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classpathjavarxtx

RxTx installation on windows java.lang.NoClassDefFoundError: gnu/io/CommPort

I put rxtxcomm.jar into jre/lib/ext folder, but I still get NoClassDefFoundError Isn't this folder automatically taken into the global classpath?

Thanks

Solution

  • yes it is taken automatically to classpath, but RXTXcomm uses JNI /native external libraries (.so and .dll files), you must provide the path to them when running your program in command line:

    java -jar yourprogram.jar -Djava.library.path="PATH_TO_EXTERNAL_LIBRARIES"

    for linux:

    suppose you unpacked the rxtx.zip to /home/user/

    if you have 32bit x86 platofrm:

    PATH_TO_EXTERNAL_LIBRARIES = /home/user/Linux/i686-unknown-linux-gnu/

    if you have 64bit x86 platform the it would be:

    PATH_TO_EXTERNAL_LIBRARIES = /home/user/Linux/x86_64-unknown-linux-gnu/

    for windows:

    suppose you downloaded and unpacked it to C:\rxtxt

    PATH_TO_EXTERNAL_LIBRARIES = C:\rxtxt\Windows\i368-mingw32\

    If you find it cumbersome to do it from command line you can do it from yout code (before opening port via RXTXcomm):

    System.setProperty("java.library.path","PATH_TO_EXTERNAL_LIBRARIES");

    EDIT:

    of course, you must put RXTXcomm.jar in your classpath in addition to all of the above. If running from command line as jar packaged program - yourprogram.jar - inside the jar you must have a META-INF folder that contains MANIFEST.MF with the following entries:

    Class-Path: lib/RXTXcomm.jar
Main-Class: pkg.Main

    and yourprogram.jar must be in folder which has folder lib in which is RXTXcomm.jar, also the class with 

    public static void main(String[] args)

    method must be called Main and reside in package named pkg (just replace pkg.Main with whatever you have).

    Then you can run your program succesfully and open a serial port if you have one. This approach also eliminates the need to copy anything in jre/lib/ext folder

    EDIT^2:

    or, if you don't want to pack your program in jar, position yourself in folder which contains the folder pkg and write:

    java -cp PATH_TO_RXTX/RXTXcomm.jar -Djava.library.path="PATH_TO_EXTERNAL_LIBRARIES" pkg.Main

    (all paths can be relative or absolute)

    EDIT^3:

    but I would recommend Java Simple Serial Connector instead of RXTXcomm:

    • it handles heavy load from multiple threads as opposed to RXTXcomm (tested in production)
    • external libraries are packed in jar so there is no need for setting java.library.path