JSP syntax to switch between HTML and XML

Question

I would like to have a single JSP page that will do the following:

If the method is GET and the querystring is NULL, draw a HTML form with a TEXTAREA and SUBMIT button
If the method is GET and the querystring is not NULL or the method is POST, genete an XML document using GET/POST variables

My first approach draft (test POST or GET) fails syntactically:

query.jsp

<%@ page import="..." %>
<%!
  private void to_xml() {
  ...                
  }
%>
<% if (request.getMethod()="POST") { %>

<?xml version="1.0" encoding="UTF-8"?>

<%
  //generate XML 
  to_xml();
} 

else { 

  //draw HTML form
%>

<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>XML Query</title>
    </head>
    <body>
        <form action="query.jsp" method="post">
            <table cellpadding="2">
                <tr><td>Query:</td></tr>
                <tr><td><textarea name="query" cols="60" rows="10" ></textarea>
                <tr><td><input type="submit" value="Go"></td></tr>
            </table>
        </form>
    </body>
</html>

<% } %>

I'm sure that there is a better way to do this, but my experience w/ JSP is limited.

BalusC · Accepted Answer · 2011-06-13T20:16:50.363

As to your concrete problem: in Java, strings are objects, not primitives. You need to compare objects by the Object#equals() method, not by equality operator == (or even more incorrectly, the assignment operator =). This is not different when writing raw Java code straight in a JSP file instead of a Java class.

<% if (request.getMethod().equals("POST")) { %>

As to the better way, just use a servlet.

Put JSP in /WEB-INF/query.jsp to prevent direct access and remove all old fashioned scriptlets so that it becomes a fullworthy view.

<!DOCTYPE html>
<html lang="en">
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>XML Query</title>
    </head>
    <body>
        <form action="query" method="post">
            <table cellpadding="2">
                <tr><td>Query:</td></tr>
                <tr><td><textarea name="query" cols="60" rows="10" ></textarea>
                <tr><td><input type="submit" value="Go"></td></tr>
            </table>
        </form>
    </body>
</html>

Create a servlet which does the controlling job:

@WebServlet(urlPatterns={"/query"})
public class QueryServlet extends HttpServlet {

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        if (request.getParameterMap().isEmpty()) {
            showJsp(request, response);
        } else {
            showXml(request, response);
        }
    }

    private void showJsp(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.getRequestDispatcher("/WEB-INF/query.jsp").forward(request, response);
    }

    private void showXml(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // ...
    }

}

Open the page by http://localhost:8080/contextname/query.

I however wonder how it's useful to mix POST/GET here since you want to intercept on the query string as well. Just remove method="post" from the <form> and replace service() method name in above example by doGet(). This way the form submit URL becomes bookmarkable as well (which is what among others Google also does).

After reading your response, some contemplation, and some research, it appears what I really want is RESTful interface to Java. While I could use Jersey or RESTEasy, perhaps implemented selected bits of JAX-RS will meet my needs. — craig, Jun 14 '11 at 20:33
That was also what I initially thought :) It's only another learning curve. Note that Jersey and RESTEasy are both concrete JAX-RS API implementations. Like as that Tomcat is a concrete JSP/Servlet API implementation. — BalusC, Jun 14 '11 at 20:35
I really only have two classes: Session and InfoObjects (BusinessObjects). I need GET/POST/DELETE for Session (auth form/authenticate/logout) and GET for InfoObjects (get one object or multiple). While I'm sure these frameworks would make this easy, I'm leary of adding additional complexity. Is there a less-complex way? — craig, Jun 14 '11 at 20:54
Well, using a plain servlet is less complex. Basically, what I've put in my answer is everything you need. But using JAX-RS will give you way much more flexibility with regard to future changes and expansions. Note that JAX-RS is designed on top of the basic Servlet API. So, it is under the covers using a plain servlet, but just with all potential boilerplate/repetitions abstracted away so that you don't need to Ctrl+C/Ctrl+V the entire JSP/Servlet code, but, say, just add one more method. — BalusC, Jun 14 '11 at 20:56
Is there a way to pass a variable defined int the Servlet to the view? Most of the examples that I've seen dynamically create the view. I would like to be able to use something the <%= XXX %> syntax. — craig, Jun 20 '11 at 00:39
*Scriptlets* are discouraged since a decade: http://stackoverflow.com/questions/3177733/how-to-avoid-java-code-in-jsp-files. Just set an attribute in request scope like `request.setAttribute("foo", foo)` and access it in the forwarded JSP by EL like `${foo}`. See also http://stackoverflow.com/tags/servlets/info and http://stackoverflow.com/tags/el/info. — BalusC, Jun 20 '11 at 00:51

JSP syntax to switch between HTML and XML

1 Answers1