JarFile from inside a *.jar or inputstream to file?

Question

I have a jar or war.

I\'m programmaticaly reading this jar, and when I find jar inside this jar I\'d like to programmaticaly read it again.

But JarFile prov

Answer 1

Update: Sorry this is probably too late for your needs, I just spotted your last question in the comments though. So I've modified the example to show each nested entry being copied directly to an OutputStream without any need to inflate the outer jar.

In this case the OutputStream is System.out but it could be any OutputStream (e.g. to a file...).

---

There's no need to use a temporary file. You can use JarInputStream instead of JarFile, pass the InputStream from the outer entry to the constructor and you can then read the contents of the jar.

For example:

JarFile jarFile = new JarFile(warFile);

Enumeration entries = jarFile.entries();

while (entries.hasMoreElements()) {
    JarEntry jarEntry = (JarEntry) entries.nextElement();

    if (jarEntry.getName().endsWith(".jar")) {
        JarInputStream jarIS = new JarInputStream(jarFile
                .getInputStream(jarEntry));

        // iterate the entries, copying the contents of each nested file 
        // to the OutputStream
        JarEntry innerEntry = jarIS.getNextJarEntry();

        OutputStream out = System.out;

        while (innerEntry != null) {
            copyStream(jarIS, out, innerEntry);
            innerEntry = jarIS.getNextJarEntry();
        }
    }
}

...

/**
 * Read all the bytes for the current entry from the input to the output.
 */
private void copyStream(InputStream in, OutputStream out, JarEntry entry)
        throws IOException {
    byte[] buffer = new byte[1024 * 4];
    long count = 0;
    int n = 0;
    long size = entry.getSize();
    while (-1 != (n = in.read(buffer)) && count < size) {
        out.write(buffer, 0, n);
        count += n;
    }
}