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Configuring EhCache 3 and Event Listeners in Spring Boot

TLDR: You can jump straight to an example project azdanov/ehcache-config-demo.

Spring offers amazing caching utilities. Throw in some @EnableCaching, @Cacheable, @CacheEvict on and the results will be cached. You can read more about Spring Caching on https://www.baeldung.com/spring-cache-tutorial.

The problem that I encountered was figuring out how to use EhCache 3 (org.ehcache) and inside Spring Boot with Java Based Configuration. A lot of how-to guides were either showing ehcache.xml or an older EhCache 2 (net.sf.ehcache) configuration convention.

Let's see how to do configure EhCache 3 programmatically.

Setup

First step is adding required dependencies to the project (Maven/Gradle):

<!-- pom.xml -->
<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-cache</artifactId>
    </dependency>
    <dependency>
        <groupId>org.ehcache</groupId>
        <artifactId>ehcache</artifactId>
        <version>3.9.0</version>
    </dependency>
    <dependency>
        <groupId>javax.cache</groupId>
        <artifactId>cache-api</artifactId>
        <version>1.1.1</version>
    </dependency>
</dependencies>

or

// build.gradle
dependencies {
  implementation 'org.springframework.boot:spring-boot-starter-cache'
  implementation 'org.ehcache:ehcache:3.9.0'
  implementation 'javax.cache:cache-api:1.1.1'
}

Configuration

Next step would be creating a configuration class:

package org.js.azdanov.ehcacheconfigdemo.configuration;

import org.ehcache.config.builders.CacheConfigurationBuilder;
import org.ehcache.config.builders.ExpiryPolicyBuilder;
import org.ehcache.config.builders.ResourcePoolsBuilder;
import org.ehcache.jsr107.Eh107Configuration;
import org.springframework.boot.autoconfigure.cache.JCacheManagerCustomizer;
import org.springframework.cache.annotation.EnableCaching;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import javax.cache.Cache;
import javax.cache.CacheManager;
import javax.cache.configuration.CacheEntryListenerConfiguration;
import javax.cache.configuration.Factory;
import javax.cache.configuration.FactoryBuilder;
import javax.cache.configuration.MutableCacheEntryListenerConfiguration;
import javax.cache.event.CacheEntryEventFilter;
import java.time.Duration;

@EnableCaching
@Configuration
public class CacheConfiguration {
    private static final Factory<? extends CacheEntryEventFilter<Integer, Integer>> NO_FILTER = null;
    private static final boolean IS_OLD_VALUE_REQUIRED = false;
    private static final boolean IS_SYNCHRONOUS = true;

    // (1)
    private final javax.cache.configuration.Configuration<Integer, Integer> jcacheConfiguration =
        Eh107Configuration.fromEhcacheCacheConfiguration(
            CacheConfigurationBuilder
                .newCacheConfigurationBuilder(Integer.class, Integer.class, ResourcePoolsBuilder.heap(100))
                .withExpiry(ExpiryPolicyBuilder.timeToLiveExpiration(Duration.ofMinutes(5)))
                .build()
        );

    CacheEntryListenerConfiguration<Integer, Integer> listenerConfiguration =
        new MutableCacheEntryListenerConfiguration<>(
            FactoryBuilder.factoryOf(CacheListener.class),
            NO_FILTER,
            IS_OLD_VALUE_REQUIRED,
            IS_SYNCHRONOUS);

    // (2)
    @Bean
    public JCacheManagerCustomizer cacheManagerCustomizer() {
        return cm -> {
            createCache(cm, "worker1");
            createCache(cm, "worker2");
        };
    }

    private void createCache(CacheManager cm, String cacheName) {
        Cache<Integer, Integer> cache = cm.getCache(cacheName);
        if (cache == null) {
            cm.createCache(cacheName, jcacheConfiguration)
                .registerCacheEntryListener(listenerConfiguration);
        }
    }
}
  1. Here's the configuration itself, which can be modified to read the values from an application.properties file or any other resource.
  2. Inside JCacheManagerCustomizer bean the individual cache creation happens.

I've added some extras where a cache event listener will be registered for each created cache.

Here's how a listener class might look like:

package org.js.azdanov.ehcacheconfigdemo.configuration;

import lombok.extern.slf4j.Slf4j;

import javax.cache.event.CacheEntryCreatedListener;
import javax.cache.event.CacheEntryEvent;

@Slf4j
public class CacheListener implements CacheEntryCreatedListener<Integer, Integer> {

    @Override
    public void onCreated(final Iterable<CacheEntryEvent<? extends Integer, ? extends Integer>> cacheEntryEvents) {
        for (CacheEntryEvent<? extends Integer, ? extends Integer> entryEvent : cacheEntryEvents) {
            log.info("Cached key: {}, with value: {}", entryEvent.getKey(), entryEvent.getValue());
        }
    }
}

Now for the last step let's mark methods inside a service with previously defined cache names:

package org.js.azdanov.ehcacheconfigdemo.service;

import lombok.RequiredArgsConstructor;
import org.springframework.cache.annotation.Cacheable;
import org.springframework.stereotype.Service;

import java.util.Random;

@RequiredArgsConstructor
@Service
public class WorkerService {

    private final Random random;

    @Cacheable(value = "worker1", key = "#bound")
    public int getFirstWork(int bound) {
        return random.nextInt(bound);
    }

    @Cacheable(value = "worker2", key = "#bound")
    public int getSecondWork(int bound) {
        return random.nextInt(bound);
    }
}

Last step

It's time to see if this works or not with a simple sanity-check 'test':

package org.js.azdanov.ehcacheconfigdemo;

import lombok.extern.slf4j.Slf4j;
import org.js.azdanov.ehcacheconfigdemo.service.WorkerService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.event.ApplicationReadyEvent;
import org.springframework.cache.annotation.EnableCaching;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.event.EventListener;

import java.util.Random;

@Slf4j
@EnableCaching
@Configuration
@SpringBootApplication
public class EhcacheConfigDemoApplication {

    @Autowired
    WorkerService workerService;

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

    @Bean
    Random random() {
        return new Random();
    }

    @EventListener(ApplicationReadyEvent.class)
    public void afterStartup() {
        log.info("Running!");
        log.info("getFirstWork(100): {}", workerService.getFirstWork(100));
        log.info("getFirstWork(50): {}", workerService.getFirstWork(50));
        log.info("getFirstWork(100): {}", workerService.getFirstWork(100));
        log.info("getFirstWork(50): {}", workerService.getFirstWork(50));
        log.info("getSecondWork(100): {}", workerService.getSecondWork(100));
        log.info("getSecondWork(50): {}", workerService.getSecondWork(50));
        log.info("getSecondWork(100): {}", workerService.getSecondWork(100));
        log.info("getSecondWork(50): {}", workerService.getSecondWork(50));
    }
}

This is the result I got in the terminal:

Running!
Cached key: 100, with value: 8
getFirstWork(100): 8
Cached key: 50, with value: 29
getFirstWork(50): 29
getFirstWork(100): 8
getFirstWork(50): 29
Cached key: 100, with value: 6
getSecondWork(100): 6
Cached key: 50, with value: 33
getSecondWork(50): 33
getSecondWork(100): 6
getSecondWork(50): 33

Seems to be working 🙂