Spring RESTFul Client – RestTemplate Example

After learning to build Spring REST based RESTFul APIs for XML representation and JSON representation, let’s build a RESTFul client to consume APIs which we have written. 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. E.g. it’s methods are headForHeaders(), getForObject(), postForObject(), put() and delete() etc.

HTTP GET Method Example

1) Get XML representation of employees collection in String format

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.xml";

RestTemplate restTemplate = new RestTemplate();
String result = restTemplate.getForObject(uri, String.class);

System.out.println(result);
}

2) Get JSON representation of employees collection in String format

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);
}

3) Using 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.POST, entity, String.class);

System.out.println(result);
}

4) Get data as mapped 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);
}

5) Passing parameters in URL

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);
}

HTTP POST Method Example

REST API Code

@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

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);
}

HTTP PUT Method Example

REST API Code

@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

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");

EmployeeVO updatedEmployee = new EmployeeVO(2, "New Name", "Gilly", "test@email.com");

RestTemplate restTemplate = new RestTemplate();
restTemplate.put ( uri, updatedEmployee, params);
}

HTTP DELETE Method Example

REST API Code

@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

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 );
}