extension mechanism and javac

[Peter Merker]

Hi!

I'm having a problem with the use of the extension mechanism and javac. I've got these directories: C:\Test\upperpackage\subpackage and C:\Libraries. In subpackage I have the class HelloWorld:

package upperpackage.subpackage;
 
import upperpackage.MessageGenerator;
 
public class HelloWorld
{
  public static void main(String[] args)
  {
    new HelloWorld();
  }
  
  private HelloWorld()
  {
    new MessageGenerator().sayHello();
  }
}

In C:\Libraries I've got testjar.jar, which contains MessageGenerator.class and Manifest.mf. This is class MessageGenerator:

package upperpackage;
 
public class MessageGenerator
{
  public void sayHello()
  {
    System.out.println("Hello World!");
  }
}

I've "jared" testjar.jar with this line in test.txt:

Class: upperpackage/MessageGenerator.class [CR]

Having test.txt and MessageGenerator.class in C:\Libraries I used this command:

C:\Libraries>jar cmf test.txt testjar.jar MessageGenerator.class

Then trying to compile HelloWorld this came up:

C:\Test>javac -Djava.ext.dirs=C:\Libraries -verbose upperpackage/subpackage/Hell
oWorld.java
[parsing started upperpackage/subpackage/HelloWorld.java]
[parsing completed 62ms]
[search path for source files: [C:\Program Files\Apache Software Foundation\Mave
n 1.0.2\bin]]
[search path for class files: [C:\Program Files\Java\jdk1.5\jre\lib\rt.jar, C:\P
rogram Files\Java\jdk1.5\jre\lib\jsse.jar, C:\Program Files\Java\jdk1.5\jre\lib\
jce.jar, C:\Program Files\Java\jdk1.5\jre\lib\charsets.jar, C:\Libraries\dsol-fu
ll-1.6.6.jar, C:\Libraries\testjar.jar, C:\Libraries\tutorial-examples-1.6.jar,
C:\Program Files\Apache Software Foundation\Maven 1.0.2\bin]]
upperpackage/subpackage/HelloWorld.java:3: cannot find symbol
symbol  : class MessageGenerator
location: package upperpackage
import upperpackage.MessageGenerator;
                    ^
[loading C:\Program Files\Java\jdk1.5\jre\lib\rt.jar(java/lang/Object.class)]
[loading C:\Program Files\Java\jdk1.5\jre\lib\rt.jar(java/lang/String.class)]
[checking upperpackage.subpackage.HelloWorld]
upperpackage/subpackage/HelloWorld.java:14: cannot find symbol
symbol  : class MessageGenerator
location: class upperpackage.subpackage.HelloWorld
    new MessageGenerator().sayHello();
        ^
[total 1563ms]
2 errors

What have I been doing wrong?

[Stefan Wagner]

Having test.txt and MessageGenerator.class in C:\Libraries is wrong, since you say, that MessageGenerator is in "upperpackage".

"import upperpackage.MessageGenerator;"

compile via javac from "C:\Test\"

C:\Test\ > javac upperpackage/subpackage/HelloWorld.java 

Another pitfall might be:

I've "jared" testjar.jar with this line in test.txt:
Class: upperpackage/MessageGenerator.class [CR]

Try

 Main-Class: upperpackage/MessageGenerator.class 

[Peter Merker]

Originally posted by Stefan Wagner:
Having test.txt and MessageGenerator.class in C:\Libraries is wrong, since you say, that MessageGenerator is in "upperpackage".

Well, I'm not having test.txt and MessageGenerator.class in C:\Libraries. There is only the jar which contains MessageGenerator.class and Manifest.mf. I also tried adding another line to the Manifest file, now having

Class: upperpackage.MessageGenerator
Name: upperpackage/MessageGenerator.class

but this didn't change things either. I disagree that MessageGenerator.class should be in upperpackage, this is certainly possible, but not what I want. I want to learn how to use a jar together with a "simple" java file.

compile via javac from "C:\Test\"

C:\Test\ > javac upperpackage/subpackage/HelloWorld.java 

This only works if MessageGenerator.class is in upperpackage (and C:\Test is in the classpath, of course). But, like I said, that's not the way I want it to be.

Another pitfall might be:

 Main-Class: upperpackage/MessageGenerator.class 

I thought that attribute Main-Class would indicate the class with the main method in a jar. As the main method in my example is in HelloWorld, this shouldn't be used, or?
[ June 06, 2005: Message edited by: Peter Merker ]

[Stefan Wagner]

Class: upperpackage.MessageGenerator
Name: upperpackage/MessageGenerator.class

but this didn't change things either. I disagree that MessageGenerator.class should be in upperpackage, this is certainly possible, but not what I want. I want to learn how to use a jar together with a "simple" java file.

 Main-Class: upperpackage/MessageGenerator.class 

I thought that attribute Main-Class would indicate the class with the main method in a jar. As the main method in my example is in HelloWorld, this shouldn't be used, or?

a) Your code contains:
import upperpackage.MessageGenerator;
so either you change that, or MessageGenerator has to be in upperpackage.
It's not a question of taste, but of function.

b) You're right, it shall contain the class containing 'main', that was my error.
I only wanted to point out, that the name of the tag is 'Main-Class:', not 'Class:'.

[ June 06, 2005: Message edited by: Stefan Wagner ]
[ June 06, 2005: Message edited by: Stefan Wagner ]
[ June 06, 2005: Message edited by: Stefan Wagner ]

[Peter Merker]

I finally found my error. It was quite stupid. When I jarred I didn't have the directory structure in the jar, that was right, Stefan. So now I invoked

C:\Test>jar -cmfv test.txt testjar.jar upperpackage/MessageGenerator.class

having test.txt in C:\Test and MessageGenerator.class in C:\Test\upperpackage. I kept the "Class:" tag in test.txt as it is a valid tag, just as Main-Class. So now I got:

C:\Test>javac -Djava.ext.dirs=C:\libraries -cp . -verbose upperpackage/subpackag
e/HelloWorld.java
[parsing started upperpackage/subpackage/HelloWorld.java]
[parsing completed 47ms]
[search path for source files: [.]]
[search path for class files: [C:\Program Files\Java\jdk1.5\jre\lib\rt.jar, C:\P
rogram Files\Java\jdk1.5\jre\lib\jsse.jar, C:\Program Files\Java\jdk1.5\jre\lib\
jce.jar, C:\Program Files\Java\jdk1.5\jre\lib\charsets.jar, C:\libraries\testjar
.jar, .]]
[loading C:\libraries\testjar.jar(upperpackage/MessageGenerator.class)] <-- THERE IT IS!!!
[loading C:\Program Files\Java\jdk1.5\jre\lib\rt.jar(java/lang/Object.class)]
[loading C:\Program Files\Java\jdk1.5\jre\lib\rt.jar(java/lang/String.class)]
[checking upperpackage.subpackage.HelloWorld]
[wrote upperpackage\subpackage\HelloWorld.class]
[total 297ms]

Running it:

C:\Test>java -Djava.ext.dirs=C:\libraries -cp . upperpackage.subpackage.HelloWor
ld
Hello World!

Thank you Stefan, you pointed me in the right direction!
[ June 07, 2005: Message edited by: Peter Merker ]