Spring Boot MCQ Questions – Page 35 of 49

Q: What is the HTTP status code and response body for a PUT request to `/api/orders/2` with the JSON body `{"status": "SHIPPED"}`?

A) Status: 200 OK, Body: {"id":2,"status":"SHIPPED"}. The PUT request targets order ID 2. The order is found, and its current status ('PROCESSING') is not 'SHIPPED', so the conflict condition is not met. The status is then updated to 'SHIPPED', and an HTTP 200 OK status with the updated order is returned.

Q: What is the console output of this Spring Boot application, demonstrating a custom qualifier?

B) Detailed Report Generated. By annotating `MyCustomQualifier` with `@Qualifier`, it becomes a custom qualifier. When `@MyCustomQualifier` is used for injection, Spring looks for beans also annotated with `@MyCustomQualifier`, thus selecting `DetailedReportingService`.

Q: If a client sends a POST request to `/config/timeout` with a request body "3000" (plain text), what will be the value of the `value` parameter in the `updateSetting` method?

A) `null`.. The `value` parameter is a simple type (String) without any binding annotation like `@RequestBody` or `@RequestParam`. Spring will not automatically bind the entire request body as a simple String to this parameter, leaving it as `null` or an empty string.

Q: What happens if a Spring Boot application attempts to inject a non-existent property `app.nonexistent` using `@Value("${app.nonexistent}")` without specifying a default value?

C) It will throw an `IllegalArgumentException` or `PropertyNotFoundException`.. If a placeholder cannot be resolved and no default value is provided, Spring will throw an `IllegalArgumentException` during application startup.

Q: Consider a Spring Boot application *without* `@EnableScheduling` on its main class, but with the following component. What is the output after 5 seconds of the application running?

B) No output related to 'importantTask'.. Without `@EnableScheduling` on a configuration class (typically the main application class), Spring Boot's scheduling capabilities are not activated. Scheduled methods marked with `@Scheduled` will be ignored, and thus `importantTask` will never execute or print anything. The application will start without errors, as the scheduler simply won't be initialized.

Q: What is the output of this Spring Boot application?

A) Processing Transformed: INPUT. The `transformer()` method creates a `Transformer` bean. The `processor()` method then takes a `Transformer` as a parameter, and Spring automatically injects the `transformer` bean into it. The `Processor` then correctly uses the injected `Transformer` to process the input string, converting it to uppercase as part of the transformation.

Q: For a form that submits data intended to create a new resource on the server (e.g., registering a new user, adding a new item), which HTTP method should generally be used to submit the form?

D) POST. The POST method is typically used to submit data that results in the creation of a new resource or causes a change in state on the server, making it suitable for form submissions that persist data.

Q: Assuming `MyEntityRepository` is a `JpaRepository`, what error will occur at runtime when `myEntityService.deleteEntity(1L)` is called with this custom repository method?

A) An `InvalidDataAccessApiUsageException` or similar error will be thrown as `JpaRepository` does not have a `delete(Long id)` method signature.. JpaRepository provides `deleteById(ID id)` and `delete(T entity)`, but not a `delete(ID id)` method. Spring Data JPA will attempt to implement the custom `void delete(Long id);`, but as it doesn't align with standard derived query methods, it will lead to a runtime `InvalidDataAccessApiUsageException` or similar error when invoked.

Q: Considering the `TaskDto` and controller below, what will the `processTask` method return if the POST request body is `{"description":"Review code", "status":"COMPLETED"}`?

A) Task: Review code, Status: COMPLETED. Jackson, used by Spring Boot, can automatically convert string values from JSON to corresponding enum constants as long as the string matches an enum constant's name (case-sensitive by default, though configurable).

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

A) Status: 400 Bad Request, Body: "Validation failed.". ResponseEntity.badRequest().body() is a convenient way to return an HTTP 400 Bad Request status along with a specific error message in the response body.

Q681 medium code output

What is the HTTP status code and response body for a PUT request to `/api/orders/2` with the JSON body `{"status": "SHIPPED"}`?

java

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

// Assume Order class has Long id, String status (e.g., "PENDING", "SHIPPED").

@RestController
@RequestMapping("/api/orders")
public class OrderController {
    private Map<Long, Order> orders = new HashMap<>();

    public OrderController() {
        orders.put(1L, new Order(1L, "PENDING"));
        orders.put(2L, new Order(2L, "PROCESSING"));
    }

    @PutMapping("/{id}")
    public ResponseEntity<Order> updateOrderStatus(@PathVariable Long id, @RequestBody Order orderUpdate) {
        if (!orders.containsKey(id)) {
            return ResponseEntity.notFound().build();
        }
        Order existingOrder = orders.get(id);
        if (orderUpdate.getStatus() == null || orderUpdate.getStatus().isEmpty()) {
            return ResponseEntity.badRequest().build(); // Status cannot be empty
        }
        if (existingOrder.getStatus().equals("SHIPPED")) {
            return ResponseEntity.status(409).build(); // Conflict: Cannot modify shipped order
        }
        existingOrder.setStatus(orderUpdate.getStatus());
        orders.put(id, existingOrder);
        return ResponseEntity.ok(existingOrder);
    }
}

Q682 medium code output

What is the console output of this Spring Boot application, demonstrating a custom qualifier?

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.stereotype.Component;
import java.lang.annotation.*;

@Target({ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER, ElementType.TYPE, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Qualifier
@interface MyCustomQualifier {}

interface ReportingService { String generateReport(); }

@Component
class BasicReportingService implements ReportingService { @Override public String generateReport() { return "Basic Report Generated"; } }

@MyCustomQualifier
@Component
class DetailedReportingService implements ReportingService { @Override public String generateReport() { return "Detailed Report Generated"; } }

@Component
class ReportRunner implements CommandLineRunner {
    @Autowired
    @MyCustomQualifier
    private ReportingService service;

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

@SpringBootApplication
class App {}

Q683 medium code error

If a client sends a POST request to `/config/timeout` with a request body "3000" (plain text), what will be the value of the `value` parameter in the `updateSetting` method?

java

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

@RestController
@RequestMapping("/config")
public class ConfigController {
    @PostMapping("/{settingName}")
    public String updateSetting(@PathVariable String settingName, String value) {
        return "Setting " + settingName + " updated to " + value;
    }
}

Q684 medium

What happens if a Spring Boot application attempts to inject a non-existent property `app.nonexistent` using `@Value("${app.nonexistent}")` without specifying a default value?

Q685 medium code output

Consider a Spring Boot application *without* `@EnableScheduling` on its main class, but with the following component. What is the output after 5 seconds of the application running?

java

import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;

@Component
public class MissingEnableScheduling {

    @Scheduled(fixedRate = 2000)
    public void importantTask() {
        System.out.println("Important scheduled task running.");
    }
}

Q686 medium code output

What is the output of this Spring Boot application?

java

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

@SpringBootApplication
public class MyApp {
    public static void main(String[] args) {
        ApplicationContext context = SpringApplication.run(MyApp.class, args);
        Processor processor = context.getBean(Processor.class);
        System.out.println(processor.process("input"));
    }
}

class Transformer {
    public String transform(String data) { return "Transformed: " + data.toUpperCase(); }
}

class Processor {
    private Transformer transformer;
    public Processor(Transformer transformer) { this.transformer = transformer; }
    public String process(String data) { return "Processing " + transformer.transform(data); }
}

@Configuration
class AppConfig {
    @Bean
    public Transformer transformer() { return new Transformer(); }

    @Bean
    public Processor processor(Transformer transformer) { // Constructor injection through @Bean parameter
        return new Processor(transformer);
    }
}

Q687 medium

For a form that submits data intended to create a new resource on the server (e.g., registering a new user, adding a new item), which HTTP method should generally be used to submit the form?

Q688 medium code error

Assuming `MyEntityRepository` is a `JpaRepository`, what error will occur at runtime when `myEntityService.deleteEntity(1L)` is called with this custom repository method?

java

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

// Repository definition
interface MyEntityRepository extends JpaRepository<MyEntity, Long> {
    void delete(Long id); // Custom method - problematic signature
}

// Service Layer
@Service
public class MyEntityService {

    private MyEntityRepository repository; // Assume injected

    public void deleteEntity(Long id) {
        repository.delete(id);
    }
}
// Assume MyEntity class exists

Q689 medium code output

Considering the `TaskDto` and controller below, what will the `processTask` method return if the POST request body is `{"description":"Review code", "status":"COMPLETED"}`?

java

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

enum TaskStatus { PENDING, IN_PROGRESS, COMPLETED }

@Data
class TaskDto {
    private String description;
    private TaskStatus status;
}

@RestController
@RequestMapping("/tasks")
public class TaskController {

    @PostMapping
    public String processTask(@RequestBody TaskDto taskDto) {
        return "Task: " + taskDto.getDescription() + ", Status: " + taskDto.getStatus().name();
    }
}

Q690 medium code output

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

java

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

@RestController
public class MyController {
    @GetMapping("/error")
    public ResponseEntity<String> getError() {
        return ResponseEntity.badRequest().body("Validation failed.");
    }
}

Q691 medium

If a `@Controller` class needs to interact with business logic, how would it typically obtain an instance of a class annotated with `@Service`?

Q692 medium code error

What error will occur when Spring Boot attempts to create a bean for `MyService`?

java

package com.example.app;

import org.springframework.stereotype.Service;

@Service
class MyService {
    private MyService() { 
        // Private constructor
    }
    
    public String getMessage() {
        return "Hello";
    }
}

Q693 medium code error

What error will occur when accessing `/api/config?max=ten` with the following Spring Boot controller?

java

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

@RestController
@RequestMapping("/api")
public class ConfigController {

    @GetMapping("/config")
    public String getConfig(@RequestParam(defaultValue = "5") int min,
                              @RequestParam(defaultValue = "100") int max) {
        return "Min: " + min + ", Max: " + max;
    }
}

Q694 medium code error

What error will prevent this Spring Boot application from starting?

java

package com.example.app;

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

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

@Service
class ServiceA {
    @Autowired ServiceB serviceB;
}

@Service
class ServiceB {
    @Autowired ServiceA serviceA;
}

Q695 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": "carl.example.com", "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
}

Q696 medium

For a RESTful DELETE operation targeting a specific resource by its ID (e.g., `/api/products/123`), why is `@PathVariable` generally preferred over `@RequestParam` in Spring Boot?

Q697 medium

How can you specify a default value for an optional query parameter in a Spring Boot GET request handler if the parameter is not provided in the request URL?

Q698 medium code output

A Spring Boot application with `@EnableScheduling` has the following component. What will be the approximate output (excluding stack traces) 6-7 seconds after the application starts?

java

import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;

@Component
public class ErrorHandlingScheduler {

    private int runCount = 0;

    @Scheduled(fixedRate = 2000)
    public void faultProneTask() {
        runCount++;
        if (runCount % 2 != 0) { // Throw error on 1st, 3rd, 5th run, etc.
            throw new RuntimeException("Task failure on run: " + runCount);
        }
        System.out.println("Fault-prone task completed successfully. Run: " + runCount);
    }
}

Q699 medium code output

What is the HTTP status code and response body for a PUT request to `/api/accounts/123` with the JSON body `{"balance": 1000.0}`?

java

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

// Assume Account class has Long id, Double balance.

@RestController
@RequestMapping("/api/accounts")
public class AccountController {
    private Map<Long, Account> accounts = new HashMap<>();

    public AccountController() {
        accounts.put(123L, new Account(123L, 500.0));
    }

    @PutMapping("/{id}")
    public ResponseEntity<Account> updateAccount(@PathVariable Long id, @RequestBody Account accountDetails) {
        if (id == null || accountDetails == null) {
            return ResponseEntity.badRequest().build();
        }
        if (!accounts.containsKey(id)) {
            // Idempotent PUT: Create if not exists
            accountDetails.setId(id);
            accounts.put(id, accountDetails);
            return new ResponseEntity<>(accountDetails, HttpStatus.CREATED);
        }
        // Update existing
        Account existingAccount = accounts.get(id);
        existingAccount.setBalance(accountDetails.getBalance());
        accounts.put(id, existingAccount);
        return new ResponseEntity<>(existingAccount, HttpStatus.OK);
    }
}

Q700 medium

If a `@RequestParam` has both `defaultValue` and `required=false` attributes set, and the parameter is missing in the HTTP request, what value will the method argument receive?

🌱 Spring Boot MCQ Questions – Page 35