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VMware GemFire Supplier

This module provides a java.util.function.Supplier that can be reused and composed in other applications. The Supplier configures an VMware GemFire client that connects to an external VMware GemFire cache server or locator to monitor an existing region. If gemfire.supplier.query is provided, the supplier will create a continuous query on the region and publish any events that meet the select criteria. If no query is provided, the supplier will publish all create and update events on the region.

Continuous Query

If a query is provided, the supplier uses the ContinuousQueryMessageProducer from Spring Integration which wraps a ContinuousQueryListenerContainer and emits a reactive stream of objects, extracted from a VMware GemFire CqEvent, which holds all of the event details. A SpEl Expression, given by the property gemfire.cq.supplier.event-expression is used to extract desired fields from the CQEvent payload. The default expression is newValue which returns the current value from the configured Region.

Cache Listener

If no query is provided, the supplier uses the CacheListeningMessageProducer from Spring Integration which wraps a CacheListener and emits a reactive stream of objects, extracted from a VMware GemFire EntryEvent, which holds all of the event details. A SpEl Expression, given by the property gemfire.supplier.entry-event-expression is used to extract desired fields from the EntryEvent payload. The default expression is newValue which returns the current value from the configured Region.

NOTE: Retrieving the value by itself is not always sufficient, especially if it does not contain the key value, or any additional context. The key is referenced by the field key. If the cached key and value types are primitives, a simple expression like key + ':' +newValue may be useful. To access the entire EntryEvent, set the expression to #root or #this.

The configured MessageProducer emits objects to the supplier implemented as Supplier<Flux<?>>. Users have to subscribe to the returned Flux to receive the data.

PDX Serialization

The supplier works with PDX serialized cache objects of type PdxInstance, which VMware GemFire uses to store objects that can be represented as JSON. If the target region uses PDX serialization and you set gemfire.client.pdx-read-serialized to true, PdxInstance objects will be returned as JSON strings.

Beans for injection

You can import the GemFireSupplierConfiguration configuration in a Spring Boot application and then inject the gemfireSupplier bean as type Supplier<Flux<T>>, where T is the expected return type. If necessary, can use the bean name gemfireSupplier as a qualifier.

Once injected, you can invoke the get method of the Supplier and then subscribe to the returned Flux to initiate the stream.

Configuration Options

Required properties:

  • gemfire.region.region-name - The name of the existing remote region.
  • gemfire.pool.host-addresses - A comma delimited list of host:port pairs. By default these are locator addresses but are cache server addresses if you set gemfire.pool.connect-type=server.

For more information on the various options available, please see:

Many of the options, common to functions that use VMware GemFire, are configured by several @ConfigurationProperties classes which are included as needed:

Examples

See this test suite for examples of how this supplier is used.