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Tuesday, November 6, 2012

J2ME – RMS local database

RmsDb.java
The Mobile Information Device Profile -- the platform for mobile Java applications -- provides a mechanism for MIDP applications to persistently store data locally, across multiple invocations and retrieve it later.

This persistent storage mechanism can be viewed as a simple record-oriented database model and is called the record management system (RMS).

The javax.microedition.rms.RecordStore class represents a RMS record store, called otherwise a database table. It provides several methods to manage as well as insert, update, and delete records in a record store.
The record store is created in platform-dependent locations, like nonvolatile device memory.

I implemented a simple java class working with RMS, that we can use in our j2me application:

D:\Programming\Java2ME\MobileApplicationDB\src\mobileapplicationdb\RmsDb.java

 1 package mobileapplicationdb;
 2 
 3 import javax.microedition.rms.RecordStore;
 4 
 5 public class RmsDb {
 6   private RecordStore rmsDb = null;
 7   static final String LOCAL_DB_NAME = "rms_db_example";
 8 
 9   public RmsDb() {
10   }
11 
12   public void openRecStore() {
13     try {
14       // The second parameter indicates that the record store
15       // should be created if it does not exist
16       rmsDb = RecordStore.openRecordStore(LOCAL_DB_NAME, true );
17     }
18     catch (Exception e) {
19         System.out.println(e.toString());        
20     }
21   }    
22   
23   public void closeRecStore() {
24     try {
25       rmsDb.closeRecordStore();
26     }
27     catch (Exception e) {
28       System.out.println(e.toString());        
29     }
30   }
31 
32   public void deleteRecStore() {
33     if (RecordStore.listRecordStores() != null) {
34       try {
35         RecordStore.deleteRecordStore(LOCAL_DB_NAME);
36       }
37       catch (Exception e) {
38         System.out.println(e.toString());        
39       }
40     }      
41   }
42 
43   public void writeRecord(String str) {
44     byte[] record = str.getBytes();
45     try {
46       rmsDb.addRecord(record, 0, record.length);      
47     }
48     catch (Exception e) {
49       System.out.println(e.toString());        
50     }
51   }
52 
53   public String readRecords() {
54     String res = "";            
55     StringBuffer buf = new StringBuffer();                
56     try {
57       byte[] recData = null;
58       int intLen;
59 
60       for (int i = 1; i <= rmsDb.getNumRecords(); i++) {        
61           recData = new byte[rmsDb.getRecordSize(i)];       
62           intLen = rmsDb.getRecord(i, recData, 0);
63           res = "Record no." + i + ": " + new String(recData, 0, intLen)+"\n";       
64           buf.append(res);        
65       }
66       res = buf.toString();
67     }
68     catch (Exception e) {
69       System.out.println(e.toString());        
70     }
71     return res;
72   }
73 
74 }
-->

Mobile phones with Codename One – Getting/Storing data from/into xml file



Today I found a short description on wikipedia about how many technologies are in mobile application development area.

You can choose your programming language that you prefer to use, and you will find which mobile platform you can address with it.

The Codename One  technology uses the java language and enables Java Developers to build true native applications for all mobile/tablet platforms. Sounds quite interesting and it is. However, for the J2ME enabled phones, personally I prefer to use the j2me language and environment with the Netbeans IDE.

But let see through a short example, what is Codename One. It declares that you have just 5 easy steps for app development:
-         downloading the codename one plugin for free (eclipse or netbeans)
-         write your code in java
-         you have a designer for the GUI
-         and you have an embedded simulator to test your app
-         Generate a native mobile application for the desired device, sending to the build server, your code to be build. (you can do this from your IDE)

You can have more information at http://www.codenameone.com/


Now, let’ see a short example code, how to read and write xml file with codename one.
After you create a codename one project in your ide, just put a button and a label onto your form using the designer.
I used the following xml file for this example:

You must import packages like:
import com.codename1.io.*;
import com.codename1.ui.*;
import com.codename1.ui.events.*;
import com.codename1.xml.*;
//import java.io.InputStreamReader;
At the button’s onclick event I associated the following code for reading XML files, and also you will see the "xml write" in commented lines:
    protected void onMain_BtnDataAction(Component c, ActionEvent event) {                    
        String fromXml = "empty";
        try {
            //open the xml file for reading
            BufferedInputStream file = new BufferedInputStream(
                    FileSystemStorage.getInstance().openInputStream("example.xml"));
            InputStreamReader reader = new InputStreamReader(file);         
           
            //processing the xml
            XMLParser parser = new XMLParser();           
            Element elem;    
            elem = parser.parse(reader);   
            fromXml = elem.getChildAt(0).getChildAt(0).getChildAt(0).getText();            
/*elem.getChildAt(0).getChildAt(0).getChildAt(0).setText("writebackintoxmlfile"); FileSystemStorage.getInstance().openOutputStream("example.xml").write(elem.toString().getBytes());*/
        }
        catch (Exception e) {
            System.out.println(e.getMessage());
        }       
        //label component - setting it's text from the XML
        findLblData().setText("XML: "+fromXml);       
        Dialog.show("Hello world","Success reading XML","OK",null);               
    }

The result, running your program: