Spring Boot MCQ Questions – Page 24 of 49

Q: What is the output of this code when the `main` method of `MainRunner` is executed?

A) MyComponent Initialized. When `SpringApplication.run(AppConfig.class, args)` is called, Spring Boot uses `AppConfig` as the primary source of configuration. Since `AppConfig` is annotated with `@SpringBootApplication`, it enables component scanning in its package (com.example.demo) and its sub-packages, thus discovering `MyComponent`.

Q: Given the Spring Boot controller below, what is the outcome regarding the view and model attributes if a request is made to `/products`?

A) Resolved View Name: productList, Model Attributes: {categories=[Electronics, Books], title=All Products}. The `@ModelAttribute` method `addCategories()` adds 'categories' to the model before any request handler method is invoked. The `showProducts` method then adds 'title', and returns 'productList' as the view name.

Q: Assuming this Spring Boot application is packaged as a JAR and executed with `java -jar myapp.jar`, what will be one of the last lines printed to the console during a successful startup?

A) Application has started successfully!. The `CommandLineRunner` bean executes after the application context is fully loaded and initialized, printing its message to the console. Option B is a typical Spring Boot log line, but the specific `CommandLineRunner` output is directly caused by the provided code snippet.

Q: What error will occur during the startup of this Spring Boot application?

A) org.springframework.beans.factory.parsing.BeanDefinitionParsingException: Configuration problem: No scope registered for scope name 'unknownScopeName'. Spring's IoC container encounters an unknown scope name defined by `@Scope("unknownScopeName")`. Since 'unknownScopeName' is not a registered scope, Spring will fail during the bean definition parsing phase with a `BeanDefinitionParsingException`.

Q: What is the output of this code?

A) Data fetched successfully from repo.. The @Repository annotated class is properly scanned and registered as a Spring bean. It is then successfully autowired into the @Service, allowing its method to be called and the returned string to be printed.

Q: What is the default scope for beans managed by the `ApplicationContext` in a Spring Boot application?

C) singleton. By default, Spring manages beans as singletons, meaning only one instance of the bean exists and is shared across the entire `ApplicationContext`.

Q: 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 { "username": "Alice", "email": "invalid-email-format", "age": 25 }`

B) HTTP 400 Bad Request, body contains "Email format is invalid". The 'email' field contains a string that does not conform to a valid email format, violating the `@Email` constraint. Spring validation will return a 400 Bad Request with the message 'Email format is invalid'.

Q: What error will occur when Spring attempts to instantiate `RestrictedComponent`?

A) org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'restrictedComponent': Could not instantiate bean class [RestrictedComponent]: Is the constructor public?. Spring requires access to a public or package-private constructor (or one annotated with `@Autowired`) to instantiate a component. A class with only private constructors prevents Spring from creating the bean, leading to a BeanCreationException.

Q: Consider the following Spring Boot controller. If `dashboard.html` attempts to display `${data.value}` where `data` is the attribute set in the controller, what is the outcome?

B) org.thymeleaf.exceptions.TemplateProcessingException: Error during execution of expression 'data.value' (dashboard.html:X:Y). The controller adds an attribute named 'myData' as a String. The template attempts to access 'data.value'. First, 'data' itself is not in the model. Even if it were `myData.value`, a String object does not have a 'value' property in the context of bean properties. Thymeleaf will throw a `TemplateProcessingException` when it cannot resolve the property or expression.

Q: What error will occur when the ApplicationContext tries to instantiate 'MyService' due to an unresolvable constructor dependency?

A) org.springframework.beans.factory.UnsatisfiedDependencyException. The `MyService` bean requires an `ExternalDependency` through its constructor. However, `ExternalDependency` is not a Spring component or a `@Bean` method result, so the ApplicationContext cannot find a suitable bean for injection. This causes an `UnsatisfiedDependencyException` during bean creation.

Q461 medium code output

What is the output of this code when the `main` method of `MainRunner` is executed?

java

// src/main/java/com/example/demo/MainRunner.java
package com.example.demo;

import org.springframework.boot.SpringApplication;

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

// src/main/java/com/example/demo/AppConfig.java
package com.example.demo;

import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.stereotype.Component;
import javax.annotation.PostConstruct;

@SpringBootApplication
class AppConfig {
    // This class is intended as the primary Spring Boot configuration
}

// src/main/java/com/example/demo/MyComponent.java
package com.example.demo;

import org.springframework.stereotype.Component;
import javax.annotation.PostConstruct;

@Component
class MyComponent {
    @PostConstruct
    public void init() {
        System.out.println("MyComponent Initialized");
    }
}

Q462 medium code output

Given the Spring Boot controller below, what is the outcome regarding the view and model attributes if a request is made to `/products`?

