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 -> Long private 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 there for (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 { @Override public 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 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<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'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; /** * 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() {@Overridepublic 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);
总结
以上所述是小编给大家介绍的Java实现文件监控器FileMonitor的实例代码，希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对我们网站的支持！如果你觉得本文对你有帮助，欢迎转载，烦请注明出处，谢谢！
本文标题: Java实现文件监控器FileMonitor的实例代码
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