java class getResource 找不到 jar 文件中列出的图标

Question

I am really stumped. I'm just an old C X11/Motif programmer trying to write a little Java program. After a week of reading the Oracle Java Documentation , as well as the Stack Overflow answers related to getResource, I still can not figure out how to retrieve the path to the icon files in my jar file.

My icons are contained within the jar file for my application. I wish to access them using the relative position within jar file. I am assuming the best way to do this is through the getResource method.

The core part of my code for my program called Fŭd (pronounced food - like the cat spells it in the comic strip " Get Fuzzy ") is as follows:

package localhost.system1;

imports not shown for brevity.

public class Fud extends JPanel
             implements FocusListener, ActionListener, ItemListener
  {
    private static final long   serialVersionUID    = 1L;
    static Food                 data                = null;
    static int                  prev                = 0;
    static int                  next                = 1;
    static int                  plus                = 2;
    static int                  minus               = 3;

    public static void main(String args[]) throws Exception
      {
        LocalDate           now             = LocalDate.now();
        int                 dateDifference  = 0;

        // load in the existing data
        data = new Food(programName);
        data.loadFood(programName);
      
        // test to see if data is up to date. Add days if not
        dateDifference = Math.abs((int)ChronoUnit.DAYS.between(now, data.day[0].date));
    if ( dateDifference != 0)
      {
        data.adjustToToday(dateDifference, programName);
      }

    /////////////////////////////////////////////////  
    // create the GUI and switch running over to it. 
    /////////////////////////////////////////////////
    Fud     fud             = new Fud();
    Class<? extends Fud>    fudClass    = fud.getClass();
    

    String  className = fudClass.getName();
    System.out.println("fudClass getname returns " + className);
    
    URL     testURL         = fudClass.getResource("prev.png");
    System.out.println("fudClass getResource returned " + testURL);
    
    // Create GUI and turn the control over to it
    javax.swing.SwingUtilities.invokeLater
      (new Runnable() 
        {
          public void run() 
            {    
              URL[] iconURL     = new URL[4];
              
              iconURL[prev]     = Fud.class.getResource("prev.png");
              iconURL[next]     = Fud.class.getResource("next.png");
              iconURL[plus]     = Fud.class.getResource("plus.png");
              iconURL[minus]    = Fud.class.getResource("minus.png");

              createAndShowGUI(fud, iconURL);
            }
        }
      );
        
  } // end of main

.
.
.
Rest of methods and subroutines  needed
.
.
.
}

When run, the code returns the following results:

fudClass getname returns localhost.system1.Fud
fudClass getResource returned null

This has me quite frustrated. No matter what I try (and I have tried a number of things) the result remains the same. I keep getting NULL for a response from the getResource method. When I query the jar file with jar -tf Fud.jar I get the following:

jar tf Fud.jar
META-INF/MANIFEST.MF
localhost/
localhost/system1/
localhost/system1/Day.class
localhost/system1/Food.class
localhost/system1/Fud$1.class
localhost/system1/Fud$2.class
localhost/system1/Fud$3.class
localhost/system1/Fud$4.class
localhost/system1/Fud$5.class
localhost/system1/Fud$6.class
localhost/system1/Fud$7.class
localhost/system1/Fud.class
minus.png
next.png
plus.png
prev.png

So the icons are in the Jar file. Can anyone tell me what I am doing wrong? In Eclipse, my project explorer looks like: eclipse Project Explorer

I added the Image directory to my project Java build in eclipse as follows: Eclipse Java Build

I built the program using Eclipse Version: 2021-12 (4.22.0) Build id: 20211202-1639. Furthermore, I am using Java 17.0.1 2021-10-19 LTS on Windows 11 Pro build 22000.434.

Answer 1

You have to add a slash in front of the resource:

Fud.class.getResource("/prev.png");

otherwise java searching in the same folder as the class is located:

So it will search in localhost/system1