develop in C, compile to Java bytecode and run on J2ME: http://spel.bth.se/index.php/Cibyl
Artikel getaggt mit J2ME
J2ME & C
Okt 31
Just shows how desparately J2ME lacks a sales model a la Apple’s AppStore: Turn Your Phone into Babel Fish.
J2ME Pattern: ActiveRecord
Okt 11
Though J2ME forces you to be close with adding classes, type-safe & convenient persistence might be something you don’t want to miss.
And as RecordStores are the primary application persistence stores, there’s some boilerplate code you can refactor out into one single common base class.
Also – especially from a pattern standpoint – it’s a must and increases the unterstandability and maintainability of your code.
So what’s the design assumptions and decisions?
- multiple RecordStores can be kept open at least as long as an application is active. So open them in startApp() and close them in pauseApp() and destroyApp(),
- use the ActiveRecord pattern rather than ValueBean/DAO to keep the number of classes small,
- never access RecordStores directly but shield them with ActiveRecords,
- keep track of the ActiveRecord instances and update them via RecordListeners,
- provide getBytes/setBytes instance methods to the ActiveRecords,
- maybe make ActiveRecords even RecordListener Singletons and refill the data on usage,
- maybe even use a single Hashtables subclass as ActiveRecords to even save more classes (requires very disciplined unit testing!),
- create few multi-purpose RecordFilter and RecordComparator subclasses per RecordStore,
Check back later for sample code.
Or just don’t code persistence manually but use the floggy J2ME persistence framework. Looks interesting, but I didn’t try it out yet.
J2ME Pattern: RMS Migrations
Okt 10
Inspired by RoR Migrations I’ll summarize how to gain similar benefits in the J2ME world with respect to it’s special needs:
- attach a version marker to each RecordStore name,
- as there’s no callback at install time and at launch time things must be quick as possible, use a fall-back mechanism on opening RecordStores,
- therefore use a custom method to open RecordStores and give it a handler for RecordStoreNotFoundException,
- use methods rather than classes to implement migrations,
- only migrate forward,
- hardcode the migration methods into the RecordStoreNotFoundException handler – there’s no Reflection in J2ME.
=>
- you can change the RMS store names and storage byte semantics whenever you like without the fear of breaking anything,
- there’s impact on startup time only if the storage semantics changed and needs to be converted,
- you don’t add myriads of classes over time,
- you need to write a converter method for each version bump of each store.
Check back later for sample code.
J2ME & Maven2
Okt 9
Huh! I just found out, there is a fine Maven2 Plugin for J2ME. It comes with an archetype to jump-start developing J2ME applications with maven.
Use the archetype like this:
$ mvn archetype:create -DarchetypeGroupId=com.pyx4me -DarchetypeArtifactId=j2me-simple -DarchetypeVersion=2.0.3-SNAPSHOT -DremoteRepositories=http://www.pyx4me.com/maven2 -DgroupId=org.example -DartifactId=myapp
And if you develop against a nokia phone, it comes even better – there’s a gammu maven plugin, too!
Also check out this blog featuring maven2 & j2me.
The Nokia 6610 has those J2ME/CLDC/MIDP capabilities. Frankly I don’t understand all of it’s findings, especially the one claiming “RMS: not implemented” – if that means javax.microedition.rms it’s just not true.
Check your phone at mobile-utopia.
If running your app from the eclipseme emulator shows the following console output
Running with storage root DefaultColorPhone Warning: Failed to initialize WMA message routing support Error: Can't remove a lock file: /opt/sun-j2me-bin-2.2/wtklib/comcon-server.port.lock Warning: Failed to initialize Bluetooth (JSR 82) support ... Warning: The attempt to finalize unexisting client. java.lang.NullPointerException at com.sun.kvem.midp.MIDP.run(Unknown Source) at com.sun.kvem.environment.EmulatorInvoker.runEmulatorImpl(Unknown Source) at com.sun.kvem.environment.EmulatorInvoker.runEmulatorSameVM(Unknown Source) at com.sun.kvem.environment.EmulatorInvoker.runEmulator(Unknown Source) at com.sun.kvem.environment.ProfileEnvironment$KVMThread.runEmulator(Unknown Source) at com.sun.kvem.environment.ProfileEnvironment$KVMThread.run(Unknown Source)
give write permission to the wtklib folder inside the WTK:
$ sudo chmod o+w /opt/sun-j2me-bin-2.2/wtklib
The following disease
... javax.microedition.rms.RecordStoreException: error opening record store file at javax.microedition.rms.RecordStore.<init>(+428) at javax.microedition.rms.RecordStore.openRecordStore(+109) at name.mro.billard.Stats.findPlayers(+6) at name.mro.billard.Stats.startApp(+4) at javax.microedition.midlet.MIDletProxy.startApp(+7) at com.sun.midp.midlet.Scheduler.schedule(+270) at com.sun.midp.main.Main.runLocalClass(+28) at com.sun.midp.main.Main.main(+116) startApp threw an Exception ...
is cured by
$ sudo chmod o+w -R /opt/sun-j2me-bin-2.2/appdb
A Sun Forum Post provided the correct hint.
da das Nokia 6610 schon ein recht betagtes Mobilfon ist und nur CLDC 1.0 und MIDP 1.0 unterstützt, sollte das im “Eclipse > Window > Preferences > J2ME > Device Management” eingestellt werden.
Ich habe also das “DefaultColorPhone” unter Beibehaltung des Namens (sic!) geklont (duplicate):
J2ME Device Management
und wie folgt eingestellt:
Edit DefaultColorPhone Definition
Anschließend läßt sich per “Eclipse > File > New > Project > J2ME > Midlet Suite” ein neues Projekt anlegen.
Vorsicht, daß auch wirklich das richtige DefaultColorPhone mit den richtigen CLDC und MIDP jars zugeordnet ist:
Package Explorer Ansicht
Und schon kann’s losgehen!
Evtl. sind die (nicht markierten) anderen jars noch nicht korrekt, aber Rom wurde auch nicht an einem Tag erbaut, oder?
wie gewohnt auf einem gentoo stable amd64 Linux.
- JDK:
$ sudo emerge dev-java/sun-jdk
- Eclipse 3.4 herunterladen und auspacken,
- J2ME Wireless Toolkit 2.2:
$ sudo su - $ echo "dev-java/sun-j2me-bin ~amd64" >> /etc/portage/package.keywords $ echo "dev-java/sun-j2me-bin examples" >> /etc/portage/package.use $ emerge dev-java/sun-j2me-bin $ # USE-Flag "j2me" setzen, z.B. via "$ sudo ufed" $ sudo emerge proguard
- J2ME Wireless Toolkit 2.5.2 heruterladen und installieren,
- EclipseMe herunterladen und auspacken.