Classpath Issues with java -jar option

[Vijay Silva]

I have an executable jar (Main-Class specified in the manifest file), which has some runtime dependecies on a group of other jars.

When running:
java -cp lib/dependentJar1.jar;lib/dependentJar2.jar -jar myJar.jar
I always get a NoClassDefFoundError for a class in the dependent jars.

If instead I try:
java -cp lib/dependentJar1.jar;lib/dependentJar2.jar;myJar.jar MyMainClass
it works!!

I also have been able to specify the class path within my executable jar's manifest file, which also works.

Is there a reason why specifying the class path with the -jar option does not work, or am I doing something wrong??

[Stefan Wagner]

If you use

java -jar a.jar

a.jar is used as source.
If the manifest contains additional jars, that is fine, but other sources specified on the commandline (and I guess in the env.-var. CLASSPATH) are ignored.

[Vijay Silva]

"other sources specified on the commandline (and I guess in the env.-var. CLASSPATH) are ignored"

Why is that? The Java usage (java -help) specifies:
java [-options] -jar jarfile [args...]
(to execute a jar file)

It does not mention anything about the class path option being ignored with the -jar option in the usage. This is very misleading.

Is there a reason why the classpath option is ignored?? What if a classpath is not specified in the manifest??

[Ernest Friedman-Hill]

The complete documentation for java.exe (for example, here) says,

When you use [the -jar] option, the JAR file is the source of all user classes, and other user class path settings are ignored.

[Stan James]

That's the best answer to a question I haven't asked yet in a long time! Now I can go back to work. Later ...

[Jesper de Jong]

Originally posted by Vijay Silva:
Is there a reason why the classpath option is ignored?? What if a classpath is not specified in the manifest??

I can think of a reason: it gives the person who made the JAR file total control over the classpath when the JAR is executed.

If java.exe would also look at the CLASSPATH environment variable, you might get into all kinds of problems because the JRE could pick up classes that are anywhere on the system. It could cause a lot of hassle, especially with users who don't know all the internals of Java and who just want to run a Java program they get from somebody, if they have their CLASSPATH (deliberately or not) set wrong.

[paramu iyer]

You can give all the dependent jars in the Class-Path of the manifestfile and then run your main application using java -jar option,I guess that will work.