Sunday, October 18, 2009

Recipe 3.17. Using Frames










Recipe 3.17. Using Frames




Problem



You need to reference an Action or JSP page from within one frame to
another.





Solution



Use the Struts

html:frame
tag to create frame elements with the proper URLs for your Struts
application, as in Example 3-20
(frame_test.jsp).




Example 3-20. Generating a frame set with Struts

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib uri="http://jakarta.apache.org/struts/tags-html" prefix="html" %>
<frameset cols="50%,*">
  <html:frame frameName="_frame1" 
                   page="/frame1.jsp" 
            marginwidth="10" 
           marginheight="10"
              scrolling="auto" 
            frameborder="1"/>
  <html:frame frameName="_frame2" 
                   page="/frame2.jsp" 
            marginwidth="10" 
           marginheight="10"
              scrolling="auto" 
            frameborder="1"/>
</frameset>





Within the individual frame's source JSP, use the
target attribute on the


html:link and
html:form

tags to refer to the other frame.
The JSP in Example 3-21
(frame1.jsp) demonstrates this approach.




Example 3-21. Frame with link to other frame

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib uri="http://jakarta.apache.org/struts/tags-html" prefix="html" %>
<%@ taglib uri="http://java.sun.com/jstl/core" prefix="c" %>

<html>
<head>
  <title>Struts Cookbook - Chapter 04: Frame Test</title>
</head>
<body bgcolor="white">
<h2>Frame 1</h2>
  <html:link href="frame2.jsp?calledBy=FRAME_1" target="_frame2">
    Call Frame2
  </html:link>
  <p>
  Message received:&nbsp;
  <c:out value="${FrameForm.map.message}"/>
</body>
</html>





Likewise, frame2.jsp shown in Example 3-22 defines a form that submits to an
Action and directs the result to
_frame1 using the target
attribute.




Example 3-22. Frame that submits to other frame

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib uri="http://jakarta.apache.org/struts/tags-html" prefix="html" %>
<%@ taglib uri="http://java.sun.com/jstl/core" prefix="c" %>

<html>
<head>
  <title>Struts Cookbook - Chapter 04: Frame Test</title>
<body bgcolor="white">
<h2>Frame 2</h2>
  Send a message to frame 1!
  <html:form action="CallFrame1" target="_frame1">
    <html:text property="message"/>
    <html:submit/>
  </html:form>
  <c:forEach var="paramValue" items="${paramValues}">
    <br />
    Parameter: <c:out value="${paramValue.key}"/><br />
    Values:
    <c:forEach var="theValue" items="${paramValue.value}">
      <c:out value="${theValue}"/><br />
    </c:forEach>
  </c:forEach>  
</body>
</html>







Discussion



There are two key concerns when using HTML frames within a Struts
application. First, the URLs of the frame elements
within the frameset tag should be generated using
the same
rules used by the Struts
html:link and html:rewrite
tagsi.e., enter the html:frame tag. It
supports the same action, page,
and href attributes as the
html:link and html:rewrite
tags. The html:frame tag supports additional
attributes specific to the HTML frame element.
Most of these attributes are pass-throughs, and the attribute value
is passed through without modification to the generated
frame element.



Second, with frame-to-frame interaction, you will probably need a
user request, made on one frame, to affect the display of another
frame displayed on the same page. The key to making this
communication work is the use of the target
attribute on the html:form and
html:link tags.



The target attribute
specifies
the window or frame that receives the results of a request. The
request can come from a form submission or link. In the Solution, a
frameset is created that contains two
frames_frame1 and
_frame2positioned on the left and right,
respectively. Frame 1, as shown in Example 3-21,
defines a link with the page attribute set to
frame2.jsp and the target set
to _frame2. Parameters are passed on the query
string that will be displayed by frame2.jsp:



<html:link href="frame2.jsp?calledBy=FRAME_1" target="_frame2">
    Call Frame2
</html:link>




Similarly, frame2.jsp, shown in Example 3-22, defines a form where the
target is specified as
_frame1:



<html:form action="CallFrame1" target="_frame1">




The form-bean and action for
this example are defined in the
struts-config.xml file:



<form-bean name="FrameForm" type="org.apache.struts.action.DynaActionForm">
  <form-property name="message" type="java.lang.String"/>
</form-bean> 
...
<action    path="/CallFrame1"
          name="FrameForm"
         scope="request"
          type="org.apache.struts.actions.ForwardAction"
     parameter="/frame1.jsp"/>




When you first access frame_test.jsp and click
the link on the lefthand frame, you'll see the data
displayed in Frame 2. Likewise, when you submit the form on the
righthand frame, you will see the results displayed in Frame 1. Figure 3-5 shows the frames after this series of
interaction.




Figure 3-5. frame_test.jsp




If the target attribute was omitted, the output
would be displayed in the same frame from where the request was made.
Think of a frame as a browser within a browser. The Solution works
the way it does because _frame1 and
_frame2 are both part of the same
frameset.



Other specially named targets are relevant to frames that are handled
in specific ways by the browser. These special targets in described
in Chapter 3.



Table 3-5. Special frame target values

Frame



Description



_blank



The browser loads the received request into a new browser window.
This target is useful for creating pop ups.



_self



The browser loads the received request into the current window or
frame. This is the default setting when the target is not specified.



_parent



The browser loads the received request into the parent window or
frameset directly containing this frame. If the current reference is
a top-level frame or window, this is equivalent to
_self.



_top



The browser loads the received request into the window at the top of
the hierarchy. This results in the request being displayed in the
entire browser window.





Frames can get complicated, particularly if you use frames within
frames as well as hidden frames. Many people prefer to steer clear of
frames because of this complexity. Carefully consider your
requirements when using frames. You may find that you can get similar
behavior without the complexity of inter-frame communication using
JSP includes or Tiles.





See Also



The Struts documentation for the html tag library
provides complete details on the html:frame tag as
well as the use of the target attribute. You can
find this at http://struts.apache.org/userGuide/struts-html.html.



A great reference for details on frames can be found in
HTML and XHTML: The Definitive Guide by Chuck
Musciano and Bill Kennedy (O'Reilly).



Recipe 14.1 provides the basics of setting up Tiles for
your application.












    Posted by at

    No comments:

    Post a Comment

    Subscribe to: Post Comments (Atom)