Spring Boot MCQ Questions – Page 11 of 49

Q: If you remove `@SpringBootApplication` and instead use `@Configuration`, `@EnableAutoConfiguration`, and `@ComponentScan` separately on the same class, what would be the functional difference in a typical Spring Boot application?

B) There would be no functional difference.. `@SpringBootApplication` is a meta-annotation that simply bundles these three annotations. Functionally, applying them individually achieves the exact same result as using the combined annotation.

Q: Given the controller, what exception will be thrown if a POST request is made to '/api/data' *without* including the 'value' parameter in the request body?

A) MissingServletRequestParameterException. When a @RequestParam is marked as 'required = true' and the parameter is absent in the request, Spring MVC throws a MissingServletRequestParameterException. This exception indicates that a mandatory request parameter is missing.

Q: Which of the following is the best way to handle an *optional* path variable in Spring Boot, meaning the segment might sometimes be absent from the URL?

C) Wrap the `@PathVariable` in `java.util.Optional `, e.g., `@PathVariable Optional id`.. While creating separate methods is an option, `java.util.Optional ` is the idiomatic way in Spring Boot to explicitly declare a path variable as optional within a single handler method.

Q: What does this code print, assuming the remote service successfully processes the request and echoes the message?

A) Received: 'Hello Feign'. The `@RequestBody` annotation ensures the provided 'Hello Feign' string is sent as the request body. The mock client simulates the service echoing the received message.

Q: Consider the following Spring component. What error will prevent the application from starting?

C) The application will start successfully, and minutesSinceEpoch will be a valid long value.. The provided SpEL expression `T(java.lang.System).currentTimeMillis() / (1000 * 60)` is syntactically correct and evaluates to a `long` value, which is compatible with the `minutesSinceEpoch` field. Therefore, the application will start without error.

Q: What error will occur when this Spring Boot application attempts to start?

C) Runtime error: IllegalStateException: Ambiguous mapping. Cannot map 'myController' method 'getData()'.. Applying both `@GetMapping` (which implies `RequestMethod.GET`) and `@RequestMapping(method = RequestMethod.POST)` to the same method for the same path creates an ambiguous mapping. Spring cannot resolve which method to invoke for a given request, leading to an `IllegalStateException` during application startup.

Q: What does this code print to the console?

B) Mouse: 75.0. The JPQL query selects `name` and `price` as an `Object[]`. The results are ordered by name, so 'Keyboard' is at index 0 and 'Mouse' at index 1. Accessing `results.get(0)[0]` gets 'Keyboard' and `results.get(1)[1]` gets 'Mouse's price, which is 75.0.

Q: Given a `User` entity and `UserRepository` (JpaRepository), what does this test code print to the console?

A) Before save: 0 After save: 1. `@DataJpaTest` creates a transactional context that automatically rolls back after each test. However, the `System.out.print` calls occur *within* this transaction, so they observe the state of the database *before* the rollback. Thus, `count()` shows 0 initially, then 1 after saving, before the transaction is finalized.

Q: Which component is primarily responsible for converting the HTTP request body (e.g., JSON) into a Java object when `@RequestBody` is used?

B) An `HttpMessageConverter` implementation.. Spring uses `HttpMessageConverter` implementations (like `MappingJackson2HttpMessageConverter` for JSON) to convert the raw HTTP request body into the specified Java object type.

Q: Given the following Dockerfile and assuming `my-springboot-app.jar` exists, what command will be executed when the Docker container starts?

A) java -jar app.jar. The `CMD` instruction specifies the command to execute when the container starts. In this case, it directly runs the JAR file using `java -jar app.jar`.

Q201 medium

If you remove `@SpringBootApplication` and instead use `@Configuration`, `@EnableAutoConfiguration`, and `@ComponentScan` separately on the same class, what would be the functional difference in a typical Spring Boot application?

Q202 medium code output

Given the controller, what exception will be thrown if a POST request is made to '/api/data' *without* including the 'value' parameter in the request body?

java

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

@Controller
public class DataController {
    @PostMapping("/api/data")
    public String handleData(@RequestParam(required = true) String value) {
        System.out.println("Received: " + value);
        return "handled";
    }
}

Q203 medium

Which of the following is the best way to handle an *optional* path variable in Spring Boot, meaning the segment might sometimes be absent from the URL?

