Best way to passing parameter to restTemplate.getForObject

Question

in order to write a clean and smart code, I'm wondering what can I do to improve my actual piece of code:

public JSONObject getCustomer(final String customerId) {
    if (customerId == null || customerId.equals("")) {
        return null;
    } else {
        final RestTemplate restTemplate = new RestTemplate();
        final String result = restTemplate.getForObject("http://localhost:6061/customers/" + customerId,
                String.class);
        return new JSONObject(result);
    }
}

Especially, I didn't like the way I composed the url, neither the check on customerId's value.

I'd like to have something like JPA, where I ask some information passing a parameter, just to be clear (in pseudocode):

public JSONObject getCustomer(final String customerId) {
    final RestTemplate restTemplate = new RestTemplate();
    final Query query = restTemplate.query("http://localhost:6061/customers/:customerId");

    query.addParameter("customerId", customerId);
    JSONObject result = query.getForObject();

    return result;
}

Then, if customerId would be null or some white spaces or not existing, I'd like that result would be null. Is there a way to do this with a standard library?

Thanks

Answer 1

First off, I would remove the else branch and refactor the condition to:

public JSONObject getCustomer(final String customerId) {
    if (isNull(customerId) || customerId.trim().isEmpty()) {
        return null;
    }
    ...
}

Second, if you have a bunch of URI variables, Spring guys recommend using a Map<String, String>:

final String templateURL = "http://localhost:6061/customers/{customerId}";
final Map<String, String> variables = new HashMap<>();

variables.put("customerId", customerId);
...

template.getForObject(templateURL, String.class, variables);

Third, the method shouldn't create a RestTemplate instance on its own. I would prefer injecting the already-tuned object into an instance field:

getTemplate().getForObject(templateURL, String.class, variables);

Finally, I would name the result more meaningful:

final String customerRepresentation = ...;

---

Some notes:

1. getCustomer actually returns a JSONObject, not a Customer.
2. templateURL hardcoded the base URL as well as the URL to customers.
3. The method does a lot of work (takes too much responsibility) - argument validation, URL construction, making a request. Try to split these responsibilities between corresponding methods.