import javax.microedition.midlet.MIDlet;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.List;
 
import javax.microedition.rms.RecordEnumeration;
import javax.microedition.rms.RecordStore;
import javax.microedition.rms.RecordStoreException;
import javax.microedition.rms.RecordListener;
 
import java.util.Vector;
import javax.microedition.lcdui.Alert;
 
 
public class StoringAppSettings extends MIDlet 
        implements CommandListener, RecordListener {
 
    private Display display;
    // List for displaying settings of application.
    private List recordList;
    // Command for adding new setting.
    private Command cmdAdd;
    // Command for deleteing all records from record store.
    private Command cmdDeleteAll;
    // Command for exiting from midlet.
    private Command cmdExit;
 
    // Name of record store of application.
    private final String RECORD_STORE_NAME = "StoringAppSettingsStore";
    // Record store of application.
    private RecordStore recordStore;
    // Array of settings deserialized from records in record store.
    private Vector appSettings;
 
    // Form for adding new setting.
    private AddSettingForm addSettingForm;
 
    // Alert to be displayed if error occurs.
    private Alert alert;    
 
    /**
     * Constructor
     */
    public StoringAppSettings() {
        initializeComponents();
    }
 
    /**
     * Initializes components of midlet 
     */
    private void initializeComponents() {
        // Get display
        display = Display.getDisplay(this);
 
        // Create recordList
        recordList = new List("App settings", List.IMPLICIT);
        cmdAdd = new Command("Add setting", Command.OK, 0);
        recordList.addCommand(cmdAdd);
        cmdDeleteAll = new Command("Delete all settings", Command.OK, 0);
        recordList.addCommand(cmdDeleteAll);
        cmdExit = new Command("Exit", Command.EXIT, 0);
        recordList.addCommand(cmdExit);
        recordList.setCommandListener(this);
 
        // Create form for adding new settings.
        addSettingForm = new AddSettingForm();
        addSettingForm.setCommandListener(this);
 
        // Create array of app settings.
        appSettings = new Vector();
 
        // Open record store, read settings from it and display settings.
        try {
            openRecordStore();
            getAppSettings();
            addSettingsToForm();
        } catch(RecordStoreException rsExc) {
            showAlert("Record store error", rsExc.getMessage(), null);
        } catch(SecurityException secExc) {
            showAlert("Security error", secExc.getMessage(), null);
        }
    }
 
    /**
     * Opens named record store of application. Record store will be created 
     * if it is not exists.
     */
    private void openRecordStore() throws RecordStoreException, SecurityException {
        recordStore = RecordStore.openRecordStore(RECORD_STORE_NAME, true);
        recordStore.addRecordListener(this);
    }
 
    /**
     * Closes record store.
     */
    private void closeRecordStore(){
        try {
            recordStore.closeRecordStore();
        } catch (RecordStoreException ex) {
            // Do nothing.
        }
    }
 
    /**
     * Reads settings from record store and adds it to array of settings.
     * @throws RecordStoreException if error occurs on working with record store.
     */
    private void getAppSettings() throws RecordStoreException {
        appSettings.removeAllElements();
 
        RecordEnumeration recEnum = recordStore.enumerateRecords(null, 
                null, false);
        while(recEnum.hasNextElement() == true) {
            int settingId = recEnum.nextRecordId();
            byte[] data = recordStore.getRecord(settingId);
            AppSetting setting = AppSetting.deserialize(data);
            if(setting != null) {
                appSettings.addElement(setting);
            }          
        }
        recEnum.destroy();
    }
 
    /**
     * Adds settings to settings list control from array of settings.
     */
    private void addSettingsToForm() {
        recordList.deleteAll();
 
        for(int index = 0; index < appSettings.size(); ++index) {
            AppSetting setting = (AppSetting)appSettings.elementAt(index);
            recordList.append(setting.toString(), null);
        }
    }
 
