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Thread: Is it possible to load classes at runtime that are discovered from a directory

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    Default Is it possible to load classes at runtime that are discovered from a directory

    I'm working on a command shell program. The idea is it's a blend between the AS/400 and a unix shell with dropdown autocompletes, syntax highlighting, etc. One feature I'd like to implement is a way for users to create their own classes for additional functionality. They would design their classes off of a standard superclass, compile them and then drop them in the classes directory. The program would look in the directory at runtime and load them. Is this possible with my program not knowing the class names before it's compiled?


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    Default Re: Is it possible to load classes at runtime that are discovered from a directory

    File Class Loader Java Tips Weblog

    db

    edit That's a link
    Last edited by Darryl.Burke; June 6th, 2010 at 07:56 AM.

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    Default Re: Is it possible to load classes at runtime that are discovered from a directory

    Thanks I'm checking it out now.

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    Default Re: Is it possible to load classes at runtime that are discovered from a directory

    Yes, in some forum software I've written I've added the ability to drop a jar file into a plugin directory and then load that during runtime. You just need to use reflection really.

    1. Open the JAR file
    2. Loop through all the entries in it
    3. If an entry ends with .class, do Class.forName with its fully qualified package name and you're off

    // Json

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    Default Re: Is it possible to load classes at runtime that are discovered from a directory

    What if the .class files are NOT on the classpath. Will Class.forName() work?
    I think you need your own class loader to read the bytes from the .class file and make a class from it.

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    Default Re: Is it possible to load classes at runtime that are discovered from a directory

    Quote Originally Posted by Norm View Post
    What if the .class files are NOT on the classpath. Will Class.forName() work?
    I think you need your own class loader to read the bytes from the .class file and make a class from it.
    That's what File Class Loader does.

    db

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    Default Re: Is it possible to load classes at runtime that are discovered from a directory

    Sorry, I missed that your earlier post was a link. Your post was a bit too subtle.

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    Default Re: Is it possible to load classes at runtime that are discovered from a directory

    I just used the URLClassLoader (Java Platform SE 6)

    final URL[] urls = { new URL("file", null, file.getAbsolutePath()) };
    final URLClassLoader classLoader = new URLClassLoader(urls, Thread.currentThread().getContextClassLoader());

    Something like that

    // Json

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    Default Re: Is it possible to load classes at runtime that are discovered from a directory

    Quote Originally Posted by Norm View Post
    Sorry, I missed that your earlier post was a link. Your post was a bit too subtle.
    I'd rather say the (lack of special) formatting for links is (more than) a bit too subtle.

    db

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    Super Moderator Json's Avatar
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    Default Re: Is it possible to load classes at runtime that are discovered from a directory

    Quote Originally Posted by Darryl.Burke View Post
    I'd rather say the (lack of special) formatting for links is (more than) a bit too subtle.

    db
    I've raised this as an issue and hopefully we'll be able to resolve that.

    // Json

  11. The Following User Says Thank You to Json For This Useful Post:

    Darryl.Burke (June 9th, 2010)

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    Default Re: Is it possible to load classes at runtime that are discovered from a directory

    Quote Originally Posted by Json View Post
    I've raised this as an issue and hopefully we'll be able to resolve that.

    // Json
    Thank you Json.

    db

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    Default Re: Is it possible to load classes at runtime that are discovered from a directory

    Quote Originally Posted by Json View Post
    I've raised this as an issue and hopefully we'll be able to resolve that.
    A workaround is to underscore (U) the link text, but it's easy to forget...

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