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(Continued from previous part...)
Generating Non-HTML Entity Body
Sometimes, you may want to send back information in the entity body that are
not in the HTML format, for example, a PDF document, or MS Word Document. In this
case, we have to set Content_Type, Content_Length and other header lines carefully
to provide correct information about the entity body for the client program.
Here is a sample JSP page to show you how to set header lines for different types
of data in the entity body.
<?xml version="1.0"?>
<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page" version="1.2">
<!-- GetFile.jsp
Copyright (c) 2002 by Dr. Herong Yang
-->
<jsp:directive.page session="false" import="java.io.*" />
<jsp:scriptlet>
String p = request.getQueryString();
boolean ok = true;
ok = p!=null;
if (ok) {
if (p.indexOf(".html")>-1) {
response.setContentType("text/html");
} else if (p.indexOf(".gif")>-1) {
response.setContentType("image/gif");
} else if (p.indexOf(".pdf")>-1) {
response.setContentType("application/pdf");
} else if (p.indexOf(".doc")>-1) {
response.setContentType("application/msword");
} else {
ok = false;
}
}
if (ok) {
try {
int l = (int) new File(p).length();
response.setContentLength(l);
byte[] b = new byte[l];
FileInputStream f = new FileInputStream(p);
f.read(b);
ServletOutputStream o = response.getOutputStream();
o.write(b,0,l);
o.flush();
o.close();
f.close();
} catch (Exception e) {
ok = false;
}
}
if (!ok) {
response.sendError(HttpServletResponse.SC_BAD_REQUEST);
}
</jsp:scriptlet>
</jsp:root>
Ideas used in this page:
- The objective of this page is to send back the content of the requested file
in entity body, and set the Content_Type and Content_Length header lines correctly.
- The requested file name is given in the query string of the HTTP request.
- The extension of the requested file name is checked to determine the Content_Type
header line.
- Then the requested file size is checked to set the Content_Length header line.
- Then the requested file is opened, and the content is copied to output stream
of the response object as a byte array.
- If any thing goes wrong, an error status code is send to the response.
Now let's see how this page works.
1. Use IE (Internet Explorer) to request: http://localhost:8080/GetFile.jsp?hello.html,
you should see the hello message properly displayed as HTML document.
2. Use IE to request: http://localhost:8080/GetFile.jsp?dot.gif,
you should see a tiny dot displayed as an image.
3. Use IE to request: http://localhost:8080/GetFile.jsp?hello.pdf,
you should see IE calling Adobe Reader to display the hello message as a PDF document.
4. Use IE to request: http://localhost:8080/GetFile.jsp?hello.doc,
you should see IE calling MS Word to display the hello message as Word document.
Of course, you have prepare such a Word document and put it on Tomcat server in
order to do this test.
5. Use IE to request: http://localhost:8080/GetFile.jsp?any.txt,
you should see IE displaying an error message. The reason is, of course, that
the requested file doesn't exist.
(Continued on next part...)
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