Spring Boot MCQ Questions – Page 16 of 49

Q: If a DELETE request is made to a Spring Boot endpoint for a resource that does not exist, which HTTP status code should typically be returned?

D) 404 Not Found. HTTP 404 Not Found is the appropriate status code when the client requests to delete a resource that simply does not exist on the server.

Q: Given the `Order` and `Customer` entities, what happens when `findOrderById` is called and then `getCustomer().getName()` is accessed *outside* an active transaction or persistence context?

C) org.hibernate.LazyInitializationException: could not initialize proxy [com.example.Customer#1] - no Session. Because the `customer` relationship is fetched lazily (`FetchType.LAZY`), the `Customer` object is not loaded from the database until it is accessed. If this access happens outside an active Hibernate session or transaction, a `LazyInitializationException` is thrown as the proxy cannot be initialized.

Q: What is the correct way to inject a property named `server.port` from `application.properties`, providing a default value of `8080` if the property is not found?

B) `@Value("${server.port:8080}")`. The syntax `${property.name:defaultValue}` allows specifying a default value to be used if the property is not present in any configuration source.

Q: What is the expected error when a client sends a GET request to /resource with an Accept header of 'application/xml'?

A) HttpMediaTypeNotAcceptableException. The @GetMapping specifies that it produces MediaType.APPLICATION_JSON_VALUE. If the client sends an Accept header requesting 'application/xml', Spring cannot fulfill the request with the specified produce type, leading to an HttpMediaTypeNotAcceptableException (HTTP 406 Not Acceptable).

Q: Which of the following annotations is often used in combination with `@Qualifier` to enable dependency injection based on a specific bean name or identifier?

C) `@Autowired`. `@Qualifier` is almost exclusively used in conjunction with `@Autowired` (or `@Inject`) to resolve ambiguity when multiple beans of the same type are candidates for injection.

Q: What occurs when the `/hello` endpoint is accessed, and a specific view named 'welcome.html' is expected for a Thymeleaf application?

D) Spring MVC will attempt to resolve a view named 'hello' based on the request mapping path.. When a `@Controller` method with a `void` return type is used, and `@ResponseBody` is not present, Spring MVC by default infers the logical view name from the request URI. For a request to `/hello`, it will try to resolve a view named 'hello'. If 'welcome.html' is expected, this would lead to a view resolution error (e.g., 500 Internal Server Error) if 'hello' view doesn't exist.

Q: Which attributes of the `@Bean` annotation allow you to explicitly specify custom initialization and destruction methods for the bean it produces?

C) `initMethod` and `destroyMethod`. The `initMethod` and `destroyMethod` attributes of the `@Bean` annotation take the names of methods to be called for bean initialization and destruction, respectively.

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

A) Application Started.. The `@Lazy` annotation delays the initialization of `LazyService` until it is first requested from the application context. Since it is never requested in the `main` method, its constructor is not called, and thus no output from `LazyService` is printed.

Q: Given a Spring Boot application with Thymeleaf, what is the most likely error if the following controller code is executed and a request is made to `/hello`, assuming no file named `nonExistentTemplate.html` exists in `src/main/resources/templates/`?

A) org.thymeleaf.exceptions.TemplateInputException: Error resolving template "nonExistentTemplate", template might not exist or might not be accessible. When Thymeleaf cannot find a template resolved by the controller's return value, it throws a TemplateInputException. Spring Boot's default setup uses Thymeleaf for HTML templates, and it expects templates in `src/main/resources/templates`.

Q: What error will likely occur when this Spring Boot application attempts to start, assuming `spring-boot-starter-web` is on the classpath?

B) A `NoUniqueBeanDefinitionException` for `WebMvcConfigurer`.. When `spring-boot-starter-web` is on the classpath, Spring Boot's auto-configuration provides its own `WebMvcConfigurer` bean. Defining another `WebMvcConfigurer` bean explicitly (as shown) will lead to a `NoUniqueBeanDefinitionException` because two beans of the same type are found when only one is expected.

Q301 medium

If a DELETE request is made to a Spring Boot endpoint for a resource that does not exist, which HTTP status code should typically be returned?

