19. Pivotal GemFire and Apache Geode Support

Spring Integration provides support for Pivotal GemFire and Apache Geode.

You need to include this dependency into your project:

Maven. 

<dependency>
    <groupId>org.springframework.integration</groupId>
    <artifactId>spring-integration-gemfire</artifactId>
    <version>5.1.3.BUILD-SNAPSHOT</version>
</dependency>

Gradle. 

compile "org.springframework.integration:spring-integration-gemfire:5.1.3.BUILD-SNAPSHOT"

GemFire is a distributed data management platform that provides a key-value data grid along with advanced distributed system features, such as event processing, continuous querying, and remote function execution. This guide assumes some familiarity with the commercial Pivotal GemFire or Open Source Apache Geode.

Spring integration provides support for GemFire by implementing inbound adapters for entry and continuous query events, an outbound adapter to write entries to the cache, and message and metadata stores and GemfireLockRegistry implementations. Spring integration leverages the Spring Data for Pivotal GemFire project, providing a thin wrapper over its components.

Starting with version 5.1, the Spring Integration GemFire module uses the Spring Data for Apache Geode transitive dependency by default. To switch to the commercial Pivotal GemFire-based Spring Data for Pivotal GemFire, exclude spring-data-geode from dependencies and add spring-data-gemfire, as the following Maven snippet shows:

<dependency>
    <groupId>org.springframework.integration</groupId>
    <artifactId>spring-integration-gemfire</artifactId>
    <exclusions>
        <exclusion>
            <groupId>org.springframework.data</groupId>
            <artifactId>spring-data-geode</artifactId>
        </exclusion>
    </exclusions>
</dependency>

<dependency>
    <groupId>org.springframework.data</groupId>
    <artifactId>spring-data-gemfire</artifactId>
</dependency>

To configure the int-gfe namespace, include the following elements within the headers of your XML configuration file:

xmlns:int-gfe="http://www.springframework.org/schema/integration/gemfire"
xsi:schemaLocation="http://www.springframework.org/schema/integration/gemfire
	http://www.springframework.org/schema/integration/gemfire/spring-integration-gemfire.xsd"

19.1 Inbound Channel Adapter

The inbound channel adapter produces messages on a channel when triggered by a GemFire EntryEvent. GemFire generates events whenever an entry is CREATED, UPDATED, DESTROYED, or INVALIDATED in the associated region. The inbound channel adapter lets you filter on a subset of these events. For example, you may want to produce messages only in response to an entry being created. In addition, the inbound channel adapter can evaluate a SpEL expression if, for example, you want your message payload to contain an event property such as the new entry value. The following example shows how to configure an inbound channel adapter with a SpEL language (in the expression attribute):

<gfe:cache/>
<gfe:replicated-region id="region"/>
<int-gfe:inbound-channel-adapter id="inputChannel" region="region"
    cache-events="CREATED" expression="newValue"/>

The preceding configuration creates a GemFire Cache and Region by using Spring GemFire’s gfe namespace. The inbound-channel-adapter element requires a reference to the GemFire region on which the adapter listens for events. Optional attributes include cache-events, which can contain a comma-separated list of event types for which a message is produced on the input channel. By default, CREATED and UPDATED are enabled. If no channel attribute is provided, the channel is created from the id attribute. This adapter also supports an error-channel. The GemFire EntryEvent is the #root object of the expression evaluation. The following example shows an expression that replaces a value for a key:

expression="new something.MyEvent(key, oldValue, newValue)"

If the expression attribute is not provided, the message payload is the GemFire EntryEvent itself.

[Note]Note

This adapter conforms to Spring Integration conventions.

19.2 Continuous Query Inbound Channel Adapter

The continuous query inbound channel adapter produces messages on a channel when triggered by a GemFire continuous query or CqEvent event. In release 1.1, Spring Data introduced continuous query support, including ContinuousQueryListenerContainer, which provides a nice abstraction over the GemFire native API. This adapter requires a reference to a ContinuousQueryListenerContainer instance, creates a listener for a given query, and executes the query. The continuous query acts as an event source that fires whenever its result set changes state.

[Note]Note

GemFire queries are written in OQL and are scoped to the entire cache (not just one region). Additionally, continuous queries require a remote (that is, running in a separate process or remote host) cache server. See the GemFire documentation for more information on implementing continuous queries.

The following configuration creates a GemFire client cache (recall that a remote cache server is required for this implementation and its address is configured as a child element of the pool), a client region, and a ContinuousQueryListenerContainer that uses Spring Data:

<gfe:client-cache id="client-cache" pool-name="client-pool"/>

<gfe:pool id="client-pool" subscription-enabled="true" >
    <!--configure server or locator here required to address the cache server -->
</gfe:pool>

<gfe:client-region id="test" cache-ref="client-cache" pool-name="client-pool"/>

<gfe:cq-listener-container id="queryListenerContainer" cache="client-cache"
    pool-name="client-pool"/>

<int-gfe:cq-inbound-channel-adapter id="inputChannel"
    cq-listener-container="queryListenerContainer"
    query="select * from /test"/>

The continuous query inbound channel adapter requires a cq-listener-container attribute, which must contain a reference to the ContinuousQueryListenerContainer. Optionally, it accepts an expression attribute that uses SpEL to transform the CqEvent or extract an individual property as needed. The cq-inbound-channel-adapter provides a query-events attribute that contains a comma-separated list of event types for which a message is produced on the input channel. The available event types are CREATED, UPDATED, DESTROYED, REGION_DESTROYED, and REGION_INVALIDATED. By default, CREATED and UPDATED are enabled. Additional optional attributes include query-name (which provides an optional query name), expression (which works as described in the preceding section), and durable (a boolean value indicating if the query is durable — it is false by default). If you do not provide a channel, the channel is created from the id attribute. This adapter also supports an error-channel.

