Programming Tutorials

Sample J2ME code that shows various functionality of RMS.

By: Henry in J2ME Tutorials on 2007-09-08  

Update: As J2ME is an old technology, it is now deprecated and not recommended to be used in new projects.

The general flow of this MIDlet is  In the constructor (See RMSMIDlet), create and populate two record stores, one of personal contacts, the other with business contacts. Display the first screen. This screen shows a list of all RMS stores found in the MIDlet suite's name space. This screen allows the user to select a record store and either display pertinent information about the record store such as size, etc., or to view  the contents of the selected store. When the contents of a record store are viewed, they are sorted by last name, though this can be changed by instantiate a SimpleComparator object with the appropriate sort order parameter. Traversal from screen to screen is handled by RMSMIDlet, commandAction.

import java.lang.*;
import java.io.*;
import java.util.*;
import javax.microedition.lcdui.*;
import javax.microedition.rms.*;
import javax.microedition.midlet.*;

public class RMSMIDlet extends MIDlet implements CommandListener {
    private Display myDisplay;  // handle to the display
    private Alert alert;        // used to display errors

    // Our commands to display on every screen.
    private Command CMD_EXIT;
    private Command CMD_DETAILS;
    private Command CMD_OK;

    // Our screens
    private List mainScr;
    private List detailScr;
    private List dataScr;

    // An array of all RMS stores found in this
    // MIDlets name space.
    private String[] recordStoreNames;

    /**
     * Seed data for creating personal contacts RMS store
     */
    private final String personalContacts[] = {
        "John", "Zach", "2225556669",
        "Mark", "Lynn", "5125551212",
        "Joy", "Beth", "2705551234",
        "Abby", "Lynn", "4085558566",
    };

    /**
     * Seed data for creating business contacts RMS store
     */
    private final String businessContacts[] = {
        "Ted", "Alan", "4125552235",
        "Sterling", "Wincle", "9995559111",
        "Deborah", "Elaine", "4445552323",
        "Suzanne", "Melissa"," 5125556064",
        "Frank", "Kenneth", "7775551212",
        "Dwight", "Poe", "1115557234",
        "Laura", "Beth", "2055558888",
        "Lisa", "Dawn", "2705551267",
        "Betty", "June", "5555551556",
        "Yvonne", "Poe", "6665558888",
        "Lizzy", "Loo", "5025557971",
        "John", "Gerald", "3335551256",
    };

    /**
     * Display a warning on the screen and revert
     * to the main screen.
     *
     * s  A warning string to display
     */
    private void doAlert(String s) {
        alert.setString(s);
        myDisplay.setCurrent(alert, mainScr);
    }

    /**
     * Notify the system we are exiting.
     */
    private void doExit() {
        destroyApp(false);
        notifyDestroyed();
    }

    /**
     * In our simple MIDlet, all screens have the same commands,
     * with the possible exception of the detailScr.
     * 
     * Also set up the command listener to call commandAction.
     * See RMSMIDlet#commandAction
     */
    private void addCommonCommands(Screen s,
                                   boolean doDetails) {
        s.addCommand(CMD_OK);
        s.addCommand(CMD_EXIT);
        if (doDetails) {
            s.addCommand(CMD_DETAILS);
        }
        s.setCommandListener(this);
    }

    /**
     * The public constructor. In our constructor, we get
     * a handle to our display and create two record stores.
     * In the event of an error, we display an alert.
     */
    public RMSMIDlet() {
        CMD_EXIT = new Command("Exit", Command.EXIT, 3);
        CMD_DETAILS = new Command("Details", Command.SCREEN, 2);
        CMD_OK = new Command("OK", Command.OK, 1);
        myDisplay = Display.getDisplay(this);
        alert = new Alert("Warning");
        alert.setTimeout(2000);

        CreateAddressBook.createRecordStore("Personal",
                                            personalContacts);
        CreateAddressBook.createRecordStore("Business",
                                            businessContacts);

        // Now, get a list of RMS stores and add their
        // names to the mainScr.
        recordStoreNames = RecordStore.listRecordStores();
        mainScr = new List("Select RMS Store", List.IMPLICIT,
                           recordStoreNames, null);
        addCommonCommands(mainScr, true);
    }

    /**
     * Called by the system to start our MIDlet.
     */
    protected void startApp() {
        myDisplay.setCurrent(mainScr);
    }

    /**
     * Called by the system to pause our MIDlet.
     * No actions required by our MIDLet.
     */
    protected void pauseApp() {}

