无法使用Java写入文件

Question

I have wrote a simple java GUI program to write the content of a text area into a file:

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

public class Convert {
    public static void main(String[] args) {
        new MyFrame();
    }
}


class MyFrame extends JFrame{
    JPanel panel = new JPanel();
    JButton button = new JButton("Convert");
    JTextArea textArea = new JTextArea(500, 400);
    String fileName = "result.txt";

    MyFrame() {
        super("converter");
        setVisible(true);
        setBounds(100, 100, 500, 500);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.add(panel);
        panel.setLayout(null);

        panel.add(button);
        button.setLocation(0, 0);
        button.setSize(this.getBounds().width, 100);

        panel.add(textArea);
        textArea.setEditable(true);
        textArea.setLocation(0, 100);
        textArea.setSize(this.getBounds().width, this.getBounds().height - 100);

        button.addActionListener(new ActionListener() {

            public void actionPerformed(ActionEvent event) {

                try {
                    File file = new File(fileName);
                    if (!file.exists()) {
                        file.createNewFile();
                    }

                    FileWriter fw = new FileWriter(file);
                    BufferedWriter bw = new BufferedWriter(fw);

                    String text = textArea.getText();
                    textArea.setText("");
                    Scanner scanner = new Scanner(text);

                    while (scanner.hasNextLine()) {

                        String line = scanner.nextLine();
                        byte[] utf8 = line.getBytes("UTF-8");
                        line = new String(utf8, "UTF-8");

                        bw.write(line);
                        System.out.println(line);
                    }

                }

                catch (Exception e) {
                    System.out.print(e.getMessage());
                }

            }
        });
    }
}

Note that the input source is in utf-8 (chinese character) and i am able to print out correctly. However, the result.txt file is empty. Even if i try bw.write("asdf") it's still empty.

Answer 1

You are missing to close the BufferedWriter. Closing it will do the flush and close of the writer and you should see the contents in your file. You need to add the following.

bw.close();

And here is where you need to put the close():

                while (scanner.hasNextLine()) {

                    String line = scanner.nextLine();
                    byte[] utf8 = line.getBytes("UTF-8");
                    line = new String(utf8, "UTF-8");

                    bw.write(line);
                    System.out.println(line);
                }
                // close the buffered
                bw.close();

Note: Ideally putting it in the finally block makes more sense because if there is an exception even then it will get close.

  try {
                File file = new File(fileName);
                if (!file.exists()) {
                    file.createNewFile();
                }

                FileWriter fw = new FileWriter(file);
                BufferedWriter bw = new BufferedWriter(fw);

                String text = textArea.getText();
                textArea.setText("");
                Scanner scanner = new Scanner(text);

                while (scanner.hasNextLine()) {

                    String line = scanner.nextLine();
                    byte[] utf8 = line.getBytes("UTF-8");
                    line = new String(utf8, "UTF-8");

                    bw.write(line);
                    System.out.println(line);
                }

            }

            catch (Exception e) {
                System.out.print(e.getMessage());
            } finally {
                try {
                    bw.close();
               } catch (Exception e) {
                System.out.print("Exception while closing the bw");
               }
            }

Answer 2

You have to make sure that you have closed the FileWriter, or in your case, the buffered writer. So all you gotta do is

bw.write(line);
System.out.println(line);
bw.close();

this will close the open buffer, and allow it to write whatever is in the buffer to the file you are creating.

Hope this helps!