COBOL Servlet Programming with AJAX and XML

AJAX ( Asynchronous JavaScript and XML) is a group of interrelated Web development techniques used on the client side to create asynchronous Web Applications. With Ajax, Web applications can send data to, and retrieve data from, a server asynchronously (in the background) without interfering with the display and behavior of the existing page.

Extensible Markup Language (XML) is a text format derived from Standard Generalized Markup Language (SGML). Compared to SGML, XML is simple. HyperText Markup Language (HTML), by comparison, is even simpler. Even so, a good reference book on HTML is an inch thick. This is because the formatting and structuring of documents is a complicated business.

Most of the excitement about XML is related to a new role as an interchangeable data serialization format. XML provides two enormous advantages as a data representation language:

•	It is text-based

•	It is position-independent

The scope of this paragraph is to show how to develop a simple web application that uses XML stream to communicate data from COBOL servlet to a Web form.

The following example called HELLO.cbl, is located in sample/eis/http/xml folder. The README.txt file explains how it works and how to deploy it.

This example needs to take the following steps:

•	Create a HTML file called index.html that is able to establish a AJAX communication to receive a XML stream from COBOL servlet program:

 

In index.html there is included a Javascript code based on JQUERY to be able to call some COBOL servlet entry point making a GET request type (default) and receiving XML data stream:

function callServer (cobolProg) {       var url = "servlet/isCobol(" + cobolProg + ")";       jQuery.ajax(url, {                     success: handleSuccess,                     error: handleError                   });       return false;    }

•	Load all COBOL Servlets using the following statement:

window.onload = callServer('HELLO');

Note the when HELLO COBOL Servlet is loaded the following code executed:

move "Hello World from isCOBOL!" to xml-hellotext.       lnk-area:>displayXML (hello-buffer).

And XML stream is returned to Web form with displayXML() command.

Running this example the result is the following: