Java - Program which remembers/saves entered fields

问题

I have a program that uses three JTextField fields as the main data entry fields. I want to have it so that when the user terminates the program and then opens it again, their last entry will still be in the fields.

How could I achieve this? Would I need some sort of database or is there a simpler way?

回答1:

the simplest way to achieve this is to add a listener to the text field and use the java preferences api:

textField = new JTextField();
    // set document listener
    textField.getDocument().addDocumentListener(new MyListener());
    // get the preferences associated with your application
    Preferences prefs = Preferences.userRoot().node("unique_string_representing_your_preferences");
    // load previous value
    textField.setText(prefs.get("your_preference_unique_key", ""));

class MyListener implements DocumentListener {

    @Override
    public void changedUpdate(DocumentEvent event) {
        final Document document = event.getDocument();
        // get the preferences associated with your application
        Preferences prefs = Preferences.userRoot().node("unique_string_representing_your_preferences");
        try {
            // save textfield value in the preferences object
            prefs.put("your_preference_unique_key", document.getText(0, document.getLength()));
        } catch (BadLocationException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void insertUpdate(DocumentEvent arg0) {
    }

    @Override
    public void removeUpdate(DocumentEvent arg0) {
    }
}

but in this way every time you change value in the text field it is saved. If you want to save it only when application is closed, you can add a WindowListener to your application and write in its

windowClosing

method the content of the previous changedUpdate.

回答2:

Would I need some sort of database..

No. A D/B is overkill for '3 strings'.

..or is there a simpler way?

There's more than one.

1. Object serialization.
2. A File with 3 lines of text.
3. XMLEncoder/Decoder.
4. A Properties file.
5. The Preferences API.
6. An app. deployed using JWS can use the PersistenceService.

That's all I can recall off the top of my head.

回答3:

I would also suggest looking at the Java Preferences system, since this can handle saving information per user or for the whole system.

As an example:

void writeMethod() {
    Preferences prefs = Preferences.userNodeForPackage(this);
    prefs.put("key", "value");
}

void readMethodInSameClass() {
    Preferences prefs = Preferences.userNodeForPackage(this);
    prefs.get("key");
}

This description may be better than the API reference.

回答4:

There are some options, you might want to save the data to a configuration file and load it at the beginning of the program.

回答5:

You could serialize them and store them in a file: http://www.tutorialspoint.com/java/java_serialization.htm

来源：https://stackoverflow.com/questions/10061796/java-program-which-remembers-saves-entered-fields