Null Pointer exception while getting request parameters - jsf

Question

<h:dataTable id="dt1" value="#{StudentMark.stuList}" var="stuList" bgcolor="#9AC8E6" border="10" cellpadding="5" cellspacing="3" rows="18" width="120%" dir="LTR" frame="hsides>
<h:column>
<f:facet name="header">
<h:outputText style=""value="Student Number" />
</f:facet>
<h:outputText style="" value="#{stuList.stuNumber}"></h:outputText>
</h:column>
<h:column>
<f:facet name="header">
<h:outputText value="Date"/>
</f:facet>
<h:outputText value="#{stuList.date}">
<f:convertDateTime type="date" pattern="dd-MM-yyyy"/></h:outputText>
</h:column>
<h:column>
<f:facet name="header">
<h:outputText value="Name"/>
</f:facet>
<h:outputText value="#{stuList.stuName}"></h:outputText>
</h:column>
<h:column>
<f:facet name="header">
<h:outputText value="Division"/>
</f:facet>
<h:outputText value="#{stuList.division}"></h:outputText>
</h:column>
<h:column>
<f:facet name="header">
<h:outputText value="Annual Marks"/>
</f:facet>
<h:outputText value="#{stuList.annualMark}"></h:outputText>
</h:column>
<h:column>
<f:facet name="header">
<h:outputText value="Student History"/>
</f:facet>
<h:form>
<h:commandButton id = "historyBtn" value="Student History" action="#{stuBean.showHistory}">
<f:param name="sNumber" value="#{stuBean.stuNumber}" />
<f:param name="sName" value="#{stuBean.stuName}" />
</h:commandButton></h:form>
</h:column>
</h:dataTable>
When i try to get the parameters passed using
FacesContext context = FacesContext.getCurrentInstance();
Map requestMap = context.getExternalContext().getRequestParameterMap();
String studentNum = (String) requestMap.get("sNumber");
String studentName = (String) requestMap.get("sName");
its showing "null" in studentName and studentNum thereby resulting with a null pointer exception.
Any ideas to resolve this???

Answer 1

I've resolved my issue.
The mistake made was I've trying to pass the parameters at the page load itself,tried making the param value as value="#{stuList.stuNumber}" and got the error resolved.
<h:form>
<h:commandLink id = "historyBtn" value="Student History" action="#{stuBean.showHistory}">
<f:param name="sNumber" value="#{stuList.stuNumber}" />
<f:param name="sName" value="#{stuList.stuName}" />
</h:commandLink></h:form>
Thanks for all the professionals for their time.

Answer 2

You are mixing POST and GET requests. h:form and h:commandbutton are for POST requests. f:param is for GET requests. If you want a GET request use h:button or h:link
For a quick overview of GET support look here it also explains how you can bind the parameter to a bean without having to go to the request parameter map.

Answer 3

I think f:param works only in h:commandLink and h:outputLink but not in h:commandButton.