Spring Boot MCQ Questions – Page 46 of 49

Q: What error will occur during application startup due to the use of `@Qualifier`?

A) org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean with name 'nonExistentImpl' available. The `@Qualifier("nonExistentImpl")` annotation specifies a bean name that does not correspond to any registered Spring bean, causing Spring to throw a `NoSuchBeanDefinitionException` at startup.

Q: What does this code print to the console?

A) Client fetched: Data from ServiceA.. Spring automatically detects and performs constructor injection for `ServiceA` into `ClientB` because both are `@Component` beans and `ClientB` has a single constructor.

Q: What is the expected outcome when Spring Boot attempts to start with this configuration?

B) The application will start successfully, but `configService` might be a CGLIB proxy.. A class can be annotated with both `@Configuration` and `@Service`. While generally not recommended as it blurs roles, Spring will process both. The `@Configuration` will ensure it's processed for bean definitions, and `@Service` makes it a component. When `@Configuration` is present, Spring often proxies the bean to handle `@Bean` methods, so `configService` might be a CGLIB proxy.

Q: What is the output of this code?

A) Printed by Spring!. The `Printer` class is a Spring component, and it is successfully autowired into the `App3` class. The `run` method then executes after the context is initialized, printing the message from the autowired bean.

Q: What is the HTTP response body when a GET request is made to '/hello'?

A) "Hello Spring Boot!". A `@RestController` method returning a String will directly write that String to the HTTP response body. By default, it's treated as plain text unless explicitly requested otherwise or a specific converter is configured.

Q: What is the output of this code when a GET request is made to '/users/101'?

A) User ID: 101. The @PathVariable annotation extracts the 'id' segment from the URL path. For a request to /users/101, '101' is bound to the 'id' parameter and included in the return string.

Q: What error will Spring Boot report when attempting to start this application?

B) A `BeanCreationException` due to `NoSuchBeanDefinitionException` for type `MyComponent`.. For Spring to process `@Bean` methods and register the returned objects as beans, the class containing these methods must be annotated with `@Configuration`. Without it, `MyComponent` will not be available in the application context, causing a `BeanCreationException` when `MyService` tries to inject it.

Q: What happens when trying to access `/api/message` in this Spring Boot application?

B) A 200 OK response with the body 'Hello from API!'.. The `@RequestMapping` annotation at the class level defines a base path `/api` for all methods within `ApiController`. The method-level `@RequestMapping("/message")` then appends to this base path. Thus, accessing `/api/message` will correctly invoke the `getMessage` method, and `@ResponseBody` ensures the string is returned as the HTTP response body.

Q: What header will be added to the response if the original request included `User-Agent: Chrome`?

A) X-Gateway-Processed: true. The route matches if the path is `/test` AND the `User-Agent` header contains 'Chrome'. Since the request meets both conditions, the `addResponseHeader` filter will execute, adding `X-Gateway-Processed: true` to the response.

Q: By default, from where does `@SpringBootApplication`'s embedded `@ComponentScan` scan for components?

B) The package of the class annotated with `@SpringBootApplication` and all its sub-packages.. The default behavior of `@ComponentScan` within `@SpringBootApplication` is to scan the current package (where the annotation is located) and all its sub-packages for Spring components.

Q901 medium code error

What error will occur during application startup due to the use of `@Qualifier`?

java

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

public interface MyService {
    String serve();
}

@Service("firstImpl")
public class MyServiceImplA implements MyService {
    @Override public String serve() { return "Service A"; }
}

@Service
public class ConsumerService {
    @Autowired
    @Qualifier("nonExistentImpl") // This qualifier does not match any bean
    private MyService myService;

    public String useService() { return myService.serve(); }
}

Q902 medium code output

What does this code print to the console?

java

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.stereotype.Component;

@Component class ServiceA {
    public String getInfo() { return "Data from ServiceA."; }
}

@Component class ClientB {
    private final ServiceA serviceA;
    public ClientB(ServiceA serviceA) { this.serviceA = serviceA; }
    public String fetchData() { return "Client fetched: " + serviceA.getInfo(); }
}

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

Q903 medium code error

What is the expected outcome when Spring Boot attempts to start with this configuration?

java

package com.example.app;

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

@Configuration
@Service
public class AppConfigService {
    public String getConfigInfo() {
        return "Config info";
    }
}

@Service
public class ConsumerService {
    @Autowired
    private AppConfigService configService;

    public String getData() {
        return configService.getConfigInfo();
    }
}

Q904 medium code output

What is the output of this code?

java

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

@Component
class Printer { public String print() { return "Printed by Spring!"; } }

@SpringBootApplication
public class App3 implements CommandLineRunner {
    @Autowired private Printer printer;
    public static void main(String[] args) { SpringApplication.run(App3.class, args); }
    @Override
    public void run(String... args) { System.out.println(printer.print()); }
}

Q905 medium code output

What is the HTTP response body when a GET request is made to '/hello'?

java

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

@RestController
public class HelloController {
    @GetMapping("/hello")
    public String sayHello() {
        return "Hello Spring Boot!";
    }
}

Q906 medium code output

What is the output of this code when a GET request is made to '/users/101'?

java

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

@RestController
public class UserController {
    @RequestMapping("/users/{id}")
    public String getUserById(@PathVariable String id) {
        return "User ID: " + id;
    }
}

Q907 medium code error

What error will Spring Boot report when attempting to start this application?

