Spring 4 Interview Questions with Answers

1. What are the main features introduced in spring 4?

Ans: Spring 4 has introduced many new features. Some of them are as follows.

1. @RestController annotation has been introduced for easiness to develop spring rest web service.
2. AsyncRestTemplate has been added to develop rest web service.
3. Java 8 and hibernate 4.3 have been supported.
4. Different time zone in spring MVC has been supported.
5. Now spring supports websocket protocol.
6. Spring messaging supports STOMP protocol.
7. Spring security JUnit test module has been added with @WithMockUser and @WithUserDetails annotations.

2. What is the use of @RestController annotation in spring 4?

Ans: Spring 4 has introduced @RestController annotation that has replaced @Controller and @ResponseBody. In spring 4 rest web service development, our service methods need not to use @ResponseBody.
@RestController = @Controller + @ResponseBody

@RestController
@RequestMapping("/data")
public class PersonController {}  

3. What is the role of AsyncRestTemplate and ListenableFuture in spring 4?

Ans: AsyncRestTemplate can return the URL output asynchronously. ListenableFuture is the return type which itself will return ResponseEntity.

ListenableFuture<ResponseEntity<String>> future = 
              asycTemp.exchange(url, method, requestEntity, responseType);
ResponseEntity<String> entity = future.get();  

4. What is the role of AsyncClientHttpRequestFactory and AsyncClientHttpRequest in spring 4?

Ans: AsyncClientHttpRequestFactory returns the instance of AsyncClientHttpRequest that represents client side asynchronous HTTP request. We use it as follows.

ListenableFuture<ClientHttpResponse> future = asyncClientHttpRequest.executeAsync();
 

5. How to use WebSocket in spring 4?

Ans: 1. Java configuration class implements AbstractWebSocketMessageBrokerConfigurer and we need to override its methods that are configureMessageBroker() and registerStompEndpoints(). 

2. Java configuration class should be annotated with @EnableWebSocketMessageBroker with @Configuration. 
3. Spring controller class uses @SendTo annotation with @MessageMapping at method level to declare result URL. 
4. To work with WebSocket, other protocol and JS library such as SockJS and STOMP Protocol are required.

6. What is the role of @CacheConfig in spring 4?

Ans: @CacheConfig is used at class level. It is used to set common cache related settings. All the methods annotated with @Cacheable override the settings of @CacheConfig.

@Service
@CacheConfig(cacheNames="mycacheone")
public class Student {}  

7. How to handle @Async exception in spring 4?

Ans: Spring 4 provides AsyncUncaughtExceptionHandler that caches exception thrown by the method annotated with @Async. We create a class implementing AsyncUncaughtExceptionHandler.

public class MyAsyncUncaughtExceptionHandler implements AsyncUncaughtExceptionHandler {
    @Override
    public void handleUncaughtException(Throwable ex, Method method, Object... params) {}
}  

8. What is the role of @WithMockUser and @WithUserDetails annotation in spring 4 security JUnit test

Ans: @WithMockUser annotation allows mock user at server side in spring security JUnit testing. There are usernameand roles attributes in @WithMockUser annotation. We use it as follows.

@Test 
@WithMockUser(username = "ram", roles={"ADMIN"})
public class SpringSecurityTest {} 

@WithUserDetails annotation provides custom UserDetailsService in spring security JUnit testing and we can use it as follows.

@Test @WithUserDetails("ram") public void testFour() { userService.methodFour(); }