Java Server Pages

Chapter 12. Bits and Pieces

In the previous chapters, I have demonstrated the standard JSP features as well as a number of custom actions through practical, complete examples. But some features are hard to fit nicely into these examples without losing focus, so they are described separately in this chapter instead. Things covered here include buffering of the response body, ways to include shared page fragments, using XML and XSL with JSP, using client-side code to provide a more interactive interface, preventing JSP pages from being cached, and a discussion about the different types of URIs used in JSP pages.

Buffering

There’s one important thing about how a JSP page is processed that has not been covered in any example so far: buffering of the response body. As you may recall from Chapter 2, an HTTP response message contains both headers and a body. The headers tell the browser things like what type of data the body contains (HTML text, an image), the size of the body, if the body can be cached, and so forth. Headers are also used to set cookies and to tell the browser to automatically get another page (a redirect). All response headers must be sent to the browser before the body is sent.

As soon as a JSP page writes something to the body of the message, the JSP container may start sending the response to the browser. It is then too late to set headers, since they have to be sent first. In a servlet, you have full control over when something is written to the response body, so ...