Building a J2ME project with Ant

For a basic MIDlet, the Wireless Toolkit’s ktoolbar application is pretty convenient. When you run it and click on “new project” it provides a GUI where you can enter the information that goes into the Jad and manifest files, then it creates the Jad and manifest files for you as well as creating directories where you can place the source code and the resources. Then all you need to do is select project > package > create package, and it builds the MIDlet for you including a Jar file and a Jad file that you can run on the emulator or run on an actual device. It will even create an obfuscated version for you — all you have to do is download proguard.jar and drop it into the WTK’s bin directory for the project > package > create obfuscated package to work.

However, as soon as you want to do anything fancy with your build at all (such as add extra steps for style checking, preprocesing, custom resource building, etc.) it’s a good idea to set up your build process to use Ant.

The nice thing about Ant is that it’s easy to use and it’s easy to extend it to do essentially anything you want. The build process is controlled through XML files which group sets of commands as “targets.” The commands themselves (ant tasks) are just calls to Java classes, so if there’s no existing command to perform some task that you’d like to have in your build process, you can write your own ant task to do it.

A MIDP project has some standard steps (compile, preverify, build the Jad file, write the corresponding Jar), and as you might imagine, other people have already written Ant tasks for all of this. So after installing Ant, the next step for a MIDP project is to download and install Antenna.

All you really need to do to install antenna is to download the jar file and drop it into your ant lib directory. Then the Antenna Home overview page gives you all the details about what ant tasks are available and what are all of the corresponding properties and attributes to set. Personally I like to start with at least one working demo or sample, so I downloaded the zip file containing the sources and samples, and decided to try the “games” example.

The “games” example copies the source files from one of the standard WTK demos (the “Games” demo) and builds it in a separate directory using Antenna. To run it, you just go into the games sample directory and type “ant”. If you look at the build.xml file, you’ll see pretty quickly that if you change the value of the “” property from “Games” to the name of any other project (subdirectory of your WTK/apps directory), you can use this same build file to build another project.

There were a couple of minor changes needed to get it to work. As indicated on the Antenna home page, I had to set my wtk.home property to the actual path of my WTK directory (in my case it was “/home/carol/jme/WTK2.2″). Plus I added a line to tell ant where to find all of the antenna tasks, again as explained on the antenna home page:

<taskdef resource=”” classpath=”full path to antenna jar”/>

There was one strange glitch though. On my first try, it gave me this cryptic error message:

[wtkbuild] Compiling 8 source files to /home/carol/jme/ant/build/classes
[wtkbuild] javac: target release 1.1 conflicts with default source release 1.5

/home/carol/jme/ant/build/build.xml:39: Compile failed; see the compiler error output for details.

This message is annoying because it’s clear there’s some sort of version number conflict regarding the compilation step “javac”. But version of what? I thought maybe my JAVA_HOME variable was messed up again or maybe there was a problem with the classpath or some other environment variable, but since my J2ME Polish project compiled okay (using javac and Ant) I figured it must be something antenna-specific. So like any good troubleshooter at a loss for leads, I googled the error message. Perhaps googling this same error message led you here. 😉 If so, you’re in luck because I tracked it down.

Google yielded a page that mentioned that this error appears when you use Ant’s Javac task and set the target without setting the source. I’m still not entirely sure what these version numbers relate to, but I did recall that the Antenna home page mentioned that the Antenna WtkBuild task extends the Javac task and sets the target to 1.1. In fact, if you look in the source code that you’ve downloaded from Antenna, it’s pretty easy to find the line where it does it. It looks like this: setTarget(“1.1”);

Now, you can add a call to setSource in the code and then rebuild and rejar the Antenna code, but — as you might guess — you can also just set this value in the build.xml file in the command where you call the “wtkbuild” task. I’m not sure what the optimal values for source and target are in this case, but through a little trial and error I found some that worked:

<wtkbuild srcdir=”${midlet.home}/src” destdir=”classes” preverify=”false” source=”1.3″ target=”1.1″/>


<wtkbuild srcdir=”${midlet.home}/src” destdir=”classes” preverify=”false” source=”1.5″ target=”1.5″/>

Some other values I tested yielded other amusing error messages such as the following:

[wtkbuild] javac: invalid source release: 1.1

For my next adventure I will write my own Ant task!!! Stay tuned!!! 😀


8 comments so far

  1. […] for setting up a build process with a tool such as Ant rather than just building with ktoolbar (as I discussed the other day). To put this in concrete terms, let’s look at a practical example that illustrates both how […]

  2. […] it’s written in Java, you can call this directly from your Ant build script (see this post for an example of calling an arbitrary Java program from an Ant script). That way you can actually […]

  3. ronak on

    i want the website name of j2me mobile tech.
    which can be useful for me.

    Ronak OZa

  4. […] * The per-handset customization is done entirely by swapping out the data files (properties and images) under the res directory.  This initial example is customized only for the WTK.  Naturally, in keeping with the strategy of DERIVE-MULTI > SELECTIVE, you would write a corresponding Ant build file that automatically generates all of the different binaries.  I’m planning to post more details on this, but for the moment you can look at my earlier post on building a Java ME project with Ant. […]

  5. Ronak_MindBLowing on

    i hv planned to build j2me application which i can use frequently i my routine well as plz provide me j2me and j2ee supported websites name.

  6. Ronak_MindBLowing on

    My self Ronak i hv just completed bca as bachelor and i m liking fwd to build website on basis of directory and to search useful information

    which people could interact frequently.!
    plz provide me the guideline and websites.

  7. faisal on

    I’m confused with above example.
    I’m using Eclipse pulsar with sun JavaME SDK 3.0
    it creates two files (*.xml,*.properties) when you export antenna files to a particular project. Could you please elaborate my situation or atleast provide some useful links thru which I can get much info.

    Thanx in Advance.

  8. carolhamer on

    Hi Faisal,

    I haven’t done a complete Java ME project with Eclipse.

    However, if it created a *.xml file and a *.properties file, I would guess that the *.xml file is the build file (with targets you can call with the command: “ant -f .xml “), and the *.properties file gives project parameters. I would guess that the *.xml file contains a reference to the *.properties file somewhere near the top — so you should have a look to make sure the path is correct so that the *.xml file can find the *.properties file.

    The Ant online manual is quite clear and readable. The use of properties is explained in the “Using Ant” section and the “Ant Tasks” section.

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