Example: Reading Three Parameters
Here's a simple example that reads parameters named "param1", "param2", and "param3", listing their values in a bulleted list. Note that although you are required to specify response settings (content type, status line, other HTTP headings) before beginning to
generate the content, there is no requirement that you read the request parameters at any particular time.
Also note that this servlet can read either GET or POST data, simply by having its "doPost" method called "doGet". This is good standard practice, since it requires very little extra work and permits flexibility on the part of the client. If you're used to the traditional CGI approach where you read POST data via the standard input, you should note that there is a similar way with servlets by first calling "getReader" or "getInputStream" on the "HttpServletRequest". This is a bad idea for regular parameters, but might be of use for uploaded files or POST data being sent by custom clients rather than via HTML forms. Note,
however, that if you read the POST data in that manner, it might no longer be found by "getParameter".
ThreeParams.java
You can also download the source or try it on-line. Note: also uses ServletUtilities.java, shown earlier.
package hall;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;
public class ThreeParams extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String title = "Reading Three Request Parameters";
out.println(ServletUtilities.headWithTitle(title) +
"<BODY>\n" +
"<H1 ALIGN=CENTER>" + title + "</H1>\n" +
"<UL>\n" +
" <LI>param1: "
+ request.getParameter("param1") + "\n" +
" <LI>param2: "
+ request.getParameter("param2") + "\n" +
" <LI>param3: "
+ request.getParameter("param3") + "\n" +
"</UL>\n" +
"<<BODY></HTML>");
}
public void doPost(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
ThreeParams Output
NEXT
This tutorial is now available as a book: Core Servlets and JavaServer Pages by Marty Hall, published by Sun Microsystems Press.
Read all about it at CoreServlets.com
Server-Side Web Applications using Java Servlets versions 2.1/2.2 and JavaServer Pages (JSP) version 1.0: A Tutorial
© 1999-2000 Marty Hall.
All source code freely available for unrestricted use.
Created for work in the Research and Technology Development Center of the Johns Hopkins University Applied Physics Lab, for courses in the Johns Hopkins Part-Time MS Program in Computer Science, and for various industry seminars and on-site Java short courses.
Please note that this is a first draft of the tutorial, so please send corrections, comments, and suggestions to me at hall@apl.jhu.edu.
Reprinted with permission from the author. Click here to visit the original version
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