JSP syntax to switch between HTML and XML_问答_开发者

JSP syntax to switch between HTML and XML

开发者 https://www.devze.com 2023-03-12 21:54 出处：网络

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 TEXTARE开发者_JS百科A and SUBMIT button

相关专题：postback xml

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 TEXTARE开发者_JS百科A 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.

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).