A Spring Boot App

The example Spring Boot Data GemFire app at PCC-Sample-App-PizzaStore uses the GemFire cluster within a PCC service instance as a System of Record. Directions for running the app are in the GitHub repository’s README.md file.

The app uses Spring Boot Data GemFire. The documentation for this opinionated extension of Spring Data GemFire is at Spring Boot for Apache Geode & Pivotal GemFire Reference Guide.

The app saves pizza orders within the GemFire servers of a PCC service instance. The app takes orders for pizza toppings and sauces with a REST interface.

In addition, the app demonstrates two distinct features of PCC:

Running an app on a TLS-enabled cluster within PCC.
GemFire continuous queries as used by a Spring Boot app.

Top Down Explanation

In this opinionated version of Spring Boot Data GemFire, at the topmost level of the app, the @SpringBootApplication annotation causes the app to have a ClientCache instance. Within the example app’s CloudcachePizzaStoreApplication class, the annotation belongs on the class header:

@SpringBootApplication
public class CloudcachePizzaStoreApplication

This app is the client within a standard client/server architecture. The PCC cluster contains the servers. The client cache is a driver for interactions with the servers, allowing eventual region creation within the client cache.

Annotate the configuration with @EnableEntityDefinedRegions to enable a runtime scan of classes that define the GemFire regions. Within GemFireConfiguration.java in this example:

@EnableEntityDefinedRegions(basePackageClasses = Pizza.class)
public class GemFireConfiguration

The Spring repository construct is the correct choice to use for the data storage, which will be a GemFire region. To implement it, annotate this example’s PizzaRepository implementation with @Repository:

@Repository
public interface PizzaRepository extends CrudRepository<Pizza, String>

A GemFire region underlies the Spring repository, storing the ordered pizzas. Annotate the Pizza class model with @Region:

@Region("Pizza")
public class Pizza {

Within the Pizza class, identify the key of the GemFire region entries with the @Id annotation. It is the name field in this example:

@Getter @Id @NonNull
private final String name;

The @SpringBootApplication annotation results in a chain of opinionated defaults, all of which are appropriate for this app. It identifies the app as a client. The client receives a GemFire client cache. Any regions will default to type PROXY. A proxy type of region forwards all region operations to the Gemfire servers; no data is stored within the app’s client cache.

See Configuring Regions for Spring details. See Region Design for PCC details on regions.

The App Contoller

The AppController class implements the REST interface, by annotating the class with @RestController:

@RestController
public class AppController

As pizzas are ordered, a CrudRepository.save() operation causes a GemFire put operation that updates the region on the GemFire server.

TLS-Enabled Cluster Demonstration

The app operates in one of two ways:

Communication with and within the GemFire cluster uses TLS encryption.
Communication with and within the GemFire cluster does not use TLS encryption.

The operation of the running app is unchanged whether TLS encryption is enabled within the Gemfire cluster or not.

Setting up this app with TLS encryption enabled demonstrates one way to set the needed GemFire properties detailed in Developing an App Under TLS. It uses Spring profiles. The manifest that sets the tls profile incorporates the GemFire properties from file /resources/application-tls.properties.

Continuous Queries in the App

The app defines two continuous queries (CQ). See Handling Events for a brief introduction to continuous queries.

The first CQ queries for any (and every) pizza order. Its callback logs the order.

The second CQ queries for pizzas with a PESTO sauce. When a pesto-sauced pizza is ordered, the callback adds that pizza to a second region called Name.

Within a Spring Boot Data GemFire app, to specify a continuous query:

annotate the class that defines the queries with @Component:
```
@Component
public class PizzaQueries
```
annotate the callback method with @ContinuousQuery and define the query, as in the app’s pesto pizza order example:
```
@ContinuousQuery(name = "PestoPizzaOrdersQuery", durable = true,
    query = "SELECT * FROM /Pizza p WHERE p.sauce.name = 'PESTO'")
public void handlePestoPizzaOrder(CqEvent event)
```
The annotation causes an implementation of all three needed items for this type of event handling. It defines the query, registers the query as a continuous query event, and it identifies the callback method to invoke when the event occurs.

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