public Builder arnNamespace(String arnNamespace) {
            this.arnNamespace = arnNamespace;
            return this;
        }
Set the ARN service namespace of the service.

<p>Must match the following regex: {@code ^[A-Z][A-Za-z0-9]+$}

@param arnNamespace ARN service namespace to set.
@return Returns the builder.
smithy-aws-traits/src/main/java/software/amazon/smithy/aws/traits/ServiceTrait.java