Gather Operator Sample

About This Guide

The Gather.sbapp sample application has two EventFlow modules. The SimpleGather example uses a Gather operator to generate an alarm (a true value) for trades of 10,000 shares or more for a stock whose price is $200 or greater. The input stream contains the fields Symbol, Volume, and Price.

Note

This is a very simple example which might be better done using a single Map operator, but it is instructive. For an example that truly requires a Gather operator, see the Compliance sample application.

The TimeoutGather example demonstrates the effect of the Optional Timeouts settings. In this case, when no input is received for ten seconds, Gather is forced to emit whatever tuple values it has accumulated, setting any fields not received to null. The input stream has two string fields: Type (which must be enqueued as either Buy or Sell) and Symbol (which can be any string).

Importing This Sample into StreamBase Studio

In StreamBase Studio, import this sample with the following steps:

  • From the top menu, click FileLoad StreamBase Sample.

  • Type operator to narrow the list of options.

  • Select Operator sample group from the Data Constructs and Operators category.

  • Click OK.

StreamBase Studio creates a single project for all the operator samples.

Running Gather.sbapp in StreamBase Studio

  1. In the Project Explorer, open the sample you just loaded.

  2. Open the src/main/eventflow folder.

  3. Open the package folder (most samples contain a single package folder. Open the top-level package folder if your sample contains more than one folder).

  4. Open the Gather.sbapp application and click the Run button. This opens the SB Test/Debug perspective and starts the application.

    If you see red marks, wait a moment for the project in Studio to load its features.

    If red marks do not resolve themselves in a moment, select the project and right-click MavenUpdate Project from the context menu.

  5. In the Application Output view, select the BigTradeAlarm output stream. No output is displayed at this point, but the dequeuer is prepared to receive output. This view will eventually show the output of the application.

  6. In the Manual Input view, select the TradesIn input stream.

  7. Enter intc, 10000, and 201 in the Symbol, Volume, and Price fields, respectively

  8. Click Send Data, and observe this data appears in the BigTradeAlarm stream:

    BigTradeAlarm=true
  9. Enter intc, 10000, and 199 in the Symbol, Volume, and Price fields, respectively

  10. Click Send Data, and observe this data appears in the BigTradeAlarm stream:

    BigTradeAlarm=false
  11. Enter intc, 1000, and 201 in the Symbol, Volume, and Price fields, respectively

  12. Click Send Data, and observe this data appears in the BigTradeAlarm stream:

    BigTradeAlarm=false
  13. Enter intc, 1000, and 187 in the Symbol, Volume, and Price fields, respectively

  14. Click Send Data, and observe this data appears in the BigTradeAlarm stream:

    BigTradeAlarm=false

To run the TimeoutGather example:

  1. In the Project Explorer, open the sample you just loaded.

  2. Open the src/main/eventflow folder.

  3. Open the package folder (most samples contain a single package folder. Open the top-level package folder if your sample contains more than one folder).

  4. Open the Gather.sbapp application and click the Run button. This opens the SB Test/Debug perspective and starts the application.

    If you see red marks, wait a moment for the project in Studio to load its features.

    If red marks do not resolve themselves in a moment, select the project and right-click MavenUpdate Project from the context menu.

  5. In the Application Output view, select the Matches output stream. No output is displayed at this point, but the dequeuer is prepared to receive output. This view will eventually show the output of the application.

  6. In the Manual Input view, select the SimpleBuySellMatch input stream.

  7. Enter Buy and intc in the Type and Symbol fields, respectively, and press Send Data.

  8. Quickly change Type from Buy to Sell and press Send Data again.

  9. Observe this data appear in the Matches stream:

    MatchedSymbol=intc
  10. Now change Type from Sell back to Buy again, and press Send Data.

  11. Do not send a Sell message. After 10 seconds, observe that the Gather operator times out, and writes the following to the Matches output stream:

    MatchedSymbol=<No Match: intc,null>

When done, press F9 or click the Stop Running Application button.

Sample Location

When you load the sample into StreamBase Studio, Studio copies the sample project's files to your Studio workspace, which is normally part of your home directory, with full access rights.

Important

Load this sample in StreamBase Studio, and thereafter use the Studio workspace copy of the sample to run and test it, even when running from the command prompt.

Using the workspace copy of the sample avoids permission problems. The default workspace location for this sample is:

studio-workspace/sample_operator

See Default Installation Directories for the default location of studio-workspace on your system.