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POJar files: why does extracting then compression a jar file create a file of a different size to the original?
 

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  1. POJar files: why does extracting then compression a jar file create a file of a different size to the original?
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    <p>I was trying to edit a single byte in an extracted Eclipse plugin jar file. I noticed that after I re-compressed the files as a jar, the resultant file was larger than the original (only 1%) and that the plugin didn't work. Eclipse booted, but shut down silently after selecting a workspace. Rolling back to the original plugin allowed it to start successfully.</p> <p>I then tried uncompressing, then compressing the plugin (not changing anything) and the resultant jar file was still bigger than the original, and also didn't work.</p> <pre><code>$ jar -xf temp/in.jar </code></pre> <p>then</p> <pre><code>$ jar -cf out.jar temp/* $ du in.jar out.jar 4216 in.jar 4236 out.jar </code></pre> <p>I guess this might be due to timestamps being changed, but I didn't think that this would stop eclipse from accepting it.</p> <p>So my question: Is there a way to uncompress a jar, change a byte, and compress it without changing the jar significantly?</p> <p>I'm using Ubuntu 10.04 - 64 bit:</p> <pre><code>Linux user 2.6.32-38-generic #83-Ubuntu SMP Wed Jan 4 11:12:07 UTC 2012 x86_64 GNU/Linux </code></pre> <p>When looking at the jar's table, there appears to be a different order:</p> <pre><code>$ jar tf in.jar | head -n 5 META-INF/ META-INF/MANIFEST.MF com/ com/android/ com/android/ide/ $ jar tf out.jar | head -n 5 META-INF/ META-INF/MANIFEST.MF about.html about.ini about.properties </code></pre> <p>Is there a way to order them differently within the jar?</p>
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    1. COTo reitterate, you want to change bytes IN THE ACTUAL BYTES of the Jar file, not those in the .class files (as in altering bytecode)?
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    2. COThis "requirement" is bogus (and absurd) - it is highly unlikely your goal is to change a byte in a jar. What are you *actually* trying to do? Maybe we can help you find a better approach than your "solution".
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    3. COI have edited the question for clarity. I wish to change a byte in one of the class files in the jar by whatever method possible. If that means extracting it, altering it, and recompressing - that's great ( currently I can't get this to work). If I could byte alter the original jar file, and it worked I would be satisfied. My goal is the result and if I can get it by an 'absurd' method, I'll take it. I'm trying to alter ADT as per this [post](https://devmaze.wordpress.com/2011/01/18/using-com-android-internal-part-4-customizing-adt/)
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