How to fix java.io.NotSerializableException Error

In this post, I’d like to share a solution to fix the NotSerializableExceptionerror in Java. You know, when developing and running Java applications, you may get the following error:

java.io.NotSerializableException: <fully qualified class name>

For example (citing the top most of exception stack trace):

java.io.NotSerializableException: com.weatherapi.entity.User
	at java.base/java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1197) ~[na:na]
	at java.base/java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1582) ~[na:na]
	at java.base/java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1539) ~[na:na]
	at java.base/java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1448) ~[na:na]
	...

The NotSerializableException error occurs because when the application tried to serialize a Java object, it found that the object’s class does not implement the Serializable interface, which is required by serialization process. For example:

public class User {
	
	...
}

The solution is make the class implements the java.io.Serializable interface and declares a field serialVersionUID, as shown below:

public class User implements Serializable {

	 public static final long serialVersionUID = 1234L;
	 
	 ...
	 
}

And don’t worry about the value of the field serialVersionUID as you can specify any long value. That’s a simple way to fix the java.io.NotSerializableException error in Java.

Watch the following video to see how I fixed this error in a real life project:

To understand about background of serialization in Java, I recommend you check the following articles:

• Why Do We Need Serialization in Java?
• Java Serialization Basic Example

Other Java File IO Tutorials:

• How to Read and Write Text File in Java
• How to Read and Write Binary Files in Java
• Java IO - Common File and Directory Operations Examples
• Java Serialization Basic Example
• Understanding Java Externalization with Examples
• How to execute Operating System Commands in Java
• 3 ways for reading user's input from console in Java
• File change notification example with Watch Service API
• Java Scanner Tutorial and Code Examples
• How to compress files in ZIP format in Java
• How to extract ZIP file in Java

About the Author:

Nam Ha Minh is certified Java programmer (SCJP and SCWCD). He began programming with Java back in the days of Java 1.4 and has been passionate about it ever since. You can connect with him on Facebook and watch his Java videos on YouTube.