Typecasting error in sessions in jsp

Question 1

Type casting using (String) Object can only type cast an object of type String.

If its not a String object then it will generate an error.. Better Method is to use

String.valueOf(object);

Here in your case it will surely generate an error if the session.getAttribute("wrongP") returns an instance of object other than String.

Question 2

Your message tells you what the problem is: java.lang.Character cannot be cast to java.lang.String

So the value of that attribute is of type Character and thus casting that to String of course will fail.

String.valueOf(...) would help, but keep in mind that the result depends on the actual type, e.g. if the attribute was a string array, it would not work.

Addtionally, if(s.equals('0')) would not work, since a string and character (which you get using the literal notation '0') are not equal.

In your case use one of the following:

Id' prefer this because there's no cast:

String s=String.valueOf( session.getAttribute("wrongP") );
if(s.equals("0")) {  //use a String here
  ...
}

This should work as well, but would have the risk of another ClassCastException it the type of the attribute changes:

Character c=(Character)session.getAttribute("wrongP");
if(s.equals('0')) {
  ...
}

Question 3

Your method session.getAttribute("wrongP") returning a char and you tries to cast it to String, that's why you are getting ClassCastException.

You have to use String.valueOf(char) to cast your char value into String:

String str = String.valueOf(session.getAttribute("wrongP"));

One more thing :

after getting String, in your if condition, you are comparing the String object with char value if(s.equals('0')).

You have to do this like :

if(s.equals("0"))

Note: Try to do minimum java code in your jsp page.

Question 4

what you have stored in session.setAttribute("attributeName",attributeValue) is not able to convert in String.