ServletRequest.getParameterMap() returns Map<String, String[]> and ServletRequest.getParameter() returns String?

Question

Can someone explain to me why ServletRequest.getParameterMap() returns type

Map<String, String[]>  

ServletRequest.getParameter() just returns type String

I'm don't understand why the map would ever map to more then one value. TIA.

Answer 1

It returns all parameter values for controls with the same name.

For example:

<input type="checkbox" name="cars" value="audi" /> Audi <input type="checkbox" name="cars" value="ford" /> Ford <input type="checkbox" name="cars" value="opel" /> Opel 

or

<select name="cars" multiple>     <option value="audi">Audi</option>     <option value="ford">Ford</option>     <option value="opel">Opel</option> </select> 

Any checked/selected values will come in as:

String[] cars = request.getParameterValues("cars"); 

It's also useful for multiple selections in tables:

<table>     <tr>         <th>Delete?</th>         <th>Foo</th>     </tr>     <c:forEach items="${list}" var="item">         <tr>             <td><input type="checkbox" name="delete" value="${item.id}"></td>             <td>${item.foo}</td>         </tr>     </c:forEach> </table> 

in combination with

itemDAO.delete(request.getParameterValues("delete"));