Spring Boot MCQ Questions – Page 15 of 49

Q: For a REST endpoint in a `@RestController` that successfully processes a request but has no specific data to return, what is an appropriate return type that allows control over the HTTP status code?

C) `ResponseEntity `. `ResponseEntity ` allows the developer to explicitly set the HTTP status code (e.g., `HttpStatus.NO_CONTENT` for a 204 response) even when no response body is needed, providing more control than simply returning `void`.

Q: What is the output of this code?

A) Configured Bean. The `@Configuration` class `AppConfig` defines a bean named `myBean` of type `ConfiguredBean`. The `ApplicationContext` finds and manages this bean, allowing it to be retrieved by type.

Q: What is the output printed to the console when the following Spring Boot `@Service` and its usage in a `CommandLineRunner` are executed? (Assume standard Spring Boot application setup and necessary imports for `org.springframework.stereotype.Service`.)

A) Hello from @Service!. The `@Service` annotation marks `SimpleMessageService` as a Spring component, making it eligible for component scanning and autowiring. When `getMessage()` is called, it returns the specified string.

Q: What is the HTTP status code returned by the following Spring Boot controller method if a DELETE request is sent to `/api/data/10` and `dataService.softDelete(10L)` successfully marks the data as deleted without physically removing it from the database?

C) HTTP 202 Accepted. The method explicitly constructs a `ResponseEntity` with `HttpStatus.ACCEPTED`. This indicates that the request has been accepted for processing, but the processing has not been completed yet (or in this case, a 'soft' delete).

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

A) Initialized via @Bean. The `@Bean` annotation supports the `name` attribute, which can take an array of strings to define multiple names (aliases) for a single bean. Here, `createComponent()` registers the bean with both 'myComponent' and 'specialComponent' as names. The `main` method successfully retrieves the bean using the alias 'specialComponent'.

Q: Given an `Item` DTO that *only* has a parameterized constructor `public Item(String name)`, and no default constructor. What error occurs when a client sends `{"name": "Laptop"}` with `Content-Type: application/json`?

A) org.springframework.http.converter.HttpMessageNotReadableException: Cannot construct instance of `com.example.demo.Item` (no Creators, like default constructor, exist): cannot deserialize from Object value (token `JsonToken.START_OBJECT`). Jackson's default deserialization process for JSON objects typically requires a no-argument (default) constructor to instantiate the DTO, then uses setters or reflection to populate fields. Without a default constructor, Jackson cannot create an instance, leading to an `HttpMessageNotReadableException`.

Q: If a request with `Host: example.com` and `User-Agent: Mozilla` arrives at the gateway, which URI will it be routed to?

A) http://localhost:8081. When multiple routes match, the first matching route defined in the `RouteLocator` (based on order of definition) is chosen. The `host_route` is defined first and matches the incoming request.

Q: If `productService.deleteProduct(id)` throws a `ProductNotFoundException` (a custom runtime exception), what HTTP status will this endpoint return?

A) 400 Bad Request. The `catch (Exception e)` block is too broad and will catch `ProductNotFoundException`. It then explicitly returns `ResponseEntity.badRequest().build()`, which corresponds to an HTTP 400 status code, even though a 404 Not Found would be more appropriate for a missing resource.

Q: Which `@RequestMapping` attribute is used to specify that a controller method should only handle HTTP POST requests?

B) `method = RequestMethod.POST`. The `method` attribute of `@RequestMapping` (or its shorthand annotations like `@PostMapping`) is used to specify the HTTP request method(s) that a handler method will process.

Q: Which of the following best describes how Spring Boot primarily implements Inversion of Control?

C) Through Dependency Injection (DI), where the container injects dependencies.. Dependency Injection is the most prominent form of IoC in Spring, allowing the container to inject required dependencies into objects rather than the objects requesting them.

