Question

I have a JarInputStream (constructed from a byte array which contains a JAR file) and want to read a specific file from it. So I iterate through the containing ZipEntries and search for the file. Then I try to write the file into a byte array.

However, the file somehow isn’t read completely. If i write it to the filesystem and open it in a text editor it just contains NULLs after the first few lines which are read correctly.

The code looks like this:

JarInputStream is = new JarInputStream(new ByteArrayInputStream(_jarFile));
ZipEntry entry = is.getNextEntry();
while (entry != null) {                 
    if (entry.getName().endsWith(".xyz")) {
        // read the *.xyz file and load it into a byte array
        int size = (int) entry.getSize();
        byte[] _xyzFile = new byte[size];
        is.read(_xyzFile, 0, size);
        break;
    }
    entry = is.getNextEntry();
}

is.close();

The size variable definitely contains the correct number of bytes, so I don’t know why reading is stopped after just a few lines.

Answer 1

is.read(_xyzFile, 0, size); does not necessarily read size bytes into the array, but up to size bytes. The method returns the actual number of bytes read.

You have to implement a loop to invoke is.read several times or use any utility library offering such functionality, e.g. IOUtils.toByteArray(InputStream) from Apache Commons-IO.