jsp:useBean defines a bean in the specified scope and which can be used later. It does not relate to Serialization at all. You got to serialize and deseriliaze using the same ObjectInputStream and ObjectOutputStream only.
The beanName attribute specifies the name of a bean as expected by the instantiate()
method of the java.beans.Beans class. For this reason, beanName can
refer either to a serialized bean or to the name of a class whose instance is to be created.
Instantiates a Bean from either a class or a serialized template, using the java.beans.Beans.instantiate method, and gives the Bean the type specified in type. The Beans.instantiate method checks whether a name represents a class or a serialized template. If the Bean is serialized, Beans.instantiate reads the serialized form (with a name like package.class.ser) using a class loader. For more information, see the JavaBeans API Specification.
So it should work with "package.class.ser" , in your case it is my.Mybean.ser. try this.