Spring – RestTemplate

After learning to build Spring REST API for XML representation and JSON representation, let’s build Spring REST client to consume APIs which we have written in linked examples.

1. RestTemplate class

Accessing a third-party REST service inside a Spring application revolves around the use of the Spring RestTemplate class. The RestTemplate class is designed on the same principles as the many other Spring *Template classes (e.g., JdbcTemplate, JmsTemplate ), providing a simplified approach with default behaviors for performing complex tasks.

Given that the RestTemplate class is designed to call REST services, It should come as no surprise that its main methods are closely tied to REST’s underpinnings, which are the HTTP protocol’s methods: HEAD, GET, POST, PUT, DELETE, and OPTIONS.

Read More: RestTemplate Configuration with HttpClient

Spring docs recommend to use the non-blocking, reactive WebClient which offers efficient support for both sync, async and streaming scenarios. RestTemplate will be deprecated in a future version.

2. Spring RestTemplate – HTTP GET Method Example

Supported methods are:

• getForObject(url, classType) – retrieve a representation by doing a GET on the URL. The response (if any) is unmarshalled to given class type and returned.
• getForEntity(url, responseType) – retrieve a representation as ResponseEntity by doing a GET on the URL.
• exchange(requestEntity, responseType) – execute the specified request and return the response as ResponseEntity.
• execute(url, httpMethod, requestCallback, responseExtractor) – execute the httpMethod to the given URI template, preparing the request with the RequestCallback, and reading the response with a ResponseExtractor.

2.1. XML Response

REST API Code

Spring REST API for HTTP GET method.

@RequestMapping(value = "/employees", produces = MediaType.APPLICATION_XML_VALUE, method = RequestMethod.GET) public String getAllEmployeesXML(Model model) {     model.addAttribute("employees", getEmployeesCollection());     return "xmlTemplate"; }

REST Client Code

Spring REST client using RestTemplate to access HTTP GET api requests.

private static void getEmployees() {     final String uri = "http://localhost:8080/springrestexample/employees.xml";           RestTemplate restTemplate = new RestTemplate();     String result = restTemplate.getForObject(uri, String.class);           System.out.println(result); }

2.2. JSON Response

REST API Code

@RequestMapping(value = "/employees", produces = MediaType.APPLICATION_JSON_VALUE,  method = RequestMethod.GET) public String getAllEmployeesJSON(Model model) {     model.addAttribute("employees", getEmployeesCollection());     return "jsonTemplate"; }

REST Client Code

private static void getEmployees() {     final String uri = "http://localhost:8080/springrestexample/employees.json";           RestTemplate restTemplate = new RestTemplate();     String result = restTemplate.getForObject(uri, String.class);           System.out.println(result); }

2.3. Custom HTTP Headers with RestTemplate

REST API Code

@RequestMapping(value = "/employees", produces = MediaType.APPLICATION_JSON_VALUE,  method = RequestMethod.GET) public String getAllEmployeesJSON(Model model) {     model.addAttribute("employees", getEmployeesCollection());     return "jsonTemplate"; }

REST Client Code

private static void getEmployees() {     final String uri = "http://localhost:8080/springrestexample/employees";           RestTemplate restTemplate = new RestTemplate();           HttpHeaders headers = new HttpHeaders();     headers.setAccept(Arrays.asList(MediaType.APPLICATION_JSON));     HttpEntity<String> entity = new HttpEntity<String>("parameters", headers);           ResponseEntity<String> result = restTemplate.exchange(uri, HttpMethod.GET, entity, String.class);           System.out.println(result); }

2.4. Get response as object

REST API Code

@RequestMapping(value = "/employees", produces = MediaType.APPLICATION_XML_VALUE, method = RequestMethod.GET) public String getAllEmployeesXML(Model model) {     model.addAttribute("employees", getEmployeesCollection());     return "xmlTemplate"; }

REST Client Code

private static void getEmployees() {     final String uri = "http://localhost:8080/springrestexample/employees";     RestTemplate restTemplate = new RestTemplate();           EmployeeListVO result = restTemplate.getForObject(uri, EmployeeListVO.class);           System.out.println(result); }

