MD5 Hashing in J2ME

MD5 (Message Digest) is a hashing algorithm that can be used to ensure data integrity, save and protect passwords/codes, generate unique keys of limited length against a long literal etc. It takes input as String and generates the Hash of that string.

In JAVA there is a built-in MD5 support in its Standard Edition (J2SE). But if we talk about its Micro Edition (J2ME) their is no support for MD5. The package of JAVA Standard Edition can also be used in Micro Edition if and only if the platform supports the SATSA-Crypto Optional Package (How to know that your platform supports SATSA-Crypto).

I have found and tested the Third-Party implementation that can generate MD5 hash and can be used in JAVA Micro Edition. You can get the MD5 source files from here.

rizzz86

J2ME Default Emulator without asking for Permission

While running J2ME project with Default Emulator it will ask for Permissions in case of File Read/Write, HTTP Connectivity etc. To get rid of this Permission on every access you have to change the Security options of Emulator. In my case I am using NetBeans IDE, so to change these options I will go through following steps:

1. Open Project Properties
2. Click on Manage Emulators Button
3. Go to Tools & Extension Tab and Click Open Preferences Option
4. On Preferences Window click on Security option
5. Select Security Policy to 'JTWI'
6. Select Security Domain as 'trusted'
7. Now run the project it will not ask for access Permissions

 rizzz86

Unit Testing for J2ME - JMUnit

In professional development environment it is a common practice to create Unit Tests. On Java platform there are lots of research and development done on Unit Tests for Enterprise Edition. As far as Java Micro Edition is concerned one of the framework available is JMUnit.

Creating and executing a test case using jmunit is quite simple and can be done without wasting much time to explore it. Following steps will guide you how to work with jmunit:

•  In your mobile application right click on package (where you want to create a unit test) and select option 'New > Empty JMUnit Test'.
• It will create a unit test class for you that will look like this:

/*
 * ABCTest.java
 * JMUnit based test
 *
 */

package hello;


import jmunit.framework.cldc10.*;

/**
 * @author rizwan
 */
public class ABCTest extends TestCase {
    
    public ABCTest() {
        //The first parameter of inherited constructor is the number of test cases
        super(0,"ABCTest");
    }            

    public void test(int testNumber) throws Throwable {
    }    
}  

• Next you will create a test method in same class and call it in test() using switch cases.
• Total count of test cases will also be mentioned in unit class constructor.
• Now the code will look like this:

/*
 * ABCTest.java
 * JMUnit based test
 *
 */

package hello;


import jmunit.framework.cldc10.*;

/**
 * @author rizwan
 */
public class ABCTest extends TestCase {
    
    public ABCTest() {
        //The first parameter of inherited constructor is the number of test cases
        super(1,"ABCTest");
    }            

    public void test(int testNumber) throws Throwable {
        switch(testNumber){
            case 0: 
                testOne();
                break;
        }
    }    

    private void testOne() throws Exception{
        String tmp = "Hello Rizwan";
        assertEquals(tmp, "Hello Rizwan");
    }
} 

• After that you have to mention 'ABCTest' as your Midlet.
• Go into 'project properties > Application Descriptor > MIDlets' and define unit test name and package here.
• Run application and you will also get Test option on screen:  
• Test the project and it will show you the results

Your mobile test case is ready !

rizzz86

Add External JAR in j2me-polish Project

To use any external jar in a j2me-polish project following steps need to be taken:

• Copy jar file in j2me-polish/import/ folder
• Add jar file in project libraries
• Update build.xml file by adding attribute 'binarylibraries="jarname1.jar;jarname2.jar"' inside < build > tag. (Multiple jars can be defined by placing semi-colon between jars)

rizzz86

Maven j2me-Archetype

I am using Netbeans6.7 for mobile project development and want to make that project a 'maven project'. I have maven configured on my machine.

To make maven based j2me project I have created a new project from File > New Project > Maven > Maven Project > j2me Archetype (2.0.4). The project created successfully and showing the properties of maven as well . . .  BUT !!

I cannot able to view the properties of mobile project (i.e. Platform Type, Device Profile and Configuration, Midlet Information etc). To execute that project it requires a class with main() method. So I have posted all that on forum and finally got the following answer:

j2me development is not supported for maven projects in netbeans :(

rizzz86

JSON source for J2ME (mobile applications)

Javascript Object Notation (JSON) is a lightweight data-interchange format. It is easy for humans to read and write. It is easy for machines to parse and generate. I am trying to use it in for mobile application development.

Today I was looking for a JSON source code for Java Micro Edition (J2ME). After lots of googling I have found it from the following link:

https://meapplicationdevelopers.dev.java.net/source/browse/meapplicationdevelopers/demobox/mobileajax/lib/json/src/org/json/me/



rizzz86

Share Common Code Between J2ME and J2SE Project -- Problem/Solution

Statement:
If you are creating a client/server project on Java, where client is a mobile device and server is a web application. Also if there is a common code between client and server then where do you place that common code ?

