How to set a parameter in a HttpServletRequest?

Question

I am using a javax.servlet.http.HttpServletRequest to implement a web application.

I have no problem to get the parameter of a request using the getParameter method. However I don't know how to set a parameter in my request.

Answer 1

You can't, not using the standard API. HttpServletRequest represent a request received by the server, and so adding new parameters is not a valid option (as far as the API is concerned).

You could in principle implement a subclass of HttpServletRequestWrapper which wraps the original request, and intercepts the getParameter() methods, and pass the wrapped request on when you forward.

Answer 2

From your question, I think what you are trying to do is to store something (an object, a string...) to foward it then to another servlet, using RequestDispatcher(). To do this you don't need to set a paramater but an attribute using

void setAttribute(String name, Object o);

and then

Object getAttribute(String name);

Answer 3

If you really want to do this, create an HttpServletRequestWrapper.

public class AddableHttpRequest extends HttpServletRequestWrapper {

   private HashMap params = new HashMap();

   public AddableingHttpRequest(HttpServletRequest request) {
           super(request);
   }

   public String getParameter(String name) {
           // if we added one, return that one
           if ( params.get( name ) != null ) {
                 return params.get( name );
           }
           // otherwise return what's in the original request
           HttpServletRequest req = (HttpServletRequest) super.getRequest();
           return validate( name, req.getParameter( name ) );
   }

   public void addParameter( String name, String value ) {
           params.put( name, value );
   }

}