Java 文件对话框另存为

Question

我正在为我的 Java 类开发一个项目，我们只需修改代码。我必须向基本文本文件文档添加“保存”和“另存为”对话框。当我第一次“另存为”时，它很好，但随后再次“另存为”，但点击“取消”，它会将文件重置为空。我已经做到了，至少标题仍然保留，但是当您点击“保存”按钮时，它的作用就像是一个空文件，并且“另存为”对话框再次出现。我希望这样当您取消“另存为”时，它会保留以前的文件而不是返回到空。我还在格式化它，所以它很时髦

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


public class JavaEdit extends Frame implements ActionListener {

String clipBoard;
String fileName; 
TextArea text;
MenuItem newMI, openMI, saveMI, saveAsMI, exitMI;
MenuItem selectAll, cutMI, copyMI, deleteMI, pasteMI;
MenuItem about;

/**
 * Constructor
 */
public JavaEdit() {
    super("JavaEdit");          // set frame title
    setLayout(new BorderLayout());  // set layout

    // create menu bar
    MenuBar menubar = new MenuBar();
    setMenuBar(menubar);

    // create file menu
    Menu fileMenu = new Menu("File");
    menubar.add(fileMenu);
    newMI = fileMenu.add(new MenuItem("New"));
    newMI.addActionListener(this);
    openMI = fileMenu.add(new MenuItem("Open"));
    openMI.addActionListener(this);
    fileMenu.addSeparator();
    saveMI = fileMenu.add(new MenuItem("Save"));
    saveMI.addActionListener(this);
    saveAsMI = fileMenu.add(new MenuItem("Save As ..."));
    saveAsMI.addActionListener(this);
    fileMenu.addSeparator();
    exitMI = fileMenu.add(new MenuItem("Exit"));
    exitMI.addActionListener(this);

    // create edit menu
    Menu editMenu = new Menu("Edit");
    menubar.add(editMenu);
    selectAll = editMenu.add(new MenuItem("Select All"));
    selectAll.addActionListener(this);
    cutMI = editMenu.add(new MenuItem("Cut"));
    cutMI.addActionListener(this);
    copyMI = editMenu.add(new MenuItem("Copy"));
    copyMI.addActionListener(this);
    pasteMI = editMenu.add(new MenuItem("Paste"));
    pasteMI.addActionListener(this);
    deleteMI = editMenu.add(new MenuItem("Delete"));
    deleteMI.addActionListener(this);

    Menu helpMenu = new Menu("Help");
    menubar.add(helpMenu);
    about = helpMenu.add(new MenuItem("About"));
    about.addActionListener(this);

    // create text editing area
    text = new TextArea();
    add(text, BorderLayout.CENTER);
}

// implementing ActionListener
public void actionPerformed(ActionEvent event) {
    Object source = event.getSource();
    if(source == newMI) {
        clearText();
        fileName = null;
        setTitle("JavaEdit");   // reset frame title
    }

    else if(source == openMI) {
        doOpen();
    }
    else if (source == saveAsMI) {

                doSaveAs();
    }
    else if (source == saveMI) {
        doSave();
    }
    else if(source == exitMI) {
        System.exit(0);
    }
    else if(source == selectAll) {
        doSelect();
    }
    else if(source == cutMI) {
        doCopy();
        doDelete();
    }
    else if(source == copyMI) {
        doCopy();
    }
    else if(source == pasteMI) {
        doPaste();
    }
    else if(source == deleteMI) {
        doDelete();
    }
    else if(source == about){
        MessageDialog dialog = new MessageDialog(this, "About",
        "JavaEdit in Java, Version 2.0, 2017");
        dialog.setVisible(true);
        return;

    }

}

/**
 * method to specify and open a file
 */
private void doOpen() {
    // display file selection dialog
    FileDialog fDialog = new FileDialog(this, "Open ...", FileDialog.LOAD);
    fDialog.setVisible(true);
    // Get the file name chosen by the user
    String name = fDialog.getFile();
    // If user canceled file selection, return without doing anything.
    if(name == null)
        return;
    fileName = fDialog.getDirectory() + name;

    // Try to create a file reader from the chosen file.
    FileReader reader=null;
    try {
        reader = new FileReader(fileName);
    } catch (FileNotFoundException ex) {
        MessageDialog dialog = new MessageDialog(this, "Error Message",
                                                 "File Not Found: "+fileName);
            dialog.setVisible(true);
            return;
    }
    BufferedReader bReader = new BufferedReader(reader);

