Spring RestTemplate GET with parameters

java

rest-template

http-requests

uri-components

byAlex Kataev·Sep 17, 2024

Let's do a GET request with RestTemplate and send parameters using UriComponentsBuilder:

UriComponentsBuilder builder = UriComponentsBuilder.fromHttpUrl("http://example.com/api/resource")
        .queryParam("param1", "value1")
        .queryParam("param2", "value2");

String result = new RestTemplate().getForObject(builder.toUriString(), String.class);

You've now done a GET to http://example.com/api/resource?param1=value1&param2=value2, and auto-encoded the parameters like a boss.

To tote along some custom headers, create an HttpHeaders instance, sprint over to HttpEntity, and finally fire off the request with restTemplate.exchange():

HttpHeaders headers = new HttpHeaders();
headers.set("CoolBeans", "123Beans");
HttpEntity<String> entity = new HttpEntity<>(headers);

// Knock-knock, anybody home?
ResponseEntity<String> response = new RestTemplate().exchange(
        builder.toUriString(), 
        HttpMethod.GET, 
        entity, 
        String.class);

Clear tactics with requests

Tailoring your requests is like making a smoothie – gather your ingredients and blend away:

GET-ing down with dynamic parameters

To handle dynamic parameters like a pro, simply chain additional calls to .queryParam(). Imagine you have a magic flute blowing out parameters:

UriComponentsBuilder builder = UriComponentsBuilder.fromHttpUrl(baseUrl);
if (magicFlutePlaying) {
    builder.queryParam("melody", fluteMelody);
}
// Play on...

String uri = builder.toUriString();

POST with a serving of JSON body and parameters

For POST requests where you're sending a JSON body alongside URL parameters, you'd have to assemble things like a master LEGO builder:

HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_JSON);

HttpEntity<YourMasterpiece> requestEntity = new HttpEntity<>(yourMasterpiece, headers);

UriComponentsBuilder builder = UriComponentsBuilder.fromHttpUrl(legoBaseUrl)
        .queryParam("instructions", "123");

URI uri = builder.build().toUri();

// As easy as building a spaceship 🚀
ResponseEntity<String> response = restTemplate.exchange(
        uri,
        HttpMethod.POST,
        requestEntity,
        String.class);

Handling peculiar cases

Because we live in a world where not everything is unicorns and rainbows 🌈. Here's how you deal with peculiar scenarios:

Path variables vs query parameters

It's like corn flakes or oatmeal for breakfast. Path variables and query parameters both have their own place and time.

// Path variable
String uri = "http://example.com/users/{userId}";

// Query parameter
UriComponentsBuilder builder = UriComponentsBuilder.fromHttpUrl(uri)
        .queryParam("detail", "astonishingFeatures");

Variable expansion

Expand variables correctly, because nobody likes a surprise pop-serving from a jack-in-the-box:

UriComponents uriComponents = UriComponentsBuilder.fromHttpUrl("http://example.com/users/{userId}")
        .buildAndExpand("42");

String uri = uriComponents.toUriString();
// Result: "http://example.com/users/42"