Create Zip file in memory

private static byte[] createZip(Map files) throws IOException {  
     ByteArrayOutputStream bos = new ByteArrayOutputStream();  
     ZipOutputStream zipfile = new ZipOutputStream(bos);  
     Iterator i = files.keySet().iterator();  
     String fileName = null;  
     ZipEntry zipentry = null;  
     while (i.hasNext()) {  
         fileName = (String) i.next();  
         zipentry = new ZipEntry(fileName);  
         zipfile.putNextEntry(zipentry);  
         zipfile.write((byte[]) files.get(fileName));  
     }  
     zipfile.close();  
     return bos.toByteArray();  
 }