Spring Boot, Caching and Hazelcast

Updated:

Marco Molteni

Why use cached objects?

For most of the professional applications the use of some form of caching is required to improve the performances and to reduce the interactions with slow medias (database, disk, external services etc.)

Example of publishing our pages without cache

In this website we store the articles of the documentation in simple MarkDown files.

When the user ask for a documentation page the Java backend executes the following operations:

search the file in the Operating System
open the file
read the content of the file and store it in a variable
close the file
build a Java object with the information of the document (title, content etc.)
send the result to the frontend using REST services

If you open the file 10 times, this operation will be repeated 10 times.

... and with cache

After the configuration of the Cache the operations are the following:

(1a) search the document in the Cache
(2a) the document is not in the cache
- search the file in the Operating System
- open the file
- read the content of the file and store it in a variable
- close the file
- build a Java object with the information of the document (title, content etc.)
(3a) store the object in the cache
(4a) send the result to the frontend using REST services

For the following requests the operations are the following:

(1b) search the document in the Cache
(2b) return the object to the frontend

For our application using the cache reduces the response time required to read a document from 100 milliseconds to 3-5 milliseconds, the cache is 20-30 time more fast ... with the default configuration.

How to configure it

We decided to use the simplest possible cache configuration: embedded mode, without optimization.

In our application we add Hazelcast:

Add the default configuration

 <dependency> 
    <groupId>com.hazelcast</groupId> 
    <artifactId>hazelcast</artifactId> 
</dependency>

Create a Spring configuration class:

package io.springdemo.config; 
 
import com.hazelcast.config.Config; 
import org.springframework.context.annotation.Bean; 
import org.springframework.context.annotation.Configuration; 
 
@Configuration 
public class CacheConfig { 
 
    @Bean 
    public Config config() { 
        return new Config(); 
    } 
}

When you add the Spring configuration Hazelcast will automatically create an instance at the next start:

INFO 6888 --- [ost-startStop-1] com.hazelcast.instance.AddressPicker     : [LOCAL] [dev] [3.9] Prefer IPv4 stack is true. 
INFO 6888 --- [ost-startStop-1] com.hazelcast.instance.AddressPicker     : [LOCAL] [dev] [3.9] Picked [192.168.0.18]:5701, using socket ServerSocket[addr=/0:0:0:0:0:0:0:0,localport=5701], bind any local is true 
INFO 6888 --- [ost-startStop-1] com.hazelcast.system                     : [192.168.0.18]:5701 [dev] [3.9] Hazelcast 3.9 (20171023 - b29f549) starting at [192.168.0.18]:5701 
INFO 6888 --- [ost-startStop-1] com.hazelcast.system                     : [192.168.0.18]:5701 [dev] [3.9] Copyright (c) 2008-2017, Hazelcast, Inc. All Rights Reserved. 
INFO 6888 --- [ost-startStop-1] com.hazelcast.system                     : [192.168.0.18]:5701 [dev] [3.9] Configured Hazelcast Serialization version: 1 
INFO 6888 --- [ost-startStop-1] c.h.s.i.o.impl.BackpressureRegulator     : [192.168.0.18]:5701 [dev] [3.9] Backpressure is disabled 
INFO 6888 --- [ost-startStop-1] com.hazelcast.instance.Node              : [192.168.0.18]:5701 [dev] [3.9] Creating MulticastJoiner 
INFO 6888 --- [ost-startStop-1] c.h.s.i.o.impl.OperationExecutorImpl     : [192.168.0.18]:5701 [dev] [3.9] Starting 4 partition threads and 3 generic threads (1 dedicated for priority tasks) 
INFO 6888 --- [ost-startStop-1] c.h.internal.diagnostics.Diagnostics     : [192.168.0.18]:5701 [dev] [3.9] Diagnostics disabled. To enable add -Dhazelcast.diagnostics.enabled=true to the JVM arguments. 
INFO 6888 --- [ost-startStop-1] com.hazelcast.core.LifecycleService      : [192.168.0.18]:5701 [dev] [3.9] [192.168.0.18]:5701 is STARTING 
INFO 6888 --- [ost-startStop-1] com.hazelcast.system                     : [192.168.0.18]:5701 [dev] [3.9] Cluster version set to 3.9 
INFO 6888 --- [ost-startStop-1] c.h.internal.cluster.ClusterService      : [192.168.0.18]:5701 [dev] [3.9]  
 
Members {size:1, ver:1} [ 
	Member [192.168.0.18]:5701 - 7a412631-59f2-44fd-87c0-82dedbcfb7f3 this 
] 
 
INFO 6888 --- [ost-startStop-1] com.hazelcast.core.LifecycleService      : [192.168.0.18]:5701 [dev] [3.9] [192.168.0.18]:5701 is STARTED

Add @Cacheable

In our project we want to cache the documents showed by the application.

We add the annotation @Cacheableto the method that read the documents in the classpath (ReadDocumentationServiceImpl.java):

@Cacheable("Document") 
    public String readClassPathFile(final String documentPath) {

Add the next start the cache will be registered:

INFO 7290 --- [           main] .d.s.w.r.o.CachingOperationNameGenerator : Generating unique operation named: getDocumentUsingGET_1

Enable the caching

To activate the caching mechanism of Spring we need add the @EnableCaching annotation in our application:

 @SpringBootApplication 
    @EnableCaching 
    @ComponentScan(basePackages = "io.springdemo") 
    public class Application { 
        public static void main(String [] args){ 
            SpringApplication.run(Application.class, args); 
        } 
    }

After the restart the cache is active.

Next steps

Cloud: share the cache between instances of the application
Handle the cache: empty the cache and reload the documents