Java实现文件监控器FileMonitor

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;/*** FileMonitor* 文件监控器** @author yx* @date 2019/12/21 0:59*/
public class FileMonitor {/*** 每2秒更新的默认监控器*/private static FileMonitor defaultFileMonitor = new FileMonitor(2 * 1000);private Timer timer_;private HashMap<File, FileEntry> files_; // File -> Longprivate List<FileEntry> fileEntrys = new java.util.concurrent.CopyOnWriteArrayList<FileEntry>();private Collection<WeakReference<FileListener>> listeners_; // of WeakReference(FileListener)private long pollingInterval = 10000;public static FileMonitor getDefaultFileMonitor() {return defaultFileMonitor;}/*** Create a file monitor instance with specified polling interval.** @param pollingInterval Polling interval in milli seconds.*/public FileMonitor(long pollingInterval) {this.pollingInterval = pollingInterval;files_ = new HashMap<File, FileEntry>();listeners_ = new ArrayList<WeakReference<FileListener>>();timer_ = new Timer("FileMonitor", true);timer_.schedule(new FileMonitorNotifier(), 0, pollingInterval);}/*** Stop the file monitor polling.*/public void stop() {timer_.cancel();timer_ = null;}public void start() {if (timer_ == null) {timer_ = new Timer(true);timer_.schedule(new FileMonitorNotifier(), 0, pollingInterval);}}/*** Add file to listen for. File may be any java.io.File (including a* directory) and may well be a non-existing file in the case where the* creating of the file is to be trepped.* <p>* More than one file can be listened for. When the specified file is* created, modified or deleted, listeners are notified.** @param file File to listen for.*/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);}}/*** 添加监控文件实体。** @param fileEntry*/public void addFileEntry(FileEntry fileEntry) {if (!fileEntrys.contains(fileEntry)) {fileEntrys.add(fileEntry);}}/*** 通过文件实体的标识判断监控文件实体是否存在。** @param id* @return*/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;}/*** 通过文件实体标识删除一个监控文件实体。** @param id*/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;}}}/*** Remove specified file for listening.** @param file File to remove.*/public void removeFile(File file) {files_.remove(file);}/*** Add listener to this file monitor.** @param fileListener Listener to add.*/public void addListener(FileListener fileListener) {// Don't add if its already therefor (Iterator<WeakReference<FileListener>> i = listeners_.iterator(); i.hasNext(); ) {WeakReference<FileListener> 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>(fileListener));}/*** Remove listener from this file monitor.** @param fileListener Listener to remove.*/public void removeListener(FileListener fileListener) {for (Iterator<WeakReference<FileListener>> i = listeners_.iterator(); i.hasNext(); ) {WeakReference<FileListener> reference = (WeakReference<FileListener>) i.next();FileListener listener = (FileListener) reference.get();if (listener == fileListener) {i.remove();break;}}}/*** This is the timer thread which is executed every n milliseconds according* to the setting of the file monitor. It investigates the file in question* and notify listeners if changed.*/private class FileMonitorNotifier extends TimerTask {@Overridepublic void run() {try {for (Iterator<FileEntry> 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<File> files = new ArrayList<File>(files_.keySet());for (Iterator<File> 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 changedif (newModifiedTime != lastModifiedTime) {//logger.debug("file changed {})", file.getAbsolutePath());fileEntry.setLastModified(newModifiedTime);// Register new modified timefiles_.put(file, fileEntry);if (fileEntry.getFileListener() != null) {fileEntry.getFileListener().fileChanged(fileEntry);} else {// Notify listenersfor (Iterator<WeakReference<FileListener>> j =listeners_.iterator(); j.hasNext(); ) {WeakReference<FileListener> reference =(WeakReference<FileListener>) j.next();FileListener listener = (FileListener) reference.get();// Remove from list if the back-end object has been GC'dif (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;/*** FileListener** @author yx* @date 2019/12/21 0:55*/
public interface FileListener {/*** * @param fileEntry*/public void fileChanged(FileEntry fileEntry);
}

package com.yx.demo.filemonitor;import java.io.File;
import java.lang.ref.WeakReference;/*** FileEntry* 文件Entry，如果FileEntry指定了FileListener，那么当文件发生变动时只触发指定的FileListener** @author yx* @date 2019/12/21 0:56*/
public class FileEntry {String id;File file;long lastModified;FileListener fileListener = null;Object userData;WeakReference<Object> reference = null;/*** 构造函数。** @param id* @param file*/public FileEntry(String id, File file) {this(id, file, file.exists() ? file.lastModified() : -1);}public FileEntry(Object reference, String id, File file) {this(id, file, file.exists() ? file.lastModified() : -1);reference = new WeakReference<Object>(reference);}/*** 构造函数。** @param id           标识* @param file         要监控的文件* @param lastmodified 最后修改日期*/public FileEntry(String id, File file, long lastmodified) {super();this.id = id;this.file = file;this.lastModified = lastmodified;}public boolean check() {if (reference != null && reference.get() == null) {//监控对象已经不存在，请求FileMonitor删除自己return false;}long newModifiedTime = file.exists() ? file.lastModified() : -1;if (lastModified != newModifiedTime) {this.lastModified = newModifiedTime;FileListener ls = this.getFileListener();if (ls == null) {return false;} else {try {ls.fileChanged(this);} catch (Exception e) {e.printStackTrace();System.err.println("执行文件监控事件监听" + e.getMessage());}return true;}} else {return true;}}public String getId() {return id;}public void setId(String id) {this.id = id;}public File getFile() {return file;}public void setFile(File file) {this.file = file;}public long getLastModified() {return lastModified;}public void setLastModified(long lastModified) {this.lastModified = lastModified;}public FileListener getFileListener() {return fileListener;}public void setFileListener(FileListener fileListener) {this.fileListener = fileListener;}public Object getUserData() {return userData;}public void setUserData(Object userData) {this.userData = userData;}
}

使用demo:

// 文件路径
String fileName = "conf/database.xml";// 文件监控
FileListener fileListener = new FileListener() {
@Override
public void fileChanged(FileEntry fileEntry) {
// TODO 文件变化后的业务处理
}
};File file = new File(fileName);
FileEntry fileEntry = new FileEntry("database", file);
// 设置文件监控
fileEntry.setFileListener(fileListener);FileMonitor.getDefaultFileMonitor().addFileEntry(fileEntry);

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