Transferring Control to Another Web Component

The mechanism for transferring control to another web component from a JSP page uses the functionality provided by the Java Servlet API as described in Accessing a Session (page 86). You access this functionality from a JSP page by using the jsp:forward element:

<jsp:forward page="/main.jsp" /> 

Note that if any data has already been returned to a client, the jsp:forward element will fail with an IllegalStateException.

jsp:param Element

When an include or forward element is invoked, the original request object is provided to the target page. If you wish to provide additional data to that page, you can append parameters to the request object by using the jsp:param element:

<jsp:include page="..." >
  <jsp:param name="param1" value="value1"/>

When jsp:include or jsp:forward is executed, the included page or forwarded page will see the original request object, with the original parameters augmented with the new parameters and new values taking precedence over existing values when applicable. For example, if the request has a parameter A=foo and a parameter A=bar is specified for forward, the forwarded request will have A=bar,foo. Note that the new parameter has precedence.

The scope of the new parameters is the jsp:include or jsp:forward call; that is, in the case of an jsp:include the new parameters (and values) will not apply after the include.