Making AJAX call using DWR (Direct Web Remoting)

This Article will explain how to make DWR (Direct Web Remoting) AJAX call from JSP

Follow the simple Steps

a         Copy the DWR jar file to the Lib directory under webcontent/WEB-INF (download from here)

b        Copy the following xml snippet to the web.xml

<servlet> 

<servlet-name>dwr-invoker</servlet-name>

<servlet-class>org.directwebremoting.servlet.DwrServlet</servlet-class>

<init-param>

                      <param-name>debug</param-name>

                      <param-value>true</param-value>

</init-param>

</servlet>

<servlet-mapping>

<servlet-name>dwr-invoker</servlet-name>

<url-pattern>/dwr/*</url-pattern>

</servlet-mapping>

c         Create or Copy the dwr.xml under the WEB-INF directory and content of the file is as follows

<!DOCTYPE dwr PUBLIC

    "-//GetAhead Limited//DTD Direct Web Remoting 2.0//EN"

    "http://getahead.org/dwr/dwr20.dtd">

<dwr>

  <allow>

    <create creator="new" javascript=" AjaxDWRTest">

      <param name="class" value="com.vaka.siva.helper.AjaxDWRTest"/>

    </create>

  </allow>

</dwr>

d        Write a class with public methods and className  should be like as specified in dwr.xml (If you need the  HTTPServletSession then we use below extra code)

public class AjaxDWRTest {

public String getDisplayedTickets(int pageIndex) {

                                               

                                                WebContext ctx = WebContextFactory.get();

                                                HttpServletRequest request = ctx.getHttpServletRequest();

                                                HttpSession session = ctx.getSession();

                                                if (session == null)return null;

                                               

//call to some helpers and do the processing

//you can make backend calls now or you can make backend calls first and store it in the session and now retrieve from session

return tktstr

}

e        In above XML , we have specified the AjaxDWRTest as javascript ,so DWR will create  that for us we just need to include the following in JSP where we need the AJAX call

<script type="text/javascript" src='<%= renderResponse.encodeURL(renderRequest.getContextPath()+ "/dwr/interface/AjaxDWRTest.js") %>'>

</script>

<script type="text/javascript" src='<%= renderResponse.encodeURL(renderRequest.getContextPath()+ "/dwr/engine.js") %>'>

f          Following is the way we invoke the callback method in JSP

//Print the table with initial values List (this is not ajax call)

<c:if test="${!empty SessionBean.initialTicketValuesMap}">

<script type="text/javascript">

               <portlet:namespace/>paintDynaSec(intialTicketValuesString);

</script>

</c:if>

//following is AJAX call , when somebody click next page then we call below

AjaxDWRTest.getDisplayedTickets(currentPageIndex, <portlet:namespace/>paintDynaSec);

//Once AJAX backend call is over then above statement will automatically calls paintDynaSec javascript function with parameter that is returned from the AJAX

function <portlet:namespace/>paintDynaSec(tktstr) {

                        ticketList.innerHTML =tktstr;

}