java

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.ui.Model;

@Controller
public class ProductController {

    @ModelAttribute("categories")
    public String[] addCategories() {
        return new String[]{"Electronics", "Books"};
    }

    @GetMapping("/products")
    public String showProducts(Model model) {
        model.addAttribute("title", "All Products");
        return "productList";
    }
}

Q463 medium code output

Assuming this Spring Boot application is packaged as a JAR and executed with `java -jar myapp.jar`, what will be one of the last lines printed to the console during a successful startup?

java

package com.example.demo;

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

@SpringBootApplication
public class MyApplication {

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

    @Bean
    public CommandLineRunner run() {
        return args -> {
            System.out.println("Application has started successfully!");
        };
    }
}

Q464 medium code error

What error will occur during the startup of this Spring Boot application?

java

import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;

@Component
@Scope("unknownScopeName") // This scope name is not defined in Spring
public class MyScopedComponent {
    public String message() {
        return "Hello from scoped component!";
    }
}

Q465 medium code output

What is the output of this code?

java

package com.example;

import org.springframework.stereotype.Repository;
import org.springframework.stereotype.Service;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;

@Repository
class SimpleDataRepository {
    public String retrieveData() {
        return "Data fetched successfully from repo.";
    }
}

@Service
class DataDisplayService {
    @Autowired SimpleDataRepository repo;
    public void displayData() {
        System.out.println(repo.retrieveData());
    }
}

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(Application.class, args);
        DataDisplayService service = context.getBean(DataDisplayService.class);
        service.displayData();
        context.close();
    }
}

Q466 medium

What is the default scope for beans managed by the `ApplicationContext` in a Spring Boot application?

Q467 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 { "username": "Alice", "email": "invalid-email-format", "age": 25 }`

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
}

Q468 medium code error

What error will occur when Spring attempts to instantiate `RestrictedComponent`?

java

import org.springframework.stereotype.Component;

@Component
public class RestrictedComponent {
    private RestrictedComponent() {
        // Initialization logic
    }
}

Q469 medium code error

Consider the following Spring Boot controller. If `dashboard.html` attempts to display `${data.value}` where `data` is the attribute set in the controller, what is the outcome?

java

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.ui.Model;

@Controller
public class DashboardController {

    @GetMapping("/dashboard")
    public String showDashboard(Model model) {
        model.addAttribute("myData", "Some string value");
        return "dashboard"; // Assumes dashboard.html tries to access ${data.value}
    }
}

Q470 medium code error

What error will occur when the ApplicationContext tries to instantiate 'MyService' due to an unresolvable constructor dependency?

java

import org.springframework.stereotype.Component;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

class ExternalDependency { // Not a Spring component
    public ExternalDependency() {}
}

@Component
class MyService {
    public MyService(ExternalDependency dependency) {
        // Constructor injection
    }
}

public class MissingDependencyApp {
    public static void main(String[] args) {
        new AnnotationConfigApplicationContext(MissingDependencyApp.class.getPackage().getName());
    }
}

Q471 medium code output

Given a `Movie` entity with a custom sequence generator, what will be the IDs of the first two saved movies?

java

import jakarta.persistence.*;

@Entity
@SequenceGenerator(name = "movie_seq", sequenceName = "MOVIE_SEQ", initialValue = 50, allocationSize = 1)
public class Movie {
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "movie_seq")
    private Long id;
    private String title;

    public Movie() {}
    public Movie(String title) { this.title = title; }
    public Long getId() { return id; }
}

// Assume movieRepository is injected and available
// Assume transaction context is active
Movie movie1 = new Movie("Inception");
movieRepository.save(movie1);
Movie movie2 = new Movie("Dunkirk");
movieRepository.save(movie2);
System.out.println("Movie 1 ID: " + movie1.getId() + ", Movie 2 ID: " + movie2.getId());

Q472 medium code error

A client attempts to delete an item via `DELETE /api/items/123`. What will be the outcome with this code snippet?

java

import org.springframework.web.bind.annotation.*;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.RequestMethod;

@RestController
@RequestMapping("/api/items")
public class ItemController {

    private ItemService itemService; // Assume injected

    @RequestMapping(value = "/{itemId}", method = RequestMethod.GET)
    public ResponseEntity<Void> deleteItem(@PathVariable String itemId) {
        itemService.deleteItem(itemId);
        return ResponseEntity.noContent().build();
    }
}

Q473 medium code output

What is the HTTP response status code when accessing `/item?id=123` with the following controller, assuming `name` is required by default?

java

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
public class ItemController {

