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You’ll build an application that enables caching on a simple book repository.

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First, let’s create a very simple model for your book

src/main/java/hello/Book.java

And a repository for that model:

src/main/java/hello/BookRepository.java

You could have used Spring Data to provide an implementation of your repository over a wide range of SQL or NoSQL stores, but for the purpose of this guide, you will simply use a naive implementation that simulates some latency (network service, slow delay, etc).

src/main/java/hello/SimpleBookRepository.java

simulateSlowService is deliberately inserting a five second delay into each getByIsbn call. This is an example that later on, you’ll speed up with caching.

Next, wire up the repository and use it to access some books.

src/main/java/hello/Application.java

@SpringBootApplication is a convenience annotation that adds all of the following:

• @Configuration tags the class as a source of bean definitions for the application context.

• @EnableAutoConfiguration tells Spring Boot to start adding beans based on classpath settings, other beans, and various property settings. Technically, Spring Boot doesn’t have anything to auto-configure when it comes to caching but a future version might.

• @ComponentScan tells Spring to look for other components, configurations, and services in the the hello package, allowing it to find the SimpleBookRepository.

If you try to run the application at this point, you’ll notice it’s quite slow even though you are retrieving the exact same book several times.

As can be seen by the timestamps, each book took about five seconds to retrieve, even though it’s the same title being repeatedly fetched.

Let’s enable caching on your SimpleBookRepository so that the books are cached within the books cache.

src/main/java/hello/SimpleBookRepository.java

You now need to enable the processing of the caching annotations

src/main/java/hello/Application.java

The @EnableCaching annotation triggers a post processor that inspects every Spring bean for the presence of caching annotations on public methods. If such an annotation is found, a proxy is automatically created to intercept the method call and handle the caching behavior accordingly.

The annotations that are managed by this post processor are Cacheable, CachePut and CacheEvict. You can refer to the javadocs and the documentation for more details.

Spring Boot automatically configures a suitable CacheManager to serve as a provider for the relevant cache. See the Spring Boot documentation for more details.

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Now that caching is enabled, you can execute it again and see the difference by adding additional calls with or without the same isbn. It should make a huge difference.

This excerpt from the console shows that the first time to fetch each title took five seconds the first time, but each subsequent call was near instantaneous.

Congratulations! You’ve just enabled caching on a Spring managed bean.

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