Java Serialization of objects in a multithreaded environment

• Serialization in Java is not inherently thread-safe.
• When serializing an object, it is important to ensure that the object is not being modified by another thread while it is being serialized.
• If an object is modified while it is being serialized, the serialized representation of the object may be inconsistent with its current state.

How to Handled Serialization of objects in a multithreaded environment

• One way to handle multithreaded access to objects during serialization is to use synchronization mechanisms such as the synchronized keyword or the java.util.concurrent.locks.ReentrantLock class. This can be used to ensure that only one thread is able to access the object at a time, preventing other threads from modifying the object while it is being serialized.
• Another way is to use the transient keyword to exclude fields that may be modified by another thread from being serialized. This can be useful for fields that are not essential for the object’s state or for fields that are recalculated when the object is deserialized.
• It’s also important to remember that if the object is a shared resource, it should be cloned before being serialized to avoid any modification while serializing.

Whenever it’s necessary to modify the serialization of a class you have to implement the special private method void writeObject(ObjectOutputStream). The ObjectOutputStream uses this method instead of the default algorithm then.

In your case you want the serialization to be synchronized with the object. So all you have to do is adding the synchronized keyword to the method. You can still use the default implementation defaultWriteObject:

private synchronized void writeObject(ObjectOutputStream out) throws IOException {
    out.defaultWriteObject();
}

In summary, serialization in Java is not inherently thread-safe. To handle multithreaded access to objects during serialization, it’s recommended to use synchronization mechanisms such as the synchronized keyword or the java.util.concurrent.locks.ReentrantLock class, or use the transient keyword to exclude fields that may be modified by another thread from being serialized or to clone the object before serializing.