jsp无法将session属性放入字符串

Question

i'm having an issue with a session attriblute in a jsp page, i would like to pass it into a string so that i can use it to query a database eg,

String group=session.getAttribute("group"); 

i know it has been correctly populated because if i put the below in a page it displays the correct value

<%=
session.getAttribute("group")
 %>

the error i am getting is

Type mismatch: cannot convert from Object to String

is there a different way to put a session variable into a String? or am i doing it completely wrong. any assistance much appreciated.

Answer 1

You have to cast it to String

String group=(String)session.getAttribute("group"); 

where session.getAttribute("group"); returns Object .

Answer 2

session.getAttribute(String name) will return an Object .

To be safe and prevent any accidental ClassCastException , I would use String.valueOf(Object obj) , like this:

String group = String.valueOf(session.getAttribute("group"));

Sources:

Difference between casting to String and String.valueOf

http://docs.oracle.com/javaee/5/api/javax/servlet/http/HttpSession.html#getAttribute(java.lang.String)

http://docs.oracle.com/javase/7/docs/api/java/lang/String.html#valueOf(java.lang.Object)

Answer 3

you just put like this:

String group=""+session.getAttribute("group"); 

append as string, simple.