Typecasting error in sessions in jsp

StackOverflow https://stackoverflow.com/questions/23540215

  •  18-07-2023
  •  | 
  •  

Question

I have a jsp file adminLogin.jsp where i check the session attributes passed on from index.jsp and from logout.jsp :

<%
      String s=(String)session.getAttribute("wrongP");
    if(s.equals('0'))
    {out.println("Wrong Details or you logged out Please Login Again <br>");
    session.invalidate();
    }

    %>
    This is login 

form
    <br>Please login<br>

            <form method="GET" action="login1">
             <br>.           Id:<input type="text" name="id"><br>Password:<input
                    type="password" name="pass"><br> <input type="submit"
                    value="Submit">
            </form>
            </div>

The error i am getting is:

HTTP Status 500 - An exception occurred processing JSP page /adminLogin.jsp at line 12

type Exception report

message An exception occurred processing JSP page /adminLogin.jsp at line 12

description The server encountered an internal error that prevented it from fulfilling this request.

exception 

org.apache.jasper.JasperException: An exception occurred processing JSP page /adminLogin.jsp at line 12

9: <body>
10: <div align="center">
11: <%
12: String s=(String)session.getAttribute("wrongP");
13: if(s.equals('0'))
14: {out.println("Wrong Details or you logged out Please Login Again <br>");
15: session.invalidate();


Stacktrace:
  org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:568)
  org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:470)
  org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
  org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
  javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
  org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)


root cause 

java.lang.ClassCastException: java.lang.Character cannot be cast to java.lang.String
  org.apache.jsp.adminLogin_jsp._jspService(adminLogin_jsp.java:72)
  org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
  javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
  org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
  org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
  org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
  javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
  org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)


note The full stack trace of the root cause is available in the Apache Tomcat/7.0.53 logs.

I type casted the attribute but i am still getting this error.

Was it helpful?

Solution

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.

OTHER TIPS

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')) {
  ...
}

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.

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

Licensed under: CC-BY-SA with attribution
Not affiliated with StackOverflow
scroll top