On Thursday 01 July 2004 19:06, lee hwaying wrote:
> hi.
Hi,
first of all, let's get clear about the focus of JSP in the
overall aspect of Java web technology. JSP is based
upon the Servlet API and provides an easy means
to generating HTML or other text output in the first
degree. Though you *can* use JSPs to deliver binary
contents (such as images), that's nothing recommendable.
For streamed content, Servlets are much easier to
handle and straightfoward. It has never been a good
idea just to put <% and %> tags into a JSP and then
code the whole program inside these.
Then, you have to hold two things apart: the HTML
page itself which is a text document and can well
be rendered by using JSPs. Note that images are
not 'embedded' in the page, but only *referred* to
by <img src=...> tags. Delivering the real content
is where Servlets come in. For delivering images
stored in a database (don't know much about
MySQL, as we're on Oracle, but in the end that
doesn't matter much), I would write a simple
Servlet that takes the byte array retrieved from
the db (or a stream or whatever) and delivers
it via HTTP. Note that HTTP is different from
HTML.. Some sample code to illustrate this:
package de.christianbollmeyer.struts.qna.servlets;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import de.christianbollmeyer.qna.Constants;
import de.christianbollmeyer.qna.persistence.PersistenceFacade;
import de.christianbollmeyer.util.ServletUtilities;
public class ImageServlet extends HttpServlet {
private static final String CONTENT_TYPE = "image/jpeg";
private static final int BUF_SIZE = 1024;
public void init(ServletConfig config) throws ServletException {
super.init(config);
}
public void doGet(HttpServletRequest request, HttpServletResponse
response) throws ServletException, IOException {
String user = request.getParameter(Constants.SC_PARAM_ID);
int userId = ServletUtilities.stringToInt(user);
if (userId == Constants.UNDEFINED) {
userId = Constants.POOL_USER;
}
response.setContentType(CONTENT_TYPE);
response.addHeader("Cache-Control", "No-cache; No-store;
Must-revalidate; Proxy-revalidate");
response.addDateHeader("Expires", 1L);
response.addHeader("Pragma", "No-cache");
byte[] buffer = new byte[BUF_SIZE];
OutputStream outstream = response.getOutputStream();
InputStream instream = null;
instream = PersistenceFacade.getInstance().getUserImage(userId);
if (instream == null) {
instream =
PersistenceFacade.getInstance().getUserImage(Constants.POOL_USER);
}
try {
int size = -1;
while (-1 != (size = instream.read(buffer, 0, BUF_SIZE))) {
outstream.write(buffer, 0, size);
}
} catch (Exception ex) {
System.out.println(ex.getMessage());
} finally {
if (instream != null) {
try { instream.close(); } catch (IOException e) { ; }
instream = null;
}
if (outstream != null) {
try { outstream.close(); } catch (IOException e) { ; }
outstream = null;
}
}
}
}
Just to get the principles. It won't compile, for the supporting
classes are missing. PersistenceFacade, for instance, reads
a user image from the db and dumbly returns it as a stream for
whatever use. The Servlet takes that and copies it bytewise
down the HTTP stream (try..catch block), with the 'image/jpeg'
MIME header being sent before (note: no HTML here at all).
You can pass a parameter to the Servlet ('user') telling the
Servlet which image to show. Then, there's some standard
code to forbid caching, but that's it. The Servlet is mapped
to a URL in web.xml, /img or whatever, and in the HTML
page including the db pictures, the references simply look
like <img src='/img?user=xyz' and the like. As this runs
(in a somewhat more sophisticated version, but still) in
a real high-volume Java application, (definitely not on
christianbollmeyer.de :-), be sure it's just 'how you do it
in Java' in terms of Best Practices.
HTH,
-- Chris (SCPJ2)
> i have search on the net for 3 days for sample code of displaying a
> byte[] from mysql image field using jsp but without success.
>
> 1. I have found sample code for php in doing that
> http://www.onlamp.com/pub/a/onlamp/2002/05/09/webdb2.html?page=1
>
> 2. It can be done via servlet. But i am reluctant to emit all html
> content using servlet in this case.
>
>
> Can anyone help? Is there a way using jsp to do so?
>
> many many thanks
> hy
>
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>
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To unsubscribe: mailto [EMAIL PROTECTED] with body: "signoff JSP-INTEREST".
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Some relevant archives, FAQs and Forums on JSPs can be found at:
http://java.sun.com/products/jsp
http://archives.java.sun.com/jsp-interest.html
http://forums.java.sun.com
http://www.jspinsider.com
