]log4j FileWatchdog工具类，用来监控文件，如有变动就执行特定的操作

今天看到log4j里的一个工具类，用来监控文件，如有变动就执行特定的操作，简单且有用，只需要实现一个doOnChange()方法即可。

 从这个文件可以看出，其实log4j.properties或者log4j.xml是可以实现在线修改的，不用重启服务，只需在web.xml里加一个org.springframework.web.util.Log4jConfigListener，再用<context-param>配置一个初始属性log4jRefreshInterval，即刷新log4j配置信息的间隔时间，单位是毫秒，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应用的话需要写一个类Foo继承org.apache.log4j.varia.ReloadingPropertyConfigurator，重写doConfigure方法，直接调用org.apache.log4j.PropertyConfigurator.configureAndWatch(String, long)；
然后在启动非web应用时加系统属性-Dlog4j.configuratorClass=Foo (这里要全路径)，用于指定log4j Configurator的实现类。
我自己写了一个MyLog4jConfigurator，已经测试通过，如下：

 

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packagecom.mashiguang;   importjava.net.URL;   importorg.apache.log4j.PropertyConfigurator; importorg.apache.log4j.spi.LoggerRepository; importorg.apache.log4j.varia.ReloadingPropertyConfigurator;   publicclass MyLog4jConfigurator extendsReloadingPropertyConfigurator {           PropertyConfigurator delegate = newPropertyConfigurator();       @Override     publicvoid doConfigure(URL url, LoggerRepository repository) {         delegate.configureAndWatch(url.getFile(),1000);     } }

 

 

FileWatchdog源码如下：

/*

 * 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 Bogaert

 

packageorg.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 G&uuml;lc&uuml;

   <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();

    }

  }

}