如何将对象保存到文件中，以便以后可以加载？

Question

I've been trying to save an object, a level in my case, into a file, so that i can later load it again. Basically just a save/load function. I can't get it to work.. I keep getting a file of 5 byte, which seems way to small for what should be in it. I know that it might have something to do with Serializable, but i dont know what. Here is my current code:

(btw, i hard coded the level into the program, because i dont know how to save it properly to a file yet. although that is the goal...)

public class BufferSaveGames {

public void saveGameOutputStream(Level level) throws FileNotFoundException {

    ObjectOutputStream output;
    try {
        output = new ObjectOutputStream((new FileOutputStream("SaveGame.dat")));
        output.writeObject(level);
        output.close();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

and the second class Level, which it is loading: (removed code not needed for example)

public class Level implements MouseListener, Serializable {

private Level currentLevel;
private int aantalPoppetjesOpLevel;
private String oplossing;
private int timer;
JPanel[][] levelGrid;
Poppetje[] lijstPoppetjes;

public Level() throws IOException{

    levelGrid = new JPanel[5][5];
    lijstPoppetjes = new Poppetje[5];

    for (int a=0;a<5;a++) {
         for (int b=0;b<5;b++) {
             levelGrid[a][b] = new JPanel();
             levelGrid[a][b].setSize(100,100);
             levelGrid[a][b].setVisible(true);
             levelGrid[a][b].setLayout(null);
             levelGrid[a][b].setOpaque(false);
             levelGrid[a][b].addMouseListener(this);
         } 
    }

    //bovenste rij
    levelGrid[0][0].setLocation(10,10);
    levelGrid[0][1].setLocation(112,10);
    levelGrid[0][2].setLocation(214,10);
    levelGrid[0][3].setLocation(316,10);
    levelGrid[0][4].setLocation(418,10);




    Poppetje roodPoppetje = new Poppetje("Rood", 4, 4);

    Poppetje oranjePoppetje = new Poppetje("Oranje", 0, 4);
    Poppetje groenPoppetje = new Poppetje("Groen", 1, 2);
    Poppetje paarsPoppetje = new Poppetje("Paars", 2, 1);
    Poppetje geelPoppetje = new Poppetje("Geel", 3, 3);
    //Poppetje blauwPoppetje = new Poppetje("Blauw");

    int tempA = roodPoppetje.getLocatieX(roodPoppetje);
    int tempB = roodPoppetje.getLocatieY(roodPoppetje);
    levelGrid[tempA][tempB].add(roodPoppetje);
    lijstPoppetjes[0] = roodPoppetje;
    lijstPoppetjes[0].addMouseListener(this);

    tempA = oranjePoppetje.getLocatieX(oranjePoppetje);
    tempB = oranjePoppetje.getLocatieY(oranjePoppetje);
    levelGrid[tempA][tempB].add(oranjePoppetje);
    lijstPoppetjes[1] = oranjePoppetje;
    lijstPoppetjes[1].addMouseListener(this);

Answer 1

That could be done with "Serialization/Deserialization". Check out this as a first approach:

http://www.wikihow.com/Serialize-an-Object-in-Java

Also try searching with "serialziation" keyword on your favorite search engine (highly probably google hehe). There are a lot of libraries that do this process in such a high level api. Also there are a lot of libraries that do this with powerful uses; like serialization through databases. Sometimes serialization is done using JSON (as it could be a more universal way to do it). Enjoy with serialization! :-)

edit: also search for JSON, beautiful tool

Answer 2

forgot to put the following line in the OutPutStream code:

            Level levelX = new Level();

this solved the problem for the very small save game that it created.