JavaServer Pages, 3rd Edition

Passing Control from One Page to Another

Before digging into the modified example pages, let’s go through the basic mechanisms for satisfying the two requirements. As shown in Figure 10-1, the userinfovalidate.jsp page passes control to one of two other pages based on the result of the input validation. JSP supports this through the <jsp:forward> action, described in Table 10-1:

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

Table 10-1. Attributes for <jsp:forward>

Attribute name	Java type	Dynamic value accepted	Description
page	String	Yes	Mandatory. A page-relative or context-relative path for the target resource.

The <jsp:forward> action stops processing of one page and starts processing the page specified by the page attribute instead, called the target page. The control never returns to the original page.

The target page has access to all information about the request, including all request parameters. You can also add additional request parameters when you pass control to another page by using one or more nested <jsp:param> action elements (see Table 10-2):

<jsp:forward page="userinfoinput.jsp" >
  <jsp:param name="msg" value="Invalid email address" />
</jsp:forward>

Table 10-2. Attributes for <jsp:param>

Attribute name	Java type	Dynamic value accepted	Description
name	String	No	Mandatory. The parameter name.
value	String	Yes	Mandatory. The parameter value.

Parameters specified with <jsp:param> elements are added to the parameters received with the original request. ...