serialver

Display the serialVersionUID of a class

$ serialver [classnames]

$ serialver -classpath [path/to/directory] [classname1:classname2:...]

$ serialver -Joption [classnames]

serialver [options] classname...

-show
    Displays a simple user interface where the class name can be entered. The serialVersionUID is displayed upon pressing the Show button, or when the Enter key is pressed.

classname
    The fully qualified name of the class (e.g., com.example.MyClass) to generate the serialVersionUID for. Can specify multiple class names to generate the IDs for multiple classes.

The serialver command in Java Development Kit (JDK) is a utility for generating the serialVersionUID field for Java classes. This is crucial for serialization, which is the process of converting an object into a stream of bytes to be stored or transmitted. When a class is serialized and later deserialized, the JVM uses the serialVersionUID to ensure compatibility between the serialized and deserialized versions of the class.

If the serialVersionUID is not explicitly defined in a class, the JVM will generate one based on the class's structure (fields, methods, etc.). However, this automatically generated ID is sensitive to even minor changes in the class definition. Changes that seem trivial (like adding a method) will cause the JVM to generate a different serialVersionUID, rendering previously serialized instances of the class incompatible. serialver provides a way to explicitly define the serialVersionUID, ensuring that deserialization will work correctly even after modifications, as long as the explicitly defined ID remains the same. The tool can be used on compiled class files or source files.

• The class must be accessible from the classpath used to run serialver.
• The class must be a valid Java class.
• Changes to a class's structure, even with a fixed serialVersionUID, may still lead to deserialization issues if the changes are significant enough to break compatibility.

To get the serialVersionUID for a class named `com.example.MyClass`, you would run:
serialver com.example.MyClass

This would output something like:
com.example.MyClass: static final long serialVersionUID = 684654879846541382L;
Which you can then copy and paste into your Java class.

It is recommended to explicitly define the serialVersionUID for any class that will be serialized. When defining the value for serialVersionUID, you can run serialver against an existing class file, or the tool can provide a default, which you can paste into the class definition. If the generated value is pasted from the serialver tool into the code, later invocations of serialver will generate the same serialVersionUID. However, deserialization errors might occur if the class structure is significantly changed, so consider if the id should be regenerated in this case.

The serialver command has been part of the Java Development Kit (JDK) since its early versions. It was introduced to address the complexities of object serialization and versioning in Java. In the absence of this tool developers would manually create and handle the serial version ID. This simplifies maintenance of serialized objects across different versions of the applications that use them.

javac(1)