Table of Contents

Micronaut Cache

Learn how to use Micronaut’s caching annotations

Authors: Sergio del Amo

Micronaut Version: 2.5.0

1. Getting Started

In this guide, you are going to use Micronaut’s caching annotations to speed up your application.

2. What you will need

To complete this guide, you will need the following:

  • Some time on your hands

  • A decent text editor or IDE

  • JDK 1.8 or greater installed with JAVA_HOME configured appropriately

3. Solution

We recommend that you follow the instructions in the next sections and create the app step by step. However, you can go right to the completed example.

4. Writing the App

Create an app using the Micronaut Command Line Interface or with Micronaut Launch.

mn create-app example.micronaut.micronautguide --build=maven --lang=java
If you don’t specify the --build argument, Gradle is used as a build tool.
If you don’t specify the --lang argument, Java is used as a language.

The previous command creates a Micronaut app with the default package example.micronaut in a folder named micronautguide.

If you are using Java or Kotlin and IntelliJ IDEA, make sure you have enabled annotation processing.

annotationprocessorsintellij

4.1. Configure the Application

In this sample application, we cache news headlines. Add Micronaut Caffeine Cache dependency which adds support for cache using Caffeine.

pom.xml
<dependency>
    <groupId>io.micronaut.cache</groupId>
    <artifactId>micronaut-cache-caffeine</artifactId>
    <scope>compile</scope>
</dependency>

Configure your caches in application.yml:

src/main/resources/application.yml
micronaut:
  caches:
    headlines: (1)
      charset: 'UTF-8'
1 Configure a cache called headlines.
Check the properties (maximum-size, expire-after-write and expire-after-access) to configure the size and expiration of your caches. It is important to keep the caches' size under control.

4.2. Micronaut Cache Api

Imagine a service which retrieves headlines for a given month. This operation may be expensive and you may want to cache it.

src/main/java/example/micronaut/NewsService.java
package example.micronaut;

import io.micronaut.cache.annotation.CacheConfig;
import io.micronaut.cache.annotation.CacheInvalidate;
import io.micronaut.cache.annotation.CachePut;
import io.micronaut.cache.annotation.Cacheable;

import javax.inject.Singleton;
import java.time.Month;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.TimeUnit;

@Singleton (1)
@CacheConfig("headlines") (2)
public class NewsService {

    Map<Month, List<String>> headlines = new HashMap<Month, List<String>>() {{
        put(Month.NOVEMBER, Arrays.asList("Micronaut Graduates to Trial Level in Thoughtworks technology radar Vol.1",
                "Micronaut AOP: Awesome flexibility without the complexity"));
        put(Month.OCTOBER, Collections.singletonList("Micronaut AOP: Awesome flexibility without the complexity"));
    }};

    @Cacheable (3)
    public List<String> headlines(Month month) {
        try {
            TimeUnit.SECONDS.sleep(3); (4)
            return headlines.get(month);
        } catch (InterruptedException e) {
            return null;
        }
    }

    @CachePut(parameters = {"month"}) (5)
    public List<String> addHeadline(Month month, String headline) {
        if (headlines.containsKey(month)) {
            List<String> l = new ArrayList<>(headlines.get(month));
            l.add(headline);
            headlines.put(month, l);
        } else {
            headlines.put(month, Arrays.asList(headline));
        }
        return headlines.get(month);
    }

    @CacheInvalidate(parameters = {"month"}) (6)
    public void removeHeadline(Month month, String headline) {
        if (headlines.containsKey(month)) {
            List<String> l = new ArrayList<>(headlines.get(month));
            l.remove(headline);
            headlines.put(month, l);
        }
    }
}
1 To register a Singleton in Micronaut’s application context annotate your class with javax.inject.Singleton.
2 Specifies the cache name headlines to store cache operation values in.
3 Indicates a method is cacheable. The cache name headlines specified in @CacheConfig is used. Since the method has only one parameter, you don’t need to specify the month parameters attribute of the the annation.
4 Emulate an expensive operation by sleeping for several seconds.
5 The return value is cached with name headlines for the supplied month. The method invocation is never skipped even if the cache headlines for the supplied month already existed.
6 Method invocation causes the invalidation of the cache headlines for the supplied month.
If you don’t annotate the class with @CacheConfig, specify the cache name in the cache annotations. E.g. @Cacheable(value = "headlines", parameters = {"month"})

4.3. Test the Cache

We can verify that the cache works as expected:

src/test/java/example/micronaut/NewsServiceTest.java
package example.micronaut;

import io.micronaut.test.extensions.junit5.annotation.MicronautTest;
import org.junit.jupiter.api.MethodOrderer;
import org.junit.jupiter.api.Order;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.TestMethodOrder;
import org.junit.jupiter.api.Timeout;

import javax.inject.Inject;
import java.time.Month;
import java.util.List;

import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
import static org.junit.jupiter.api.Assertions.assertEquals;

@TestMethodOrder(MethodOrderer.OrderAnnotation.class) (1)
@MicronautTest (2)
class NewsServiceTest {

    @Inject (3)
    NewsService newsService;

    @Timeout(4) (4)
    @Test
    @Order(1) (5)
    public void firstInvocationOfNovemberDoesNotHitCache() {
        List<String> headlines = newsService.headlines(Month.NOVEMBER);
        assertEquals(2, headlines.size());
    }

    @Timeout(1) (4)
    @Test
    @Order(2) (5)
    public void secondInvocationOfNovemberHitsCache() {
        List<String> headlines = newsService.headlines(Month.NOVEMBER);
        assertEquals(2, headlines.size());
    }

    @Timeout(4) (4)
    @Test
    @Order(3) (5)
    public void firstInvocationOfOctoberDoesNotHitCache() {
        List<String> headlines = newsService.headlines(Month.OCTOBER);
        assertEquals(1, headlines.size());
    }

    @Timeout(1) (4)
    @Test
    @Order(4) (5)
    public void secondInvocationOfOctoberHitsCache() {
        List<String> headlines = newsService.headlines(Month.OCTOBER);
        assertEquals(1, headlines.size());
    }

    @Timeout(1) (4)
    @Test
    @Order(5) (5)
    public void addingAHeadlineToNovemberUpdatesCache() {
        List<String> headlines = newsService.addHeadline(Month.NOVEMBER, "Micronaut 1.3 Milestone 1 Released");
        assertEquals(3, headlines.size());
    }

    @Timeout(1) (4)
    @Test
    @Order(6) (5)
    public void novemberCacheWasUpdatedByCachePutAndThusTheValueIsRetrievedFromTheCache() {
        List<String> headlines = newsService.headlines(Month.NOVEMBER);
        assertEquals(3, headlines.size());
    }

    @Timeout(1) (4)
    @Test
    @Order(7) (5)
    public void invalidateNovemberCacheWithCacheInvalidate() {
        assertDoesNotThrow(() -> {
            newsService.removeHeadline(Month.NOVEMBER, "Micronaut 1.3 Milestone 1 Released");
        });
    }

    @Timeout(1) (4)
    @Test
    @Order(8) (5)
    public void octoberCacheIsStillValid() {
        List<String> headlines = newsService.headlines(Month.OCTOBER);
        assertEquals(1, headlines.size());
    }

    @Timeout(4) (4)
    @Test
    @Order(9) (5)
    public void novemberCacheWasInvalidated() {
        List<String> headlines = newsService.headlines(Month.NOVEMBER);
        assertEquals(2, headlines.size());
    }
}
1 Used to configure the test method execution order for the annotated test class.
2 Annotation used to define a Micronaut test
3 Inject NewsService bean.
4 Timeout annotation fails a test if its execution exceeds a given duration. It helps us verify that we are leaveraging the cache.
5 Used to configure the order in which the test method should executed relative to other tests in the class.

4.4. Controller

Create a controller which engages the previous service:

src/main/java/example/micronaut/News.java
package example.micronaut;

import io.micronaut.core.annotation.Introspected;

import java.time.Month;
import java.util.List;

@Introspected
public class News {
    private Month month;

    private List<String> headlines;

    public News() {

    }

    public News(Month month, List<String> headlines) {
        this.month = month;
        this.headlines = headlines;
    }

    public Month getMonth() {
        return month;
    }

    public void setMonth(Month month) {
        this.month = month;
    }

    public List<String> getHeadlines() {
        return headlines;
    }

    public void setHeadlines(List<String> headlines) {
        this.headlines = headlines;
    }
}
src/main/java/example/micronaut/NewsController.java
package example.micronaut;

import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;

import java.time.Month;

@Controller
public class NewsController {

    private final NewsService newsService;

    public NewsController(NewsService newsService) {
        this.newsService = newsService;
    }

    @Get("/{month}")
    public News index(Month month) {
        return new News(month, newsService.headlines(month));
    }
}

Add a test:

src/test/java/example/micronaut/NewsControllerTest.java
package example.micronaut;

import io.micronaut.http.HttpRequest;
import io.micronaut.http.client.HttpClient;
import io.micronaut.http.client.annotation.Client;
import io.micronaut.http.uri.UriBuilder;
import io.micronaut.runtime.server.EmbeddedServer;
import io.micronaut.test.extensions.junit5.annotation.MicronautTest;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.Timeout;

import javax.inject.Inject;
import java.time.Month;
import java.util.Arrays;

import static org.junit.jupiter.api.Assertions.assertEquals;

@MicronautTest
public class NewsControllerTest {

    @Inject
    EmbeddedServer server;

    @Inject
    @Client("/")
    HttpClient client;

    @Timeout(4) (1)
    @Test
    void fetchingOctoberHeadlinesUsesCache() {
        HttpRequest request = HttpRequest.GET(UriBuilder.of("/").path(Month.OCTOBER.name()).build());
        News news = client.toBlocking().retrieve(request, News.class);
        String expected = "Micronaut AOP: Awesome flexibility without the complexity";
        assertEquals(Arrays.asList(expected), news.getHeadlines());

        news = client.toBlocking().retrieve(request, News.class);
        assertEquals(Arrays.asList(expected), news.getHeadlines());
    }
}
1 We call the endpoint twice and verify with the @Timeout annotation that the cache is being used.

5. Running the Application

To run the application use the ./mvnw mn:run command which will start the application on port 8080.

6. Generate a Micronaut app’s Native Image with GraalVM

We are going to use GraalVM, the polyglot embeddable virtual machine, to generate a Native image of our Micronaut application.

Native images compiled with GraalVM ahead-of-time improve the startup time and reduce the memory footprint of JVM-based applications.

Use of GraalVM’s native-image tool is only supported in Java or Kotlin projects. Groovy relies heavily on reflection which is only partially supported by GraalVM.

6.1. Native Image generation

The easiest way to install GraalVM is to use SDKMan.io.

# For Java 8
$ sdk install java 21.1.0.r8-grl

# For Java 11
$ sdk install java 21.1.0.r11-grl

You need to install the native-image component which is not installed by default.

$ gu install native-image

To generate a native image using Maven run:

$ ./mvnw package -Dpackaging=native-image

The native image will be created in target/application and can be run with ./target/application.

You should be able to execute curl localhost:8080/NOVEMBER and see results

7. Next steps

Read about Micronaut’s Cache Advice. Moreover, check the Micronaut Cache project for more information.

8. Help with Micronaut

Object Computing, Inc. (OCI) sponsored the creation of this Guide. A variety of consulting and support services are available.

Meet the Team.