1.3 Reading from an Object Stream

Reading an object from a stream, like writing, is straightforward:

// Deserialize a string and date from a file.
    FileInputStream in = new FileInputStream("tmp");
    ObjectInputStream s = new ObjectInputStream(in);
    String today = (String)s.readObject();
    Date date = (Date)s.readObject();

First an InputStream, in this case a FileInputStream, is needed as the source stream. Then an ObjectInputStream is created that reads from the InputStream. Next, the string "Today" and a Date object are read from the stream. Generally, objects are read with the readObject method and primitives are read from the stream with the methods of DataInput.

The readObject method deserializes the next object in the stream and traverses its references to other objects recursively to create the complete graph of objects serialized.

Primitive data types are read from the stream with the methods in the DataInput interface, such as readInt, readFloat, or readUTF. Individual bytes and arrays of bytes are read with the methods of InputStream. Except for serializable fields, primitive data is read from block-data records.

ObjectInputStream can be extended to utilize customized information in the stream about classes or to replace objects that have been deserialized. Refer to the resolveClass and resolveObject method descriptions for details.