    /**
     * Adds setting to record store.
     * @param name - name of new record.
     * @param value - value of new record.
     */
    private void addSetting(String name, String value) {
        try {
            AppSetting setting = new AppSetting(name, value);
            byte[] data = setting.serialize();
            recordStore.addRecord(data, 0, data.length);
        } catch(RecordStoreException rsExc) {
            showAlert("Record store error", rsExc.getMessage(), recordList);
        }
    }
 
    /**
     * Deletes record store and creates it again.
     */
    private void deleteAllSettings() {
        try {
            recordStore.closeRecordStore();
            RecordStore.deleteRecordStore(RECORD_STORE_NAME);
 
            openRecordStore();
 
        } catch(RecordStoreException rsExc) {
            showAlert("Record store error", rsExc.getMessage(), recordList);
        }   
    }
 
    /**
     * From MIDlet.
     * Signals the MIDlet that it has entered the Active state.
     */    
    public void startApp() {
        display.setCurrent(recordList);
    }
 
    /**
     * From MIDlet.
     * Signals the MIDlet to enter the Paused state.
     */    
    public void pauseApp() {
        // No implementation required
    }
 
    /**
     * From MIDlet.
     * Signals the MIDlet to terminate and enter the Destroyed state.
     */    
    public void destroyApp(boolean unconditional) {
        closeRecordStore();
    }
 
    /**
     * Performs exit from midlet.
     */    
    private void exitMIDlet() {
        notifyDestroyed();
    }
 
    /**
     * Shows alert with specified title and text. If next displayable is not
     * specified then application will be closed after alert closing.
     * @param title - Title of alert.
     * @param message - text of alert.
     * @param nextDisp - next displayable. Can be null.
     */
    private void showAlert(String title, String message, Displayable nextDisp) {
        alert = new Alert(title);
        alert.setString(message);
        alert.setTimeout(Alert.FOREVER);
 
        if(nextDisp != null) {
            display.setCurrent(alert, nextDisp);
        } else {
            display.setCurrent(alert);
            alert.setCommandListener(this);
        }
    }
 
    /**
     * From CommandListener.
     * Indicates that a command event has occurred on Displayable d.
     * @param cmd - a Command object identifying the command.
     * @param d - the Displayable on which this event has occurred.
     */    
    public void commandAction(Command cmd, Displayable d) {
        if(d == recordList) {
            if(cmd == cmdAdd) {
                addSettingForm.clear();
                display.setCurrent(addSettingForm);
            }
            if(cmd == cmdDeleteAll) {
                deleteAllSettings();
                appSettings.removeAllElements();
                addSettingsToForm();
            }
            if(cmd == cmdExit) {
                exitMIDlet();
            }
        }
        if(d == addSettingForm) {
            if(cmd == addSettingForm.getSaveCommand()) {
                addSetting(addSettingForm.getName(), addSettingForm.getValue());
                display.setCurrent(recordList);
            }
            if(cmd == addSettingForm.getBackCommand()) {
                display.setCurrent(recordList);
            }
        }
        if(d == alert) {
            // Handle "ok" command from alert
            exitMIDlet();
        }
    }
 
    /**
     * From RecordListener.
     * Called when a record has been added to a record store.
     * @param store - the RecordStore in which the record is stored
     * @param recordId - the recordId of the record that has been added
     */
    public void recordAdded(RecordStore store, int recordId) {
        try {
            getAppSettings();
            addSettingsToForm();
        } catch(RecordStoreException rsExc ) {
            showAlert("Record store error", rsExc.getMessage(), recordList);
        }
    }
 
    /**
     * From RecordListener.
     * Called after a record in a record store has been changed. 
     * @param store - the RecordStore in which the record is stored
     * @param recordId - the recordId of the record that has been added
     */
    public void recordChanged(RecordStore store, int recordId) {
        // No implementation required.
    }
 
