FileMonitor.java

package com.sandwich.util.io;

import java.io.File;
import java.io.IOException;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Vector;

public class FileMonitor {
	
	private final List<FileListener> listeners = new Vector<FileListener>();
	private final DataFileHelper<Map<String, Long>> fileHashesHelper;
	
	private final Map<String, Long> fileHashesByDirectory;
	
	final File fileSystemPath;
	
	public FileMonitor(File fileSystemPath, File dataFile) {
		this.fileSystemPath = fileSystemPath;
		if(!this.fileSystemPath.exists()){
			throw new IllegalArgumentException(fileSystemPath+ " cannot be found.");
		}
		fileHashesHelper = new DataFileHelper<Map<String,Long>>(
				dataFile, new HashMap<String,Long>());
		fileHashesByDirectory = fileHashesHelper.read();
	}
	
	public String getFilesystemPath() {
		return fileSystemPath.getAbsolutePath();
	}
	
	public void close(){
		listeners.clear();
	}

	public void addFileSavedListener(FileListener listener){
		listeners.add(listener);
	}
	
	public void removeFileSavedListener(FileListener listener){
		listeners.remove(listener);
	}
	
	synchronized void notifyListeners(){
		try {
			Map<String, Long> currentHashes = getFilesystemHashes();
			for(String fileName : currentHashes.keySet()){
				Long currentHash 	= currentHashes.get(fileName);
				Long previousHash 	= fileHashesByDirectory.get(fileName);
				
				fileHashesByDirectory.put(fileName, currentHash);
				File file = new File(fileName);
				
				for(FileListener listener : listeners){
					if(previousHash == null && currentHash != null){
						listener.newFile(file);
					}else if(currentHash == null && previousHash != null){
						listener.fileDeleted(file);
					}else if(!currentHash.equals(previousHash)){
						listener.fileSaved(file);
					}
				}
			}
		} catch (IOException e) {
			throw new RuntimeException(e);
		}
	}
	
	Map<String, Long> getFilesystemHashes() throws IOException {
		final HashMap<String,Long> fileHashes = new HashMap<String,Long>();
		new ForEachFileAction(){
			public void onFile(File src) throws IOException {
				fileHashes.put(src.getAbsolutePath(), src.lastModified());
			}
		}.operate(fileSystemPath);
		return fileHashes;
	}

	public boolean isFileModifiedSinceLastPoll(String filePath, Long lastModified) {
		Long previousHash = fileHashesByDirectory.get(filePath);
		return !lastModified.equals(previousHash);
	}

	public void updateFileSaveTime(File file) {
		fileHashesByDirectory.put(file.getAbsolutePath(), file.lastModified());
	}

	public void writeChanges() {
		try {
			fileHashesHelper.write(getFilesystemHashes());
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
	
}