Spring Boot MCQ Questions – Page 22 of 49

Q: What does this code print to the console when run as a Spring Boot application?

A) Sending email notification.. When multiple beans of the same type exist (`MessageService` implementations), Spring requires disambiguation. `@Qualifier("emailService")` explicitly tells the IoC container to inject the bean named 'emailService', which is `EmailService`.

Q: An application configures a `DataSource` for JPA, which is then used by an `EntityManagerFactory` and ultimately by a `@Repository`. If the `DataSource` is configured with a non-existent JDBC driver class name, what error will occur during application startup?

A) org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource' defined in class 'JpaConfig': Invocation of init method failed; nested exception is java.lang.ClassNotFoundException: non.existent.Driver. The `DriverManagerDataSource` attempts to load the JDBC driver class specified by `setDriverClassName()`. If this class does not exist, a `ClassNotFoundException` will be thrown during the bean creation process for the `dataSource` bean, which is wrapped in a `BeanCreationException`.

Q: Consider a scenario where a DELETE request is made to `/api/reports/summary`. What HTTP status code and body would be returned by this Spring Boot controller method if the `reportService.clearSummary()` call succeeds?

B) HTTP 204 No Content, with an empty body.. By default, a `@DeleteMapping` method that returns `void` and does not have an explicit `@ResponseStatus` annotation will result in an HTTP 204 No Content status code upon successful completion, indicating no content to return.

Q: If the Spring Boot application above is packaged as `myapp.jar` and executed as `java -jar myapp.jar --spring.profiles.active=dev`, what will be the output from the `CommandLineRunner`?

A) Running in Development Profile!. The `--spring.profiles.active=dev` command-line argument activates the 'dev' profile, causing only the `devRunner` bean, which is annotated with `@Profile("dev")`, to be initialized and executed.

Q: What will be the outcome when running this Spring Boot application?

A) org.springframework.beans.factory.NoUniqueBeanDefinitionException. Spring finds two beans of type `MessageService` (`emailService` and `smsService`) and cannot decide which one to inject into the `Notifier` without a `@Qualifier`, leading to a `NoUniqueBeanDefinitionException`.

Q: What is the primary difference between `@Controller` and `@RestController` in Spring Boot applications, especially when building RESTful APIs?

A) `@RestController` automatically serializes return values to JSON/XML, while `@Controller` requires `@ResponseBody` on each method.. `@RestController` is a convenience annotation that combines `@Controller` and `@ResponseBody`, automatically serializing method return values into the response body. `@Controller` typically returns view names unless explicitly marked with `@ResponseBody`.

Q: What happens if a `@PathVariable` in a Spring Boot controller method is declared as `int` but the corresponding URI segment contains a non-numeric string?

B) A `TypeMismatchException` will be thrown, resulting in a 400 Bad Request error.. Spring Boot attempts to convert the path variable to the specified type. If the conversion fails, typically a `TypeMismatchException` occurs, leading to a 400 Bad Request HTTP status.

Q: To change the base package for component scanning when using `@SpringBootApplication`, which attribute should be used?

A) `scanBasePackages`. The `scanBasePackages` attribute of `@SpringBootApplication` (or `@ComponentScan`) allows you to explicitly define one or more base packages to scan for components, overriding the default behavior.

Q: What is the console output when a GET request is made to `/data` in this Spring Boot application?

A) Interceptor: Pre-handle Controller: Processing Data Interceptor: Post-handle Interceptor: After-completion. `preHandle` executes before the controller, `postHandle` executes after the controller but before view rendering, and `afterCompletion` executes after the complete request has finished, including view rendering or an exception.

Q: What does the following Spring Boot related JWT code print after successfully parsing a token and extracting a claim?

A) SUPER_ADMIN. The code first generates a JWT with a custom claim `customRole` set to `SUPER_ADMIN`. It then parses the token with the correct key and extracts the `Claims` body. Finally, it retrieves the value associated with the `customRole` key, which is `SUPER_ADMIN`.

