Java libraries in Linux

Chrax · 12-03-2005, 02:48 PM

I'm running Ubuntu Breezy (5.10), and I just installed the libcommons-cli-java package, so that I could take advantage of its argument parsing features.

It installed the file /usr/share/java/commons-cli-1.0.jar and the symlink (to the aforementioned file) /usr/share/java/commons-cli.jar.

Unzipping the jar gets us:

Code:

Archive:  commons-cli.jar
   creating: META-INF/
  inflating: META-INF/MANIFEST.MF
   creating: org/
   creating: org/apache/
   creating: org/apache/commons/
   creating: org/apache/commons/cli/
  inflating: org/apache/commons/cli/AlreadySelectedException.class
  inflating: org/apache/commons/cli/BasicParser.class
  inflating: org/apache/commons/cli/CommandLine.class
  inflating: org/apache/commons/cli/CommandLineParser.class
  inflating: org/apache/commons/cli/GnuParser.class
  inflating: org/apache/commons/cli/HelpFormatter$1.class
  inflating: org/apache/commons/cli/HelpFormatter$StringBufferComparator.class
  inflating: org/apache/commons/cli/HelpFormatter.class
  inflating: org/apache/commons/cli/MissingArgumentException.class
  inflating: org/apache/commons/cli/MissingOptionException.class
  inflating: org/apache/commons/cli/Option.class
  inflating: org/apache/commons/cli/OptionBuilder.class
  inflating: org/apache/commons/cli/OptionGroup.class
  inflating: org/apache/commons/cli/Options.class
  inflating: org/apache/commons/cli/ParseException.class
  inflating: org/apache/commons/cli/Parser.class
  inflating: org/apache/commons/cli/PatternOptionBuilder.class
  inflating: org/apache/commons/cli/PosixParser.class
  inflating: org/apache/commons/cli/TypeHandler.class
  inflating: org/apache/commons/cli/UnrecognizedOptionException.class

So my question is, how do I import this? I've tried

Code:

import org.apache.commons.cli.*

which is how the examples I've seen do it. But the only way I've been able to compile with this, is by unzipping into my working directory.

If someone could tell me where I need to place/rename the jar, any environment variables to set, or anything at all that could help, I would appreciate it.

Thanks,
Chris

paulsm4 · 12-03-2005, 06:22 PM

Java relies on something called a "class path".

Java has a default classpath; you can augment/override this via an environment variable
(EXAMPLE:
export CLASSPATH=".:/usr/share/java/commons-cli-1.0.jar")

or with the "java -cp" command line argument
(EXAMPLE:
java -cp .:/usr/share/java/commons-cli-1.0.jar myApp)

It turns out that CLASSPATH (and whether or not your app will actually run) has little to do with the "import" statement. The latter is a "compile time thing"; the former is an "execution time thing".

It also turns out that you can include either a directory (as you would expect) or a .Jar file in your CLASSPATH. This means that you do *not* necessarily have to extract the contents of a .Jar file in order to use it.

Here are a couple of links which might help:

http://www.freshsources.com/Sep99.html
<= Somewhat dated, but still good!

http://mindprod.com/jgloss/classpath.html
<= For Windows, but still applicable

'Hope that helps .. PSM

Basel · 12-04-2005, 12:20 AM

Quote:

Java has a default classpath; you can augment/override this via an environment variable
(EXAMPLE:
export CLASSPATH=".:/usr/share/java/commons-cli-1.0.jar")

To make sure that the .jar file is in the class path add the above line to ~/.bashrc or ~/.bash_profile
It is a good idea to add $CLASSPATH to your class path so that previously set libraries are included as well.

paulsm4 · 12-04-2005, 01:28 AM

Actually, Chrax, I would encourage you to play with *BOTH* the $CLASSPATH environment variable *AND* the "-classpath" command line option.

One can make a strong case that the "$CLASSPATH" environment variable is obsolete. It certainly doesn't scale well beyond "hello world" test programs and specific apps (which launch their own individual JVM from inside of a script).

In any case, please post back and let us know if you solved the problem!

Your .. PSM

Chrax · 12-05-2005, 11:03 PM

Yes, I got it. Thanks.

I've never played with Java libraries before. C and Perl are much more straightforward as far as includes go, but then, they don't really have anything like the equivalent of .jar's.