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;
}
}
}
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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
