What Causes new ObjectInputStream() to Block and How to Resolve It?

What causes new ObjectInputStream() to block when reading data in Java?

ObjectInputStream ois = new ObjectInputStream(new FileInputStream("datafile.dat"));

The new ObjectInputStream() constructs an input stream that reads serialized objects from a stream, such as a file. However, it can block indefinitely in certain situations. The most common reasons include waiting for the data to be sent over the stream, issues with the underlying socket, or improper handling of the stream itself. This article delves into these issues and provides practical solutions for developers.

try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream("datafile.dat"))) {
    Object object = ois.readObject(); // Ensure data is written and available
} catch (EOFException e) {
    System.out.println("End of stream reached: " + e.getMessage());
} catch (IOException | ClassNotFoundException e) {
    e.printStackTrace();
}

Causes

• The underlying stream hasn't been properly initialized and is empty.
• Network delays or issues if used in conjunction with a socket.
• Serialization problems due to version incompatibility between sender and receiver.
• Improper stream closing or data flushing on the sending side.

Solutions

• Ensure that the file or stream being read from has data written to it before initializing ObjectInputStream.
• Check the network connection and ensure that the server is sending data correctly if using sockets.
• Verify that objects sent are compatible with the expected serialized versions.
• Always flush and close the output streams appropriately on the sender's side.

Mistake: Not checking if the stream is empty before initialization.

Solution: Always verify the data availability in the stream.

Mistake: Forgetting to flush data from the output stream after writing.

Solution: Make sure to flush the output stream to ensure all data is sent before reading.

Mistake: Assuming that all serialized objects will be compatible across versions.

Solution: Implement proper versioning or handle serialization exceptions.