BufferedWriter output=new BufferedWriter(new FileWriter(file));
                
                String out=textArea.getText();
                out=out.replaceAll("\n", "\r\n");
                output.write(out);
                
                output.close();

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.io.*;

class Demo extends JFrame implements ActionListener
{
    private JButton but = new JButton("保存");
    private JTextField tf = new JTextField(30);
    public Demo()
    {
        this.getContentPane().add(but,"North");
        this.getContentPane().add(tf);
        but.addActionListener(this);
        this.pack();
        this.setLocationRelativeTo(null);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setVisible(true);
    }
    public static void main(String[]args)
    {
        new Demo();
    }
    
    public void actionPerformed(ActionEvent e)
    {
        try
        {
            FileDialog fd = new FileDialog(new Dialog(this));
            fd.setVisible(true);
            File f = new File(fd.getDirectory()+"\\"+fd.getFile());
            String content = tf.getText().replaceAll("\n","\r\n");
            BufferedWriter br = new BufferedWriter(new FileWriter(f));
            tf.write(br);
            br.close();
        }catch(Exception ex)
        {
            
        }
    }
}