Java FIX for java.io.Not Serializable Exception: java.util.Optional

1. Problem description

How to solve java util Optional serializable exception?

Full stack trace:

Exception in thread "main" java.io.NotSerializableException: java.util.Optional
	at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1184)
	at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
	at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
	at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
	at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
	at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)

Here is my code which explains what I've tried so far

Below code tries to serialize field Optional age

As the result we get:

Exception in thread "main" java.io.NotSerializableException: java.util.Optional

My code to get this exception:

import java.io.ByteArrayOutputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.Optional;

public class JavaUtilOptionalNotSerializableException {

    private static class Foo implements Serializable {
        private static final long serialVersionUID = 1L;

        private final String name;
        private final Optional<Integer> age;

        private Foo(String name, Integer age) {
            this.name = name;
            this.age = Optional.ofNullable(age);
        }

        public String getName() {
            return name;
        }

        public Optional<Integer> getAge() {
            return age;
        }
    }

    public static void main(String[] args) throws Exception {
        /*
          Exception in thread "main" java.io.NotSerializableException:
          java.util.Optional
        */
        tryToSerialize();
    }

    private static void tryToSerialize() throws Exception {
        Foo foo = new Foo("123", 456);
        byte[] arr;
        try (ByteArrayOutputStream baos = new ByteArrayOutputStream();
             ObjectOutputStream oos = new ObjectOutputStream(baos)) {
            oos.writeObject(foo);
            arr =  baos.toByteArray();
        }
        assert arr != null;
    }
}

2. Solution with java Optional

Solution no 1 to this problem is just do not use optional as field value

Instead use it as return type from the getter method
eg:

private final Integer age; // diff1: without Optional

public Optional<Integer> getAge() {
    // diff2: each method invocation return new Optional
    return Optional.ofNullable(age);
}

Entire code which solves your problem:

import java.io.ByteArrayOutputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.Optional;

public class JavaUtilOptionalSolution {

    private static class Foo implements Serializable {
        private static final long serialVersionUID = 1L;

        private final String name;
        private final Integer age; // diff1: without Optional

        private Foo(String name, Integer age) {
            this.name = name;
            this.age = age;
        }

        public String getName() {
            return name;
        }

        public Optional<Integer> getAge() {
            // diff2: each method invocation return new Optional
            return Optional.ofNullable(age);
        }
    }

    public static void main(String[] args) throws Exception {
        // serialization works
        tryToSerialize();
    }

    private static void tryToSerialize() throws Exception {
        Foo foo = new Foo("123", 456);
        byte[] arr;
        try (ByteArrayOutputStream baos = new ByteArrayOutputStream();
             ObjectOutputStream oos = new ObjectOutputStream(baos)) {
            oos.writeObject(foo);
            arr =  baos.toByteArray();
        }
        assert arr != null;
    }
}

3. Solution with Guava - Serializable Optional

Guava internally

// com.google.common.base.Optional

public abstract class Optional implements Serializable {
    // ..
}

References

1. Optional - Java docs
2. Serializable Optional - Guava docs