"The serializable class Login does not declare a static final serialVersionUID field of type long"
If your class implements "Serializable" (HttpServlet does) you need an id because if the Servlet-Context
is relaunched and your sessions should be made persistant / restored.
(If you don't need this feature, you don't need a serialVersionId.)
"Object serialization is the process of saving an object's state to a sequence of bytes,
as well as the process of rebuilding those bytes into a live object at some future time."
import java.io.FileOutputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
public class myExampleClass implements Serializable {
public static void main(String [] args)
{
myExampleObject time = new myExampleObject();
FileOutputStream fos = new FileOutputStream(filename);
ObjectOutputStream out = new ObjectOutputStream(fos);
out.writeObject( time );
}
http://java.sun.com/developer/technicalArticles/Programming/serialization/
http://www.mactech.com/articles/mactech/Vol.14/14.04/JavaSerialization/index.html
http://mindprod.com/jgloss/serialization.html
SerialVersionUID generation may differ by compiler, SUID is a measure of backwards compatibility,
to ensure different clients with different JVM's won't have compiler generated incompatibilities
you should generate your own SUID and update it when you update the code.
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SOLUTION
Eclipse IDE: click on the light bulb and choose add default serial version id.
// default serial version id inserted by Eclipse
private static final long serialVersionUID = 1L;