Q204 medium code output

What does this code print, assuming the remote service successfully processes the request and echoes the message?

java

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;

@FeignClient(name = "messageService", url = "http://localhost:8081")
interface MessageServiceClient {
    @PostMapping("/messages")
    String postMessage(@RequestBody String message);
}

public class TestApplication {
    public static void main(String[] args) {
        MessageServiceClient client = msg -> "Received: '" + msg + "'"; // Mock implementation
        System.out.println(client.postMessage("Hello Feign"));
    }
}

Q205 medium code error

Consider the following Spring component. What error will prevent the application from starting?

java

java
@Component
public class SpelCalculator {
    @Value("#{T(java.lang.System).currentTimeMillis() / (1000 * 60)}")
    private long minutesSinceEpoch;

    public long getMinutesSinceEpoch() {
        return minutesSinceEpoch;
    }
}


properties
# application.properties (no relevant properties)

Q206 medium code error

What error will occur when this Spring Boot application attempts to start?

java

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class MyController {

    @GetMapping("/api/v1/data")
    @RequestMapping(method = RequestMethod.POST, value = "/api/v1/data")
    public String getData() {
        return "Data";
    }
}

Q207 medium code output

What does this code print to the console?

java

package com.example;

import jakarta.persistence.*;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import java.util.List;

@Entity
public class Product {
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private double price;

    public Product() {}
    public Product(Long id, String name, double price) { this.id = id; this.name = name; this.price = price; }
    public String getName() { return name; }
    public double getPrice() { return price; }
}

interface ProductRepository extends JpaRepository<Product, Long> {
    @Query("SELECT p.name, p.price FROM Product p ORDER BY p.name")
    List<Object[]> findNameAndPriceProjectionJPQL();
}

// Assume ProductRepository is autowired as 'productRepository'
// And the database contains:
// Product(id=1, name='Mouse', price=25.00)
// Product(id=2, name='Keyboard', price=75.00)
List<Object[]> results = productRepository.findNameAndPriceProjectionJPQL();
System.out.println(results.get(0)[0] + ": " + results.get(1)[1]);

Q208 medium code output

Given a `User` entity and `UserRepository` (JpaRepository), what does this test code print to the console?

java

import com.example.demo.entity.User;
import com.example.demo.repository.UserRepository;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;

@DataJpaTest
class TransactionalRollbackTest {
    @Autowired
    private UserRepository userRepository;

    @Test
    void testTransactionalBehavior() {
        System.out.println("Before save: " + userRepository.count());
        userRepository.save(new User("Charlie"));
        System.out.print("After save: " + userRepository.count());
    }
}

Q209 medium

Which component is primarily responsible for converting the HTTP request body (e.g., JSON) into a Java object when `@RequestBody` is used?

Q210 medium code output

Given the following Dockerfile and assuming `my-springboot-app.jar` exists, what command will be executed when the Docker container starts?

dockerfile

FROM openjdk:17-jre-slim
WORKDIR /app
COPY target/my-springboot-app.jar app.jar
EXPOSE 8080
CMD ["java", "-jar", "app.jar"]

Q211 medium code output

Consider a Spring Boot REST controller with a `@PostMapping("/register")` method that accepts a `@Valid @RequestBody UserRegistrationDto userDto`. What is the HTTP status code and response body content when the following JSON request is sent to `/register`? `POST /register HTTP/1.1 Content-Type: application/json { "email": "test@example.com", "age": 30 }`

java

import javax.validation.constraints.NotNull;
import javax.validation.constraints.Email;
import javax.validation.constraints.Min;

public class UserRegistrationDto {
    @NotNull(message = "Username must not be null")
    private String username;

    @NotNull(message = "Email must not be null")
    @Email(message = "Email format is invalid")
    private String email;

    @NotNull(message = "Age must not be null")
    @Min(value = 1, message = "Age must be at least 1")
    private Integer age;

    // Getters and setters are implicitly present
}

Q212 medium

Which of the following statements accurately describes a characteristic of RESTful APIs built with `@RestController` regarding state management?