Q421 medium code output

What does this code print to the console when run as a Spring Boot application?

java

import org.springframework.stereotype.Component;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

interface MessageService { String send(); }

@Component("emailService")
class EmailService implements MessageService { @Override public String send() { return "Sending email notification."; } }

@Component("smsService")
class SmsService implements MessageService { @Override public String send() { return "Sending SMS notification."; } }

@Component
class NotificationSender implements CommandLineRunner {
    @Autowired
    @Qualifier("emailService")
    private MessageService service;
    @Override
    public void run(String... args) { System.out.println(service.send()); }
}

@SpringBootApplication
public class App { public static void main(String[] args) { SpringApplication.run(App.class, args); } }

Q422 medium code error

An application configures a `DataSource` for JPA, which is then used by an `EntityManagerFactory` and ultimately by a `@Repository`. If the `DataSource` is configured with a non-existent JDBC driver class name, what error will occur during application startup?

java

package com.example.config;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.jdbc.datasource.DriverManagerDataSource;
import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
import org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter;
import javax.sql.DataSource;

@Configuration
public class JpaConfig {
    @Bean
    public DataSource dataSource() {
        DriverManagerDataSource dataSource = new DriverManagerDataSource();
        dataSource.setDriverClassName("non.existent.Driver"); // This line causes the error
        dataSource.setUrl("jdbc:h2:mem:testdb");
        dataSource.setUsername("sa");
        dataSource.setPassword("");
        return dataSource;
    }

    @Bean
    public LocalContainerEntityManagerFactoryBean entityManagerFactory(DataSource dataSource) {
        LocalContainerEntityManagerFactoryBean em = new LocalContainerEntityManagerFactoryBean();
        em.setDataSource(dataSource);
        em.setPackagesToScan("com.example.domain");
        em.setJpaVendorAdapter(new HibernateJpaVendorAdapter());
        return em;
    }
}
// Assuming a @Repository class uses this EntityManagerFactory.

Q423 medium code output

Consider a scenario where a DELETE request is made to `/api/reports/summary`. What HTTP status code and body would be returned by this Spring Boot controller method if the `reportService.clearSummary()` call succeeds?

java

import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.*;

@RestController
@RequestMapping("/api/reports")
public class ReportController {

    private ReportService reportService;

    // Constructor injected reportService

    @DeleteMapping("/summary")
    public void clearSummary() {
        reportService.clearSummary();
        // No explicit @ResponseStatus, no return value
    }
}

Q424 medium code output

If the Spring Boot application above is packaged as `myapp.jar` and executed as `java -jar myapp.jar --spring.profiles.active=dev`, what will be the output from the `CommandLineRunner`?

java

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Profile;
import org.springframework.boot.CommandLineRunner;

@SpringBootApplication
public class MyApplication {

    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }

    @Profile("dev")
    @Bean
    public CommandLineRunner devRunner() {
        return args -> {
            System.out.println("Running in Development Profile!");
        };
    }

    @Profile("!dev") // For any profile NOT dev, or no profile
    @Bean
    public CommandLineRunner defaultRunner() {
        return args -> {
            System.out.println("Running in Default Profile.");
        };
    }
}

Q425 medium code error

What will be the outcome when running this Spring Boot application?

java

public interface MessageService {
    String getMessage();
}

@Service("emailService")
public class EmailService implements MessageService {
    @Override
    public String getMessage() { return "Email message"; }
}

@Service("smsService")
public class SmsService implements MessageService {
    @Override
    public String getMessage() { return "SMS message"; }
}

@Component
public class Notifier {
    @Autowired
    private MessageService messageService; // Ambiguity here

    public void notifyUser() {
        System.out.println(messageService.getMessage());
    }
}

Q426 medium

What is the primary difference between `@Controller` and `@RestController` in Spring Boot applications, especially when building RESTful APIs?

Q427 medium

What happens if a `@PathVariable` in a Spring Boot controller method is declared as `int` but the corresponding URI segment contains a non-numeric string?

Q428 medium

To change the base package for component scanning when using `@SpringBootApplication`, which attribute should be used?

Q429 medium code output

What is the console output when a GET request is made to `/data` in this Spring Boot application?

java

import org.springframework.context.annotation.Configuration;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@Component
class MyInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) {
        System.out.println("Interceptor: Pre-handle");
        return true;
    }
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) {
        System.out.println("Interceptor: Post-handle");
    }
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {
        System.out.println("Interceptor: After-completion");
    }
}

@Configuration
class WebConfig implements WebMvcConfigurer {
    private final MyInterceptor myInterceptor;
    public WebConfig(MyInterceptor myInterceptor) { this.myInterceptor = myInterceptor; }
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(myInterceptor).addPathPatterns("/data");
    }
}

@RestController
class DataController {
    @GetMapping("/data")
    public String getData() {
        System.out.println("Controller: Processing Data");
        return "Data";
    }
}

Q430 medium code output

What does the following Spring Boot related JWT code print after successfully parsing a token and extracting a claim?