java

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

// Missing @Configuration annotation
public class MyConfig {
    public MyComponent myComponent() { return new MyComponent("Configured Data"); }
}

public class MyComponent {
    private String data; 
    public MyComponent(String data) { this.data = data; }
    public String getData() { return data; }
}

@Service
public class MyService {
    @Autowired
    private MyComponent myComponent;
}

Q908 medium code error

What happens when trying to access `/api/message` in this Spring Boot application?

java

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
@RequestMapping("/api")
public class ApiController {

    @RequestMapping("/message")
    @ResponseBody
    public String getMessage() {
        return "Hello from API!";
    }
}

Q909 medium code output

What header will be added to the response if the original request included `User-Agent: Chrome`?

java

import org.springframework.cloud.gateway.route.RouteLocator;
import org.springframework.cloud.gateway.route.builder.RouteLocatorBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class GatewayConfig {
    @Bean
    public RouteLocator customRouteLocator(RouteLocatorBuilder builder) {
        return builder.routes()
                .route("response_header_route", r -> r.path("/test")
                        .and().header("User-Agent", ".*Chrome.*")
                        .filters(f -> f.addResponseHeader("X-Gateway-Processed", "true"))
                        .uri("http://localhost:8085"))
                .build();
    }
}

Q910 medium

By default, from where does `@SpringBootApplication`'s embedded `@ComponentScan` scan for components?

Q911 medium

On which of the following can the `@Value` annotation be effectively used in a Spring component?

Q912 medium code output

Given the `Product` class (with `id` and `name` properties) below, what is the HTTP response body when a POST request is made to '/api/products' with the JSON body `{"id": 5, "name": "Laptop"}`?

java

import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;

// Assuming Product class is defined as: class Product { private Long id; private String name; // Getters, Setters, default constructor }

@RestController
public class ProductController {
    @PostMapping("/api/products")
    public String addProduct(@RequestBody Product product) {
        return "Added product: " + product.getName() + " with ID " + product.getId();
    }
}

Q913 medium code output

What is the HTTP response body when making a GET request to `/greet?name=Alice` with the following controller?

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 GreetingController {

    @GetMapping("/greet")
    @ResponseBody
    public String greetUser(@RequestParam String name) {
        return "Hello, " + name + "!";
    }
}

Q914 medium

What is the primary annotation used by Spring Boot to automatically inject dependencies into a component by type?

Q915 medium

At which stage of the Spring bean lifecycle does a BeanPostProcessor's postProcessBeforeInitialization method execute?

Q916 medium code output

Considering both a filter and an interceptor are active for the `/resource` endpoint, what is the expected console output for a GET request to `/resource`?

java

import org.springframework.context.annotation.Configuration;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
import org.springframework.web.filter.OncePerRequestFilter;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@Component
class CombinedFilter extends OncePerRequestFilter {
    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws ServletException, IOException {
        System.out.println("Filter: Entering");
        filterChain.doFilter(request, response);
        System.out.println("Filter: Exiting");
    }
}

@Component
class CombinedInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) { System.out.println("Interceptor: Pre-handle"); return true; }
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) { System.out.println("Interceptor: Post-handle"); }
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) { System.out.println("Interceptor: After-completion"); }
}

@Configuration
class WebConfigWithInterceptors implements WebMvcConfigurer {
    private final CombinedInterceptor interceptor; 
    public WebConfigWithInterceptors(CombinedInterceptor interceptor) { this.interceptor = interceptor; }
    @Override
    public void addInterceptors(InterceptorRegistry registry) { registry.addInterceptor(interceptor).addPathPatterns("/resource"); }
}

@RestController
class ResourceController {
    @GetMapping("/resource")
    public String getResource() {
        System.out.println("Controller: Executing resource logic");
        return "Resource";
    }
}
// Assume CombinedFilter is registered for all paths.

Q917 medium code error

Given `MyCustomId` is a simple POJO without any custom converters, what error occurs when accessing `/data/complexValue123` with the following controller?

java

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

class MyCustomId {
    private String id;
    public MyCustomId(String id) { this.id = id; }
    public String getId() { return id; }
}

@RestController
public class ComplexDataController {
    @GetMapping("/data/{complexId}")
    public String getComplexData(@PathVariable MyCustomId complexId) {
        return "Complex Data ID: " + complexId.getId();
    }
}

Q918 medium code error

What is the error in this Spring Boot application when it tries to configure `MyContextAwareBean`?

java

import org.springframework.context.ApplicationContextAware;
import org.springframework.context.ApplicationContext;
import org.springframework.stereotype.Component;

@Component
public class MyContextAwareBean implements ApplicationContextAware {
    private ApplicationContext context;

    @Override
    public void setApplicationContext(String invalidContext) { // Incorrect parameter type
        // This method will not be called by Spring
    }

    public ApplicationContext getContext() { return context; }
}

Q919 medium code output

What is the expected outcome if a client sends a POST request with `Content-Type: text/plain` and a body `{"message":"hello"}` to the following Spring Boot controller method?

java

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

@Data
class MessageDto {
    private String message;
}

@RestController
@RequestMapping("/messages")
public class MessageController {

    @PostMapping
    public String receiveMessage(@RequestBody MessageDto messageDto) {
        return "Received: " + messageDto.getMessage();
    }
}

Q920 medium code error

What error will occur when Spring Boot tries to start the application with these two components?

java

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

@Component
class ServiceA {
    private final ServiceB serviceB;

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

@Component
class ServiceB {
    private final ServiceA serviceA;

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

🌱 Spring Boot MCQ Questions – Page 46