Creating Dispatcher Applications Using Pie Charts

This sample illustrates how to produce graphics output by using the Application Dispatcher. It requires that you have SAS/GRAPH software licensed and installed.

• The Input Component
• The Program Component

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The Input Component

The HTML page for this sample application provides the most essential information. To keep the program code simple, the only variables that have been used are the _SERVICE, _PROGRAM, and _DEBUG Dispatcher variables. Because none of these values dynamically change the program code, every invocation of this application produces the same graphic. The purpose of this sample is to provide a simple "how to" explanation for creating graphics.

The HTML code for this application is installed with the Dispatcher package in a default location at http://yourserver/sasweb/IntrNet8/dispatch/webgraph.html. The code produces a form that similar to this:

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The Program Component

The following describes the steps performed by a Dispatcher program

1. The first output that must be produced is a valid content-type header. This is true of all Dispatcher programs. Because this program uses a GIF graphics driver, the content type is image/gif.
2. A DATA step is used to write out the header.
3. Graphics options are set.
4. The graphics procedure is invoked with a GIF driver.
5. The output is directed to the special _WEBOUT fileref.

Here is the complete code for this Dispatcher program.

   data _null_;
      file _webout;
      put 'Content-type: image/gif';
      put;
   run;


   goptions gsfname=_webout gsfmode=replace dev=gif733
      ftext=swiss;

   pattern1 value=solid color=yellow;
   pattern2 value=solid color=cyan;
   pattern3 value=solid color=green;
   pattern4 value=solid color=black;
   pattern5 value=solid color=red;
   pattern6 value=solid color=blue;

   proc gchart data=sashelp.retail;
      pie year/sumvar=sales;
      pattern v=s;
   run;
   quit;

The resulting graphic is a pie chart of the sashelp.retail data set. The gsfname option directs the SAS/GRAPH procedure to write the image output to the special fileref and back to the Web browser. Notice the gsfmode=replace option. This is very important. It is tempting to use an append mode here because you have already written to a header in the previous DATA step. Don't use the append mode. A gsfmode of replace must always be used, otherwise the procedure may skip writing out some critical GIF initialization information.

It is impossible to overwrite data already sent to _WEBOUT. Because the Application Dispatcher uses TCP/IP sockets to flow the data from your program to the Web browser, the _WEBOUT fileref is always appending. As with standard output and pipes, _WEBOUT cannot replace what has been previously written.