Spring Boot MCQ Questions – Page 25 of 49

Q: What error occurs when accessing `/search/user name` (note the space) with the following controller?

A) HTTP Status 400 Bad Request. URLs must be properly encoded. A space character in a URL path segment is invalid without percent-encoding (e.g., `%20`). Most web servers or servlet containers will reject such a malformed request with an HTTP 400 Bad Request status before it reaches Spring MVC.

Q: When using `@Valid` with `@RequestBody` in a POST controller method, how can you gracefully capture and process validation errors within the method itself?

B) By adding a `BindingResult` parameter immediately after the validated object. By adding a `BindingResult` parameter right after the validated `@RequestBody` object, Spring populates this object with any validation errors, allowing the method to handle them programmatically without throwing an exception immediately.

Q: A specific controller method, when successfully executed, should always return an HTTP 201 Created status. Which annotation can be directly applied to the method to achieve this without using `ResponseEntity`?

C) `@ResponseStatus(HttpStatus.CREATED)`. The `@ResponseStatus` annotation can be applied to a handler method (or an exception class) to set a fixed HTTP status code that will be returned for successful invocations of that method.

Q: Given the Spring Boot controller above, what will be the HTTP response body when a GET request is made to `/search?query=java`?

A) Searching for: java. The `@RequestParam String query` extracts the `query` parameter from the URL's query string. For `/search?query=java`, `query` becomes `"java"`, resulting in the specified output.

Q: What is the output after saving two `Category` entities, given the `name` column has a unique constraint?

D) org.springframework.dao.DataIntegrityViolationException: Unique constraint violation.. Attempting to save two entities with the same value in a `@Column(unique = true)` field will lead to a database unique constraint violation. Spring Data JPA typically wraps such low-level exceptions in a more specific `DataIntegrityViolationException`.

Q: To implement custom validation logic for a field or object in a Spring Boot form (e.g., ensuring a field's value meets specific business rules beyond standard JSR-303), what is the most common approach using Bean Validation?

B) Define a custom annotation annotated with `@Constraint` and specify an associated `ConstraintValidator` implementation.. The standard and most flexible way to add custom validation rules in Spring Boot is by creating a custom annotation (e.g., `@MyCustomValidation`) annotated with `@Constraint` and providing an accompanying `ConstraintValidator` implementation that defines the validation logic.

Q: What is the output of this code snippet, assuming `userRepository` contains a `User` with `id=1` and `name="Bob"` and no `User` with `id=99`?

A) Bob, User not found. `findById(1L)` will return an `Optional` containing the User object, and `map(User::getName)` will extract 'Bob'. `findById(99L)` will return an empty `Optional`, triggering `orElse("User not found")`.

Q: Consider this code structure. What would be the output?

A) Report: Log message. Both `LoggerService` and `ReportingService` are marked with `@Component`, making them Spring beans. The `@Autowired` annotation on the `logger` field in `ReportingService` successfully injects an instance of `LoggerService`.

Q: Consider a Spring Boot `@Controller` method designed to render a view. Which of the following is a common return type for such a method to specify the logical view name?

B) `String`. Returning a `String` from a `@Controller` method is a common and straightforward way to specify the logical view name that the `ViewResolver` should process.

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": "David", "email": "david@example.com", "age": 28 }`

A) HTTP 200 OK, body contains "User registered successfully!". All fields in the request (`username`, `email`, `age`) are provided with valid values that satisfy all defined validation constraints. Therefore, the request proceeds successfully, returning a 200 OK status.

Q481 medium code error

What error occurs when accessing `/search/user name` (note the space) with the following controller?

java

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

@RestController
public class SearchController {
    @GetMapping("/search/{query}")
    public String performSearch(@PathVariable String query) {
        return "Searching for: " + query;
    }
}

Q482 medium

When using `@Valid` with `@RequestBody` in a POST controller method, how can you gracefully capture and process validation errors within the method itself?

Q483 medium

A specific controller method, when successfully executed, should always return an HTTP 201 Created status. Which annotation can be directly applied to the method to achieve this without using `ResponseEntity`?

Q484 medium code output

Given the Spring Boot controller above, what will be the HTTP response body when a GET request is made to `/search?query=java`?

java

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

@RestController
public class SearchController {
    @GetMapping("/search")
    public String searchProduct(@RequestParam String query) {
        return "Searching for: " + query;
    }
}

Q485 medium code output

What is the output after saving two `Category` entities, given the `name` column has a unique constraint?

java

import jakarta.persistence.*;

@Entity
public class Category {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(unique = true)
    private String name;

    public Category() {}
    public Category(String name) { this.name = name; }
}

// Assume categoryRepository is injected and available
// Assume transaction context is active
try {
    categoryRepository.save(new Category("Electronics"));
    categoryRepository.save(new Category("Electronics")); // Attempt to save again with same unique name
    System.out.println("Both categories saved successfully.");
} catch (Exception e) {
    System.out.println(e.getClass().getName() + ": Unique constraint violation.");
}

Q486 medium

To implement custom validation logic for a field or object in a Spring Boot form (e.g., ensuring a field's value meets specific business rules beyond standard JSR-303), what is the most common approach using Bean Validation?

Q487 medium code output

What is the output of this code snippet, assuming `userRepository` contains a `User` with `id=1` and `name="Bob"` and no `User` with `id=99`?

java

public class UserService {
    private UserRepository userRepository;

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

    public String getUserNameById(Long id) {
        return userRepository.findById(id)
                             .map(User::getName)
                             .orElse("User not found");
    }
}

// In a test context or main method:
UserService service = new UserService(userRepository);
String name1 = service.getUserNameById(1L);
String name2 = service.getUserNameById(99L);
System.out.println(name1 + ", " + name2);

Q488 medium code output

Consider this code structure. What would be the output?

java

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

@Component class LoggerService { public String log() { return "Log message"; } }

@Component class ReportingService {
    @Autowired private LoggerService logger;
    public String generateReport() { return "Report: " + logger.log(); }
}

@SpringBootApplication
public class DemoApplication {
    public static void main(String[] args) {
        var context = SpringApplication.run(DemoApplication.class, args);
        var reporter = context.getBean(ReportingService.class);
        System.out.println(reporter.generateReport());
    }
}

Q489 medium

Consider a Spring Boot `@Controller` method designed to render a view. Which of the following is a common return type for such a method to specify the logical view name?

Q490 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": "David", "email": "david@example.com", "age": 28 }`

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
}

Q491 medium

To ensure that a new instance of a bean is created every time it is requested from the Spring container, which annotation or attribute would you use?

Q492 medium code error

What error will occur during application startup for this Spring Boot application?

java

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Lazy;
import org.springframework.stereotype.Service;
import org.springframework.web.bind.annotation.*;

@RestController
public class ControllerA {
    @Autowired ControllerB controllerB;

    @GetMapping("/test")
    public String test() { return "Controller A"; }
}

@RestController // Intentionally another controller to create circularity
public class ControllerB {
    @Autowired ControllerA controllerA;

    @GetMapping("/another")
    public String another() { return "Controller B"; }
}

Q493 medium code error

What will happen when this Spring Boot application attempts to shut down?

java

import org.springframework.beans.factory.DisposableBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class AppConfig {

    @Bean
    public CleanUpService cleanUpService() {
        return new CleanUpService();
    }
}

class CleanUpService implements DisposableBean {
    @Override
    public void destroy() throws Exception {
        System.out.println("CleanUpService performing essential cleanup...");
        throw new IllegalStateException("Critical cleanup task failed!");
    }
}

Q494 medium code output

What is the expected output when this Spring Boot application starts?

java

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.stereotype.Component;

// In com.example.app.main
@SpringBootApplication
@ComponentScan("com.example.app.other") // Explicitly scans 'other' package
public class MainApplication {
    public static void main(String[] args) {
        var context = SpringApplication.run(MainApplication.class, args);
        try {
            var service = context.getBean(OtherService.class);
            System.out.println(service.message());
        } catch (Exception e) {
            System.out.println(e.getClass().getSimpleName());
        }
    }
}

// In com.example.app.other
@Component class OtherService {
    public String message() { return "Found in other package!"; }
}

Q495 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": "Carl", "email": null, "age": 22 }`

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
}

Q496 medium code output

Given the Spring Boot application and assuming `src/main/resources/static/data.txt` contains the text 'Hello from resource!', what will be the output when the application is packaged as a JAR and executed?

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;
import org.springframework.core.io.ClassPathResource;
import org.springframework.util.StreamUtils;
import java.nio.charset.StandardCharsets;

@SpringBootApplication
public class MyApplication {

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

    @Bean
    public CommandLineRunner resourceReader() {
        return args -> {
            try {
                ClassPathResource resource = new ClassPathResource("static/data.txt");
                String content = StreamUtils.copyToString(resource.getInputStream(), StandardCharsets.UTF_8);
                System.out.println("Resource Content: " + content);
            } catch (Exception e) {
                System.err.println("Error reading resource: " + e.getMessage());
            }
        };
    }
}

Q497 medium code error

What error will Spring Boot generate during application startup for this `MyService` class?

java

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

@Service
public class MyService {
    @Autowired
    private int port; // Error: Cannot autowire primitive 'int'

    public String getServiceInfo() {
        return "Running on port: " + port;
    }
}

Q498 medium code error

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

java

public interface DataProcessor {
    String process(String data);
}

@Service("csvProcessor")
public class CsvProcessor implements DataProcessor {
    @Override
    public String process(String data) { return "Processed CSV: " + data; }
}

@Component
public class ReportGenerator {
    @Autowired
    @Qualifier("jsonProcessor") // No bean named "jsonProcessor"
    private DataProcessor processor;

    public void generateReport() {
        System.out.println(processor.process("sample"));
    }
}

Q499 medium code output

What is the output of this Spring Boot application?

java

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

class OptionalService { // No @Component annotation
    public String say() { return "I am optional."; }
}

@Component
class MyRunner implements CommandLineRunner {
    @Autowired(required = false)
    private OptionalService service;

    @Override
    public void run(String... args) {
        if (service != null) {
            System.out.println("Service is present: " + service.say());
        } else {
            System.out.println("OptionalService is null.");
        }
    }
}

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

Q500 medium code output

Given the following Spring Boot controller and DTO, and a POST request with `Content-Type: application/json` and body `{"id": "123"}`, what kind of error or output would you expect when `updateProduct` is called?

java

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

@Data
class ProductDto {
    private String id;
    private String name; 
}

@RestController
@RequestMapping("/products")
public class ProductController {

    @PutMapping
    public String updateProduct(@RequestBody ProductDto productDto) {
        return "Product updated: " + productDto.getId() + ", " + productDto.getName();
    }
}

🌱 Spring Boot MCQ Questions – Page 25