Creating Jar Files

Jar File not working?

1. Make sure the jar file contains your assets. Right-click on it and choose 7-zip > open archive. Click and drag and missing assets into the jar file
2. Try running it from command line to see any error messages. Follow the directions to run a jar file from command line: Open Windows Powershell to access the command line to create the jar file, "cd" into the directory containing the jar file, now run the jar file. The following command should launch your game:

   H:\>java -jar spaceinvaders.jar

   If there are exceptions, they will be printed in the console.

Create a working JAR File in Windows

1. You must use Windows Powershell to access the command line to create the jar file. You will need to make sure that the JDK programs are in the class path. If your JDK is located at "C:\Program Files\Java\jdk1.6.0_03\bin", you can temporarily add it as follows:

   H:\>set path="C:\Program Files\Java\jdk1.6.0_03\bin"

2. Create a text file called mainClass.txt that is located in the same directory as Game.class. It should contain the following line:

    Main-Class: Game
    

   Note: There must be a hard-return at the end of the file, otherwise it will not work.
3. Put everything in a jar file, all the class files and the image files. To create a jar file that works with spaceinvaders do the following:

   H:\>jar cmf mainClass.txt spaceinvaders.jar *.class sprites/*.gif

4. Now test that your jar file works. The following command should launch your game:

   H:\>java -jar spaceinvaders.jar

Accessing Text Files in a JAR

• Use the CS 11 version of getFileContents to read in a text file: FileInputOutput.java.

Accessing Images and Sound in a JAR

• In general, the first step in accessing a JAR resource involves creating a URL. This might require modifying your program. For example, you can no longer use the following code fragment to read in an image that is stored in a file as follows

      Image image = Toolkit.getDefaultToolkit().getImage(filename);
  

  Instead, create the URL object using

      URL url = YourClassName.class.getResource(filename); 
      Image image = Toolkit.getDefaultToolkit().getImage(url);
  

  Or, if the code is in a static method of class X, then create the URL with

      URL url = X.class.getResource(filename); 
  

  Now, the resource can be accessed the same way, regardless of whether it is in a JAR or the current directory.

Click here for a working example of Space Invaders!