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Thread: Read/Write class file

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    Default Read/Write class file

    Please I'm trying to extract strings from a class file, modify and write to the file, but I don't know how to do it. Since class files are not text files, I can't use the normal way of reading and writing.
    I would appreciate if someone could help by giving me a Java code to achieve this.
    Please help me...


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    Super Moderator Norm's Avatar
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    Default Re: Read/Write class file

    There is documentation for the contents of class files. I don't remember where it is stored. An internet search should find it.
    This may help: http://docs.oracle.com/javase/specs/...sFile.doc.html

    Once you get the layout of the bytes for the class file, you will be able to read the bytes in the file and find the values of the Strings used.

    Given the format definition you may be able to write out the updated class file,
    but it will be lots of work to create the code.

    There are java decompilers.

    What are you trying to do? Is there a better way?
    If you don't understand my answer, don't ignore it, ask a question.

  3. The Following User Says Thank You to Norm For This Useful Post:

    Anaphase21 (December 26th, 2013)

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    Default Re: Read/Write class file

    Thanks for response @Norm.
    Actually I'm building a J2ME application that will translate the class strings from one language to the other. I'm done with the translation code and now needs a way of obtaining the strings, translating, then writing it back. From oracle's documentation of the VM specification, I learnt that strings are stored in the Constant pool as utf8 encoding. I also learnt the value for the string constant as 8. I don't have much knowledge about the class file format. Atleast, I would appreciate if the algorithm for doing this task is shown to me.

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    Default Re: Read/Write class file

    Algorithm? Read the specifications, look at some class files in a hex editor to see what they look like and write some code that reads the bytes and finds the desired parts of the file.
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Read/Write class file

    Ok! I will try that. When I get hooked up, I will come back.

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