    /**
     * Called by the system to end our MIDlet.
     * No actions required by our MIDLet.
     */
    protected void destroyApp(boolean unconditional) {}

    /**
     * Generate a screen with a sorted list of the contents
     * of the selected RMS store identified by index
     * If any errors encountered, display an alert and
     * redisplay the mainScr.
     *
     * index  an index into recordStoreNames
     */
    public void genDataScr(int index) {
        SimpleComparator rc;
        RecordEnumeration re;
        RecordStore rs;
        dataScr = null;
        byte record[];

        try {
            rs = RecordStore.openRecordStore(
                                recordStoreNames[index], false);
        } catch (RecordStoreException e) {
            doAlert("Could not open " + recordStoreNames[index]);
            return;
        }

        // Create an enumeration that sorts by last name
        rc = new SimpleComparator(
                     SimpleComparator.SORT_BY_LAST_NAME);
        try {
            re = rs.enumerateRecords(null, rc, false);
        } catch (RecordStoreNotOpenException e) {
            doAlert("Could not create enumeration: " + e);
            return;
        }

        // Create a screen and append the contents of the
        // selected RMS store.
        dataScr = new List(recordStoreNames[index] + " Data",
                           List.IMPLICIT);
        addCommonCommands(dataScr, false);

        try {
            while (re.hasNextElement()) {
                byte[] b = re.nextRecord();
                dataScr.append(SimpleRecord.getFirstName(b) +
                               " " + SimpleRecord.getLastName(b),
                               null);
            }
        } catch (Exception e) {
            doAlert("Could not build list: " + e);
            dataScr = null;
        } finally {
            try {
                rs.closeRecordStore();
            } catch (RecordStoreException e) {}
        }
    }

    /**
     * Generate a screen that shows some of the details
     * of the selected RMS store.
     *
     * RMS store information displayed:
     * - name
     * - number of records
     * - size, in bytes
     * - available size, in bytes
     * - version number
     *
     * index  an index into recordStoreNames
     */
    public void genDetailScr(int index) {
        RecordStore rs;
        detailScr = null;

        try {
            rs = RecordStore.openRecordStore(
                                        recordStoreNames[index],
                                        false);
        } catch (Exception e) {
            doAlert("Could not open " + recordStoreNames[index]);
            return;
        }

        detailScr = new List(recordStoreNames[index] + " Details",
                             List.IMPLICIT);
        addCommonCommands(detailScr, false);


        try {
            detailScr.append("Name: "  + rs.getName(), null);
            detailScr.append("# recs: " +
                             rs.getNumRecords(), null);
            detailScr.append("Size: " + rs.getSize(), null);
            detailScr.append("Avail: " + 
                             rs.getSizeAvailable(),null);
            detailScr.append("Version: " +
                             rs.getVersion(), null);
        } catch (Exception e) {
            detailScr = null;
            doAlert("Failed to retrieve data");
            return;
        } finally {
            try {
                rs.closeRecordStore();
            } catch (RecordStoreException e) {}
        }
    }

    /***
     * Respond to command selections.
     * Commands are:
     * EXIT: if selected, then exit
             (see RMSMIDlet, doExit)
     * OK:   if selected, interpreted in the context of
     *       the current screen.
     *
     * This method implements a state machine that drives
     * the MIDlet from one state (screen) to the next.
     */
    public void commandAction(Command c,
                              Displayable d) {

        // Every screen has an EXIT command.
        // Handle this consistently for all screens.
        if (c == CMD_EXIT) {
            doExit();
            return;
        }

        // switch based on screen.
        if (d == mainScr) {

            // main screen: two commands to handle. If
            // OK was selected, then generate the dataScr
            // and make it active. If DETAILS was selected,
            // generate the detailScr and make it active.
            if ((c == List.SELECT_COMMAND) || (c == CMD_OK)) {
                genDataScr(mainScr.getSelectedIndex());
                myDisplay.setCurrent(dataScr);
            } else if (c == CMD_DETAILS) {
                genDetailScr(mainScr.getSelectedIndex());
                myDisplay.setCurrent(detailScr);
            }

        } else if (d == detailScr) {

            // If OK selected, go back to mainScr
            if (c == CMD_OK) {
                myDisplay.setCurrent(mainScr);
            }

        } else if (d == dataScr) {

            // If OK selected, go back to mainScr
            if (c == CMD_OK) {
                myDisplay.setCurrent(mainScr);
            }

        }
    }
}