OCEJWCD .- 11. Asynchronous web applications

OCEJWCD (SCWCD) - 1Z0-899 - Web Component Developer Certification

11.1. Understand the interactions that are essential to asynchronous web pages

In asynchronous processing the web container can continue serving other requests without waiting for a response from a resource (the thread is not blocked).

11.2. Understand the role of AJAX-style client side programming

AJAX Asynchronous JavaScript and XML

Exchanges data with the server, and updates parts of a web page without reloading the whole page.

XMLHttpRequest
var xmlhttp = new XMLHttpRequest();

Send request to a server

- open(method, url, async) - -> the url can be txt xml, asp, php files in the server

- send(), send(string) -- > in post request

xmlhttp.open("GET", "hello.txt", true);
xmlhttp.send();

Get a response from a server

xmlhttp.responseText
xmlhttp.responseXML

onReadyStateChange Event

xmlhttp.onreadystatechange=function()
  {...

-xmlhttp.readyState, when is 4 is OK

-xmlhttp.status, when is 200 is OK

11.3. Implement asynchronous servlets using the facilities of Java EE6

Annotations:
asyncSupported can be used with @WebServlet or @WebFilter
Example:
  @WebServlet(url="/foo" asyncSupported=true)

AsyncContext

Is obtained by the ServletRequest methods
  startAsync(servletRequest, servletResponse) or startAsync()
Example:
AsyncContext aCtx = req.startAsync(req, res);

Methods to dispatch the request back to the container:

AsyncContext.dispatch(), AsyncContext.dispatch(path), or AsyncContext.dispatch(servletContext, path) 
Example:
ctx.dispatch("/render.jsp");

AsynchronousListener

AsyncListener interface defines a Listener that will be notified in the event that an asynchronous operation initiated on a servlet request.
http://docs.oracle.com/javaee/6/api/javax/servlet/AsyncListener.html

Methods:

• onComplete(event)
• onError(event)
• onStartAsync(event)
• onTimeOut(event)

Example:

req.addAsyncListener(new AsyncListener() {...

Asynchronous application example in:

https://blogs.oracle.com/enterprisetechtips/entry/asynchronous_support_in_servlet_3

OCEJWCD (SCWCD) - 1Z0-899 - Web Component Developer Certification