This is a simple demonstration of how to dynamically update a web-page with text fetched from a web server.
Name:
Reply:
When you click on the "Send" button the browser calls the onclick event,
which calls the update()
function:
function update() { var name = dwr.util.getValue("demoName"); Demo.sayHello(name, loadinfo); }
dwr.util.getValue()
is a utility to get the value of any
element, in this case an input field, but it could be a div or a select
box.
DWR is asynchronous due to the way Javascript works so it won't halt the web
browser while we are waiting for the background HTTP request to return.
So the parameter loadinfo
names a function to be called when the
call has returned.
On the server, DWR calls the Demo.sayHello()
Java method:
public String sayHello(String name) { return "Hello, " + name; }
When this method returns, DWR calls loadinfo()
function which
moves the text to the reply span:
function loadinfo(data) { dwr.util.setValue("demoReply", data); }
dwr.util.setValue()
is a utility that takes the data you pass in
the second parameter and works out how to fit it to go into the HTML element
specified by id in the first parameter. This function is one of several neat
Javascript utilities that make working with DWR much easier.
We could simplify things by writing the 2 Javascript functions together like this:
function update() { var name = dwr.util.getValue("demoName"); Demo.sayHello(name, function(data) { dwr.util.setValue("demoReply", data); }); }
And that's it. In effect we have written much less than 10 lines of code to get data from the server, and display it in the browser.
<p> Name: <input type="text" id="demoName"/> <input value="Send" type="button" onclick="update()"/> <br/> Reply: <span id="demoReply"></span> </p>
function update() { var name = dwr.util.getValue("demoName"); Demo.sayHello(name, function(data) { dwr.util.setValue("demoReply", data); }); }
package org.getahead.dwrdemo.simpletext; public class Demo { public String sayHello(String name) { return "Hello, " + name; } }
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE dwr PUBLIC "-//GetAhead Limited//DTD Direct Web Remoting 2.0//EN" "http://getahead.org/dwr/dwr20.dtd"> <dwr> <allow> <create creator="new" javascript="Demo"> <param name="class" value="org.getahead.dwrdemo.simpletext.Demo"/> </create> </allow> </dwr>