Q302 medium code output

Given the `Order` and `Customer` entities, what happens when `findOrderById` is called and then `getCustomer().getName()` is accessed *outside* an active transaction or persistence context?

java

import jakarta.persistence.*;

@Entity
public class Customer { @Id private Long id; private String name; /* getters, setters */ }

@Entity
@Table(name = "orders")
public class Order {
    @Id private Long id;
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "customer_id")
    private Customer customer;
    /* getters, setters */
}

// Simulate a repository method call outside a transaction
// Assume orderRepository and customerRepository are injected
Order order = orderRepository.findById(1L).orElse(null); // Order exists with customer_id = 1
String customerName = null;
if (order != null) {
    customerName = order.getCustomer().getName();
}
System.out.println(customerName);

Q303 medium

What is the correct way to inject a property named `server.port` from `application.properties`, providing a default value of `8080` if the property is not found?

Q304 medium code error

What is the expected error when a client sends a GET request to /resource with an Accept header of 'application/xml'?

java

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

@RestController
public class ResourceController {

    @GetMapping(value = "/resource", produces = MediaType.APPLICATION_JSON_VALUE)
    public String getResource() {
        return "{ \"data\": \"value\" }";
    }
}

Q305 medium

Which of the following annotations is often used in combination with `@Qualifier` to enable dependency injection based on a specific bean name or identifier?

Q306 medium code error

What occurs when the `/hello` endpoint is accessed, and a specific view named 'welcome.html' is expected for a Thymeleaf application?

java

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

@Controller
public class GreetingController {

    @GetMapping("/hello")
    public void showHelloPage() {
        // Logic here
    }
}

Q307 medium

Which attributes of the `@Bean` annotation allow you to explicitly specify custom initialization and destruction methods for the bean it produces?

Q308 medium code output

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

java

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

@Component @Lazy class LazyService {
    public LazyService() { System.out.println("LazyService initialized."); }
    public String serve() { return "Lazy data"; }
}

@SpringBootApplication
public class DemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
        System.out.println("Application Started.");
        // LazyService bean is NOT retrieved here
    }
}

Q309 medium code error

Given a Spring Boot application with Thymeleaf, what is the most likely error if the following controller code is executed and a request is made to `/hello`, assuming no file named `nonExistentTemplate.html` exists in `src/main/resources/templates/`?

java

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

@Controller
public class MyController {

    @GetMapping("/hello")
    public String sayHello(Model model) {
        model.addAttribute("message", "Hello World!");
        return "nonExistentTemplate";
    }
}

Q310 medium code error

What error will likely occur when this Spring Boot application attempts to start, assuming `spring-boot-starter-web` is on the classpath?

java

package com.example.app;

import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.SpringApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

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

    @Configuration
    static class MyWebConfig {
        @Bean
        public WebMvcConfigurer webMvcConfigurer() {
            return new WebMvcConfigurer() {};
        }
    }
}

Q311 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.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;

@Component
class SingletonBean { public SingletonBean() { System.out.println("SingletonBean instantiated."); } }

@SpringBootApplication
public class App {
    public static void main(String[] args) {
        ApplicationContext context = SpringApplication.run(App.class, args);
        SingletonBean bean1 = context.getBean(SingletonBean.class);
        SingletonBean bean2 = context.getBean(SingletonBean.class);
        System.out.println(bean1 == bean2);
    }
}

Q312 medium code error

What error will occur when Spring Boot tries to start the application?

java

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Component;

@Component
class ReportingService {
    public String generateReport() { return "Report"; }
}

@Component
class ReportConsumer {
    @Autowired
    @Qualifier("nonExistentQualifier")
    private ReportingService service;
}

Q313 medium code output

In a Spring Security context, if an `Authentication` object is stored in `SecurityContextHolder`, what would this code snippet print?

