无法读取jar文件中的图像

Question

当我构建一个jar文件并运行它时,由于找不到imageicon,它会显示一个空指针异常

new ImageIcon(getClass().getClassLoader().getResource("icons/exit.png")));

这是我运行jar文件时得到的错误

Exception in thread "main" java.lang.NullPointerException
        at javax.swing.ImageIcon.<init>(Unknown Source)
        at mediaplayer.MediaPlayer.buildtoolbar(MediaPlayer.java:130)
        at mediaplayer.MediaPlayer.<init>(MediaPlayer.java:81)
        at mediaplayer.MediaPlayer.main(MediaPlayer.java:464)

但是,当我在NetBeans中运行该项目时,它的工作正常

当我列出jar中的所有文件时,这是输出

META-INF/
META-INF/MANIFEST.MF
helliker/
helliker/id3/
icons/
mediaplayer/
Thumbs.db
exit.png
ff1.png
helliker/id3/BinaryParser.class
helliker/id3/CorruptHeaderException.class
helliker/id3/ID3Exception.class
helliker/id3/ID3FieldDataException.class
helliker/id3/ID3Tag.class
helliker/id3/ID3v1Tag.class
helliker/id3/ID3v2ExtendedHeader.class
helliker/id3/ID3v2Footer.class
helliker/id3/ID3v2FormatException.class
helliker/id3/ID3v2Frame.class
helliker/id3/ID3v2Frames.class
helliker/id3/ID3v2Header.class
helliker/id3/ID3v2Tag.class
helliker/id3/MP3Comparator.class
helliker/id3/MP3File.class
helliker/id3/MP3FileFilter.class
helliker/id3/MPEGAudioFrameHeader.class
helliker/id3/NoMPEGFramesException.class
helliker/id3/NullsoftID3GenreTable.class
helliker/id3/Playlist.class
helliker/id3/PlaylistException.class
helliker/id3/XingVBRHeader.class
icons/Thumbs.db
icons/exit.png
icons/ff1.png
icons/label.jpg
icons/openpl.gif
icons/pause1.png
icons/play1.png
icons/playlist.png
icons/rr.png
icons/rr1.PNG
icons/stop.png
label.jpg
mediaplayer/MediaPlayer$1.class
mediaplayer/MediaPlayer$PlaylistFilter.class
mediaplayer/MediaPlayer.class
mediaplayer/PlaylistManager$1.class
mediaplayer/PlaylistManager$MP3Filter.class
mediaplayer/PlaylistManager$PlaylistFilter.class
mediaplayer/PlaylistManager.class
mediaplayer/Settings.class
mediaplayer/TagEditor.class
mediaplayer/Thumbs.db
openpl.gif
pause1.png
play1.png
playlist.png
rr.png
rr1.PNG

Answer 1

在问题中如何实际构建jar文件缺少一些信息,但具有以下目录布局

??? bin
?   ??? com
?   ?   ??? example
?   ?       ??? ImageIconTest.class
?   ??? icons
?       ??? exit.png
??? src
    ??? MANIFEST.MF
    ??? com
        ??? example
            ??? ImageIconTest.java

和以下代码 ImageIconTest.java

package com.example;
import javax.swing.ImageIcon;

public class ImageIconTest {
   public void run() {
      ImageIcon ii = new ImageIcon(getClass().getClassLoader().getResource("icons/exit.png"));
      System.out.println(ii);
   }
   public static void main(String[] args) {
      ImageIconTest app = new ImageIconTest();
      app.run();
   }
}

您可以使用文件系统正确运行示例

$ java -classpath bin com.example.ImageIconTest

使用包含以下内容的MANIFEST.MF文件:

Manifest-Version: 1.0
Main-Class: com.example.ImageIconTest

你可以将它打包成一个可执行的jar文件并从jar文件中运行它:

$ jar cvfm app.jar src/MANIFEST.MF -C bin .
$ java -jar app.jar

这两种方法都运行正常,重要的细节是确保图标目录包含在jar文件中的适当位置.

列出jar文件内容时,它应如下所示:

  0 Tue Nov 06 12:27:56 CET 2012 META-INF/
107 Tue Nov 06 12:27:56 CET 2012 META-INF/MANIFEST.MF
  0 Tue Nov 06 12:27:56 CET 2012 com/
  0 Tue Nov 06 12:27:56 CET 2012 com/example/
950 Tue Nov 06 12:27:56 CET 2012 com/example/ImageIconTest.class
  0 Tue Nov 06 12:00:36 CET 2012 icons/
873 Tue Nov 06 12:00:36 CET 2012 icons/exit.png

请注意icons目录的位置.