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quickstarts/tutorials/workflow/java/monitor-pattern/README.md

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Monitor Pattern

This tutorial demonstrates how to run a workflow in a loop. This can be used for recurring tasks that need to be executed on a certain frequency (e.g. a clean-up job that runs every hour). For more information on the monitor pattern see the Dapr docs.

Inspect the code

Open the MonitorWorkflow.java file in the tutorials/workflow/java/monitor-pattern/src/main/java/io/dapr/springboot/examples/monitor/ folder. This file contains the definition for the workflow that calls the CheckStatus activity to checks to see if a fictional resource is ready. The CheckStatus activity uses a random number generator to simulate the status of the resource. If the status is not ready, the workflow will wait for one second and is continued as a new instance.

graph LR
   SW((Start
   Workflow))
   CHECK[CheckStatus]
   IF{Is Ready}
   TIMER[Wait for a period of time]
   NEW[Continue as a new instance]
   EW((End
   Workflow))
   SW --> CHECK
   CHECK --> IF
   IF -->|Yes| EW
   IF -->|No| TIMER
   TIMER --> NEW
   NEW --> SW

Run the tutorial

  1. Use a terminal to navigate to the tutorials/workflow/java/monitor-pattern folder.

  2. Build and run the project using Maven.

    mvn spring-boot:test-run

  3. Use the POST request in the monitor.http file to start the workflow, or use this cURL command:

    curl -i --request POST http://localhost:8080/start/0

    The input for the workflow is an integer with the value 0.

    The expected app logs are as follows:

    [monitor-pattern]  io.dapr.springboot.examples.monitor.CheckStatusActivity : Received input: 0
[monitor-pattern]  io.dapr.springboot.examples.monitor.CheckStatusActivity : Received input: 1
[monitor-pattern]  io.dapr.springboot.examples.monitor.CheckStatusActivity : Received input: 2
[monitor-pattern]  io.dapr.springboot.examples.monitor.CheckStatusActivity : Received input: 3
[monitor-pattern]  io.dapr.springboot.examples.monitor.CheckStatusActivity : Received input: 4
[monitor-pattern]  io.dapr.springboot.examples.monitor.CheckStatusActivity : Received input: 5

    Note that the number of app log statements can vary due to the randomization in the CheckStatus activity.

  4. Use the GET request in the monitor.http file to get the status of the workflow, or use this cURL command:

    curl --request GET --url http://localhost:8080/output

    The expected serialized output of the workflow is:

    "\"Status is healthy after checking 5 times.\""

    The actual number of checks can vary since some randomization is used in the CheckStatus activity.

  5. Stop the application by pressing Ctrl+C.