webMethods Flow Tutorial - No.6 Create a SEQUENCE Operation

Knowledge base
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Duration:  10 minutes

SEQUENCE operations are a means of grouping blocks of code that include processing variations.  SEQUENCE is commonly used to combine processing variations to support graceful error-handling, similar to a try-catch block in Java.  In this tutorial, you will add SEQUENCE steps to the customWriteToLog Flow service. 

Prerequisites #

This tutorial builds on concepts, techniques, and objects covered previously in:

  • 1. Create an IS Package and Folders
  • 2. Create and Run a Flow Service
  • 3. Create Document Types
  • 4. Create a LOOP Operation
  • 5. Create a BRANCH Operation
  • The tutorials above must be completed or you can import the solution: Completed Export of 5. Create a BRANCH Operation.zip using these instructions: Import an IS Package
  • The IS must be started.  Instructions on how to start the IS are found in the Prerequisites part of the 1. Create an IS Package and Folders. 

Step Outline #

You use SEQUENCE to implement a try-catch block by:

  • Wrapping an existing service with SEQUENCE steps
  • Verifying that service writes an error to the server log 

Step 1:  Add SEQUENCE Steps to the Service #

In this step:  You will wrap the OrderRequestToOrderResponse Flow Service with SEQUENCE steps:

To wrap the service with SEQUENCE steps:

  • Open the FLOW_Tutorial.services:OrderRequestToOrderResponse service:

  • Select the SEQUENCE tool to add a SEQUENCE step at the beginning of the service:

  • Use the Shift toolbar button to indent all the steps under the initial SEQUENCE step:

  • Enter the text Try in the SEQUENCE Properties Comments field, and ensure that the Exit on field is set to FAILURE:

  • Add a new SEQUENCE step as a parent of the SEQUENCE(Try) step:

  • Enter Try-Catch in the Properties Comments field, and enter SUCCESS in the Exit on field:

  • Add a third SEQUENCE step directly after the SEQUENCE(Try) step as a child of the SEQUENCE(Try-Catch) step:

  • Enter the text Catch in the Comments field, and enter DONE in the Exit on field:

  • Click and drag the Invoke… in the Insert part of the Palette and drop it on top of the SEQUENCE(Catch) step to add a call to the service pub.flow:getLastError:

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  • Follow the same process to add a call to the service FLOW_Tutorial.services:customWriteToLog (the one you created in the first tutorial) after the call to pub.flow:getLastError:

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Designer displays the calls in the flow service:

Note:  Ensure that the calls are indented correctly so that they are children of the SEQUENCE(Catch) step.

You can now map the inputs for the customWriteToLog service.

To map the inputs:

  • Select the customWriteToLog step, then select the Pipeline tab
  • Expand the lastError document reference in the Pipeline In area, and select the error string variable.
  • Right-click on the string1 node under Service In in the customWriteToLog area, and select Set Value:

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  • Set the value of string1 to:

* Error occurred *

  • Link the lastError/error node to string2:

After you Save the service, you can test it in Designer.

Step 2:  Load Input Data and Run the Service #

In this step:  You will load a different input file and run the service.

You will run the service and input data by loading the following input file:

FLOW_Tutorial_6_Input.xml

To load the input file and run the service:

  • Click the flow editor and select the arrow down part of the Run (
    ) menu from the Designer toolbar and choose to Run As->Run Flow Service

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Designer displays the Input dialog.

  • Select Load…

Designer displays the Open file explorer.

  • Locate and select the file:

FLOW_Tutorial_6_Input.xml

Designer displays the data loaded from the input file.  Notice that the first Order in the input has an invalid non-numeric Quantity.

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  • Select OK to run the service

Designer runs the service and displays the Results view:

The error record shows an exception caused by the input 2z0.  The first order in the input file contains a value of 2z0 for quantity.  The value 2z0 is not a valid number; consequently, the cost calculation operations failed.

You can now verify that the error is written to the server log file.

Step 3: Verify the Error in the Server Log #

In this step:  You will log into the integration server admin user interface to verify that the CustomWriteToLog service wrote the error to the log file. 

To log into the integration server admin web user interface:

The Integration Server displays the Authentication Required dialog:

Use the following values to log into the Integration Server:

Field Value
Username: Administrator
Password: manage

Note:  These values may be stored from previous sessions.  In this case, simply select OK.

Firefox displays the Integration Server Administration main page.

  • Select Logs > Server from the left menu:

The Logs > Server page also displays the error:

Conclusion #

You have now programmed the customWriteToLog service to handle errors and write to the log.  You can use the techniques in this tutorial to program more advanced error-handling functions, such as alerts and corrective action.

To import the solution of this tutorial download Completed Export of 6. Create a SEQUENCE Operation.zip and follow the directions in the Import an IS Package tutorial. 


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