ObjectInputStream.read() returning -1, but readObject returns the object

Question

Am to serialize an object and deserialize the object but I get:

1. 0 for available()
2. -1 for read()

3. EOFException for readByte()

   public static Element getCacheObject(String key, String cacheName, String server) throws IOException, ClassNotFoundException, ConnectException {
       String url = StringUtils.join(new String[] { server, cacheName, key}, "/");
       GetMethod getMethod = new GetMethod(url);
       ObjectInputStream oin = null;
       InputStream in = null;
       int status = -1;
       Element element = null;
       try {
           status = httpClient.executeMethod(getMethod);
           if (status == HttpStatus.SC_NOT_FOUND) { // if the content is deleted already               
               return null;
           }
           in = getMethod.getResponseBodyAsStream();
           oin = new ObjectInputStream(in);
           System.out.println("oin.available():" + oin.available()); // returns 0
           System.out.println("oin.read():" + oin.read()); // returns -1
           element = (Element) oin.readObject(); // returns the object
       }
       catch (Exception except) {
           except.printStackTrace();
           throw except;
       }
       finally {
           try {
               oin.close();
               in.close();
           }
           catch (Exception except) {
               except.printStackTrace();
           }
       }
   
       return element;
   }
   

What am I missing here?

Answer 1

I think you see this behaviour because you first create ObjectInputStream from InputStream and only then check available on InputStream. If you check constructor of ObjectInputStream you can see following:

public ObjectInputStream(InputStream in) throws IOException {
    verifySubclass();
    bin = new BlockDataInputStream(in);
    handles = new HandleTable(10);
    vlist = new ValidationList();
    enableOverride = false;
    readStreamHeader();
    bin.setBlockDataMode(true);
} 

There is a method readStreamHeader that reads header from input stream. So it is possible that all data is read from InputStream during construction of ObjectInputStream.