#Value annotated field returning null method of #Service annotated class - spring-boot

Question

I'm facing a strange issue while accessing a property using #Value annotation in a #Service annotated class with Spring Boot 2.2.1.RELEASE. The field is resolving to null and I'm not sure how to debug it.
#Service
public class MyService {
#Value("${my.username}")
private String username;
#Value("${my.password}")
private String password;
private RestTemplate restTemplate = getRestTemplate();
private RestTemplate getRestTemplate() {
final CredentialsProvider credentialsProvider = new BasicCredentialsProvider();
log.debug("Generating NTCredentials for RestTemplate using user: {} and password: {}", username, password);
credentialsProvider
.setCredentials(AuthScope.ANY,
new NTCredentials(username, password, null, "DOMAIN"));
HttpClient client = HttpClientBuilder.create().setDefaultCredentialsProvider(credentialsProvider).build();
HttpComponentsClientHttpRequestFactory clientHttpRequestFactory = new HttpComponentsClientHttpRequestFactory();
clientHttpRequestFactory.setHttpClient(client);
return new RestTemplate(clientHttpRequestFactory);
}
}
In this code, inside the getRestTemplate() method the username and password are always coming as null.
I have confirmed that the properties are present in the application.properties file.
Any help would be really appreciated!
Edit 1:
#Slf4j
#Service
public class MyService {
#Value("${my.url}")
private String url;
private String username;
private String password;
private RestTemplate restTemplate = getRestTemplate();
public MyService(#Value("${my.username}") String username, #Value("${my.password}") String password) {
System.out.println(">> Inside Constructor");
this.username = username;
this.password = password;
}
public String updateDetails(String data) {
HttpEntity<String> entity = new HttpEntity<>(data);
ResponseEntity<String> response = restTemplate.exchange(url, HttpMethod.POST, entity, String.class);
return response.getBody();
}
private RestTemplate getRestTemplate() {
System.out.println(">> Inside RestTemplate Method");
final CredentialsProvider credentialsProvider = new BasicCredentialsProvider();
log.debug("Generating NTCredentials for RestTemplate using user: {} and password: {}", username, password);
credentialsProvider.setCredentials(AuthScope.ANY, new NTCredentials(username, password, null, "DOMAIN"));
HttpClient client = HttpClientBuilder.create().setDefaultCredentialsProvider(credentialsProvider).build();
HttpComponentsClientHttpRequestFactory clientHttpRequestFactory = new HttpComponentsClientHttpRequestFactory();
clientHttpRequestFactory.setHttpClient(client);
return new RestTemplate(clientHttpRequestFactory);
}
}
Logs :
2019-11-25 19:56:47.069 INFO 20336 --- [ restartedMain] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization completed in 1293 ms
>> Inside RestTemplate Method
2019-11-25 19:56:47.361 DEBUG 20336 --- [ restartedMain] c.d.u.u.services.MyService : Generating NTCredentials for RestTemplate using user: null and password: null
>> Inside Constructor
[2
As you see, the getRestTemplate() is getting called before the constructor is getting called. Also, the user and password values are coming as null inside the getRestTemplate() method. However, if I do the initialization of the restTemplate inside the constructor then everything works fine.
this.restTemplate = getRestTemplate();
I thought the constructor was always called first. Could someone please explain this?

Answer 1

Use constructor injection
#Service
public class MyService {
private String username;
private String password;
#Autowired // optional if it is only single constructor
public MyService(#Value("${my.username}") String username, #Value("${my.password}") String password){
this.username=username;
this.password=password;
///its already here
}
This way you are guaranteed that values must be provided and available on object construction - thus it will be later on when you will call any of methods of that class.
If values are not provided OR SpEL is invalid, app will not boot.

Answer 2

You are calling getRestTemplate(); at the same time the class level field is being declared, which is before the class has been inflated by Spring framework, thus the properties aren't yet available.
Try setting the values in the class's constructor instead. You can do this by changing your variable declaration to : private RestTemplate restTemplate; and adding this constructor:
public MyService() {
this.restTemplate = getRestTemplate();
}

Answer 3

I think it has to do with the way you are accessing the restTemplate for instantiating the private variable. I do it this way.
#Autowire private RestTemplate restTemplate;
#Bean public RestTemplate restTemplate() {
...
}
This way Spring has control over when variables are instantiated.