Spring Boot MCQ Questions – Page 28 of 49

Q: Given a `MyController` class with a `@GetMapping("/test")` method that returns "Hello from Controller!", what is the output of this test code?

A) Hello from Controller!. `@WebMvcTest` slices the application context to only include web components. `MockMvc` simulates an HTTP request to `/test` and then prints the response body directly to the console.

Q: What does this Spring Boot application print to the console?

B) Sending SMS notification. While `EmailNotificationService` is marked `@Primary`, the `@Qualifier` annotation takes precedence. It explicitly selects the bean named 'smsNotification' for injection.

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

B) Runtime error: IllegalStateException: Ambiguous mapping. Cannot map 'myController' method 'greetUser'.. Spring Boot detects an ambiguous mapping at startup because two different methods are mapped to the exact same path and HTTP method, leading to an IllegalStateException during context initialization.

Q: What is the output of this code?

A) 1: INIT 2: POST_CONSTRUCT 3: POST_CONSTRUCT. The constructor is called first (1), followed by `@PostConstruct` method (2) as part of the bean's lifecycle managed by `ApplicationContext`. Only after these lifecycle methods complete is the bean fully initialized and available for retrieval and use (3).

Q: Consider the following Spring Boot controller method signature: `@GetMapping("/users/{userId}/posts/{postId}") public String getUserPost(@PathVariable String userId, @PathVariable String postId)`. How are `userId` and `postId` values extracted?

B) Both are extracted as path variables, corresponding to their respective placeholders in the URI.. Multiple `@PathVariable` annotations can be used in a single method signature to extract multiple values from different segments of the URI path template.

Q: Given the Spring Boot application, what will be the output?

B) Processing with SlowProcessor. The `@Qualifier("slowProcessor")` annotation explicitly requests the bean named 'slowProcessor', which is defined in `AppConfig`.

Q: What is the expected error when accessing this endpoint with GET /report?

A) HttpMessageNotWritableException. By default, Spring Boot uses Jackson for JSON serialization. A class like 'CustomReport' without public getters, setters, or a default constructor is not a valid POJO for Jackson, leading to an HttpMessageNotWritableException when Spring tries to convert it to JSON.

Q: Given the `User` and `Address` classes below, what will be the value of `user.getAddress().getStreet()` if a form is submitted with data 'name=Charlie&address.street=Oak Ave&address.city=Springfield'?

A) Oak Ave. Spring MVC supports nested object binding. The 'address.street' parameter directly maps to the 'street' property of the 'address' object within the 'User' model attribute. The User constructor initializes Address, preventing NullPointerException during binding.

Q: How do you typically add data that needs to be displayed in a view template (e.g., Thymeleaf, JSP) from within a `@Controller` method?

A) By adding attributes to the `Model` interface parameter of the method.. The `Model` interface (or `ModelAndView` object) is the standard way to pass data from a `@Controller` to a view. Attributes added to the `Model` become available to the view template for rendering.

Q: What is the primary concept behind Inversion of Control (IoC) in Spring Boot applications?

B) The Spring container manages the lifecycle and dependencies of application objects.. IoC means the Spring container takes over the responsibility of creating, configuring, and managing the lifecycle of objects, rather than the application code doing it.

Q541 medium code output

Given a `MyController` class with a `@GetMapping("/test")` method that returns "Hello from Controller!", what is the output of this test code?

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.get;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

@WebMvcTest(controllers = MyController.class)
class MyControllerTest {
    @Autowired
    private MockMvc mockMvc;

    @Test
    void testEndpointReturnsMessage() throws Exception {
        this.mockMvc.perform(get("/test"))
            .andExpect(status().isOk())
            .andDo(result -> System.out.print(result.getResponse().getContentAsString()));
    }
}

Q542 medium code output

What does this Spring Boot application print to the console?

java

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

interface NotificationService { String notifyUser(); }

@Component
@Primary
class EmailNotificationService implements NotificationService { @Override public String notifyUser() { return "Sending email notification (Primary)"; } }

@Component("smsNotification")
class SmsNotificationService implements NotificationService { @Override public String notifyUser() { return "Sending SMS notification"; } }

