Java Classpath Problems

Question

I've compiled and I am now trying to run this program from the terminal in OSX and Fendora using the following command from within the ie directory:

java ie.moguntia.webcrawler.Psucker http://www.wikipedia.org test

However I get the following error:

Exception in thread "main" java.lang.NoClassDefFoundError: ie/moguntia/webcrawler/Psucker
Caused by: java.lang.ClassNotFoundException: ie.moguntia.webcrawler.Psucker
    at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:247)

I haven't ran applications that used packages from the command line before so I am therefore unable to figure out the error.

I have attempted to set the classpath using export CLASSPATH=. so that the current directory would be added to the classpath.

The directory structure is as follows:

ie/moguntia/webcrawler/

Answer 1

Depending on where your compiled classes are located, you need to include this location in the java command, eg if they are in the classes directory:

java -cp classes ie.moguntia.webcrawler.PSucker http://www.wikipedia.org test

or if they are in the current directory:

java -cp . ie.moguntia.webcrawler.PSucker http://www.wikipedia.org test

or just

java ie.moguntia.webcrawler.PSucker http://www.wikipedia.org test

Here's how I was able to run this (unzip, cd to directory, compile, find classes, run):

(13:55:52) ~/Desktop/temp → ll
total 32
-rw-r--r--@ 1 Nils.Winkler  staff    14K 12 Mär 13:41 multiweb.zip

(13:56:01) ~/Desktop/temp → unzip multiweb.zip -d multiweb
Archive:  multiweb.zip
   creating: multiweb/CVS/
   creating: multiweb/ie/
   creating: multiweb/ie/CVS/
   creating: multiweb/ie/moguntia/
   creating: multiweb/ie/moguntia/CVS/
   creating: multiweb/ie/moguntia/threads/
   creating: multiweb/ie/moguntia/threads/CVS/
  inflating: multiweb/ie/moguntia/threads/ControllableThread.java  
  inflating: multiweb/ie/moguntia/threads/MessageReceiver.java  
  inflating: multiweb/ie/moguntia/threads/ObjectQueue.java  
  inflating: multiweb/ie/moguntia/threads/Queue.java  
  inflating: multiweb/ie/moguntia/threads/ThreadController.java  
   creating: multiweb/ie/moguntia/webcrawler/
   creating: multiweb/ie/moguntia/webcrawler/CVS/
  inflating: multiweb/ie/moguntia/webcrawler/PSucker.java  
  inflating: multiweb/ie/moguntia/webcrawler/PSuckerThread.java  
  inflating: multiweb/ie/moguntia/webcrawler/SaveURL.java  
  inflating: multiweb/ie/moguntia/webcrawler/URLQueue.java  
  inflating: multiweb/ie/moguntia/webcrawler/WSDLCrawler.java  
  inflating: multiweb/ie/moguntia/webcrawler/WSDLCrawlerThread.java 

(13:56:08) ~/Desktop/temp → cd multiweb

(13:56:57) ~/Desktop/temp/multiweb → javac ie/moguntia/webcrawler/*.java
Note: Some input files use unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

(13:57:11) ~/Desktop/temp/multiweb → find . -name *.class
./ie/moguntia/threads/ControllableThread.class
./ie/moguntia/threads/MessageReceiver.class
./ie/moguntia/threads/Queue.class
./ie/moguntia/threads/ThreadController.class
./ie/moguntia/webcrawler/PSucker.class
./ie/moguntia/webcrawler/PSuckerThread.class
./ie/moguntia/webcrawler/SaveURL.class
./ie/moguntia/webcrawler/URLQueue.class
./ie/moguntia/webcrawler/WSDLCrawler.class
./ie/moguntia/webcrawler/WSDLCrawlerThread.class

(13:57:18) ~/Desktop/temp/multiweb → java ie.moguntia.webcrawler.PSucker http://www.wikipedia.org test
[0] http://www.wikipedia.org

Answer 2

It should work if you run it from outside the ie directory.

Note that relying on the CLASSPATH environment variable is generally not recommended; instead explicitly put the classpath on hte command line using the -cp switch