I also faces the same and go through the following phases before deciding what to do. The two points that came in mind right away are:

• Create a J2SE Project and place common code there. Make your client and server project dependant on that common project.
• Create a J2ME Project and place common code there. Make your client and server project dependant on that common project.
  

First I have created J2SE as a Common Project:

When I execute the client (J2ME) project with a dependency of common project (J2SE), I got the following error:

Running with storage root DefaultColorPhone
Method............: 100d2aa8 'com/sun/midp/midlet/MIDletState.createMIDlet (stat
ic)'
Stack Chunk.......: e58cd4
Frame Pointer.....: e58d30
Current IP........: 10128592 = 10128584 + offset 14
Previous Frame....: e58cf4
Previous IP.......: 1012052b (offset 22)
Frame size........: 8 (1 arguments, 7 local variables)
Argument[0].......: e59a9c
Local[1]..........: 0
Local[2]..........: e58cf4
Local[3]..........: e68858
Local[4]..........: e58d08
Local[5]..........: 100dcdd0
Local[6]..........: e58cd4
Local[7]..........: 1015f0a0
Operand[1]........: e59a9c

Method............: 100cd0e4 'com/sun/midp/midlet/Selector.run (virtual)'
Stack Chunk.......: e58cd4
Frame Pointer.....: e58cf4
Current IP........: 1012052b = 10120515 + offset 22
Previous Frame....: 0
Previous IP.......: 1
Frame size........: 6 (1 arguments, 5 local variables)
Argument[0].......: e59d10
Local[1]..........: e68a68
Local[2]..........: e59a9c
Local[3]..........: 0
Local[4]..........: 0
Local[5]..........: 0
Operand[1]........: e68a68

VM status:
Instruction pointer.: 10128592 (offset within invoking method: 14)
Next instruction....: 0x4c
Frame pointer.......: e58d30
Local pointer.......: e58d10
Stack size..........: 128; sp: e58d48; ranges: e58cdc-e58edc;
Contents of the current stack frame:
e58d10: e59a9c (lp)
e58d14: 0
e58d18: e58cf4
e58d1c: e68858
e58d20: e58d08
e58d24: 100dcdd0
e58d28: e58cd4
e58d2c: 1015f0a0
e58d30: e58cf4 (fp)
e58d34: 1012052b
e58d38: e58d0c
e58d3c: 100d2aa8
e58d40: e58cd4
e58d44: 0 (end of frame)
e58d48: e59a9c (sp)
Execution stack contains 112 items:
e59d10
e68a68
e59a9c
0
0
0
0
1
e58cd8
100cd0e4
e58cd4
0
e68a68
e59a9c
0
e58cf4
e68858
e58d08
100dcdd0
e58cd4
1015f0a0
e58cf4
1012052b
e58d0c
100d2aa8
e58cd4
0
e59a9c

Execution completed.
429584 bytecodes executed
10 thread switches
486 classes in the system (including system classes)
2380 dynamic objects allocated (72064 bytes)
1 garbage collections (0 bytes collected)
ALERT: java/lang/ClassFormatError: Bad version information.
Execution completed.
429584 bytecodes executed
10 thread switches
486 classes in the system (including system classes)
2380 dynamic objects allocated (72064 bytes)
1 garbage collections (0 bytes collected)

After reading some forums I recompile my common project (J2SE) on jdk1.4 and add it as a dependency in client project (J2ME) again (previously I have compiled it on jdk1.5). This time the client (J2ME) executes and works successfully.


ISSUES:

In Java the development toolkit for mobile (J2ME) contains limited features as compared to the standard edition (J2SE). If you are creating your project on J2SE then you must not use any feature of J2SE in project that is not provided by J2ME (mobile edition have limited features).

In jdk1.5 there are some major specification changes due to which it generates different byte-code number that results in "ALERT: java/lang/ClassFormatError: Bad version information". So you need to run/compile your common (J2SE) project on jdk1.3/1.4




Next I have created J2ME as a Common Project:

I am using Netbeans 6.7 for development, so I have created 'Java ME > Mobile Class Library' project for common code. The Mobile Class Library is a mobile project but does not contain any Midlets. It uses IDE-generated Ant build scripts and special tasks to pre-process, build, obfuscate, preverify, debug, run and depoly your library in JAVA ME Environment.

I moved all my common code in this mobile project and then use it as a dependency for both client (J2ME) and server (J2SE) projects and it works properly for both editions. Doing this ensures the compatability of both versions because mobile edition features are already supported by standard edition. Also you will be free from jdk-versioning issue that was faced in previously.

Conclusion:
So create 3 different projects, one is a client (J2ME), another is a server (J2SE) and a common project (J2ME) that will be used by client and server.



rizzz86