Q213 medium code output

What content will the MockMvc test assert to be in the response body?

java

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
import org.springframework.test.web.servlet.MockMvc;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.delete;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

@WebMvcTest(controllers = TestController.class)
class TestControllerTest {
    @Autowired
    private MockMvc mockMvc;

    @Test
    void testDeleteEndpoint() throws Exception {
        mockMvc.perform(delete("/api/items/5"))
               .andExpect(status().isAccepted())
               .andExpect(content().string("Item 5 deleted."));
    }
}

// Assuming TestController has:
// @RestController
// class TestController {
//    @DeleteMapping("/api/items/{id}")
//    public ResponseEntity<String> deleteItem(@PathVariable Long id) {
//        return ResponseEntity.accepted().body("Item " + id + " deleted.");
//    }
// }

Q214 medium code error

Consider a Spring Boot application where a `MyDao` class is annotated with `@Repository`. If the `PersistenceExceptionTranslationPostProcessor` bean is NOT defined in the application's configuration, and `saveData` throws a Hibernate `ConstraintViolationException`, what type of exception will propagate to the caller of `myService.performSave()`?

java

package com.example.dao;
import org.springframework.stereotype.Repository;
import org.hibernate.exception.ConstraintViolationException;

@Repository
public class MyDao {
    public void saveData() {
        // Simulate a raw persistence exception
        throw new ConstraintViolationException("Duplicate entry", new Exception(), "unique_constraint");
    }
}

package com.example.service;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import com.example.dao.MyDao;

@Service
public class MyService {
    @Autowired
    private MyDao myDao;

    public void performSave() {
        myDao.saveData();
    }
}
// Assuming app config is missing @Bean PersistenceExceptionTranslationPostProcessor

Q215 medium code output

What does this code print to the console?

java

package com.example;

import jakarta.persistence.*;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;
import java.util.Optional;

@Entity
public class Product {
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private double price;

    public Product() {}
    public Product(Long id, String name, double price) { this.id = id; this.name = name; this.price = price; }
    public String getName() { return name; }
    public double getPrice() { return price; }
}

interface ProductRepository extends JpaRepository<Product, Long> {
    @Query(value = "SELECT * FROM product WHERE name = :productName", nativeQuery = true)
    Optional<Product> findByNameExactNative(@Param("productName") String name);
}

// Assume ProductRepository is autowired as 'productRepository'
// And the database contains:
// Product(id=1, name='Webcam', price=50.00)
// Product(id=2, name='Microphone', price=70.00)
// Assume 'product' is the correct table name.
Optional<Product> webcam = productRepository.findByNameExactNative("Webcam");
Optional<Product> speaker = productRepository.findByNameExactNative("Speaker");
System.out.println(webcam.isPresent() + ", " + speaker.isPresent());

Q216 medium

Which of the following statements best describes the purpose of the `ModelAndView` object in Spring MVC?

Q217 medium code error

What error occurs when accessing `/reports` with the following controller?

java

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

@RestController
public class ReportController {
    @GetMapping("/reports")
    public String getReport(@PathVariable String reportId) {
        return "Report ID: " + reportId;
    }
}

Q218 medium

When a bean is defined using `@Component` on a class named `MyComplexCalculator` without an explicit bean name, what is the default qualifier value that `@Qualifier` would use to refer to this bean?

Q219 medium code output

Given the following Java code snippet using JJWT for token generation, what will be printed to the console?

java

import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.SignatureAlgorithm;
import io.jsonwebtoken.security.Keys;
import java.security.Key;
import java.util.Date;

public class JwtGenerator {
    public static void main(String[] args) {
        Key key = Keys.secretKeyFor(SignatureAlgorithm.HS256);
        String jwt = Jwts.builder()
                .setSubject("testUser")
                .setIssuedAt(new Date(0L)) // Epoch time for consistency
                .setExpiration(new Date(10000L)) // Expire in 10 seconds from epoch
                .signWith(key)
                .compact();
        System.out.println(jwt.startsWith("eyJ"));
    }
}

Q220 medium code output

What is the HTTP status code and response body when a POST request is sent to `/auth/login` if `AuthenticationFailedException` is thrown, given the Spring Boot setup?

java

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;
import java.util.Map;

class AuthenticationFailedException extends RuntimeException {
    public AuthenticationFailedException(String message) { super(message); }
}

@RestController
class AuthController {
    @PostMapping("/auth/login")
    public String login() {
        throw new AuthenticationFailedException("Invalid credentials");
    }
}

@RestControllerAdvice
class AuthExceptionHandler {
    @ExceptionHandler(AuthenticationFailedException.class)
    public ResponseEntity<Map<String, String>> handleAuthFailed(AuthenticationFailedException ex) {
        return ResponseEntity.status(HttpStatus.UNAUTHORIZED)
                             .body(Map.of("error", ex.getMessage()));
    }
}

🌱 Spring Boot MCQ Questions – Page 11