Policy to wrap route with a cache

[Balazs Szeti]

Hi Camel Users,

In Spring we have the @Cacheable
<https://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-caching.html>
annotation that provides an easy way to wrap a method call with a cache.
The method result is cached and the method is not executed the next time
the it's called with the same input parameters.

I was wondering if we have something similar for Camel routes, where we can
cache the "result" of a route and execute the next time only if nothing is
found in the cache.

I haven't found any solution out-of-the-box, but a few blogs
<https://medium.com/@joelicious/camel-3scale-component-part-2-355faaaba5e0>
about doing similar caching in certain specific scenarios using the Policy
for processors. So I tried to put together a more generic solution:
See CachePolicy class:
https://gist.github.com/bszeti/552bf7a1f05a75fc2964a4ce7ce889b5

This is how it can be used in a route:
https://gist.github.com/bszeti/4f855cd80cd69e3953ff990b0ae056a2

public class CachedRoute extends RouteBuilder{
    @Override
    public void configure() throws Exception {
      from("direct:cachedRoute")
        *.policy(getUserDataCachePolicy())*

.setProperty("userData").method(userDataService.class,"lookupUserDataByName");
    }

    //Cache user data by user name. If user data is found in cache the rest
of the route is not executed.
    *private Policy getUserDataCachePolicy()*{
        CachePolicy cachePolicy = new CachePolicy();
        cachePolicy.setCache(cacheManager.getCache("userDataCache"));

        //User name is the cache key
        cachePolicy.setKeyExpression(simple("${header.userName}"));

        //What to do with the cached object if found
        cachePolicy.setApplyCachedObject(new BiConsumer<Exchange, Object>()
{
            public void accept(Exchange exchange, Object cached){
                exchange.setProperty("userData",cached);
            }
        });

        //Cache userData at the end of the route
        cachePolicy.setValueExpression(exchangeProperty("userData"));

        return cachePolicy;
    }


It would be great to know if someone tried anything similar and especially
if the "AsyncCallback()" looks OK in CachePolicy.wrap(). I found that piece
always a bit tricky...

Thanks,
Balazs