Read directory inside JAR with InputStreamReader

Question

So, this question has been asked a million times i believed and I've been reading them for a couple of hours and trying several options given by some people but none of them work for me.

I want to list all the files inside a directory inside the application's JAR, so in IDE this works:

File f = new File(this.getClass().getResource("/resources/").getPath());

for(String s : f.list){
   System.out.println(s);
}

That gives me all the files inside the directory.

Now, i've tried this also:

InputStream in = this.getClass().getClassLoader().getResourceAsStream("resources/");
    InputStreamReader inReader = new InputStreamReader(in);
    Scanner scan = new Scanner(inReader);

    while (scan.hasNext()) {
        String s = scan.next();
        System.out.println("read: " + s);
    }

    System.out.println("END OF LINE");

And from IDE it prints ALL the files in the directory. Outside IDE prints: "END OF LINE".

Now, I can find an entry inside a Jar with this too:

        String s = new File(this.getClass().getResource("").getPath()).getParent().replaceAll("(!|file:\\\\)", "");
        JarFile jar = new JarFile(s);

            JarEntry entry = jar.getJarEntry("resources");

        if (entry != null){
            System.out.println("EXISTS");
            System.out.println(entry.getSize());
        }

That's some horrible coding i had to do to that String.

Anyway... I can't get the list of resources inside the "resources" directory within the Jar... How can I do this???

Answer 1

There's no way to simply get a filtered list of internal resources without first enumerating over the contents of the Jar file.

Luckily, that's actually not that hard (and luckily for me you've done most of the hardwork).

Basically, once you have a reference to the JarFile, you simple need to ask for its' entries and iterate over that list.

By checking the JarEntry name for the required match (ie resources), you can filter the elements you want...

For example...

import java.io.File;
import java.io.IOException;
import java.util.Enumeration;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;

public class ReadMyResources {

    public static void main(String[] args) {
        new ReadMyResources();
    }

    public ReadMyResources() {
        JarFile jf = null;
        try {            
            String s = new File(this.getClass().getResource("").getPath()).getParent().replaceAll("(!|file:\\\\)", "");
            jf = new JarFile(s);

            Enumeration<JarEntry> entries = jf.entries();
            while (entries.hasMoreElements()) {
                JarEntry je = entries.nextElement();
                if (je.getName().startsWith("resources")) {
                    System.out.println(je.getName());
                }
            }
        } catch (IOException ex) {
            ex.printStackTrace();
        } finally {
            try {
                jf.close();
            } catch (Exception e) {
            }
        }
    }

}

Caveat

This type of question actually gets ask a bit. Rather then trying to read the contents of the Jar at runtime, it would be better to produce some kind of text file which contained a list of the available resources.

This could be produced by your build process dynamically before the Jar file is created. It would be a much simpler solution to then read this file in (via getClass().getResource(), for example) and then look up each resource list in the text file...IMHO

Answer 2

For Spring Framework users, have a look at PathMatchingResourcePatternResolver to do something like the following:

PathMatchingResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();
Resource[] resources = resolver.getResources("classpath:path/to/resource/*.*");

for (Resource resource : resources) {
    InputStream inStream = resource.getInputStream();
    // Do something with the input stream
}