Set
the delay to observe between each check of the file changes. */ public voidsetDelay(longdelay)
{ this.delay
= delay; } abstract protected voiddoOnChange(); protected voidcheckAndConfigure()
{ booleanfileExists; try{ fileExists
= file.exists(); }catch(SecurityException
e) { LogLog.warn("Was
not allowed to read check file existance, file:["+ filename+"]."); interrupted
= true;//
there is no point in continuing return; } if(fileExists)
{ longl
= file.lastModified(); //
this can also throw a SecurityException if(l
> lastModif) { //
however, if we reached this point this lastModif
= l; //
is very unlikely. doOnChange(); warnedAlready
= false; } }else{ if(!warnedAlready)
{ LogLog.debug("["+filename+"]
does not exist."); warnedAlready
= true; } } } public voidrun()
{ while(!interrupted)
{ try{ Thread.sleep(delay); }catch(InterruptedException
e) { //
no interruption expected } checkAndConfigure(); } }} |