[Note]Note

This adapter conforms to Spring Integration conventions.

19.3 Outbound Channel Adapter

The outbound channel adapter writes cache entries that are mapped from the message payload. In its simplest form, it expects a payload of type java.util.Map and puts the map entries into its configured region. The following example shows how to configure an outbound channel adapter:

<int-gfe:outbound-channel-adapter id="cacheChannel" region="region"/>

Given the preceding configuration, an exception is thrown if the payload is not a Map. Additionally, you can configure the outbound channel adapter to create a map of cache entries by using SpEL. The following example shows how to do so:

<int-gfe:outbound-channel-adapter id="cacheChannel" region="region">
    <int-gfe:cache-entries>
        <entry key="payload.toUpperCase()" value="payload.toLowerCase()"/>
        <entry key="'thing1'" value="'thing2'"/>
    </int-gfe:cache-entries>
</int-gfe:outbound-channel-adapter>

In the preceding configuration, the inner element (cache-entries) is semantically equivalent to a Spring map element. The adapter interprets the key and value attributes as SpEL expressions with the message as the evaluation context. Note that this can contain arbitrary cache entries (not only those derived from the message) and that literal values must be enclosed in single quotes. In the preceding example, if the message sent to cacheChannel has a String payload with a value Hello, two entries ([HELLO:hello, thing1:thing2]) are written (either created or updated) in the cache region. This adapter also supports the order attribute, which may be useful if it is bound to a PublishSubscribeChannel.

19.4 Gemfire Message Store

As described in EIP, a message store lets you persist messages. This can be useful when dealing with components that have a capability to buffer messages (QueueChannel, Aggregator, Resequencer, and others) if reliability is a concern. In Spring Integration, the MessageStore strategy interface also provides the foundation for the claim check pattern, which is described in EIP as well.

Spring Integration’s Gemfire module provides GemfireMessageStore, which is an implementation of both the the MessageStore strategy (mainly used by the QueueChannel and ClaimCheck patterns) and the MessageGroupStore strategy (mainly used by the Aggregator and Resequencer patterns).

The following example configures the cache and region by using the spring-gemfire namespace (not to be confused with the spring-integration-gemfire namespace):

<bean id="gemfireMessageStore" class="o.s.i.gemfire.store.GemfireMessageStore">
    <constructor-arg ref="myRegion"/>
</bean>

<gfe:cache/>

<gfe:replicated-region id="myRegion"/>


<int:channel id="somePersistentQueueChannel">
    <int:queue message-store="gemfireMessageStore"/>
<int:channel>

<int:aggregator input-channel="inputChannel" output-channel="outputChannel"
    message-store="gemfireMessageStore"/>

Often, it is desirable for the message store to be maintained in one or more remote cache servers in a client-server configuration. In this case, you should configure a client cache, a client region, and a client pool and inject the region into the MessageStore. The following example shows how to do so:

<bean id="gemfireMessageStore"
    class="org.springframework.integration.gemfire.store.GemfireMessageStore">
    <constructor-arg ref="myRegion"/>
</bean>

<gfe:client-cache/>

<gfe:client-region id="myRegion" shortcut="PROXY" pool-name="messageStorePool"/>

<gfe:pool id="messageStorePool">
    <gfe:server host="localhost" port="40404" />
</gfe:pool>

Note that the pool element is configured with the address of a cache server (you can substitute a locator here). The region is configured as a PROXY so that no data is stored locally. The region’s id corresponds to a region with the same name in the cache server.

Starting with version 4.3.12, the GemfireMessageStore supports the key prefix option to allow distinguishing between instances of the store on the same GemFire region.

19.5 Gemfire Lock Registry

Starting with version 4.0, the GemfireLockRegistry is available. Certain components (for example, the aggregator and the resequencer) use a lock obtained from a LockRegistry instance to ensure that only one thread is manipulating a group at any given time. The DefaultLockRegistry performs this function within a single component. You can now configure an external lock registry on these components. When you use a shared MessageGroupStore with the GemfireLockRegistry, it can provide this functionality across multiple application instances, such that only one instance can manipulate the group at a time.

[Note]Note

One of the GemfireLockRegistry constructors requires a Region as an argument. It is used to obtain a Lock from the getDistributedLock() method. This operation requires GLOBAL scope for the Region. Another constructor requires a Cache, and the Region is created with GLOBAL scope and with the name, LockRegistry.

19.6 Gemfire Metadata Store

Version 4.0 introduced a new Gemfire-based MetadataStore (Section 12.5, “Metadata Store”) implementation. You can use the GemfireMetadataStore to maintain metadata state across application restarts. This new MetadataStore implementation can be used with adapters such as:

To get these adapters to use the new GemfireMetadataStore, declare a Spring bean with a bean name of metadataStore. The feed inbound channel adapter automatically picks up and use the declared GemfireMetadataStore.

[Note]Note

The GemfireMetadataStore also implements ConcurrentMetadataStore, letting it be reliably shared across multiple application instances, where only one instance can store or modify a key’s value. These methods give various levels of concurrency guarantees based on the scope and data policy of the region. They are implemented in the peer cache and client-server cache but are disallowed in peer regions that have NORMAL or EMPTY data policies.

[Note]Note

Since version 5.0, the GemfireMetadataStore also implements ListenableMetadataStore, which lets you listen to cache events by providing MetadataStoreListener instances to the store, as the following example shows:

GemfireMetadataStore metadataStore = new GemfireMetadataStore(cache);
metadataStore.addListener(new MetadataStoreListenerAdapter() {

    @Override
    public void onAdd(String key, String value) {
         ...
    }

});