In this getting started chapter we will look a demo to illustrate basic usage of Oracle Coherence when using it with Spring. This demo provides an example of using Coherence Spring’s Cache Abstraction.

The demo application is basically a super-simple event manager. We can create Events and assign People to them using an exposed REST API. The data is saved in an embedded HSQL database. The caching is implemented at the service layer.

When an Event is created, it is not only persisted to the database but also put to the Coherence Cache. Therefore, whenever an Event is retrieved, it will be returned from the Coherence Cache. You can also delete Events, in which case the Event will be evicted from the cache. You can perform the same CRUD operations for people as well.

1. How to Run the Demo

In order to get started, please checkout the code from the coherence-community/coherence-spring[Coherence Spring Repository] GitHub repository.

Clone GitHub Repository
 $ git clone https://github.com/coherence-community/coherence-spring.git
 $ cd coherence-spring

You now have checked out all the code for Coherence Spring. The relevant demo code for this Quickstart demo is under samples/coherence-spring-demo/.

There you will find 3 Maven sub-modules:

  • coherence-spring-demo-classic

  • coherence-spring-demo-boot

  • coherence-spring-demo-core

The first two Maven modules are essentially variations of the same app. The third module contains shared code.

coherence-spring-demo-classic

Provides a demo using Spring Framework without Spring Boot

coherence-spring-demo-boot

Provides a demo using Spring Boot

coherence-spring-demo-core

Contains common code shared between the two apps

In this chapter we will focus on the Spring Boot version. Since we checked out the project, let’s build it using Maven:

Build the project
 $ ./mvnw clean package -pl samples/coherence-spring-demo/coherence-spring-demo-boot

Now we are ready to run the application:

Run the Spring Boot application
 $ java -jar samples/coherence-spring-demo/coherence-spring-demo-boot/target/coherence-spring-demo-boot-4.0.0-SNAPSHOT.jar

2. Interacting with the Cache

Once the application is started, the embedded database is empty. Let’s create an event with 2 people added to them using curl:

Create the first event
 curl --request POST 'http://localhost:8080/api/events?title=First%20Event&date=2020-11-30'

This call will create and persist an Event to the database. However, there is more going on. The created Event is also added to the Coherence Cache. The magic is happening in the Service layer, specifically in DefaultEventService#createAndStoreEvent(), which is annotated with @CachePut(cacheNames="events", key="#result.id").

The cacheNames attribute of the @CachePut annotation indicates the name of the underlying cache to use. As caches are basically just a Map, we also need a key. In this case we use the expression #result.id to retrieve the primary key of the Event as it was persisted. Thus, the saved Event is added to the cache named events and ultimately also returned and printed to the console:

Return result of the created event
 {
   "id" : 1,
   "title" : "First Event",
   "date" : "2020-11-30T00:00:00.000+00:00"
 }

We see that an Event with the id 1 was successfully created. Let’s verify that the cache put worked by inspecting the cache using the open-source tool VisualVM.

VisuamVM
Figure 1. VisualVM - Cache Put

Under the MBeans tab you will find the Cache MBeans, including and entry for the events cache, providing numerous statistical information regarding the cache.

Retrieving Cache Statistics
 $ curl --request GET 'http://localhost:8080/api/statistics/events'

You should see an entry for TotalPuts of 1.

When using VisualVM consider installing the respective Coherence VisualVM Plugin as it provides some additional insights and visualizations.

Next, lets retrieve the Event using id 1:

Retrieve Event
 curl --request GET 'http://localhost:8080/api/events/1'

The Event is returned. Did you notice? No SQL queries were executed as the value was directly retrieved from the Cache. Let’s check the statistics again, this time via the Coherence VisualVM Plugin:

VisuamVM Get Value From Cache
Figure 2. Cache Statistics via Coherence VisualVM Plugin

We will see now how values are being returned from the cache by seeing increasing cacheHits, e.g., "cacheHits" : 1. Let’s evict our Event with id 1 from the cache named events:

Evict Event
 curl --request DELETE 'http://localhost:8080/api/events/1'

If you now retrieve the event again using:

Retrieve Event
 curl --request GET 'http://localhost:8080/api/events/1'

you will see an SQL query executed in the console, re-populating the cache. Feel free to play along with the Rest API. We can, for example, add people:

Add people
 curl --request POST 'http://localhost:8080/api/people?firstName=Conrad&lastName=Zuse&age=85'
 curl --request POST 'http://localhost:8080/api/people?firstName=Alan&lastName=Turing&age=41'
List people
 curl --request GET 'http://localhost:8080/api/people'

Or assign people to events:

Assign People to Events
 curl --request POST 'http://localhost:8080/api/people/2/add-to-event/1'
 curl --request POST 'http://localhost:8080/api/people/3/add-to-event/1'

3. Behind the Scenes

What is involved to make this all work? Using Spring Boot, the setup is incredibly simple. We take advantage of Spring Boot’s AutoConfiguration capabilities, and the sensible defaults provided by Coherence Spring.

In order to activate AutoConfiguration for Coherence Spring you need to add the coherence-spring-boot-starter dependency as well as the desired dependency for Coherence.

POM configuration
 <dependency>
     <groupId>com.oracle.coherence.spring</groupId>
     <artifactId>coherence-spring-boot-starter</artifactId> (1)
     <version>4.0.0-SNAPSHOT</version>
 </dependency>
 <dependency>
     <groupId>com.oracle.coherence.ce</groupId>
     <artifactId>coherence</artifactId>                     (2)
     <version>22.09</version>
 </dependency>
1 Activate Autoconfiguration by adding the coherence-spring-boot-starter dependency
2 Add the desired version of Coherence (CE or Commercial)

In this quickstart example we are using Spring’s Caching abstraction and therefore, we use the spring-boot-starter-cache dependency as well:

POM configuration for Spring Cache Abstraction
 <dependency>
     <groupId>org.springframework.boot</groupId>
     <artifactId>spring-boot-starter-cache</artifactId>
 </dependency>

For caching you also must activate caching using the @EnableCaching annotation.

Spring Boot App configuration
 @SpringBootApplication
 @EnableCaching                                             (1)
 public class CoherenceSpringBootDemoApplication {

     public static void main(String[] args) {
         SpringApplication.run(CoherenceSpringBootDemoApplication.class, args);
     }

 }
1 Activate the Spring Cache Abstraction

Please see the relevant chapter on Caching in the Spring Boot reference guide.

With @EnableCaching in place, Coherence’s autoconfiguration will also provide a CoherenceCacheManager bean to the application context.