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POhow to check if a jar file is valid?
 

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  1. POhow to check if a jar file is valid?
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    <p>my webapp allows a user to upload a jar file. however, after the jar file is uploaded, it is corrupted. i have verified this by comparing the md5 checksum (winmd5free). </p> <p>the uploaded jar file looks "normal" and "right"</p> <ul> <li>the file size compared to the original looks right (at the KB level)</li> <li>i can open the uploaded jar file using 7z and view its content (resources and class files), and everything is the same compared to the original</li> </ul> <p>when i open up the uploaded jar file (using Notepad++), i did notice that the binary contents are different from the original. also, when i used JarInputStream to read the jar entries, there were no entries.</p> <pre><code>JarInputStream is = new JarInputStream(new FileInputStream(new File("uploaded.jar"))); JarEntry entry = null; while(null != (entry = is.getNextJarEntry())) { System.out.println(entry.getName()); } </code></pre> <p>furthermore, when i double click on the jar (Windows), i get the following message.</p> <blockquote> <p>Error: Invalid or corrupt jarfile</p> </blockquote> <p>my questions are</p> <ul> <li>is there a way to programmatically check if a jar file is valid? i would have expected JarInputStream to detect this right away, but it shows no problems at all</li> <li>when i double click on the jar file, in windows, is it java.exe that is giving me the invalid or corrupt jarfile message?</li> <li>how come when an invalid jar file is passed in as part of the classpath, no error/exception is thrown? e.g. <em>java -cp uploaded.jar;libs* com.some.class.Test</em> ?</li> </ul> <p>please note that this has nothing to do with jar signing and/or checking the signing of a jar. it is simply checking if a file (uploaded or not) is a valid jar file (not necessarily if the jar's class files are valid, as there is another SO post on this issue already).</p> <p>results for running </p> <blockquote> <p>jar -tvf uploaded.jar</p> </blockquote> <pre><code>java.util.zip.ZipException: error in opening zip file at java.util.zip.ZipFile.open(Native Method) at java.util.zip.ZipFile.&lt;init&gt;(ZipFile.java:127) at java.util.zip.ZipFile.&lt;init&gt;(ZipFile.java:88) at sun.tools.jar.Main.list(Main.java:977) at sun.tools.jar.Main.run(Main.java:222) at sun.tools.jar.Main.main(Main.java:1147) </code></pre>
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    1. USJane Wayne
    1. USJane Wayne
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    1. COOn the command line, run the jar command like this: `jar -tvf <jarname>`. The 't' says "test", 'v' I believe means "verbose", and 'f' means "file". You can also open a JAR in any ZIP program.
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    2. COthanks, i will use java.util.zip.ZipFile to see if i can programmatically check (see modified addition of stack trace from running those options with the jar tool).
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