Spring RestTemplate GET with parameters

I have to make a REST call that includes custom headers and query parameters. I set my HttpEntity with just the headers (no body), and I use the RestTemplate.exchange() method as follows:

HttpHeaders headers = new HttpHeaders();
headers.set("Accept", "application/json");

Map<String, String> params = new HashMap<String, String>();
params.put("msisdn", msisdn);
params.put("email", email);
params.put("clientVersion", clientVersion);
params.put("clientType", clientType);
params.put("issuerName", issuerName);
params.put("applicationName", applicationName);

HttpEntity entity = new HttpEntity(headers);

HttpEntity<String> response = restTemplate.exchange(url, HttpMethod.GET, entity, String.class, params);

This fails at the client end with the dispatcher servlet being unable to resolve the request to a handler. Having debugged it, it looks like the request parameters are not being sent.

When I do a an exchange with a POST using a request body and no query parameters it works just fine.

Does anyone have any ideas?

Solution 1:

To easily manipulate URLs / path / params / etc., you can use Spring's UriComponentsBuilder class to create a URL template with placehoders for the parameters, then provide the value for those parameters in the RestOperations.exchange(...) call. It's cleaner than manually concatenating strings and it takes care of the URL encoding for you:

HttpHeaders headers = new HttpHeaders();
headers.set(HttpHeaders.ACCEPT, MediaType.APPLICATION_JSON_VALUE);
HttpEntity<?> entity = new HttpEntity<>(headers);

String urlTemplate = UriComponentsBuilder.fromHttpUrl(url)
        .queryParam("msisdn", "{msisdn}")
        .queryParam("email", "{email}")
        .queryParam("clientVersion", "{clientVersion}")
        .queryParam("clientType", "{clientType}")
        .queryParam("issuerName", "{issuerName}")
        .queryParam("applicationName", "{applicationName}")
        .encode()
        .toUriString();

Map<String, ?> params = new HashMap<>();
params.put("msisdn", msisdn);
params.put("email", email);
params.put("clientVersion", clientVersion);
params.put("clientType", clientType);
params.put("issuerName", issuerName);
params.put("applicationName", applicationName);

HttpEntity<String> response = restOperations.exchange(
        urlTemplate,
        HttpMethod.GET,
        entity,
        String.class,
        params
);

Solution 2:

The uriVariables are also expanded in the query string. For example, the following call will expand values for both, account and name:

restTemplate.exchange("http://my-rest-url.org/rest/account/{account}?name={name}",
    HttpMethod.GET,
    httpEntity,
    clazz,
    "my-account",
    "my-name"
);

so the actual request url will be

http://my-rest-url.org/rest/account/my-account?name=my-name

Look at HierarchicalUriComponents.expandInternal(UriTemplateVariables) for more details. Version of Spring is 3.1.3.

Solution 3:

Since at least Spring 3, instead of using UriComponentsBuilder to build the URL (which is a bit verbose), many of the RestTemplate methods accept placeholders in the path for parameters (not just exchange).

From the documentation:

Many of the RestTemplate methods accepts a URI template and URI template variables, either as a String vararg, or as Map<String,String>.

For example with a String vararg:

restTemplate.getForObject(
   "http://example.com/hotels/{hotel}/rooms/{room}", String.class, "42", "21");

Or with a Map<String, String>:

Map<String, String> vars = new HashMap<>();
vars.put("hotel", "42");
vars.put("room", "21");

restTemplate.getForObject("http://example.com/hotels/{hotel}/rooms/{room}", 
    String.class, vars);

Reference: https://docs.spring.io/spring/docs/current/spring-framework-reference/integration.html#rest-resttemplate-uri

If you look at the JavaDoc for RestTemplate and search for "URI Template", you can see which methods you can use placeholders with.