Re: Java server won't run after reboot

From: Bob Smith (bob_at_netprt.com)
Date: 05/31/04

  • Next message: Bob Smith: "Re: Java server won't run after reboot" 
    Date: Mon, 31 May 2004 11:17:15 -0600 (MDT)
To: techlist@voyager.phys.utk.edu, redhat-list@redhat.com

    Working with classpaths in Java isn't too hard, but there are some rules
    to follow.

    1. Simplest scenario: Executing in the same directory, and there are no
    package definitions in your source code. Example: HelloWorld, no package
    definition. Execute from that directory, no classpath definition needed.
    eg.

    Class HelloWorld { ... }

    2. Next simplest: You compile without packages defined:
    using the same directory for source and compiled classes, or if you
    compiled classes to a different directory:

    export CLASSPATH=<pathtoyourclasslocation>
    example directory: /opt/myapp/lib/
    then
    export CLASSPATH=/opt/myapp/lib/
    and call it:
    java HelloWorld

    3. Adding a package definition to your source code, and there is a
    definite source code hierachy. Using the package example below:

    package project.testjava;
    Class HelloWorld { ... }

    Your directory structure should look like this:
    <pathtoyoursourcelocation>/project/testjava/HelloWorld.java

    Assuming that you compile your code in the same directory and deposit the
    class files there, then set your classpath as follows:

    export CLASSPATH=<pathtoyoursourcelocation>
    e.g. Using /opt/myapp/source/ as <pathtoyoursourcelocation>:
    ex. export CLASSPATH=/opt/myapp/source/

    and call the application as follows:

    java project.testjava.HelloWorld

    --------------------------------------------

    If you compile to a different location, then your directory structure will
    look like this after a compilation:

    <pathtoyoursourcelocation>/project/testjava/HelloWorld.java
    <pathtoyourclasslocation>/project/testjava/HelloWorld.class

    Then set the classpath as follows:
    export CLASSPATH=<pathtoyourclasslocation>
    e.g. Using /opt/myapp/lib as <pathtoyourclasslocation>
    export CLASSPATH=/opt/myapp/lib

    and call the application as follows:

    java project.testjava.HelloWorld

    3. You've compiled to a jarfile, e.g. MyHelloWorld.jar
    export CLASSPATH=<pathtojar>/MyHelloWorld.jar
    e.g. Using /opt/myapp/lib as <pathtoyourclasslocation>
    export CLASSPATH=/opt/myapp/lib

    and call as follows:
    java project.testjava.HelloWorld

    -Bob

    > On Saturday 29 May 2004 05:44 pm, you wrote:
    >> That didn't work. I still get the NoClassDefFoundError. Any other
    >> ideas?
    >
    > You're right !! it doesn't work. I just try this myself, and whenever I
    > try to
    > execute from outside the directory where the java files is located, I got
    > the
    > same error. I thought I've seen this and what I suggested was the
    > solution,
    > obviously not ! (Now it should be obvious that I am not a java developer
    > myself, I just play with it sometime)
    >
    > After some searching myself, I only have this solution:
    >
    > If for example, my java program is in ~/project/testjava/helloworld.java,
    > I
    > can put in helloworld.java:
    >
    > package project.testjava;
    > <rest of the src code>
    >
    > then I need to go to ~, and compile it from there:
    > javac project/testjava/helloworld.java
    >
    > and running it from there would work tpp:
    > java project/testjava/helloworld
    >
    > The problems with the solution: First, I can't find a way so that I can
    > use
    > absolute path during compile and running (which is probably what you want
    > in
    > your case, since you're going to put the command in rc.local). So what I
    > want
    > is something so that I can say:
    >
    > javac /home/<username>/project/testjava/helloworld.java
    > java /home/<username>/project/testjava/helloworld
    >
    > when I tried, the solution does not work. I can't also figure out what to
    > put
    > in after the "package" keyword in the source code to make the absolute
    > path
    > work.
    >
    > Secondly, the source code is dependent on what directory you want to
    > compile
    > and run the java program from. Unless I am missing something, that is just
    > plain stupid !! Source code of a program should never be dependent on
    > where
    > the program is running from.
    >
    > So that's it. I am kinda stuck right now too. I don't know if that would
    > help
    > you, but if you find the real solution, please let me know, cause right
    > now
    > it bugs the hell out of me too ! (BTW, I have a task of writing some java
    > program in the near future, so this would be good to know).
    >
    > I know this is going OT, but if anyone else on the list know a solution,
    > please help.
    >
    > RDB
    >
    >
    >> On Sat, 2004-05-29 at 11:59, Reuben D. Budiardja wrote:
    >> > On Saturday 29 May 2004 12:16 pm, Michael Sullivan wrote:
    > <snip>I wrote a java server that I want to start every time
    >> > > my server PC restarts. I created a /usr/local/classes directory and
    >> > > copied Server.class and the support classes it uses there. Id cd'd
    >> to
    >> > > /usr/local/classes and issued a java Server from there and it works
    >> > > fine, but if I issue a java /usr/local/classes/Server from anywhere
    >> > > outside the /usr/local/classes directory it tells me
    >> > >
    >> > > Exception in thread "main" java.lang.NoClassDefFoundError:
    >> > > /usr/local/classes/Server
    > <snip>
    >> > Try the following:
    >> > set the environment variable CLASSPATH to /usr/local/classes so that
    >> Java
    >> > knows where to find your classes. Asumming you're using bash:
    >> > $> export CLASSPATH=$CLASSPATH:/usr/local/classes
    >> >
    >
    >
    > --
    > Reuben D. Budiardja
    > Department of Physics and Astronomy
    > The University of Tennessee, Knoxville, TN
    > ---------------------------------------------------------
    > "To be a nemesis, you have to actively try to destroy
    > something, don't you? Really, I'm not out to destroy
    > Microsoft. That will just be a completely unintentional
    > side effect."
    > - Linus Torvalds -
    >
    >
    > --
    > redhat-list mailing list
    > unsubscribe mailto:redhat-list-request@redhat.com?subject=unsubscribe
    > https://www.redhat.com/mailman/listinfo/redhat-list
    > 

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