testfilelock.java

文本编辑器

import java.io.*;
import java.nio.*;
import java.nio.channels.*;
import java.nio.charset.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.JOptionPane;


public class TestFileLock implements ActionListener{
	private Frame frame;
	private FileDialog fd_load;
	private FileDialog fd_save;
	private TextArea ta;
	private String file = "";
	private MenuItem save;

	private RandomAccessFile raf;
	private FileChannel fci;
	private FileLock flock;
	private CharsetEncoder encoder;
	private CharsetDecoder decoder;
	
	
	public static void main( String args[]) {
		new TestFileLock().init();
	}
	
	public void init(){
		frame = new Frame("My Notepad");
		MenuBar mb = new MenuBar();
		Menu file = new Menu("文件");
		Menu help = new Menu("帮助");
		MenuItem open = new MenuItem("打开");
		save = new MenuItem("保存");
		save.setEnabled(false);
		file.add(open);
		file.add(save);
		mb.add(file);
		mb.add(help);		
		frame.setMenuBar(mb);
		ta = new TextArea();
		frame.add(ta,"Center");		
		open.addActionListener(this);
		save.addActionListener(this);
		frame.addWindowListener(new WindowAdapter(){
			public void windowClosing(WindowEvent e){
				System.exit(0);	
			}	
		});  
		frame.setSize(600,400);
		frame.setLocation(300,100);
		frame.setVisible( true);		
		fd_load = new FileDialog(frame,"打开文件",FileDialog.LOAD);
		fd_save = new FileDialog(frame,"保存文件",FileDialog.SAVE);
		
		Charset charset = Charset.forName(System.getProperty("file.encoding"));
		encoder = charset.newEncoder();
		decoder = charset.newDecoder();
	}

	public void actionPerformed(ActionEvent e){
		String s = e.getActionCommand();
		if(s.equals("打开")){
			fd_load.setVisible(true);
			String d = fd_load.getDirectory();
			String f = fd_load.getFile();
			if((d != null) && (f != null)){
				String destfile = d + f;
				if(destfile.equals(file)){
					return;	
				}else{
					this.closeFile();
					file = destfile;
					this.loadFile();
				}	
			}
		}else if(s.equals("保存")){
			this.saveFile();
		}
	}	
	public void loadFile(){
		try{
			raf = new RandomAccessFile(file,"rw");
			fci = raf.getChannel();
			flock = fci.tryLock();
			if(flock == null){
				ta.setText("");
				JOptionPane.showMessageDialog(null, 
					"文件正在使用中，无法以独占的方式打开！",
					"错误提示", JOptionPane.ERROR_MESSAGE);	
				file = "";
				raf.close();
				raf = null;
			}else{
				int length = (int)fci.size();
				ByteBuffer bb = ByteBuffer.allocate(length);
				fci.read(bb);
				bb.flip();
				CharBuffer cb = decoder.decode(bb);
				ta.setText(cb.toString());
				frame.setTitle("My Notepad - " + file);
				save.setEnabled(true);
			}
		}catch(IOException e){
			e.printStackTrace();	
		}
	}
	public void saveFile(){
		String content = ta.getText();
		try{
			CharBuffer cb = CharBuffer.wrap(content.toCharArray());
			ByteBuffer bb = encoder.encode(cb);
			raf.setLength(0);
			fci.write(bb);
			fci.force(true);
		}catch(IOException e){
			e.printStackTrace();	
		}
	}
	public void closeFile(){
		try{
			if(flock != null){
				flock.release();
			}
			if(raf != null){
				raf.close();	
			}
			file = "";
			frame.setTitle("My Notepad");
			save.setEnabled(false);
		}catch(IOException e){
			e.printStackTrace();	
		}	
	}	
}