java

import io.jsonwebtoken.Claims;
import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.SignatureAlgorithm;
import io.jsonwebtoken.security.Keys;
import java.security.Key;

public class ClaimExtractor {
    public static void main(String[] args) {
        Key key = Keys.secretKeyFor(SignatureAlgorithm.HS256);
        String jwt = Jwts.builder()
                .setSubject("adminUser")
                .claim("customRole", "SUPER_ADMIN")
                .signWith(key)
                .compact();
        
        Claims claims = Jwts.parserBuilder()
                .setSigningKey(key)
                .build()
                .parseClaimsJws(jwt)
                .getBody();
        System.out.println(claims.get("customRole"));
    }
}

Q431 medium

Consider an interface `NotificationService` with two implementations: `EmailNotificationService` and `SMSNotificationService`. Both are Spring components. How would you inject specifically the `EmailNotificationService` into another component?

Q432 medium code error

Given the Spring Boot controller method below, what type of error will occur?

java

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class MyController {
    @GetMapping("/immutable-test")
    public ResponseEntity<String> testImmutability() {
        ResponseEntity<String> response = ResponseEntity.ok("Initial Body");
        response.getHeaders().add("X-Custom-Header", "New Value");
        return response;
    }
}

Q433 medium code output

What is the output of this code snippet, assuming `userRepository` is a JpaRepository and initially contains no users?

java

public class UserService {
    private UserRepository userRepository;

    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    public String updateOrCreateUser(Long id, String name, String email) {
        User user = userRepository.findById(id).orElse(new User());
        user.setName(name);
        user.setEmail(email);
        userRepository.save(user);
        return user.getId() != null ? "User saved with ID: " + user.getId() : "New user created";
    }
}

// In a test context or main method:
UserService service = new UserService(userRepository);
String result = service.updateOrCreateUser(null, "David", "david@example.com");
System.out.println(result);

Q434 medium code error

What type of error will occur when Spring tries to initialize the `MyService` bean?

java

import org.springframework.stereotype.Component;

@Component
public class MyService {
    private final String serviceConfig;

    // Spring tries to find a bean of type String, but none exists by default
    public MyService(String serviceConfig) {
        this.serviceConfig = serviceConfig;
    }

    public String getConfig() {
        return "Config: " + serviceConfig;
    }
}

Q435 medium code output

What is the HTTP response status code when making a `GET` request to `/submit-form` with the following controller?

java

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
public class FormController {

    @PostMapping("/submit-form")
    @ResponseBody
    public String processForm() {
        return "Form submitted successfully!";
    }
}

Q436 medium code error

What error will occur when Spring attempts to inject dependencies into `ServiceA`?

java

import org.springframework.stereotype.Component;
import org.springframework.beans.factory.annotation.Autowired;

@Component
public class ServiceA {
    @Autowired
    private NonExistentService nonExistentService;

    public void doWork() {
        // ...
    }
}

Q437 medium code output

What is the output of this code when accessing the '/test' endpoint?

java

import org.springframework.web.bind.annotation.*;

@RestController
public class MyController {

    @GetMapping("/test")
    public String testMethod() {
        throw new RuntimeException("An unexpected error occurred!");
    }

    @ExceptionHandler(RuntimeException.class)
    public String handleRuntimeException(RuntimeException ex) {
        return "Error caught: " + ex.getMessage();
    }
}

Q438 medium code error

What is the primary error when Spring Boot attempts to start this application?

java

import org.springframework.stereotype.Service;
import org.springframework.stereotype.Repository;

@Service
public class UserService {
    private UserRepository userRepository;

    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }
}

// UserRepository.java (in the same package)
// Missing @Repository or @Component annotation
public class UserRepository {
    public String findById(Long id) {
        return "DB: User " + id;
    }
}

Q439 medium code output

What is the HTTP response body when a GET request is made to `/orders/101/items/5005`?

java

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class OrderController {
    @GetMapping("/orders/{userId}/items/{itemId}")
    public String getOrderItem(@PathVariable Long userId, @PathVariable Long itemId) {
        return "Order details for User " + userId + ", Item " + itemId;
    }
}

Q440 medium code output

What is the output of this code when accessing '/info'?

java

import org.springframework.web.bind.annotation.*;
import org.springframework.http.HttpStatus;

@RestController
public class InfoController {

    @GetMapping("/info")
    public String getInfo() {
        throw new UnsupportedOperationException("Feature is not available");
    }

    @ExceptionHandler(UnsupportedOperationException.class)
    @ResponseStatus(HttpStatus.NOT_IMPLEMENTED)
    public String handleUnsupportedOperation(UnsupportedOperationException ex) {
        return "Status 501: " + ex.getMessage();
    }
}

🌱 Spring Boot MCQ Questions – Page 22