Creating Continuous Queries Using Spring Data GemFire

To create continuous queries with the Spring Data GemFire library, you must have the following:

Spring Data GemFire v2.0.1 release
Spring Boot v2.0.0+

To create continuous queries, do the following items:

Specify attributes subscriptionEnabled and readyForEvents for the ClientCacheApplication annotation. Apply this annotation to the Spring Boot client application class:

@ClientCacheApplication(name = "GemFireSpringApplication", readyForEvents = true,
  subscriptionEnabled = true)

The annotation for a durable event queue for continuous queries also sets the durableClientId and keepAlive attributes. For example:

@ClientCacheApplication(name = "GemFireSpringApplication",
  durableClientId = "durable-client-id", keepAlive = true,
  readyForEvents = true, subscriptionEnabled = true)

Annotate the method that handles the events to specify the query. To make the event queue durable across server failures and restarts, include the durable = true attribute in the annotation, as is done in the example:
```
@Component
public class ContinuousQuery {

    @ContinuousQuery(name = "yourQuery",
       query = "SELECT * FROM /yourRegion WHERE someAttribute == true",
       durable = true)
    public void handleChanges(CqEvent event) {
      //PERFORM SOME ACTION
    }
}
```
The class that contains the method with the @ContinuousQuery annotation must have the @Component annotation, such that the continuous query is wired up correctly for the server.

For more information, see the Spring Data GemFire documentation.

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