Serializing a lambda

Question

I have the below code, which throws a NotSerializableException when I try to serialize the lambda.

public static void main(String[] args) throws Exception {
    File myFile = Files.createTempFile("lambda", "ser").toFile();
    try (ObjectOutput oo = new ObjectOutputStream(new FileOutputStream(myFile))) {
        Runnable r = () -> System.out.println("Can I be serialized?");
        oo.writeObject(r);
    }

    try (ObjectInput oi = new ObjectInputStream(new FileInputStream(myFile))) {
        Runnable  r = (Runnable) oi.readObject();
        r.run();
    }
}

I don't want to create a SerializableRunnable "dummy" interface for this. Please help!

Answer 1

With the release of Java 8, Oracle introduced the lambda expressions. It lets you cast an object to an intersection of types by adding multiple bounds. In the case of serialization, it is therefore possible to write:

Runnable r = (Runnable & Serializable)() -> System.out.println("Serializable!");

And the lambda expression automatically becomes serializable.