Reading content of a JAR file (at runtime)?

Question

I have read the posts:

Viewing contents of a .jar file
and
How do I list the files inside a JAR file?

But I, sadly, couldn't find a good solution to actually read a JAR's content (file by file).

Furthermore, could someone give me a hint, or point to a resource, where my problem is discussed?

I just could think of a not-so-straight-forward-way to do this:
I could somehow convert the list of a JAR's resources to a list of inner-JAR URLs, which I then could open using openConnection().

http://stackoverflow.com/questions/749533 http://stackoverflow.com/questions/435890 http://stackoverflow.com/questions/251336/is-something-similar-to-serviceloader-in-java-1-5 http://stackoverflow.com/questions/1429172/list-files-inside-a-jar http://stackoverflow.com/questions/205573/java-at-runtime-find-all-classes-in-app-that-extend-a-base-class http://stackoverflow.com/questions/347248/how-can-i-get-a-list-of-all-the-implementations-of-an-interface-programmatically http://stackoverflow.com/questions/1456930/read-all-classes-from-java-package-in-classpath — erickson, Sep 23 '09 at 02:30

score 11 · Accepted Answer · edited Jul 02 '21 at 13:07

11

You use JarFile to open a Jar file. With it you can get ZipEntry or JarEntry (they can be seen as the same thing) by using 'getEntry(String name)' or 'entires'. Once you get an Entry, you can use it to get InputStream by calling 'JarFile.getInputStream(ZipEntry ze)'. Well you can read data from the stream.

edited Jul 02 '21 at 13:07

Gasol

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answered Sep 22 '09 at 23:44

NawaMan

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Ah, thank you! I've somehow totally overseen JarFile's getInputStream! – ivan_ivanovich_ivanoff Sep 22 '09 at 23:46

score 4 · Answer 2 · edited Sep 20 '12 at 09:23

Here is the complete code which reads all the file contents inside the jar file.

public class ListJar {
    private static void process(InputStream input) throws IOException {
        InputStreamReader isr = new InputStreamReader(input);
        BufferedReader reader = new BufferedReader(isr);
        String line;

        while ((line = reader.readLine()) != null) {
            System.out.println(line);
        }
        reader.close();
    }

    public static void main(String arg[]) throws IOException {
        JarFile jarFile = new JarFile("/home/bathakarai/gold/click-0.15.jar");

        final Enumeration<JarEntry> entries = jarFile.entries();
        while (entries.hasMoreElements()) {
            final JarEntry entry = entries.nextElement();
            if (entry.getName().contains(".")) {
                System.out.println("File : " + entry.getName());
                JarEntry fileEntry = jarFile.getJarEntry(entry.getName());
                InputStream input = jarFile.getInputStream(fileEntry);
                process(input);
            }
        }
    }
}

score 3 · Answer 3 · edited Sep 12 '19 at 09:49

Here is how I read it as a ZIP file,

   try {
        ZipInputStream is = new ZipInputStream(new FileInputStream("file.jar"));
        ZipEntry ze;

        byte[] buf = new byte[4096];
        int len;

        while ((ze = is.getNextEntry()) != null) {

            System.out.println("----------- " + ze);
            len = ze.getSize();

            // Dump len bytes to the file
            ...
        }
        is.close();
    } catch (Exception e) {
        e.printStackTrace();
    }

This is more efficient than JarFile approach if you want decompress the whole file.

Reading content of a JAR file (at runtime)?

3 Answers3

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