Spring Boot MCQ Questions – Page 30 of 49

Q: If a PUT request is made to `/api/books/999` where `999` is an ID that does not exist in the database, what will be the immediate runtime error in the `updateBook` method?

A) `java.util.NoSuchElementException: No value present`. Calling `get()` on an empty `Optional` (which `findById` returns if the entity is not found) will immediately throw a `NoSuchElementException`.

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

B) Runtime error: IllegalArgumentException: Ambiguous mapping: cannot map parameters [version=1, version=2].. Spring does not allow multiple conditions for the same parameter key within a single `@RequestMapping` (or `@GetMapping`). This creates an ambiguous mapping for parameter matching, leading to an `IllegalArgumentException` during application startup.

Q: What error will occur when calling `/user?id=abc` in this Spring Boot application?

A) A 400 Bad Request error (Type Mismatch).. The `@RequestParam("id") int userId` expects an integer value for the `id` parameter. When `id=abc` is provided, Spring's type conversion fails to convert 'abc' to an `int`, resulting in a 400 Bad Request error (specifically, a `MethodArgumentTypeMismatchException`).

Q: Assuming a DTO `Product { public String name; public double price; }` and default JSON serialization, what is the HTTP status and body output?

A) Status: 200 OK, Body: {"name":"Laptop","price":1200.5}. When a Java object is returned as a ResponseEntity body and content negotiation allows JSON, Spring Boot (with Jackson) automatically serializes the object into a JSON string. ResponseEntity.ok() ensures a 200 OK status.

Q: What is wrong with this Spring Boot DELETE endpoint implementation?

A) The method parameter `id` is not annotated, leading to a `MissingPathVariableException`.. The `id` method parameter needs `@PathVariable("id")` to correctly bind the path variable from the URL. Without it, Spring will treat 'id' as a request parameter, resulting in a `MissingPathVariableException`.

Q: Consider a Spring Boot controller with the following method. If a DELETE request is sent to `/api/resources/remove?name=old_resource` and the `resourceService.deleteByName("old_resource")` method successfully deletes exactly one resource, what HTTP status code and body will the client receive?

A) HTTP 200 OK, with body "Resource 'old_resource' deleted.". The method explicitly returns `ResponseEntity.ok()` with a success message when `deleted` is true. Thus, the client will receive an HTTP 200 OK status with the specified success message in the body.

Q: What does this code print to the console when run as a Spring Boot application?

A) MyService created. MyService message from Runner.. `MyConfig` defines `MyService` as a Spring bean using `@Bean`. The IoC container then detects this bean and injects it into `MyRunner` using `@Autowired`, allowing `MyRunner` to call its method.

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

A) Status: 200 OK, Body: "Hello Spring!". ResponseEntity.ok() is a shortcut to create a ResponseEntity with HTTP status 200 OK and the provided body. The method explicitly returns 'Hello Spring!' as its body.

Q: Consider the following Spring Boot application. What will be printed to the console when this application runs?

A) ServiceB uses: Message from ServiceA. ServiceA is a Spring component and is automatically wired into ServiceB via constructor injection. Spring successfully creates and provides the ServiceA instance.

Q: What error will occur when accessing `/api/settings?debug=yes` with the following Spring Boot controller?

C) Status 400 (Bad Request) - MethodArgumentTypeMismatchException: Failed to convert value of type 'java.lang.String' to required type 'boolean'. Spring's default conversion for boolean `@RequestParam` expects 'true' or 'false' (case-insensitive). 'yes' cannot be converted, leading to a `MethodArgumentTypeMismatchException` and a 400 Bad Request status.

Q581 medium code error

If a PUT request is made to `/api/books/999` where `999` is an ID that does not exist in the database, what will be the immediate runtime error in the `updateBook` method?

java

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

@RestController
@RequestMapping("/api/books")
public class BookController {
    private BookRepository bookRepository; // Assume injected

    @PutMapping("/{id}")
    public ResponseEntity<Book> updateBook(@PathVariable Long id, @RequestBody Book bookDetails) {
        Optional<Book> existingBookOptional = bookRepository.findById(id);
        Book existingBook = existingBookOptional.get(); // Potential error line
        existingBook.setTitle(bookDetails.getTitle());
        return ResponseEntity.ok(bookRepository.save(existingBook));
    }
}
// Assume Book and BookRepository exist

Q582 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(value = "/api/resource", params = {"version=1", "version=2"})
    public String getResourceByVersion() {
        return "Resource";
    }
}

Q583 medium code error

What error will occur when calling `/user?id=abc` in this Spring Boot application?

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 UserController {

    @GetMapping("/user")
    @ResponseBody
    public String getUserById(@RequestParam("id") int userId) {
        return "User ID: " + userId;
    }
}

Q584 medium code output

Assuming a DTO `Product { public String name; public double price; }` and default JSON serialization, what is the HTTP status and body output?

java

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

class Product {
    public String name = "Laptop";
    public double price = 1200.50;
}

@RestController
public class MyController {
    @GetMapping("/product")
    public ResponseEntity<Product> getProduct() {
        return ResponseEntity.ok(new Product());
    }
}

Q585 medium code error

What is wrong with this Spring Boot DELETE endpoint implementation?

java

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

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

    private ProductService productService; // Assume injected

    @DeleteMapping("/{id}")
    public ResponseEntity<Void> deleteProduct(String id) {
        productService.deleteProduct(id);
        return ResponseEntity.noContent().build();
    }
}

Q586 medium code output

Consider a Spring Boot controller with the following method. If a DELETE request is sent to `/api/resources/remove?name=old_resource` and the `resourceService.deleteByName("old_resource")` method successfully deletes exactly one resource, what HTTP status code and body will the client receive?

java

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

@RestController
@RequestMapping("/api/resources")
public class ResourceController {

    private ResourceService resourceService;

    // Constructor injected resourceService

    @DeleteMapping("/remove")
    public ResponseEntity<String> deleteResourceByName(@RequestParam String name) {
        boolean deleted = resourceService.deleteByName(name);
        if (deleted) {
            return ResponseEntity.ok("Resource '" + name + "' deleted.");
        } else {
            return ResponseEntity.status(404).body("Resource '" + name + "' not found.");
        }
    }
}

Q587 medium code output

What does this code print to the console when run as a Spring Boot application?

java

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

class MyService { public String doSomething() { return "MyService created."; } }

@Configuration
class MyConfig { @Bean public MyService myService() { return new MyService(); } }

@Component
class MyRunner implements CommandLineRunner {
    @Autowired
    private MyService service;
    @Override
    public void run(String... args) {
        System.out.println(service.doSomething() + " MyService message from Runner.");
    }
}

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

Q588 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("/hello")
    public ResponseEntity<String> sayHello() {
        return ResponseEntity.ok("Hello Spring!");
    }
}

Q589 medium code output

Consider the following Spring Boot application. What will be printed to the console when this application runs?

java

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

@Component
class ServiceA {
    public String getMessage() {
        return "Message from ServiceA";
    }
}

@Component
class ServiceB {
    private final ServiceA serviceA;

    @Autowired
    public ServiceB(ServiceA serviceA) {
        this.serviceA = serviceA;
    }

    public void printMessage() {
        System.out.println("ServiceB uses: " + serviceA.getMessage());
    }
}

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

Q590 medium code error

What error will occur when accessing `/api/settings?debug=yes` with the following Spring Boot controller?

java

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

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

    @GetMapping("/settings")
    public String getSettings(@RequestParam boolean debug) {
        return "Debug mode: " + debug;
    }
}

Q591 medium

To manually define a bean within a Spring Boot application using Java configuration, what two annotations are typically used together to define a class that contains bean creation methods and the methods themselves, respectively?

Q592 medium

When Thymeleaf is included as a dependency in a Spring Boot project, where does Spring Boot typically expect to find Thymeleaf template files by default?

Q593 medium code error

A Spring Boot application attempts to use `@Repository` with a `PersistenceExceptionTranslationPostProcessor` to translate persistence exceptions. However, no `PlatformTransactionManager` bean is defined or configured. If an exception occurs within a method of `InventoryRepository`, what type of exception will propagate, indicating the translation mechanism is not fully functional?

java

package com.example.dao;
import org.springframework.stereotype.Repository;
import jakarta.persistence.EntityManager;
import jakarta.persistence.PersistenceContext;
import org.hibernate.exception.ConstraintViolationException;

@Repository
public class InventoryRepository {
    @PersistenceContext
    private EntityManager entityManager;

    public void updateStock(Long productId, int quantity) {
        // Simulate a DB write that might cause an error
        // entityManager.merge(product);
        throw new ConstraintViolationException("Stock cannot be negative", null, "STOCK_CONSTRAINT");
    }
}

package com.example.config;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor;

@Configuration
public class AppConfig {
    @Bean
    public PersistenceExceptionTranslationPostProcessor exceptionTranslation() {
        return new PersistenceExceptionTranslationPostProcessor();
    }
    // MISSING: @Bean PlatformTransactionManager transactionManager(EntityManagerFactory emf) { ... }
}

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

@Service
public class InventoryService {
    @Autowired
    private InventoryRepository inventoryRepository;

    @Transactional
    public void processUpdate(Long productId, int quantity) {
        inventoryRepository.updateStock(productId, quantity);
    }
}
// Assuming @EnableTransactionManagement is present.

Q594 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.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
@SpringBootApplication
public class MyApplication {
    @Bean
    public String greetingBean() {
        return "Hello Spring Beans!";
    }
    public static void main(String[] args) {
        String greeting = SpringApplication.run(MyApplication.class, args).getBean("greetingBean", String.class);
        System.out.println(greeting);
    }
}

Q595 medium

In a Spring Boot `@Controller`, how would you typically bind data from an HTML form submission directly into a Java object (e.g., a `User` object)?

Q596 medium

After a form submission with validation errors, which Thymeleaf attribute is commonly used to display error messages associated with a specific field (e.g., for a 'username' field)?

Q597 medium code output

What is the output of this code when a GET request is made to '/greet'?

java

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

@RestController
public class GreetingController {
    @RequestMapping("/greet")
    public String sayHello() {
        return "Hello from Spring Boot!";
    }
}

Q598 medium

Which `ResponseEntity` static builder method should you use to return an HTTP 201 (Created) status code with a newly created resource in the response body?

Q599 medium

Can `@Autowired` be used within a `@Configuration` class to inject dependencies into a `@Bean` method that creates another bean?

Q600 medium code error

What is the expected runtime error when accessing this endpoint with GET /users/123?

java

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

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

    @GetMapping("/{userId}")
    public String getUser(@PathVariable String id) {
        return "User ID: " + id;
    }
}

🌱 Spring Boot MCQ Questions – Page 30