Android + Picasso: changing URL cache expiration

Question

I am using Picasso to download and display images in views all accros my application. Those images are changing very rarely (they are considered valid for a few months).

Answer 1

Before thinking about HTTP behavior, make sure you set a large max size for the disk cache:

cache = Cache(File(application.filesDir, "photos"), Long.MAX_VALUE)

(MAX_VALUE is not recommended for production.) Don't store the cache in application.cacheDir, because android can clear that whenever it wants.

Add an interceptor to set max-stale, which tells the disk cache to use all old files:

    val httpClient = OkHttpClient.Builder().cache(cache).addInterceptor { chain ->
        // When offline, we always want to show old photos.
        val neverExpireCacheControl = CacheControl.Builder().maxStale(Int.MAX_VALUE, TimeUnit.SECONDS).build()
        val origRequest = chain.request()
        val neverExpireRequest = origRequest.newBuilder().cacheControl(neverExpireCacheControl).build()

        chain.proceed(neverExpireRequest)
    }.build()

    return Picasso.Builder(application).downloader(OkHttp3Downloader(httpClient)).loggingEnabled(true).build()

I discovered this solution by debugging CacheStrategy.getCandidate(). Take a look there if this doesn't solve your problem.