code: public Observable<FirewallRuleInner> getFirewallRuleAsync(String resourceGroupName, String accountName, String firewallRuleName) {
          return getFirewallRuleWithServiceResponseAsync(resourceGroupName, accountName, firewallRuleName).map(new Func1<ServiceResponse<FirewallRuleInner>, FirewallRuleInner>() {
              @Override
              public FirewallRuleInner call(ServiceResponse<FirewallRuleInner> response) {
                  return response.body();
              }
          });
      }
docs: Gets the specified Data Lake Store firewall rule.
  
  @param resourceGroupName The name of the Azure resource group that contains the Data Lake Store account.
  @param accountName The name of the Data Lake Store account from which to get the firewall rule.
  @param firewallRuleName The name of the firewall rule to retrieve.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the FirewallRuleInner object