    // Try to read from the file one line at a time.
    StringBuffer textBuffer = new StringBuffer();
    try {
        String textLine = bReader.readLine();
        while (textLine != null) {
            textBuffer.append(textLine + '\n');
            textLine = bReader.readLine();
        }
        bReader.close();
        reader.close();
    } catch (IOException ioe) {
        MessageDialog dialog = new MessageDialog(this, "Error Message",
                                   "Error reading file: "+ioe.toString());
        dialog.setVisible(true);
        return;
    }
    setTitle("JavaEdit: " +name);   // reset frame title
    text.setText(textBuffer.toString());
}
private void doSaveAs() {

    FileDialog fDialog = new FileDialog(this, "Save As ...", FileDialog.SAVE);
    fDialog.setVisible(true);

       fileName = fDialog.getFile();
       String name = fileName.toString();

         setTitle("JavaEdit: " + name);   // reset frame title
         fDialog.setFile(name);


         FileWriter fileCharStream = null;  // File stream for writing file
         try {

            fileCharStream = new FileWriter(fileName); // May throw IOException
            // Use file output stream
               fileCharStream.write(text.getText());

         } catch (IOException excpt) {
             MessageDialog dialog = new MessageDialog(this, "Error Message",
                    fileName);
             dialog.setVisible(true);
             return;
         } finally {
            closeFileWriter(fileCharStream); // Ensure file is closed!
         }

}


private void doSave()  {     

    if(fileName == null  )
    {
        doSaveAs();
    }
    FileWriter out = null;
         try {
               out =new FileWriter(fileName);

              out.write(text.getText());

            }
            catch (IOException excpt) {
                MessageDialog dialog = new MessageDialog(this, "Error Message",
                        fileName);
             dialog.setVisible(true);
             return;
            } finally {
                closeFileWriter(out); // Ensure file is closed!
            }// Ensure file is closed!


}
    static void closeFileWriter(FileWriter fileName) {
      try {
         if (fileName != null) { // Ensure "file" references a valid object

            fileName.close(); // close() may throw IOException if fails

         }
      } catch (IOException closeExcpt) {
             closeExcpt.getMessage();
      }

      return;
   }


  private void doSelect() {
        text.selectAll();
    }

/**
 * method to clear text editing area
 */
private void clearText() {
    text.setText("");
}

/**
 * method to copy selected text to the clipBoard
 */
private void doCopy() {
    clipBoard = new String(text.getSelectedText());
}

/**
 * method to delete selected text
 */
private void doDelete() {
    text.replaceRange("", text.getSelectionStart(), text.getSelectionEnd());
}

/**
 * method to replace current selection with the contents of the clipBoard
 */
private void doPaste() {
    if(clipBoard != null) {
        text.replaceRange(clipBoard, text.getSelectionStart(),
                          text.getSelectionEnd());
    }
}

/**
 * class for message dialog
 */
class MessageDialog extends Dialog implements ActionListener {
    private Label message;
    private Button okButton;

    // Constructor
    public MessageDialog(Frame parent, String title, String messageString) {
        super(parent, title, true);
        setSize(400, 100);
        setLocation(150, 150);
        setLayout(new BorderLayout());

        message = new Label(messageString, Label.CENTER);
        add(message, BorderLayout.CENTER);

        Panel panel = new Panel(new FlowLayout(FlowLayout.CENTER));
        add(panel, BorderLayout.SOUTH);
        okButton = new Button(" OK ");
        okButton.addActionListener(this);
        panel.add(okButton);


        this.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                setVisible(false);
                dispose();
            }
        });


    }

    // implementing ActionListener
    public void actionPerformed(ActionEvent event) {
        setVisible(false);
        dispose();
    }



}

/**
 * the main method
 */
public static void main(String[] argv) {
    // create frame
    JavaEdit frame = new JavaEdit();
    Dimension size = Toolkit.getDefaultToolkit().getScreenSize();
    frame.setSize(size.width-80, size.height-80);
    frame.setLocation(20, 20);

    // add window closing listener
    frame.addWindowListener(new WindowAdapter() {
        public void windowClosing(WindowEvent e) {
            System.exit(0);
        }
    });

    // show the frame
    frame.setVisible(true);
}
}

Answer 1

简单地检查返回的文件是否为空:

String name = fDialog.getFile();
// if Cancel is pressed we just exit
if (name == null) {
    return;
}
// otherwise we save it
fileName = name;
...