You can use ObjectOutputStream

You write the object (obj in the code below) to the ObjectOutputStream, your object you want to convert to an input stream must implement Serializable.

    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    ObjectOutputStream oos = new ObjectOutputStream(baos);


    oos.writeObject(obj);

    oos.flush();
    oos.close();

    InputStream is = new ByteArrayInputStream(baos.toByteArray());

In try block you should write:

ObjectInputStream ois = new ObjectInputStream(is);
Object object = ois.readObject();

ObjectInputStream is initialized with another stream, e.g. BufferedInputStream or your input stream is.

To be able to write (serialise) your objects to streams, your class should implement Serializable interface. In most cases you don't need to do anything except for adding the "implements Serializable" clause in your class definition:

class Person implements Serializable {
// your class's fields and methods
}

Then, of course, you are not writing to the input stream, but to an output stream:

Person p = new Person();
// some more code here...
OutputStream os = new FileOutputStream("persons.txt"); // open file as a stream
os.write(person); // write person object to the stream
os.close(); // close the stream

To convert to a byte array you will have to use serialization still:

ByteArrayOutputStream baos = new ByteArrayOutputStream();
baos.write(person);
byte[] bytes = baos.toByteArray();

You can convert a JSONObject into its String representation, and then convert that String into an InputStream.

The code in the question has a JSONObject being cast into File, but I am not sure if that works as intended. The following, however, is something I have done before (currently reproduced from memory):

String str = json.getJSONObject("data").toString();
InputStream is = new ByteArrayInputStream(str.getBytes());

Note that the toString() method for JSONObject overrides the one in java.lang.Object class.

From the Javadoc:

Returns: a printable, displayable, portable, transmittable representation of the object, beginning with { (left brace) and ending with } (right brace).