Best way to Cache JSON from API in SWIFT?
You have many tools already at your disposal.
NSURLCache
All your requests are already stored in the NSURLCache in the NSURLSessionConfiguration on the NSURLSession stored inside the sharedInstance of the Alamofire Manager. Those stored requests already follow all the caching policy rules provided by the servers you are hitting. You can control the caching behavior by setting the requestCachePolicy on your own custom NSURLSessionConfiguration. I'd also suggest you read through this awesome NSHipster article that walks you through the ins and outs of NSURLCache and how to control it.
Creating custom
Managerobjects is covered in the current Alamofire docs.
Downloading JSON to Disk
You can also download the JSON directly to disk using Alamofire.download instead of using Alamofire.request. This will download the payload to a fileURL that you provide in the destination closure. This would give you full control over the caching of the file after that point. You would need to create your own caching policy around these files afterwards if you wanted to follow the caching header rules provided by the server.
Populating Table View
Once you have your data downloaded to disk, you need to load it into an NSData blob and parse it into JSON to populate your table view. This should be pretty straight forward. You need the destination NSURL that you specified to Alamofire when you started your download. Then load the file data into an NSData blob. Finally, use NSJSONSerialization to convert the NSData object into a JSON AnyObject which can be parsed into model objects to populate your table view.
Obviously you don't "have" to parse the JSON into model objects, but this helps protect your table view from malformed JSON data.
Storing JSON for Offline Usage
If you stick with this approach, you'll need to track your cache expiration dates in something like CoreData or SQLite. You can do this by either caching the paths to the JSON files on disk, or store the model objects directly in CoreData or SQLite. This could get fairly complicated and I would not recommend this approach unless you absolutely don't want to cache your model objects.
Offline Usage
Generally, if you need to cache data for offline usage, you want to store your model objects in something like CoreData. You would use the Alamofire request method coupled with a responseJSON serializer to parse the data into JSON. Then you would convert the JSON into model objects. From there, you'd save your model objects in CoreData, then finally populate your table view with the model objects.
The nice thing about this approach is that you have all your model objects cached in the case that your table view is accessed when the device is offline. Coupling this design with queries to your NSURLCache to see if your request is cached let's you avoid unnecessary server calls and parsing logic when you already have your model objects generated.
Given the updates to your original question, I would recommend this approach.
You can use this cache open source. It cache data on disk and memory. Can cache many swift type, and custom class which inherit NSObject and conform NSCoding protocol.
https://github.com/huynguyencong/DataCache
To implement:First, it use NSCache for mem cache. NSCache use like a dictionary.Second, save cache to disk, use NSFileManager methods.