如何将值从jsp传递到java类

Question

My Jsp page

<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@page contentType="application/xml" trimDirectiveWhitespaces="true" %>
<%@ page import="com.raos.kookooivr.CallStatusValues" %>

<c:choose>

    <c:when test='${(param.event == "Conference" || param.event == "Hangup" || param.event == "Disconnect") && requestScope.state == "conferenceStarted"}'>
        <%     
            String session_id = request.getParameter("sid");
            out.print(CallStatusValues.getsessionid(session_id));
            String called_no = request.getParameter("cid");
            out.print(CallStatusValues.getcalledno(called_no));
            String actualtime = request.getParameter("total_call_duration");
            out.print(CallStatusValues.getactualtime(actualtime));
            String start_time = request.getParameter("start_time");
            out.print(CallStatusValues.getstarttime(start_time));
            String end_time = request.getParameter("time");
            out.print(CallStatusValues.getendtime(end_time));
        %>
    </c:when>
</c:choose>

My Java Class

package com.raos.kookooivr;

public class CallStatusValues
{
    public static String getsessionid(String session_id) 
    { 
        System.out.println(session_id);
        return session_id;
    }

    public static String getcalledno(String called_no) 
    { 
        System.out.println(called_no);
        return called_no; 
    }

    public static String getactualtime(String actualtime) 
    { 
        System.out.println(actualtime);
        return actualtime;
    }

    public static String getstarttime(String start_time) 
    { 
        System.out.println(start_time);
        return start_time;
    }

    public static String getendtime(String end_time) 
    { 
        System.out.println(end_time);
        return end_time;
    }
}

I am getting 500 Error.

I am trying to pass the values of " String session_id = request.getParameter("sid"); " to my java class and trying to print the session id

public static String getsessionid(String session_id) 
        { 
            System.out.println(session_id);
            return session_id;
        }

I need help to get the values from jsp to be printed using my java class. Example my sid is 123456. Then, that session id should be passed from my jsp file to my java class.

Answer 1

I'm afraid there are multiple problems with your code.

• You can't use static methods - web servlets are multi-threaded, and need model class instances per thread (which usually maps to an instance per web session).
• Your naming conventions are non-standard. The correct name for your session_id variable is sessionId and the getter should be getSessionId() - note the capitalization. This meets the Java Bean naming conventions.
• The way you are coupling code to the model class (which incidentally has nowhere to store the data) is non-standard.
• Writing java code in a JSP is generally regarded as code smell for new projects. It is more normal to just use EL and tags in the JSP and move any Java code out into the model and controller.

I suggest you download a simple working J2EE JSP servlet project and analyse how it works. Then start to modify it to suit your requirements. Something like http://crunchify.com/servlet-tutorial-getting-starting-with-jsp-servlet-example should get you started.

Answer 2

Unsure that you are doing what you want to do.

Here is what actually happens :

• a client sends a request that ends in calling the JSP page
• the servlet container calls the JSP with the context of the calling request
• the JSP runs server side with the context of the calling request meaning that:
  • nothing has been rendered at that time
  • all the parameters "sid", "cid", etc. are those that the caller passed
• if any of the required parameters were not passed in calling request, you get a NullPointerException that ends in an Error 500

BTW using a class with static methods that way from a JSP, is at least uncommon... It could make sense if you need to be able to to complex computations inside the JSP, but in that case, you'd better use a servlet to do the processing, store result in request attribute and forward to the servlet.