Java实现文件监控器FileMonitor的实例代码

应用场景：

代码可以实现文件变化后的监听，如文件变化，自动重新加载文件内容，实现配置文件的热部署。

代码： 

package com.yx.demo.filemonitor;
 
import java.io.File;
import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Timer;
import java.util.TimerTask;
 

public class FileMonitor {
 
  
  private static FileMonitor defaultFileMonitor = new FileMonitor(2 * 1000);
 
  private Timer timer_;
  private HashMap files_; // File -> Long
  private List fileEntrys = new java.util.concurrent.CopyOnWriteArrayList();
  private Collection> listeners_; // of WeakReference(FileListener)
 
  private long pollingInterval = 10000;
 
  public static FileMonitor getDefaultFileMonitor() {
    return defaultFileMonitor;
  }
 
  
  public FileMonitor(long pollingInterval) {
    this.pollingInterval = pollingInterval;
 
    files_ = new HashMap();
    listeners_ = new ArrayList>();
 
    timer_ = new Timer("FileMonitor", true);
    timer_.schedule(new FileMonitorNotifier(), 0, pollingInterval);
  }
 
  
  public void stop() {
    timer_.cancel();
    timer_ = null;
  }
 
  public void start() {
    if (timer_ == null) {
      timer_ = new Timer(true);
      timer_.schedule(new FileMonitorNotifier(), 0, pollingInterval);
    }
  }
 
  
  public void addFile(String id, File file) {
    if (!files_.containsKey(file)) {
 
      FileEntry entry = new FileEntry(id, file, file.exists() ? file.lastModified() : -1);
      files_.put(file, entry);
    }
  }
 
  
  public void addFileEntry(FileEntry fileEntry) {
    if (!fileEntrys.contains(fileEntry)) {
      fileEntrys.add(fileEntry);
    }
  }
 
  
  public boolean fileEntryExists(String id) {
    if (id == null) {
      return false;
    }
 
    for (int i = 0; i < fileEntrys.size(); i++) {
      if (id.equals(fileEntrys.get(i).getId())) {
 return true;
      }
    }
 
    return false;
  }
 
  
  public void removeFileEntry(String id) {
    if (id == null) {
      return;
    }
 
    for (int i = 0; i < fileEntrys.size(); i++) {
      if (id.equals(fileEntrys.get(i).getId())) {
 fileEntrys.remove(i);
 return;
      }
    }
  }
 
  
  public void removeFile(File file) {
    files_.remove(file);
  }
 
  
  public void addListener(FileListener fileListener) {
    // Don't add if its already there
    for (Iterator> i = listeners_.iterator(); i.hasNext(); ) {
      WeakReference reference = i.next();
      FileListener listener = (FileListener) reference.get();
      if (listener == fileListener) {
 return;
      }
    }
 
    // Use WeakReference to avoid memory leak if this becomes the
    // sole reference to the object.
    listeners_.add(new WeakReference(fileListener));
  }
 
  
  public void removeListener(FileListener fileListener) {
    for (Iterator> i = listeners_.iterator(); i.hasNext(); ) {
      WeakReference reference = (WeakReference) i.next();
      FileListener listener = (FileListener) reference.get();
      if (listener == fileListener) {
 i.remove();
 break;
      }
    }
  }
 
  
  private class FileMonitorNotifier extends TimerTask {
    @Override
    public void run() {
      try {
 for (Iterator i = fileEntrys.iterator(); i.hasNext(); ) {
   try {
     FileEntry entry = i.next();
     if (entry == null || !entry.check()) {
i.remove();
     }
   } catch (Throwable t) {
     t.printStackTrace();
     System.out.println("执行文件监控发生错误:" + t.getMessage());
   }
 }
 
 // Loop over the registered files and see which have changed.
 // Use a copy of the list in case listener wants to alter the
 // list within its fileChanged method.
 Collection files = new ArrayList(files_.keySet());
 
 for (Iterator i = files.iterator(); i.hasNext(); ) {
   File file = i.next();
   try {
     FileEntry fileEntry = files_.get(file);
     long lastModifiedTime = fileEntry.getLastModified();
     long newModifiedTime = file.exists() ? file.lastModified() : -1;
 
     //logger.debug(file.getAbsolutePath());
     //logger.debug("  {}=>{}", lastModifiedTime, newModifiedTime);
     // Chek if file has changed
     if (newModifiedTime != lastModifiedTime) {
//logger.debug("file changed {})", file.getAbsolutePath());
fileEntry.setLastModified(newModifiedTime);
// Register new modified time
files_.put(file, fileEntry);
 
if (fileEntry.getFileListener() != null) {
  fileEntry.getFileListener().fileChanged(fileEntry);
} else {
  // Notify listeners
  for (Iterator> j =
      listeners_.iterator(); j.hasNext(); ) {
    WeakReference reference =
 (WeakReference) j.next();
    FileListener listener = (FileListener) reference.get();
 
    // Remove from list if the back-end object has been GC'd
    if (listener == null) {
      j.remove();
    } else {
      listener.fileChanged(fileEntry);
    }
  }
}
     }
   } catch (Throwable t) {
     if (file != null) {
t.printStackTrace();
System.out.println(
    "file monitor execute error, file=" + file.getAbsolutePath() +
 t.getMessage());
     } else {
System.out.println(
    "file monitor execute error, file=null" + t.getMessage());
     }
   }
 }
      } catch (Throwable t) {
 System.out.println("执行文件监控发生错误" + t.getMessage());
      }
    }
  }
}
package com.yx.demo.filemonitor;
 

public interface FileListener {
 
 public void fileChanged(FileEntry fileEntry);
}

package com.yx.demo.filemonitor; 

import java.io.File;
import java.lang.ref.WeakReference;

public class FileEntry {
  String id;
  File file;
  long lastModified;
  FileListener fileListener = null;
  Object userData;
  WeakReference