Sun Lihua (NWSS/Sydney) [[EMAIL PROTECTED]] writes:
> 1. in the spec 0.92, it introduces two models using JSP, but
> as to the model
> 2, there is no word in the spec or the samples on how to call JSP file
> directly from Servlet or other Java classes. How could I use
> it? Will this
> be introduced in spec 1.0?
The servlet doesn't "call" the JSP, it either redirects or forwards to it.
One method would be to use HttpServletResponse.sendRedirect(String) from
within the servlet to tell the client browser to go to the JSP. However,
this causes an extra round trip from the client to the server.
The preferred method (IMHO) in the 0.92 spec is to use
RequestDispatcher.forward(String) to have the web server "automagically"
forward input from a second URL within the same connection. You can get a
RequestDispatcher by calling ServletContext.getRequestDispatcher(). Note
that this is a new addition to the servlet spec (2.1 I think), and is not
supported by all JSP implementations. I know for a fact that it is support
in JRun 2.3. Check the JSP FAQ for more information on JSP implementations.
(This API is detailed in the 0.92 spec - it's way at the end.)
> 2. the purpose of JSP is to seperate the dynamic content
> generation from the
> presentation, so I think not only should we be able to call
> JSP file from
> Servlet, but also from any Java classes, is it in the
> consideration of spec
> 1.0?
Umm, how would a random Java class "call" a JSP file? Since the purpose
of a JSP file is to output HTML, it doesn't really make much sense to call a
JSP. But if you really wanted to do it, your Java code could simple open an
HTML connection to the web server where the JSP lives and request the URL of
the JSP.
Since the point of model 2 in JSP is to remove logic from the JSP, there's
not much point in "calling" the JSP.
> 3. is there a way to pass parameters to JSP file? because the
> workhorse for
> JSP file is servlet, which is a Java class, so I think there
> should be a way
> to define the variables in JSP file, and pass parameters
> dynamically to JSP
> file from other java classes, just as the ordinary Java class.
In the servlet, create the object you want to access in the JSP. The
object should be "JavaBean-like" and use get/set methods to access data.
Then stuff the object into the current HttpSession, like so:
MyDataBean bean = new MyDataBean ();
HttpSession sess = req.getSession(true);
sess.putValue("databean", MyDataBean );
Then in the JSP you forward() to, use the following JSP tags to get the
bean and access it:
<usebean name=databean type=com.tradiant.MyDataBean lifespan=session>
</usebean>
<display property=databean:myData>
Note that the name of the object you put into the session and the name in
the <usebean> tag are the same - that's the trick to passing objects between
servlets and JSPs.
Also very important to note is that the lifespan is set to "session". If
set to "page", a new Bean will always be created. If set to "application",
well that's okay, but the bean is goingto hang around for ever, and it would
be available to every client, not just the one that made the initial
connection.
> 4. in spec 0.92, at the top of page 13, the four implicit
> variables are:
> servletrequest, servletresponse, in and out.
> but on page 29, those four implicit variables have become to:
> request, response, in and out.
>
> which one is correct? (actually, "request" is an implicit
> bean, so I think
> page 29 should be changed according to page 13.
I don't have page numbers on my speq (HTML version), so I can't find the
passages in question to try and answer this.
Hope this helps.
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