{"id":168,"date":"2004-08-08T09:15:53","date_gmt":"2004-08-08T15:15:53","guid":{"rendered":"http:\/\/www.mooreds.com\/wordpress\/?p=168"},"modified":"2004-08-08T09:15:53","modified_gmt":"2004-08-08T15:15:53","slug":"decreasing-the-size-of-a-midlet-jar","status":"publish","type":"post","link":"https:\/\/www.mooreds.com\/wordpress\/archives\/168","title":{"rendered":"Decreasing the size of a midlet jar"},"content":{"rendered":"

The J2ME application I have been working on has been ready for testing for quite some time, but I didn’t want to get a new AT&T phone. For J2ME, you really need a GSM phone–I don’t think any of the older TDMA models support it. But the GSM network coverage<\/a> doesn’t match the coverage of the TDMA network–especially out west (aside: isn’t that magnifying glass pretty cool?). So I put off buying a phone until my summer road tripping was done. <\/p>\n

I’ve had a Nokia 6160 for almost 4 years. Even though friends mocked the size of it, it was a great phone–durable, good talk time. I thought I’d try another Nokia, and got one of the lower end GSM phones, the 6200<\/a>. This supported J2ME, and weighed maybe half as much. I was all stoked to try the application on my brand new phone.<\/p>\n

I started download the jad file, and was getting ‘File Too Large’ errors. A couple of searches later, I found Nokia’s developer device matrix<\/a> which is much more useful than the User Guide or the customer facing description of phones<\/a>. Whoops. Most of the Series 40 (read: affordable) Nokia devices only supported J2ME applications which were, when jarred up, less than 64K in size. <\/p>\n

Our application, however, was about 78K. This highlights one of the differences between J2ME and J2SE\/J2EE. When coding in the latter world, I was never concerned about code size–getting the job done quickly was paramount, and if I needed to use 13 libraries which bloated the final size of my application, I did. On a cell phone, however, there’s no appeal to adding memory or changing the JVM configuration to optimize memory use. If the Nokia phone only accepts jars of 64K or less, I had three options:<\/p>\n

1. Write off the Nokia Series 40 platform. Ugh–I like Nokias, and other folks do too.<\/p>\n

2. Do some kind of magic URL classloading. This seemed complicated and I wasn’t sure how to do it.<\/p>\n

3. Decrease the size of the jar file.<\/p>\n

Now, the 78K jar had already been run through an obfuscator<\/a>. I wasn’t going to get any quick and easy gains from automated software. I posted a question on the JavaRanch<\/a> J2ME forum and received some useful replies<\/a>. Here’s the sequence I went through:<\/p>\n

1. Original size of the application: 79884 bytes.<\/p>\n

2. Removal of extra, unused classes: 79881. You can see that the obfuscator did a good job of winnowing out unused classes without my help.<\/p>\n

3. Changed all the data objects (5-6 classes), which had been written in classic J2SE style with getters and setters for their properties, to have public variables instead: 79465<\/p>\n

4. Combined 3 of the data object classes into one generic class: 78868<\/p>\n

5. Combined 5 networking classes into 2: 74543<\/p>\n

6. Removed all the logging statements: 66044. (Perl to the rescue–$ perl -p -i -e 's!Log\\.!\/\/Log.!' `find . -name \"*.java\" -print |xargs grep -l 'Log\\.'`<\/code>)<\/p>\n

7. Next, I played around with the jode<\/a> obfuscator which Michael Yuan<\/a> recommended. I was able to radically decrease the size of the jar file, but, unfortunately, that jar file didn’t work on the phone. I also got a ton of exceptions:<\/p>\n

<\/p>\n
java.util.NoSuchElementException\n        at jode.bytecode.BytecodeInfo$1.next(BytecodeInfo.java:123)\n        at jode.obfuscator.modules.LocalOptimizer.calcLocalInfo(LocalOptimizer.java:370)\n        at jode.obfuscator.modules.LocalOptimizer.transformCode(LocalOptimizer.java:916)\n        at jode.obfuscator.MethodIdentifier.doTransformations(MethodIdentifier.java:175)\n        at jode.obfuscator.ClassIdentifier.doTransformations(ClassIdentifier.java:659)\n        at jode.obfuscator.PackageIdentifier.doTransformations(PackageIdentifier.java:320)\n        at jode.obfuscator.PackageIdentifier.doTransformations(PackageIdentifier.java:322)\n        at jode.obfuscator.PackageIdentifier.doTransformations(PackageIdentifier.java:322)\n        at jode.obfuscator.PackageIdentifier.doTransformations(PackageIdentifier.java:322)\n        at jode.obfuscator.ClassBundle.doTransformations(ClassBundle.java:421)\n        at jode.obfuscator.ClassBundle.run(ClassBundle.java:526)\n        at jode.obfuscator.Main.main(Main.java:189)\n<\/code><\/pre>\n<\/div>\n
I'm sure I just didn't use it right, but the jar file size was so close to the limit that I abandoned jode.<\/p>\n
8.  Instead, I put all the classes in one file (perl to the rescue, again) and compiled that: 64057 bytes.  The jar now downloads and works on my Nokia 6200 phone.  <\/p>\n
When I have to do this again, I'll definitely focus on condensing classes, basically replacing polymorphism with if<\/code> statements.  After removing extraneous Strings and concatenating all your classes into one .java file (both of which are one time shots), condensing classes is the biggest bang for your buck.<\/p>\n","protected":false},"excerpt":{"rendered":"
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