I’ve noticed that request.getParameter() always return a string for the parameter that corresponds to a text field in my form, even when the field is empty. To find out if the field is empty, I need to use code like this:
if (request.getParameter("foo").length() == 0) {
...
}
But in your book, you have examples where you test if the parameter value is null instead. When is the value null and when is it an empty string? |
| Answer: Most (all?) browers send empty form text fields to the server as an HTTP request parameter with an empty value. Hence, the value for a text field will rarely be null. Typically it’s an empty string. But it never hurts to test for both null and empty string to be on the safe side: String foo = request.getParameter("foo");
if (foo == null || foo.trim().length() == 0) {
...
}
For checkboxes, radio buttons and select lists, on the other hand, the browser only sends a parameter if the item is selected. For these types of form elements, you must always be prepared to handle a null value. |
Hans Bergsten
Software Adventures