@Component
class AppRunner implements CommandLineRunner {
    @Autowired
    @Qualifier("smsNotification")
    private NotificationService service;

    @Override
    public void run(String... args) { System.out.println(service.notifyUser()); }
}

@SpringBootApplication
class App {}

Q543 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.RestController;

@RestController
public class MyController {

    @GetMapping("/api/hello")
    public String helloWorld() {
        return "Hello from GET!";
    }

    @GetMapping("/api/hello")
    public String greetUser() {
        return "Greetings!";
    }
}

Q544 medium code output

What is the output of this code?

java

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

@Component
class MyLifecycleBean {
    private String state = "INIT";
    public MyLifecycleBean() { System.out.println("1: " + state); }
    @PostConstruct
    public void postConstruct() { state = "POST_CONSTRUCT"; System.out.println("2: " + state); }
    public String getState() { return state; }
}

@SpringBootApplication
public class App9 {
    public static void main(String[] args) {
        ApplicationContext ctx = SpringApplication.run(App9.class, args);
        MyLifecycleBean bean = ctx.getBean(MyLifecycleBean.class);
        System.out.println("3: " + bean.getState());
    }
}

Q545 medium

Consider the following Spring Boot controller method signature: `@GetMapping("/users/{userId}/posts/{postId}") public String getUserPost(@PathVariable String userId, @PathVariable String postId)`. How are `userId` and `postId` values extracted?

Q546 medium code output

Given the Spring Boot application, what will be the output?

java

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;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

interface DataProcessor { String process(); }

class SimpleProcessor implements DataProcessor { private String name; public SimpleProcessor(String name) { this.name = name; } @Override public String process() { return "Processing with " + name; } }

@Configuration
class AppConfig {
    @Bean(name = "fastProcessor")
    public DataProcessor fastProcessor() { return new SimpleProcessor("FastProcessor"); }

    @Bean(name = "slowProcessor")
    public DataProcessor slowProcessor() { return new SimpleProcessor("SlowProcessor"); }
}

@Component
class DataRunner implements CommandLineRunner {
    @Autowired
    @Qualifier("slowProcessor")
    private DataProcessor processor;

    @Override
    public void run(String... args) { System.out.println(processor.process()); }
}

@SpringBootApplication
class App {}

Q547 medium code error

What is the expected error when accessing this endpoint with GET /report?

java

import org.springframework.web.bind.annotation.*;
import java.util.Collections;

class CustomReport { // Missing getters/setters and default constructor for serialization
    String name = "Test";
    public CustomReport(String name) { this.name = name; }
}

@RestController
public class ReportController {

    @GetMapping("/report")
    public CustomReport getReport() {
        return new CustomReport("Monthly");
    }
}

Q548 medium code output

Given the `User` and `Address` classes below, what will be the value of `user.getAddress().getStreet()` if a form is submitted with data 'name=Charlie&address.street=Oak Ave&address.city=Springfield'?

java

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

// Address.java
public class Address {
    private String street; private String city;
    public String getStreet() { return street; }
    public void setStreet(String street) { this.street = street; }
    public String getCity() { return city; }
    public void setCity(String city) { this.city = city; }
}

// User.java
public class User {
    private String name; private Address address;
    public User() { this.address = new Address(); } // Important for nested binding
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public Address getAddress() { return address; }
    public void setAddress(Address address) { this.address = address; }
}

@Controller
public class NestedFormController {
    @PostMapping("/user/update")
    public String updateUser(@ModelAttribute User user) {
        // user object is processed here
        return "profile";
    }
}

Q549 medium

How do you typically add data that needs to be displayed in a view template (e.g., Thymeleaf, JSP) from within a `@Controller` method?

Q550 medium

What is the primary concept behind Inversion of Control (IoC) in Spring Boot applications?

