Loading Icon resource error

问题

In Eclipse, when I run the code, this works:

import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;


   public class Main {

    public static void main(String[] args) {

        JFrame frame = new JFrame("test viewing images");

        frame.setSize(600,300);     
        frame.setLocationRelativeTo(null); // centered on monitor   
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);


        /**
         * Menu Bar stuff
         */

        JMenuBar menuBar;
        JMenu menu;
        JMenuItem menuItem;

        // MENU BAR 
        menuBar = new JMenuBar();
        frame.setJMenuBar(menuBar);
        menuBar.setVisible(true);

        // MENU 1
        menu = new JMenu("File");
        menuBar.add(menu);

            // MENU 1 ITEM
            ImageIcon icon = new ImageIcon("src/Action-exit-icon.png");     
            menuItem = new JMenuItem("Exit Program", icon);
            menu.add(menuItem);


        frame.setVisible(true);

    }

   }

And here's the File Structure from my Package Explorer:

ShowImage (project)
 > src / Main.java
 > src / Action-exit-icon.png

Also, this workspace is located in Z:\eclipse_projects

I can see the ImageIcon icon = new ImageIcon("src/Action-exit-icon.png"); is working nicely, and the menuBar does it's job.

Now let's Export this project, and I'll email the JAR to a friend of mine.

1. Right-click project > Select Export
2. Select Java > Runnable JAR File
3. I choose the Main File in Launch configuration
4. Export destination: my desktop
5. Library handling: Extract required libraries into generated JAR
6. go to my desktop, double-click the ShowImage.jar

The JFrame shows up, but the Action-exit-icon.png isn't appearing at all.

When I open the ShowImage.jar, to view it's contents, I see the Main.class, Action-exit-icon.png, META-INF.

Ok, I'm seriously confused about how to reference an image, or any resource now. What am I doing wrong?

回答1:

new ImageIcon("src/Action-exit-icon.png"); 

The String constructor for an ImageIcon presumes the string to represent a File path.

This image is obviously an application resource, and will become an embedded resource by the time of deployment (in a Jar). Therefore it must be accessed by URL from the run-time class-path of the app., like so:

new ImageIcon(getClass().getResource("/src/Action-exit-icon.png")); 

---

Overhauling the code, I get this:

import java.awt.Color;
import javax.swing.*;

public class JavaGui148 {

    public JComponent getGUI() {
        JPanel p = new JPanel();

        p.setBackground(Color.GREEN);

        return p;
    }

    public JMenuBar getMenuBar() {
        /**
         * Menu Bar stuff
         */
        JMenuBar menuBar;
        JMenu menu;
        JMenuItem menuItem;

        // MENU BAR 
        menuBar = new JMenuBar();
        menuBar.setVisible(true);

        // MENU 1
        menu = new JMenu("File");
        menuBar.add(menu);

        // MENU 1 ITEM
        ImageIcon icon = new ImageIcon(getClass().getResource(
                "/src/Action-exit-icon.png"));
        menuItem = new JMenuItem("Exit Program", icon);
        menu.add(menuItem);

        return menuBar;
    }

    public static void main(String[] args) {
        Runnable r = new Runnable() {

            @Override
            public void run() {
                JavaGui148 gui = new JavaGui148();

                JFrame f = new JFrame("Demo");
                f.setJMenuBar(gui.getMenuBar());
                f.add(gui.getGUI());
                // Ensures JVM closes after frame(s) closed and
                // all non-daemon threads are finished
                f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
                // See http://stackoverflow.com/a/7143398/418556 for demo.
                f.setLocationByPlatform(true);

                // ensures the frame is the minimum size it needs to be
                // in order display the components within it
                f.pack();
                // should be done last, to avoid flickering, moving,
                // resizing artifacts.
                f.setVisible(true);
            }
        };
        // Swing GUIs should be created and updated on the EDT
        // http://docs.oracle.com/javase/tutorial/uiswing/concurrency/initial.html
        SwingUtilities.invokeLater(r);
    }
}

来源：https://stackoverflow.com/questions/13943913/loading-icon-resource-error