Question

I am having trouble correctly generating a Jar for my Java implementation. I am not a Java master ( Thus why I am using Make and not Ant). I didn’t think I cared about a Jar until I realized my Windows machine didn’t hava javac. Then I thought to myself “If only I had a jar”

So I hacked a few lines together in a Makefile trying

The relevant lines are

all: client server jar

client: bin bin/Job.class bin/JobQueue.class bin/Client.class bin/FileTransfer.class

server: bin bin/Job.class bin/JobQueue.class bin/Server.class bin/ServerThread.class bin/FileTransfer.class

jar: client server
    jar cfe HBNQServer Server bin/Server.class bin/Job.class bin/JobQueue.class bin/ServerThread.class bin/FileTransfer.class
    jar cfe HBNQClient Client bin/Client.class bin/Job.class bin/JobQueue.class bin/FileTransfer.class

However when I attempt to run it I get a No Class Found Exception.

$ java -jar HBNQServer
Exception in thread "main" java.lang.NoClassDefFoundError: Server
Caused by: java.lang.ClassNotFoundException: Server
    at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:248)

I am sure the mistake is painfully obvious to anyone more familiar with “Jaring” files.

If I left any important code out, it may be found Here

Answer 1

I believe your problem is the bin prefix. If you jar a class file, it must be in a directory identical to its fully qualified package name. For example, if you implement a com.mycompany.Server class, the corresponding path in the jar file must be com/mycompany/Server.class. In your case, everything is in the bin directory in the jar file, so it can’t find your (presumably un-package-qualified) classes. Either put all of your classes in the bin package, or jar them up without the bin prefix.

Something like this might work:

jar: client server
    cd bin; jar cfe ../HBNQServer Server Server.class Job.class JobQueue.class ServerThread.class FileTransfer.class
    cd bin; jar cfe ../HBNQClient Client Client.class Job.class JobQueue.class FileTransfer.class