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TechTip: Automatically Refresh Web Pages

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Most of you have been in airports or train stations and seen the big screens that inform you that a plane or train is boarding, late, or cancelled. This information has to come from somewhere, and it has to be controlled by some kind of timer. This tip will show you a technique to do that sort of thing.

I've seen my share of dull examples showing item masters or customer sales. But everybody has a favorite song, so I'll use "top hits" for my example. You can vote and even learn something useful too!

To give you an overview, here is what you get:

  1. A "top hits" program, which also lets you cast a vote
  2. A setup program from which you can dynamically change the look of the hit list
  3. A way to prompt for colors
  4. Some JavaScript knowledge you might not be aware of

So the tone is set. Let's roll.

How to Refresh a Web Page

There are two ways (that I am aware of) you can refresh a Web page.
You can use a meta tag, which is placed in the section of the HTML document, or you can use JavaScript.

The meta tag looks like this:



This tells the browser that it should reload the page every 10 seconds by calling program form010.

(Note: In IE 7.0, you can disable the meta refresh, so if you have done that and also disabled JavaScript, this won't work.)

I have always used the meta tag method, but some clever people do things a better way. On GrizzlyWeb.com, I found a very good and useful JavaScript Refresh example that also taught me something about JavaScript that I never knew.

When you use JavaScript in an HTML document, you can write


Press F5 to re-display Pop-up

You can test it here.

To refresh the page, use one of three methods:

  • window.location.href (for JavaScript below 1.1)
  • window.location.replace (for JavaScript 1.1)
  • window.location.reload (for JavaScript 1.2)

Basically, they do the same thing; the difference is in the cache and history controlling. If you want to dig into it, check out the JavaScript Refresh example. Otherwise, just accept what your browser is doing.

Now, you need to control the refreshing, so let's look at how to get some data to refresh. I have created two sample files: WWWHITLIST holds the information about the songs in the "top hits" list, and WWWSETUP holds information about the way the list will look, the number of entries to show, refresh time, and more.

The RPG CGI program FORM010 is pretty straightforward. The flow is like this:

  1. Read input from HTML form/Query string (if any).
  2. Read setup data (I have only one record in WWWSETUP). If no data is found in setup file, a default record is created.
  3. Read HTML skeleton file from the IFS (thanks to Scott Klement for the API wrapper).
  4. Create HTML reply/read hit list data.
  5. Wait for next refresh.

The default hit list looks like this:

http://www.mcpressonline.com/articles/images/2002/autorefreshV4--01190700.jpg

Figure 1: RPG CGI program FORM010 creates the default hit list with a refresh time of 10 seconds. (Click images to enlarge.)

Cast a Vote

For viewers to cast a vote, RPG CGI program FORM010 must be called with a parameter called "votemode" and must be set to Y (in uppercase). When this is done, the refresh is suspended, and the list looks like this:

http://www.mcpressonline.com/articles/images/2002/autorefreshV4--01190701.jpg
Figure 2: The program is ready to accept votes.

Every time someone votes, the list will refresh. If you open another browser and load the list in refresh mode, you will of course see it change every time the refresh time is reached.

Set Up the List

I have created RPG CGI program FORM011 to change the look and feel of the list. When loaded, the program looks like this:

http://www.mcpressonline.com/articles/images/2002/autorefreshV4--01190702.jpg
Figure 3: RPG CGI program FORM011 changes the look and feel of the list.

You can clearly see what you can change, and the program works the same way as any other update program except that the input is coming from an HTML form.

I found the "color prompter" at >free-color-picker.com. In my opinion, it's very clever and also easy to implement. So, for example, if you want to change the background header color, click the button. You'll see the following:

http://www.mcpressonline.com/articles/images/2002/autorefreshV4--01190703.jpg
Figure 4: Prompt for a color.

When you click on a color, the color value will be transferred back to the HTML form and the pop-up will close.

Downloading and Installing

  1. Create a directory in your root directory called /root/mcpressonline by entering the following command: md '/root/mcpressonline/'
  2. Create a dir called autorefresh inside mcpressonline. Enter the following: md '/root/mcpressonline/autorefresh'
    Note: If you place it somewhere else, you must change the following files to reflect your placement: javascript file 302pop.js and variable IFSpath in FORM010 and FORM010.
  3. Download refresh.zip. Unzip and upload everything to '/root/mcpressonline/autorefresh'. It should look like this:

    http://www.mcpressonline.com/articles/images/2002/autorefreshV4--01190704.jpg
  4. Compile >WWWHITLIST, WWWHITLISL, and WWWSETUP or restore save file wwwhitlist.savf to your i5 (saved with TGTRLS(V5R1M0)).
  5. Save copy book for BUFIO_H to your i5.
  6. Download and save the source to FORM010 and FORM011 on your i5.

Before compiling...

  • Change the "your-data-lib" in the RPG sources to where you placed the data files.
  • Change "root-dir" in constant IFSpath to your actual root dir.
  • In FORM010, change "your-server" to your Web server name in variable reloadURL.

When you have installed everything and compiled the RPG programs (compile instructions can be found in the header description), you can test the list.

Load the list: http://your-server-name/cgi-bin/form010

Cast a vote: http://your-server-name/cgi-bin/form010?votemode=Y

Set up the list: http://your-server-name/cgi-bin/form011

When you want to add new songs to the list, enter data into WWWHITLIST using DFU or your favorite database editor.

Happy New Year

Once again, I hope this tip has proved how a little JavaScript, some good old RPG, and a few creative thoughts can help you build applications that serve data in ways you might not have thought of before.

Jan Jorgensen is a programmer at Electrolux Laundry Systems Denmark. He works with RPG, HTML, JavaScript, and Perl. You can reach him at This email address is being protected from spambots. You need JavaScript enabled to view it..

Jan Jorgensen

Jan Jorgensen is one of the owners of www.reeft.dk, which specializes in mobile and i5 solutions. He works with RPG, HTML, JavaScript, Perl, and PHP. You can reach him at This email address is being protected from spambots. You need JavaScript enabled to view it.. 

 

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