    @GetMapping("/item")
    @ResponseBody
    public String getItemDetails(
            @RequestParam long id,
            @RequestParam String name) {
        return "Item: " + name + " (" + id + ")";
    }
}

Q474 medium code output

What is the output of this code?

java

package com.example;

import org.springframework.stereotype.Repository;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;

@Repository("primaryProductRepo")
class PrimaryProductRepository {
    public String getProductName() {
        return "Primary Product";
    }
}

@Repository
class SecondaryProductRepository {
    public String getProductName() {
        return "Secondary Product";
    }
}

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(Application.class, args);
        PrimaryProductRepository primaryRepo = (PrimaryProductRepository) context.getBean("primaryProductRepo");
        System.out.println(primaryRepo.getProductName());
        context.close();
    }
}

Q475 medium code output

A user named "user" with role "USER" attempts to access the `/api/user/data` endpoint after logging in. What is the expected HTTP status code and response body?

java

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
import org.springframework.security.core.userdetails.User;
import org.springframework.security.core.userdetails.UserDetails;
import org.springframework.security.core.userdetails.UserDetailsService;
import org.springframework.security.provisioning.InMemoryUserDetailsManager;
import org.springframework.security.web.SecurityFilterChain;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import static org.springframework.security.config.Customizer.withDefaults;

@Configuration
@EnableWebSecurity
public class SecurityConfig {
    @Bean
    public SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception {
        http.authorizeHttpRequests(authorize -> authorize
                .requestMatchers("/api/public/**").permitAll()
                .requestMatchers("/api/admin/**").hasRole("ADMIN")
                .anyRequest().authenticated()
            ).formLogin(withDefaults()).csrf(csrf -> csrf.disable());
        return http.build();
    }
    @Bean
    public UserDetailsService userDetailsService() {
        UserDetails user = User.withUsername("user").password("{noop}password").roles("USER").build();
        return new InMemoryUserDetailsManager(user);
    }
}

@RestController
public class MyController {
    @GetMapping("/api/public/data") public String getPublicData() { return "Public data"; }
    @GetMapping("/api/admin/data") public String getAdminData() { return "Admin data"; }
    @GetMapping("/api/user/data") public String getUserData() { return "User data"; }
}

Q476 medium code error

A Spring Boot controller has a handler method to process form submissions. If an HTML form is configured to submit with `method="post"` to `/submitData`, but the controller method is defined as shown, what error will the client receive?

java

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ModelAttribute;

public class DataForm {
    private String value;
    // Getters and Setters, default constructor...
}

@Controller
public class DataController {
    @GetMapping("/submitData")
    public String processData(@ModelAttribute DataForm dataForm) {
        return "dataSuccess";
    }
}

Q477 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.context.annotation.Lazy;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@Component @Lazy
class LazyService { 
    public LazyService() { System.out.println("LazyService initialized."); }
    public void doWork() { System.out.println("LazyService working."); }
}

@Component
class EagerClient implements CommandLineRunner {
    @Autowired
    private LazyService lazyService;
    public EagerClient() { System.out.println("EagerClient created."); }
    @Override
    public void run(String... args) {
        // lazyService is not explicitly used here.
        System.out.println("EagerClient run method completed.");
    }
}

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

Q478 medium code output

Consider a Spring Boot application annotated with `@EnableEurekaClient`. If its `application.yml` only contains the application name and server port (without explicit Eureka client configuration), which `defaultZone` URL will it attempt to connect to?

yaml

spring:
  application:
    name: user-service

server:
  port: 8083

Q479 medium code output

What is the output of this code?

java

import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import org.springframework.stereotype.Component;

interface MyBean { String getName(); }
@Component("beanA") class BeanA implements MyBean { public String getName() { return "A"; } }
@Component("beanB") class BeanB implements MyBean { public String getName() { return "B"; } }

@SpringBootApplication
public class App7 {
    public static void main(String[] args) {
        ApplicationContext ctx = SpringApplication.run(App7.class, args);
        MyBean bean = (MyBean) ctx.getBean("beanB");
        System.out.println(bean.getName());
    }
}

Q480 medium code error

A client calls `DELETE /api/items/{id}` for an `id` that does NOT exist in the database. What will be the outcome of the `itemRepository.deleteById(id)` call in the service layer?

java

import org.springframework.stereotype.Service;
import org.springframework.data.jpa.repository.JpaRepository;

interface ItemRepository extends JpaRepository<Item, Long> {}

@Service
public class ItemService {

    private ItemRepository itemRepository; // Assume injected

    public void deleteItem(Long id) {
        itemRepository.deleteById(id);
        // No explicit check for existence or exception handling if not found
    }
}
// Assume Item class exists

🌱 Spring Boot MCQ Questions – Page 24