Implement a caching mechanism

[josealonso]

The Etag, as well known as Entity Tag, is an HTTP header corresponding to the current status of a requested resource.
When an API receives a request, it will calculate a hash value. This value is the ETag.

Consumers can send the ETag value on the header If-None-Match. The API server will process the request and calculate the ETag again, comparing it with the value sent by the client. If it matches, the API server will response the status code 304 Not Modified. The client will then update the cache as it knows the response is still valid.

Credit goes to @ivan1405

[josealonso]

Configuring the Etag header is easy in Spring Boot:

@Bean
public ShallowEtagHeaderFilter shallowEtagHeaderFilter() {
    return new ShallowEtagHeaderFilter();
}

Explained here