2.5. URL Parameters

REST API Code

@RequestMapping(value = "/employees/{id}") public ResponseEntity<EmployeeVO> getEmployeeById (@PathVariable("id") int id) {     if (id <= 3) {         EmployeeVO employee = new EmployeeVO(1,"Lokesh","Gupta","howtodoinjava@gmail.com");         return new ResponseEntity<EmployeeVO>(employee, HttpStatus.OK);     }     return new ResponseEntity(HttpStatus.NOT_FOUND); }

REST Client Code

private static void getEmployeeById() {     final String uri = "http://localhost:8080/springrestexample/employees/{id}";           Map<String, String> params = new HashMap<String, String>();     params.put("id", "1");           RestTemplate restTemplate = new RestTemplate();     EmployeeVO result = restTemplate.getForObject(uri, EmployeeVO.class, params);           System.out.println(result); }

3. Spring RestTemplate – HTTP POST Method Example

Supported methods are:

• postForObject(url, request, classType) – POSTs the given object to the URL, and returns the representation found in the response as given class type.
• postForEntity(url, request, responseType) – POSTs the given object to the URL, and returns the response as ResponseEntity.
• postForLocation(url, request, responseType) – POSTs the given object to the URL, and returns returns the value of the Location header.
• exchange(url, requestEntity, responseType)
• execute(url, httpMethod, requestCallback, responseExtractor)

REST API Code

Spring REST API for HTTP POST method.

@RequestMapping(value = "/employees", method = RequestMethod.POST) public ResponseEntity<String> createEmployee(@RequestBody EmployeeVO employee) {     System.out.println(employee);     return new ResponseEntity(HttpStatus.CREATED); }

REST Client Code

Spring REST client using RestTemplate to access HTTP POST api requests.

private static void createEmployee() {     final String uri = "http://localhost:8080/springrestexample/employees";       EmployeeVO newEmployee = new EmployeeVO(-1, "Adam", "Gilly", "test@email.com");       RestTemplate restTemplate = new RestTemplate();     EmployeeVO result = restTemplate.postForObject( uri, newEmployee, EmployeeVO.class);       System.out.println(result); }

4. Spring RestTemplate – HTTP PUT Method Example

Supported methods are:

• put(url, request) – PUTs the given request object to URL.

REST API Code

Spring REST API for HTTP PUT method.

@RequestMapping(value = "/employees/{id}", method = RequestMethod.PUT) public ResponseEntity<EmployeeVO> updateEmployee(@PathVariable("id") int id, @RequestBody EmployeeVO employee) {     System.out.println(id);     System.out.println(employee);     return new ResponseEntity<EmployeeVO>(employee, HttpStatus.OK); }

REST Client Code

Spring REST client using RestTemplate to access HTTP PUT api requests.

private static void updateEmployee() {     final String uri = "http://localhost:8080/springrestexample/employees/{id}";           Map<String, String> params = new HashMap<String, String>();     params.put("id", "2");           EmployeeVO updatedEmployee = new EmployeeVO(2, "New Name", "Gilly", "test@email.com");           RestTemplate restTemplate = new RestTemplate();     restTemplate.put ( uri, updatedEmployee, params); }

5. Spring RestTemplate – HTTP DELETE Method Example

Supported methods are:

• delete(url) – deletes the resource at the specified URL.

REST API Code

Spring REST API for HTTP DELETE method.

@RequestMapping(value = "/employees/{id}", method = RequestMethod.DELETE) public ResponseEntity<String> updateEmployee(@PathVariable("id") int id) {     System.out.println(id);     return new ResponseEntity(HttpStatus.OK); }

REST Client Code

Spring REST client using RestTemplate to access HTTP DELETE api requests.

private static void deleteEmployee() {     final String uri = "http://localhost:8080/springrestexample/employees/{id}";           Map<String, String> params = new HashMap<String, String>();     params.put("id", "2");           RestTemplate restTemplate = new RestTemplate();     restTemplate.delete ( uri,  params ); }

Feel free to copy and modify above Spring RestTemplate examples for building the Spring REST client in your MVC application