java

import org.springframework.security.core.Authentication;
import org.springframework.security.core.context.SecurityContextHolder;
import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;
import java.util.Collections;

public class SecurityContextDemo {
    public static void main(String[] args) {
        // Simulate successful JWT authentication
        Authentication auth = new UsernamePasswordAuthenticationToken("jwtUser", null, Collections.emptyList());
        SecurityContextHolder.getContext().setAuthentication(auth);

        // Retrieve and print principal name
        Authentication currentAuth = SecurityContextHolder.getContext().getAuthentication();
        if (currentAuth != null) {
            System.out.println(currentAuth.getName());
        } else {
            System.out.println("No authentication found");
        }
    }
}

Q314 medium code output

What is the HTTP status code and the 'Location' header value returned by this Spring Boot controller method?

java

import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RestController;
import java.net.URI;

@RestController
public class MyController {
    @PostMapping("/create")
    public ResponseEntity<Void> createResource() {
        return ResponseEntity.created(URI.create("/api/resource/1")).build();
    }
}

Q315 medium code output

What is the output of this code snippet configuring Feign client logging?

java

import feign.Logger;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.cloud.openfeign.FeignClient;

@Configuration
class FeignConfig {
    @Bean
    Logger.Level feignLoggerLevel() {
        return Logger.Level.HEADERS;
    }
}

@FeignClient(name = "logService", url = "http://localhost:8087", configuration = FeignConfig.class)
interface LogServiceClient {
    String dummyCall();
}

public class TestApplication {
    public static void main(String[] args) {
        // Assuming FeignConfig is loaded and applied
        Logger.Level configuredLevel = new FeignConfig().feignLoggerLevel();
        System.out.println("Feign logging level set to: " + configuredLevel.name());
    }
}

Q316 medium code output

Consider a Spring Boot application with `@EnableEurekaClient`. If its `application.yml` contains the following configuration, what will be the typical log output during startup related to Eureka client connectivity?

yaml

spring:
  application:
    name: my-service

server:
  port: 8080

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8762/eureka/

Q317 medium code output

Given the following Spring Boot controller and DTO, and a POST request with `Content-Type: application/json` and body `{"name": "Alice", "age": 30}`, what will be the output (return value) of the `createUser` method?

java

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

@Data
class UserDto {
    private String name;
    private int age;
}

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

    @PostMapping
    public String createUser(@RequestBody UserDto userDto) {
        return "User received: " + userDto.getName() + ", " + userDto.getAge();
    }
}

Q318 medium code error

Considering only `MainRunner.main()` is executed, why might a `@RestController` defined in `MyApplication` not be detected?

java

package com.example.app;

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

@SpringBootApplication
@RestController
class MyApplication {
    // Rest Controller methods
}

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

Q319 medium code output

What is the HTTP status returned by the `createTask` method when a POST request is made to `/tasks` with the JSON body `{"description": "ab"}` (Content-Type: application/json)?

java

import org.springframework.web.bind.annotation.*;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import javax.validation.Valid;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.Size;

class Task {
    @NotNull
    @Size(min = 3)
    private String description;
    public String getDescription() { return description; }
    public void setDescription(String description) { this.description = description; }
}

@RestController
@RequestMapping("/tasks")
class TaskController {
    @PostMapping
    public ResponseEntity<String> createTask(@Valid @RequestBody Task task) {
        return new ResponseEntity<>("Task created: " + task.getDescription(), HttpStatus.CREATED);
    }
}

Q320 medium code output

What will be printed to the console by this Spring Boot application?

java

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

interface DataFormatter {
    String format(String data);
}

@Component("csvFormatter")
class CsvFormatter implements DataFormatter {
    @Override
    public String format(String data) {
        return "CSV: " + data;
    }
}

@Component("jsonFormatter")
class JsonFormatter implements DataFormatter {
    @Override
    public String format(String data) {
        return "JSON: " + data;
    }
}

@Component
class DataProcessor {
    private final DataFormatter formatter;

    @Autowired
    public DataProcessor(@Qualifier("jsonFormatter") DataFormatter formatter) {
        this.formatter = formatter;
    }

    public void process() {
        System.out.println(formatter.format("sample_data"));
    }
}

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

🌱 Spring Boot MCQ Questions – Page 16