List files inside a jar

Question

I have this code which reads all the files from a directory.

    File textFolder = new File("text_directory");

    File [] texFiles = textFolder.listFiles( new FileFilter() {
           public boolean accept( File file ) {
               return file.getName().endsWith(".txt");
           }
    });

Works great. It fills the array with all the files that end with ".txt" from directory "text_directory"

Question:

How can I read in a similar fashion the contents of a directory within a jar file?

So what I really want to do is list in a similar fashion all the images inside my jar, so I can load them with:

ImageIO.read(this.getClass().getResource("CompanyLogo.png"));

That one works because the "CompanyLogo" is "hardcoded" but the number of images inside the jar could be from 10 to 200.

EDIT

So I guess my main problem would be, how to know the name of the jar where my main class lives.

Granted I could read it using java.util.Zip

My Structure is like this:

They are like:

 
    my.jar!/Main.class
    my.jar!/Aux.class
    my.jar!/Other.class
    my.jar!/images/image01.png
    my.jar!/images/image02a.png
    my.jar!/images/imwge034.png
    my.jar!/images/imagAe01q.png
    my.jar!/META-INF/manifest 

Right now I'm able to load for instance "images/image01.png" using:

    ImageIO.read(this.getClass().getResource("images/image01.png));

But only because I know the file name, for the rest I have to load them dinamically.

Thanks in advance.

Answer 1

A jar file is just a zip file with a structured manifest. You can open the jar file with the usual java zip tools and scan the file contents that way, inflate streams, etc. Then use that in a getResourceAsStream call, and it should be all hunky dory.

EDIT / after clarification

It took me a minute to remember all the bits and pieces and I'm sure there are cleaner ways to do it, but I wanted to see that I wasn't crazy. In my project image.jpg is a file in some part of the main jar file. I get the class loader of the main class (SomeClass is the entry point) and use it to discover the image.jpg resource. Then some stream magic to get it into this ImageInputStream thing and everything is fine.

InputStream inputStream = SomeClass.class.getClassLoader().getResourceAsStream("image.jpg");
JPEGImageReaderSpi imageReaderSpi = new JPEGImageReaderSpi();
ImageReader ir = imageReaderSpi.createReaderInstance();
ImageInputStream iis = new MemoryCacheImageInputStream(inputStream);
ir.setInput(iis);
....
ir.read(0); //will hand us a buffered image

Answer 2

Given an actual jar file, you can list the contents using JarFile.entries(). You will need to know the location of the jar file though - you can't just ask the classloader to list everything it could get at.

You should be able to work out the location of the jar file based on the URL returned from ThisClassName.class.getResource("ThisClassName.class") but it may be a tiny bit fiddly.

Answer 3

Here's a method I wrote for a "run all JUnits under a package". You should be able to adapt it to your needs.

private static void findClassesInJar(List<String> classFiles, String path) throws IOException {
    final String[] parts = path.split("\\Q.jar\\\\E");
    if (parts.length == 2) {
        String jarFilename = parts[0] + ".jar";
        String relativePath = parts[1].replace(File.separatorChar, '/');
        JarFile jarFile = new JarFile(jarFilename);
        final Enumeration<JarEntry> entries = jarFile.entries();
        while (entries.hasMoreElements()) {
            final JarEntry entry = entries.nextElement();
            final String entryName = entry.getName();
            if (entryName.startsWith(relativePath)) {
                classFiles.add(entryName.replace('/', File.separatorChar));
            }
        }
    }
}

Edit: Ah, in that case, you might want this snippet as well (same use case :) )

private static File findClassesDir(Class<?> clazz) {
    try {
        String path = clazz.getProtectionDomain().getCodeSource().getLocation().getFile();
        final String codeSourcePath = URLDecoder.decode(path, "UTF-8");
        final String thisClassPath = new File(codeSourcePath, clazz.getPackage().getName().repalce('.', File.separatorChar));
    } catch (UnsupportedEncodingException e) {
        throw new AssertionError("impossible", e);
    }
}

Answer 4

CodeSource src = MyClass.class.getProtectionDomain().getCodeSource();
if (src != null) {
  URL jar = src.getLocation();
  ZipInputStream zip = new ZipInputStream(jar.openStream());
  /* Now examine the ZIP file entries to find those you care about. */
  ...
} 
else {
  /* Fail... */
}

Answer 5

Given that you have created the jar, you might as well include the list of files within it rather than attempting any tricks.

Answer 6

So I guess my main problem would be, how to know the name of the jar where my main class lives.

Assuming that your project is packed in a Jar (not necessarily true!), you can use ClassLoader.getResource() or findResource() with the class name (followed by .class) to get the jar that contains a given class. You'll have to parse the jar name from the URL that gets returned (not that tough), which I will leave as an exercise for the reader :-)

Be sure to test for the case where the class is not part of a jar.

Answer 7

erickson's answer worked perfectly:

Here's the working code.

CodeSource src = MyClass.class.getProtectionDomain().getCodeSource();
List<String> list = new ArrayList<String>();

if( src != null ) {
    URL jar = src.getLocation();
    ZipInputStream zip = new ZipInputStream( jar.openStream());
    ZipEntry ze = null;

    while( ( ze = zip.getNextEntry() ) != null ) {
        String entryName = ze.getName():
        if( entryName.startsWith("images") &&  entryName.endsWith(".png") ) {
            list.add( entryName  );
        }
    }

 }
 webimages = list.toArray( new String[ list.size() ] );

And I have just modify my load method from this:

File[] webimages = ... 
BufferedImage image = ImageIO.read(this.getClass().getResource(webimages[nextIndex].getName() ));

To this:

String  [] webimages = ...

BufferedImage image = ImageIO.read(this.getClass().getResource(webimages[nextIndex]));

Answer 8

Hi all,

there are two very useful utilities both called jarscan :

www.inetfeedback.com/jarscan

jarscan.dev.java.net

see also this question : stackoverflow.com/questions/759923/jarscan-scan-all-jar-files-in-all-subfolders-for-specific-class

jgran