code: public Observable<RedisFirewallRuleInner> getAsync(String resourceGroupName, String cacheName, String ruleName) {
          return getWithServiceResponseAsync(resourceGroupName, cacheName, ruleName).map(new Func1<ServiceResponse<RedisFirewallRuleInner>, RedisFirewallRuleInner>() {
              @Override
              public RedisFirewallRuleInner call(ServiceResponse<RedisFirewallRuleInner> response) {
                  return response.body();
              }
          });
      }
docs: Gets a single firewall rule in a specified redis cache.
  
  @param resourceGroupName The name of the resource group.
  @param cacheName The name of the Redis cache.
  @param ruleName The name of the firewall rule.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the RedisFirewallRuleInner object