Java create InputStream from ZipInputStream entry

Question

I would like to write a method that read several XML files inside a ZIP, from a single InputStream.

The method would open a ZipInputStream, and on each xml file, get the corresponding InputStream, and give it to my XML parser. Here is the skeleton of the method :

private void readZip(InputStream is) throws IOException {

    ZipInputStream zis = new ZipInputStream(is);
    ZipEntry entry = zis.getNextEntry();

    while (entry != null) {

        if (entry.getName().endsWith(".xml")) {

            // READ THE STREAM
        }
        entry = zis.getNextEntry();
    }
}

The problematic part is the "// READ THE STREAM". I have a working solution, which consist to create a ByteArrayInputStream, and feed my parser with it. But it uses a buffer, and for large files I get an OutOfMemoryError. Here is the code, if someone is still interested :

int count;
byte buffer[] = new byte[2048];
ByteArrayOutputStream out = new ByteArrayOutputStream();
while ((count = zis.read(buffer)) != -1) { out.write(buffer, 0, count); }       
InputStream is = new ByteArrayInputStream(out.toByteArray());

The ideal solution would be to feed the parser with the original ZipInputStream. It should works, because it works if I just print the entry content with a Scanner :

Scanner sc = new Scanner(zis);
while (sc.hasNextLine())
{
    System.out.println(sc.nextLine());
}

But... The parser I'm currently using (jdom2, but I also tried with javax.xml.parsers.DocumentBuilderFactory) closes the stream after parsing the data :/ . So I'm unable to get the next entry and continue.

So finally the question is :

• Does anybody know a DOM parser that doesn't close its stream ?
• Is there another way to have an InputStream from a ZipEntry ?

Thanks.

Answer 1

You could wrap the ZipInputStream and intercept the call to close().