RestTemplate in Spring

Overview

RestTemplate reduces boilerplate code and enforces RESTful principles.

In this post, we will discuss different ways in which we can use RestTemplate

• HTTP GET call
• HTTP POST call
• HTTP Exchange call
• HTTP DELETE call

GET call

Get entry point has two methods

• getForEntity: returns ResponseEntity which can be used to get ResponseStatus code and other parameters.

RestTemplate restTemplate = new RestTemplate();
String apiUrl = "http://dummy.restapiexample.com/api/v1/employees";

//get Response Entity
ResponseEntity<String> response = restTemplate.getForEntity(apiUrl , String.class);
assertThat(response.getStatusCode(), equalTo(HttpStatus.OK));

• getForObject: convert and returns Object passed to it as the parameter. In case RestTemplate is not able to parse will throw RestClientException.

//get Object
User user = restTemplate.getForObject(apiUrl , User.class);
assertThat(user.getName(), notNullValue());
assertThat(user.getId(), is(234L));

POST call

Post entry point has the following methods

• postForObject: convert and returns Object passed to it as the parameter. In case RestTemplate is not able to parse will throw RestClientException.

String apiUrl = "http://dummy.restapiexample.com/api/v1/create";
RestTemplate restTemplate = new RestTemplate();
HttpEntity<User> request = new HttpEntity<>(new User("Test"));

// post for Object, returns User Object
User user = restTemplate.postForObject(apiUrl, request, User.class);
assertThat(user, notNullValue());
assertThat(user.getName(), is("Temp"));

• postForLocation: returns the Location of that newly created Resource.

// post for Location, returns URI
URI location = restTemplate.postForLocation(apiUrl, request);
assertThat(location, notNullValue());

• postForEntity: Can be used to submit a Form and return ResponseEntity which can be used to get ResponseStatus code and other parameters

// post for Entity can be used to submit a Form

//setting header to "application/x-www-form-urlencoded"
HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);

// converting form variable to Map
MultiValueMap<String, String> map= new LinkedMultiValueMap<>();
map.add("salary", "123");
map.add("name", "Test");

// finally build Request
HttpEntity<MultiValueMap<String, String>> request = new HttpEntity<>(map, headers);

ResponseEntity<String> response = restTemplate.postForEntity(apiUrl, request , String.class);
  
assertThat(response.getStatusCode(), is(HttpStatus.CREATED));

Exchange call

Exchange entry point gives a more generic way of using HTTP calls.

We will see how we can do POST call using exchange method

String apiUrl = "http://dummy.restapiexample.com/api/v1/create";
RestTemplate restTemplate = new RestTemplate();
HttpEntity<User> request = new HttpEntity<>(new User("Temp"));
ResponseEntity<User> response = restTemplate
	.exchange(apiUrl, HttpMethod.POST, request, User.class);

assertThat(response.getStatusCode(), is(HttpStatus.CREATED));

DELETE

String entityUrl = "http://dummy.restapiexample.com/api/v1/update/2"
restTemplate.delete(entityUrl);

Common Methods

DELETE 	=> 	delete(url, java.lang.Object...)
	
GET 	=>	getForObject(url, responseType, urlVariables(Map))
		getForEntity(url, responseType, urlVariables)
	
POST 	=> 	postForLocation(url, responseType, urlVariables)
		postForObject(url, objToPost, responseType, urlVariables(Map))
	
PUT 	=> 	put(url, objToPost, urlVariables)

All methods throws RestClientException

Note

• Internally the template uses HttpMessageConverter instances to convert HTTP messages to and from POJOs.
• By default, the RestTemplate relies on standard JDK facilities to establish HTTP connections. You can switch to use a different HTTP library.
• Such as Apache HttpComponents, Netty, and OkHttp through the HttpAccessor.setRequestFactory(org.springframework.http.client.ClientHttpRequestFactory) property.
• More detail on Java Doc can be found here.

RestTemplate restTemplate = new RestTemplate();
String apiUrl = "http://dummy.restapiexample.com/api/v1/employees";

//get Response Entity
ResponseEntity<String> response = restTemplate.getForEntity(apiUrl , String.class);
assertThat(response.getStatusCode(), equalTo(HttpStatus.OK));