Netbeans的Java-.jar意外问题

Question

First of all, I am aware of Stack Overflow (and any competent forum-like website) policy of "search first, ask last", and, doing my homework, I searched various sources to find a solution to my issue. That said, I, failing to find any suitable answers, was left no choice but to ask this problem personally.

I have somewhat moderate programming skills, especially regarding the Java language. I am working on this 2D game with the default Java SE JDK. More specifically JDK 7u4. In this project, we have a class that manages most I/O operations. One of its methods returns the path to a file:

public static URL load(String resource) {
    return ZM.class.getResource(resource);
}

Now, this method works fine when running the project on Netbeans (version 7.1). However, when building and cleaning the project, the resulting .jar file does not seem to agree with its creator. When running the .jar on command line, the JVM caught a NullPointerException . It seemed that the file was not being able to be read inside the .jar. Following my programmers instinct, I started debugging the project. My first attempt was to check whether the load method was the faulty member. I ran some tests and obtained a couple of interesting results:

When running the application on Netbeans and with "ZM.class" as the methods argument, it returned:

/D:/Projects/GeometryZombiesMayhem/build/classes/geometryzombiesmayhem/ZM.class

But when running it from the .jar file, it returned:

file:/D:/Projects/GeometryZombiesMayhem/dist/GeometryZombiesMayhem.jar!/geometryzombiesmayhem/ZM.class

Naturally, I tried removing the initial file: string from it. No effect. Then I tried taking the exclamation mark from [...].jar![...] . Again, nothing. I tried removing all the possible permutations from the path. No luck.

Testing the method against the very own .jar file worked okay. Now, when I try to access the inside of the file, it doesn't let me. On earlier versions of this project it worked just fine. I am not really sure of what is going on. Any help is welcome.

Thank you in advance, Renato

Answer 1

When loading resources from a jar file, I've always used a classLoader. Everything seems to work the same whether you run from within the IDE, launch the executable jar file or run the program from a web site using JNLP.

Try loading the resource this way instead:

 try {
      ClassLoader cl = ZM.getClass().getClassLoader();     
      ImageIcon img  = new ImageIcon(cl.getResource("images/programIcon.jpg"));
      // do stuff with img.
 }
 catch(Exception failed) {
     System.out.println(failed);
 }

One more suggestion - you should create a separate folder for resources. In my example above, images is a folder inside of my src folder. This way it will automatically become part of the jar when I build it, but I am keeping resources separate from source code.

Answer 2

I suppose your problem is in loading an image from your jar file.

Here is how i do it

URL imageurl = Myclassanme.class.getResource("/test/Ergophobia.jpg"); 
Image myPicture = Toolkit.getDefaultToolkit().getImage(imageurl);
JLabel piclabel = new JLabel(new ImageIcon( myPicture ));
piclabel.setBounds(0,0,myPicture.getWidth(null),myPicture.getHeight(null));

This way I can get the Ergophobia.jpg file inside 'test' package.