Q551 medium code error

What error occurs when accessing `/files/document.pdf` with the following controller?

java

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

@RestController
public class FileController {
    @GetMapping("/files/{filename:[a-zA-Z]+\.txt}")
    public String downloadFile(@PathVariable String filename) {
        return "Downloading: " + filename;
    }
}

Q552 medium code output

Given the `BookController` below, what will be the HTTP status and body if a DELETE request is made to `/api/books/purge` and `bookService.deleteAllBooks()` successfully empties the entire book collection?

java

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

@RestController
@RequestMapping("/api/books")
public class BookController {

    private BookService bookService;

    // Constructor injected bookService

    @DeleteMapping("/purge")
    @ResponseStatus(HttpStatus.OK)
    public String purgeBooks() {
        bookService.deleteAllBooks();
        return "All books have been purged.";
    }
}

Q553 medium code error

What is the expected outcome when Spring Boot attempts to initialize the application context with this configuration?

java

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class MyConfig {
    @Bean
    public String nullStringBean() {
        return null;
    }
}

Q554 medium code output

Based on the Spring Boot code, what will be the HTTP status code and response body when a GET request is made to `/process/null`?

java

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

@RestController
class ProcessController {
    @GetMapping("/process/null")
    public String processNull() {
        String data = null;
        return data.toLowerCase(); // Throws NullPointerException
    }
}

@RestControllerAdvice
class GenericErrorHandler {
    @ExceptionHandler(Exception.class)
    public ResponseEntity<String> handleAllExceptions(Exception ex) {
        return new ResponseEntity<>("An unexpected error occurred: " + ex.getMessage(), HttpStatus.INTERNAL_SERVER_ERROR);
    }
}

Q555 medium code output

What is the HTTP status code and response body returned by this Spring Boot controller method?

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("/status")
    public ResponseEntity<Integer> getCustomStatus() {
        return new ResponseEntity<>(123, HttpStatus.ACCEPTED);
    }
}

Q556 medium

What happens if you have multiple classes annotated with `@SpringBootApplication` in a single Spring Boot project?

Q557 medium code error

Consider the following controller method. If `myTemplate.html` attempts to access `${myObject.data}` after `/display` is requested, what is the error?

java

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

class MyData {
    public String info = "Hello";
}

@Controller
public class MyObjectController {

    @GetMapping("/display")
    public String displayPage(Model model) {
        model.addAttribute("myObject", new MyData());
        // The template myTemplate.html has th:text="${myObject.data}"
        return "myTemplate"; 
    }
}

Q558 medium code output

Consider the following Spring Boot controller method. What HTTP status code and body would be returned if a DELETE request is made to `/api/users/456` and the user is successfully deleted?

java

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

@RestController
@RequestMapping("/api/users")
public class UserController {

    private UserService userService;

    // Constructor injected userService

    @DeleteMapping("/{id}")
    public ResponseEntity<Void> deleteUser(@PathVariable Long id) {
        userService.deleteUser(id);
        return ResponseEntity.noContent().build();
    }
}

Q559 medium code output

Observe the Spring Boot application below. What will be the exact sequence of outputs printed to the console?

java

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.context.annotation.Lazy;

@Component
class EagerService {
    public EagerService() {
        System.out.println("EagerService initialized.");
    }
    public String getStatus() { return "Eager service ready"; }
}

@Lazy
@Component
class LazyService {
    public LazyService() {
        System.out.println("LazyService initialized.");
    }
    public String getStatus() { return "Lazy service ready"; }
}

@Component
class MyRunner {
    private final EagerService eagerService;
    private final LazyService lazyService;

    @Autowired
    public MyRunner(EagerService eagerService, LazyService lazyService) {
        this.eagerService = eagerService;
        this.lazyService = lazyService;
        System.out.println("MyRunner created.");
    }

    public void run() {
        System.out.println(eagerService.getStatus());
        System.out.println(lazyService.getStatus());
    }
}

@SpringBootApplication
public class MyApplication {
    public static void main(String[] args) {
        var context = SpringApplication.run(MyApplication.class, args);
        MyRunner runner = context.getBean(MyRunner.class);
        runner.run();
    }
}

Q560 medium code output

What is the output when accessing `/welcome?name=Alice`?

java

import org.springframework.web.bind.annotation.*;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

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

    @GetMapping("/welcome")
    public String welcomeUser(@RequestParam(defaultValue = "Guest") String name) {
        return "Welcome, " + name + "!";
    }
}

🌱 Spring Boot MCQ Questions – Page 28