COBOL Servlet Programming with AJAX and JSON

JSON or JavaScript Object Notation, is an open standard format that uses text easy to understand to transmit data objects consisting of attribute-value pairs. It is used primarily to transmit data between a server and web application, as an alternative to XML.

Although originally derived from the JavaScript scripting language, JSON is an independent data format, and code for parsing and generating JSON data is readily available in a large variety of programming languages.

Here we will show how to develop a simple web application of data file management that uses JSON stream to communicate data from COBOL servlet to HTML pages.

The following example is located in sample/eis/http/json folder. The README.txt file explains how it works and how to deploy it.

This example needs to take the following steps:

•	Having a HTML file that is able to establish a AJAX communication using JSON stream to a COBOL servlet program:

In awebx.htm 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 JSON data stream:

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

•	Load all COBOL Servlet entry points using the following statement:

callServer("AWEBX"); // program initialization

Note the once AWEBX COBOL Servlet is loaded the INIT paragraph is executed:

INIT.            set declaratives-off to true.            move low-values to r-awebx-email.            open i-o awebxfile.            set declaratives-on to true.            if file-status > "0z" and file-status not = "41"               open output awebxfile               close awebxfile               open i-o awebxfile.            comm-area:>displayJSON (ok-page).            goback.

associates to every HTML button a AWEBX entry point to be executed when the button is clicked :

<input type="submit" value="Insert" onclick="return callServer('AWEBX_INSERT');"> <input type="submit" value="Search" onclick="return callServer('AWEBX_SEARCH');"> <input type="submit" value="Next"   onclick="return callServer('AWEBX_NEXT');"> <input type="submit" value="Update" onclick="return callServer('AWEBX_UPDATE');"> <input type="submit" value="Delete" onclick="return callServer('AWEBX_DELETE');">

Note that the above HTML is able to call the following COBOL servlet entry-point:

INSERT-VALUES.             entry "AWEBX_INSERT" using comm-area.             ...             goback.           SEARCH-VALUES.             entry "AWEBX_SEARCH" using comm-area.             ...             goback.           NEXT-VALUES.             entry "AWEBX_NEXT" using comm-area.             ...             goback.           UPDATE-VALUES.             entry "AWEBX_UPDATE" using comm-area.             ...             goback.

•	Define in HTML some fields to input data suitable for data management like name, surname, email, country etc:

<input type="text" name="name" size="25" placeholder="Name"/><br/>       <input type="text" name="surname" size="25" placeholder="Surname"/><br/>       <input type="text" name="email" size="25" placeholder="E-mail"/><br/>       <select name="country"  placeholder="Country">        <option value="" selected="selected" disabled="disabled">Country</option>         <option value="us">US</option>         <option value="it">Italy</option>         <option value="fi">Finland</option>         <option value="nl">The Netherlands</option>         <option value="de">Germany</option>         <option value="fr">France</option>         <option value="sp">Spain</option>         <option value="uk">United Kingdom</option>       </select><br/>

•	On COBOL Servlet create a working storage structure that matches the field name of previous HTML. It can be done with identified by clause:

01 comm-buffer identified by "_comm_buffer".           03  filler identified by "_status".               05 response-status pic x(2).           03  filler identified by "_message".               05 response-message pic x any length.           03  filler identified by "name".               05  json-name pic x any length.           03  filler identified by "surname".               05  json-surname pic x any length.           03  filler identified by "email".               05  json-email pic x any length.           03  filler identified by "country".               05  json-country pic x any length.

•	On COBOL Servlet manage GET request by accept() answering with a JSON stream by displayJSON(). For example if "insert" is submitted the following entry point is invoked:

INSERT-VALUES.            entry "AWEBX_INSERT" using comm-area.            comm-area:>accept(comm-buffer).            move spaces to error-status.            perform check-values.            if error-status = spaces               move json-name    to r-awebx-name               move json-surname to r-awebx-surname               move json-email   to r-awebx-email               move json-country to r-awebx-country               write rec-awebxfile               move "Operation successful" to ok-message;;               comm-area:>displayJSON (ok-page)            else               comm-area:>displayJSON (error-page).            goback.

•	In a similar way when a "next" command is submitted, the records are retuning back as JSON stream with displayJSON() command:

NEXT-VALUES.            entry "AWEBX_NEXT" using comm-area.            read awebxfile next            move r-awebx-name    to json-name            move r-awebx-surname to json-surname            move r-awebx-email   to json-email            move r-awebx-country to json-country            move "OK" to response-status            move "" to response-message;;            comm-area:>displayJSON (comm-buffer).            goback.

This is the output form of awebx.htm used in previous example: