Learning J2ME and Floggy

02Feb10

I’m looking to make an app for my phone that allows me to record my mood each day and plot the data on a graph.

I don’t know Java very well, so I am learning it on the way. I am trying hard not to be impatient; I am tempted to cram as much information into my skull as possible and, in doing so, cause a great deal of frustration.

The first hurdle that I needed to overcome was learning how to save information within J2ME. The standard way of saving anything is to use the Record Management Store API, which, I have read, is exceedingly difficult to use for anything beyond the simplest examples. To this end, others have released their own libraries to make saving data less of a pain.

The solution which I have settled upon is Floggy. In their own words, Floggy is “a free object persistence framework for J2ME/MIDP applications”. Sounds great. Despite their claim that Floggy makes record storage much simpler, I still found using it confusing, though it could have been worse with RMS alone.

I searched Google for a simple example midlet to demonstrate the use of Floggy. (The official examples, a ‘barbecue calculator’ and hospital app, are too complicated for me to grasp.) This site has a short, simple example that saves two items: a name and an age variable. However, it didn’t show me how to load back the data! There isn’t much point to storing it when you can’t get it back.

I modified the example and put in a ‘load file’ command. It works! I’m ecstatic. Here it is:

ExampleFloggy.java

import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Form;
import javax.microedition.lcdui.TextField;
import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;
import net.sourceforge.floggy.persistence.*;

public class ExampleFloggy extends MIDlet implements CommandListener {

    private TextField tfield;

    private Display display;
    private Form form;
    private TextField tfieldN;

    private Command savecmd;
    private Command loadcmd;
    private Command exitcmd;


    public ExampleFloggy() {
        tfield = new TextField("name:", "", 15, TextField.ANY);
        tfieldN = new TextField("age:", "0", 15, TextField.NUMERIC);

        savecmd = new Command("save", "save file", Command.SCREEN, 0);
        loadcmd = new Command("load", "load file", Command.ITEM, 0);
        exitcmd = new Command("exit","exit",Command.EXIT,0);

        form = new Form("Floggy example.");
        form.append(tfield);
        form.append(tfieldN);
        form.addCommand(savecmd);
        form.addCommand(loadcmd);
        form.addCommand(exitcmd);
        form.setCommandListener(this);
    }

    protected void destroyApp(boolean arg0) throws MIDletStateChangeException {
        notifyDestroyed();
    }

    protected void pauseApp() {
    }

    protected void startApp() throws MIDletStateChangeException {
        display = Display.getDisplay(this);
        display.setCurrent(form);
    }

    public void commandAction(Command cmd, Displayable arg1) {
        if (cmd == savecmd) {
            Date dateOut = new Date(tfield.getString(), Integer.parseInt(tfieldN.getString()));
            int id;
            try {
                id = PersistableManager.getInstance().save(dateOut);
                Date dateIn =  new Date();
                PersistableManager.getInstance().load(dateIn, id);
                form.append(dateIn.toString());
            } catch (FloggyException e) {
                e.printStackTrace();
            }

        } else if (cmd==exitcmd){
            try {
                destroyApp(true);
            } catch (MIDletStateChangeException e) {
                e.printStackTrace();
            }
        } else if (cmd==loadcmd) {
            try {
                ObjectSet set = PersistableManager.getInstance().find(Date.class, null, null);
                Date dateIn = new Date();
                set.get(0, dateIn);
                tfield.setString(dateIn.getName());
                tfieldN.setString(Integer.toString(dateIn.getAge()));
            } catch (FloggyException e) {
                e.printStackTrace();
            }
        }
    }

}

Date.java (save in the same folder as ExampleFloggy.java)

import net.sourceforge.floggy.persistence.Persistable;

public class Date implements Persistable {

    private String name;
    private int age;
    private transient int num;

    public Date() {
    }

    public Date(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String toString() {
        return "";
    }

    public String getName() {
        return this.name;
    }

    public int getAge() {
        return this.age;
    }

}

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Tags: j2me