JAVA command line options -cp and -jar don't work together?

Question

Running JSDK 1.4.2 under Windows. I have a Java application that tries to dynamically load a class name that the user enters as follows:
try {
classResult = java.lang.Class.forName(strFilterName);
catch (ExceptionInInitializerError e) {
strErrorMessage = "ExceptionInInitializerError loading class: " + strFilterName;
catch (LinkageError e) {
strErrorMessage = "LinkageError loading class: " + strFilterName;
catch (ClassNotFoundException e) {
strErrorMessage = "ClassNotFoundException loading class: " + strFilterName;
This works fine if the classes that make up my application are left as class files in the classpath, but fails to work if they have been collected and run from a JAR file. Note: I can even dynamically load the class when running from the JAR file, if the class I'm trying to load is within that JAR file too. The problem really occurrs when the dynamically loaded class is located someplace else in my classpath. I've tried using various combinations of the "-cp" and "-jar" Java command line options - but when loading and running from a JAR file - the "-cp" parameters seem to be ignored. Is this a bug? Has anyone ever seen this before?
I run my program from the JAR file using this command:
java -cp .;e:\entmgr\filters -jar EntMgr.jar
Where "e:\entmgr\filters" is where the class I'm trying to dynamically load is. (This class has no package name, but loads perfectly as long as I'm not running the application from the JAR file). The class name specified by the user has to be fully specified with a package name (if it has one).
I have tried forcing the "java.lang.Class.forName(strFilterName);" call to use the system class loader, the parent of the system class loaded, and even the null bootstrap class loader - all with no success.
I am suspecting that the class loader that is loading and running my main program from the JAR file, is just not paying any attention to the "-cp" parameter when the "-jar" parameter is present. Indeed, I have never seen any change in the failure, no matter what I put in the "-cp" parameter when using the JAR file.
When I run this without using the JAR file, here is the command I execute:
java -cp .;davidp\snmp;filters davidp.snmp.EntMgr
Where this is executed in a directory that has a "filters" and "davidp\snmp" directory. In this case, because the "filters" directory is in my class path - I can dynamically load my class from it using just its simple name (i.e. "TestTrapFilter").
So, is there some bug that precludes the "-cp" parameter from working correctly when the "-jar" parameter is used? Is there some other way to initialize or set up the classloader I'm using, so it can find things outside of the JAR file I'm running from? I would hope that it is possible to get the same behavior from my program, no matter if it is run from a JAR file or not.
Thanks for any assistence!
Dave

Answer 1

These posts are pretty old, but this page came up in a google search while I was having the same problem, so I thought I would throw my own (Later found) solution in.
The -cp and -jar options did not work together for me, but I later learned that they didn't really have to (and you don't have to mess with jar manifest files).
While on the command line, if you want to set a specific class path and also run a jar, all you need to do is add the jar to whatever extra class path you need to use in the -cp <arg>, and then specify which class you want run from inside the jar.
IE:
java -cp <YourSpecialClasspath>: <PathToJar> <ClassToRunInsideOfJar>
in my case it was like:
java -cp /home/user/WebRCP.jar:./StandaloneInstaller.jar InstallLoader
Remember to put a ":" in between the two arguments for the class path (-cp).
Hope this helps someone in the future,
-Josh