    /**
     * From RecordListener.
     * Called after a record has been deleted from a record store.
     * @param store - the RecordStore in which the record is stored
     * @param recordId - the recordId of the record that has been added
     */
    public void recordDeleted(RecordStore store, int recordId) {
        // No implementation required.
    }
}

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
 
/**
 * Setting of application. Consist of pair "name - value"
 */
public class AppSetting {
    // Name of setting.
    private String name;
    // Value of setting.
    private String value;
 
    /**
     * Constructor.
     * @param name - name of new setting.
     * @param value - value of new setting.
     */
    public AppSetting(String name, String value) {
        this.name = name;
        this.value = value;
    }
 
    /**
     * Deserializes app setting from data buffer and returns it.
     * @param data - data for creating new setting.
     * @return new setting.
     */
    public static AppSetting deserialize(byte[] data) {
        String name = null;
        String value = null;
 
        try {
            ByteArrayInputStream byteInStream = new ByteArrayInputStream(data);
            DataInputStream dataInStream = new DataInputStream(byteInStream);
 
            name = dataInStream.readUTF();
            value = dataInStream.readUTF();
 
            dataInStream.close();
            byteInStream.close();
 
        } catch(IOException exc) {
            return null;
        }
 
        return new AppSetting(name, value);
    }
 
    /**
     * Serilizes setting to array of bytes.
     * @return array of bytes representing serialized setting.
     */
    public byte[] serialize() {
        byte[] data = null;
 
        try {
            ByteArrayOutputStream byteOutStream = new ByteArrayOutputStream();
            DataOutputStream dataOutStream = new DataOutputStream(byteOutStream);
 
            dataOutStream.writeUTF(name);
            dataOutStream.writeUTF(value);
 
            dataOutStream.flush();
            data = byteOutStream.toByteArray();
 
            dataOutStream.close();
            byteOutStream.close();
 
        } catch(IOException exc) {
            return null;
        }
 
        return data;
    }
 
    /**
     * Gets name of setting.
     * @return name of setting.
     */
    public String getName() {
        return name;
    }
 
    /**
     * Gets value of setting.
     * @return value of setting.
     */
    public String getValue() {
        return value;
    }
 
    /**
     * Returns textual representation of setting.
     * @return textual representation of setting.
     */
    public String toString() {
        return name + ": " + value;
    }
}

import javax.microedition.lcdui.Form;
import javax.microedition.lcdui.TextField;
import javax.microedition.lcdui.Command;
 
/**
 * Form for receiving from user name, and value of the new setting.
 */
public class AddSettingForm extends Form {
    // Text field for entering name of new setting.
    private TextField nameField;
    // Text field for entering value of new setting.
    private TextField valueField;
 
    // Command for saving new setting in record store.
    private Command cmdSave;
    // Command for altering saving new setting.
    private Command cmdBack;
 
    /**
     * Constructor. 
     */
    public AddSettingForm() {
        super("Add setting");
 
        nameField = new TextField("Name", null, 30, 0);
        append(nameField);
        valueField = new TextField("Value", null, 30, 0);
        append(valueField);
 
        cmdSave = new Command("Save", Command.SCREEN, 0);
        addCommand(cmdSave);
        cmdBack = new Command("Back", Command.BACK, 0);
        addCommand(cmdBack);
    }
 
    /**
     * Clears antered values in text fields of form.
     */
    public void clear() {
       nameField.setString(null);
       valueField.setString(null);
    }
 
    /**
     * Gets from name text field name of new setting and returns it.
     * @return name of new setting.
     */
    public String getName() {
        return nameField.getString();
    }
 
    /**
     * Gets from value text field value of new setting and returns it.
     * @return value of new setting.
     */
    public String getValue() {
        return valueField.getString();
    }
 
    /**
     * @return command for saving new setting in record store. 
     */
    public Command getSaveCommand() {
        return cmdSave;
    }
 
    /**
     * @return command for altering saving new setting.
     */
    public Command getBackCommand() {
        return cmdBack;
    }
}