Servlet Redirecting

How to do Redirecting?

• The HttpServletReponse interface has a method, sendRedirect(), that sends the response to another path.
  A Redirect example:

  ...
  // If the request has a parameter, searchEngine, we sends a Redirect
  // to the url value of that parameter. Else we return a message back to the client
  String url = request.getParameter("searchEngine");
  if (url != null) {
    response.sendRedirect(url);
  }
  else {
    PrintWriter printWriter = response.getWriter();
    printWriter.println("No search engine was selected.");
  }
  ...

• This method can accept relative URLs.
• The servlet container must convert the relative URL to an absolute URL before sending the response to the client.
• If the location is relative without a leading '/' the container interprets it as relative to the current request URI.
• If the location is relative with a leading '/' the container interprets it as relative to the servlet container root.
  A simple Servlet Redirect program:

  public class ResponseRedirectionServlet extends HttpServlet
  {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws IOException
    {
      String url = request.getParameter("searchEngine");
  
      if (url != null)
      {
        response.sendRedirect(url);
      }
      else
      {
        PrintWriter printWriter = response.getWriter();
  
        printWriter.println("No search engine was selected.");
      }
    }
  }
  

  How to try examples.
• The Servlet above will redirect the request to a url, given as a request parameter, using the response sendRedirect() method.
  The html startup file, index.html, for the browser can be like this:

      <form method="post" action="ResponseRedirectionServlet">
        Please indicate your favorite search engine.
        <table>
          <tr>
            <td><input type="radio" name="searchEngine"
                       value="http://www.google.com">Google</td>
          </tr>
          <tr>
            <td><input type="radio" name="searchEngine"
                       value="http://www.msn.com">MSN</td>
          </tr>
          <tr>
            <td><input type="radio" name="searchEngine"
                       value="http://www.yahoo.com">Yahoo!</td>
          </tr>
          <tr>
            <td colspan="2"><input type="submit" value="Submit" /></td>
          </tr>
        </table>
      </form>
      

  How to try examples.
  The form will look like:
  
  
• When the user press the submit button he will be redirected to selected option url.
• All source code examples in this session is part of a complete example, ServletResponseRedirect, that you can download.