null pointer exception help

Question

I'm getting a NullPointerException that I couldnt handle. I'm a newbie in java so I'd appreciate any help.

<%
Employee employees[] = (Employee []) request.getAttribute("arr");
Integer arr_size= (Integer) request.getAttribute("arr_size");
for(int i=0;i<employees.length;i++){ %>
<tr><td><b>.</b></td><td><%=employees[i].getName()%></td><td>
    <%=employees[i].getLname()%></td><td><%=employees[i].getType()%></td><td>
    <%=employees[i].getEmail()%></td><td><a href="">Edit Employee Details</a></td>
</tr>
<%}%>

arr array and arr_size is passed from a servlet and I jsp gives an NullPointerException.

I tried checking if employees and arr_size is null or not but it doesn't change anything.

thanks.

Answer 1

Even if the array itself isn't null, it's quite possible that employees[i] would be null - leading to a NullPointerException. You could avoid this by skipping such elements:

for(int i=0;i<employees.length;i++) { 
    if (employees[i] == null) {
        continue;
    }
%>

It's not terribly elegant, mind you. I'd also suggest using the enhanced for loop if you're compiling with Java 5, which would make the code cleaner:

<%
Employee employees[] = (Employee []) request.getAttribute("arr");
for (Employee employee : employees) {
    if (employee == null) {
        continue;
    } %>
<tr><td><b>.</b></td><td><%=employee.getName()%></td><td>
    <%=employee.getLname()%></td><td><%=employee.getType()%></td><td>
    <%=employee.getEmail()%></td><td><a href="">Edit Employee Details</a></td>
</tr>
<%}%>

Note that I've ignored arr_size as you didn't appear to be using it. What was it meant to represent?

Finally, I'd suggest moving logic outside your JSP if at all possible...

Answer 2

They only thing that I can see that you haven't checked yet is the elements of your employees array. If employees[i] is null at any point, referencing it will throw a NullPointerException.

Try this:

for(int i=0;i<employees.length;i++){ 
  Employee e = employees[i];
  if (e != null) {%>
    //current code you have goes here
  <% }} %>

instead of the current for loop