using guava cache without a load function

Question

My java app has a cache, and I'd like to swap out the current cache implementation and replace it with the guava cache.

Unfortunately, my app's cache usage doesn't seem to match the way that guava's caches seem to work. All I want is to be able to create an empty cache, read an item from the cache using a "get" method, and store an item in the cache with a "put" method. I do NOT want the "get" call to be trying to add an item to the cache.

It seems that the LoadingCache class has the get and put methods that I need. But I'm having trouble figuring out how to create the cache without providing a "load" function.

My first attempt was this:

LoadingCache<String, String> CACHE = CacheBuilder.newBuilder().build();

But that causes this compiler error: incompatible types; no instance(s) of type variable(s) K1,V1 exist so that Cache conforms to LoadingCache

Apparently I have to pass in a CacheLoader that has a "load" method.

(I guess I could create a CacheLoader that has a "load" method that just throws an Exception, but that seems kind of weird and inefficient. Is that the right thing to do?)

I'd be tempted to say that (from what information you've posted), it doesn't sound hugely like it's a cache as opposed to just being a Map. — Sean Parsons
– Sean Parsons, Commented Nov 23, 2012 at 17:15
@Sean Parsons: IMHO the more important difference between Cache and Map is that the former may forget things anytime. The loading is an additional feature. — maaartinus
– maaartinus, Commented Nov 23, 2012 at 17:19

Iulian Popescu · Accepted Answer · 2018-02-09 16:00:46Z

58

CacheBuilder.build() returns a non-loading cache. Just what you want. Just use

Cache<String, String> cache = CacheBuilder.newBuilder().build();

edited Feb 9, 2018 at 16:00

Iulian Popescu

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answered Nov 23, 2012 at 16:55

JB Nizet

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4 Comments

CreativeManix Over a year ago

For me it shows compile time error. it could not convert from <object,object> to <string,string> generic. I am using this lib for android.

Zai Over a year ago

@CreativeManix You have to use Cache class not LoadingCache.

Eric Hartford Over a year ago

wish that Google would explain this in the documentation - the only examples they give are LoadingCache.

alianos- Over a year ago

(edited previous comment). You can then use .getIfPresent(Object key) to retrieve stuff without providing a loader.

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