Key Resolver 类
The key resolver that caches the key after resolving to IKey.
public class CachingKeyResolver implements IKeyResolver
|CachingKeyResolver(int capacity, final IKeyResolver keyResolver)||
Retrieves an IKey implementation for the specified key identifier. Implementations should check the format of the kid to ensure that it is recognized. Null, rather than an exception, should be returned for unrecognized key identifiers to enable chaining of key resolvers.