在外部Jar中访问类

Question

I am having problems having my Java programs see classes that are packaged in an external jar. I am running under Windows 7. I have the classes embedded in a jar called ParserUtilities.jar. I established the path with a CLASSPATH variable using the System utility and the Environment tab. I confirmed that the CLASSPATH is set correctly. When I type echo %CLASSPATH%, I see C:\\Program Files\\Java\\externaljars\\ParserUtilities.jar which is correct. But when I type java -jar Parse.jar (my executable) I get the error Exception in thread "main" java.lang.NoClassDefFoundError: com/artificialmed/Initialize

Some additional information:

1. When I put the ParserUtilities.jar in the ..\\lib\\ext directory, everything works.
2. I am running java version 1.6.0_16. Java(TM) SE Runtime Environment
3. In experimenting, I typed java -cp C:\\Program Files\\Java\\jre6\\lib\\ext>java -cp C:\\Program Files\\Java\\externaljars\\ParserUtilities.jar

and got this error "Could not find the main class: Files\\Java\\externaljars\\ParserUtilities.jar" but there is no main class (its just a collection of classes I use in a bunch of programs).

I do not have a Java SDK loaded in the environment, just a java JRE (Is this the issue?).

Answer 1

Try adding "" around the classpath entry since you have a space in the directory (Program Files). The error message "Files\\Java\\externaljars\\ParserUtilities.jar" would indicate that is the problem.

Answer 2

From Sun's documentation on the -jar option to the java command: "When you use this option, the JAR file is the source of all user classes, and other user class path settings are ignored." I believe that means that both your CLASSPATH environment variable as well as any -cp arguments that you might provide on the command line are both going to be ignored.

So, you have the following options:

1. Package everything into one jar, and then you can execute it by running java -jar JarWithEverything.jar .

2. Keep things in separate jars and provide both jars as arguments on the command line, so that you type something like this:

   java -cp "C:\\Program Files\\Java\\externaljars\\ParserUtilities.jar";"C:\\Program Files\\Java\\externaljars\\Parser.jar" com.artificialmed.Initialize

3. Keep things in separate jars and put one or both jars in your CLASSPATH environment variable instead of providing them on the command line.