Q281 medium

For a REST endpoint in a `@RestController` that successfully processes a request but has no specific data to return, what is an appropriate return type that allows control over the HTTP status code?

Q282 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.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

class ConfiguredBean { public String getType() { return "Configured Bean"; } }

@Configuration
class AppConfig { @Bean public ConfiguredBean myBean() { return new ConfiguredBean(); } }

@SpringBootApplication
public class App2 {
    public static void main(String[] args) {
        ApplicationContext ctx = SpringApplication.run(App2.class, args);
        ConfiguredBean bean = ctx.getBean(ConfiguredBean.class);
        System.out.println(bean.getType());
    }
}

Q283 medium code output

What is the output printed to the console when the following Spring Boot `@Service` and its usage in a `CommandLineRunner` are executed? (Assume standard Spring Boot application setup and necessary imports for `org.springframework.stereotype.Service`.)

java

import org.springframework.stereotype.Service;

@Service
class SimpleMessageService {
    public String getMessage() {
        return "Hello from @Service!";
    }
}

// In a @SpringBootApplication's CommandLineRunner, after autowiring:
// System.out.println(simpleMessageService.getMessage());

Q284 medium code output

What is the HTTP status code returned by the following Spring Boot controller method if a DELETE request is sent to `/api/data/10` and `dataService.softDelete(10L)` successfully marks the data as deleted without physically removing it from the database?

java

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

@RestController
@RequestMapping("/api/data")
public class DataController {

    private DataService dataService;

    // Constructor injected dataService

    @DeleteMapping("/{id}")
    public ResponseEntity<String> softDeleteData(@PathVariable Long id) {
        dataService.softDelete(id);
        return new ResponseEntity<>("Data marked as deleted.", HttpStatus.ACCEPTED);
    }
}

Q285 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);
        MyComponent component = context.getBean("specialComponent", MyComponent.class);
        System.out.println(component.getName());
    }
}

class MyComponent {
    private String name;
    public MyComponent(String name) { this.name = name; }
    public String getName() { return name; }
}

@Configuration
class AppConfig {
    @Bean(name = {"myComponent", "specialComponent"})
    public MyComponent createComponent() {
        return new MyComponent("Initialized via @Bean");
    }
}

Q286 medium code error

Given an `Item` DTO that *only* has a parameterized constructor `public Item(String name)`, and no default constructor. What error occurs when a client sends `{"name": "Laptop"}` with `Content-Type: application/json`?

java

package com.example.demo;
import org.springframework.web.bind.annotation.*;
import org.springframework.http.ResponseEntity;

public class Item {
    private String name;
    public Item(String name) { this.name = name; }
    public String getName() { return name; }
}

@RestController
public class ItemController {
    @PostMapping("/items")
    public ResponseEntity<String> createItem(@RequestBody Item item) {
        return ResponseEntity.ok("Item created: " + item.getName());
    }
}

Q287 medium code output

If a request with `Host: example.com` and `User-Agent: Mozilla` arrives at the gateway, which URI will it be routed to?

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("host_route", r -> r.host("example.com")
                        .uri("http://localhost:8081"))
                .route("agent_route", r -> r.header("User-Agent", ".*Mozilla.*")
                        .uri("http://localhost:8082"))
                .build();
    }
}

Q288 medium code error

If `productService.deleteProduct(id)` throws a `ProductNotFoundException` (a custom runtime exception), what HTTP status will this endpoint return?

java

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

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

    private ProductService productService; // Assume injected

    @DeleteMapping("/{id}")
    public ResponseEntity<Void> deleteProduct(@PathVariable Long id) {
        try {
            productService.deleteProduct(id);
            return ResponseEntity.noContent().build();
        } catch (Exception e) {
            return ResponseEntity.badRequest().build();
        }
    }
}

Q289 medium

Which `@RequestMapping` attribute is used to specify that a controller method should only handle HTTP POST requests?

Q290 medium

Which of the following best describes how Spring Boot primarily implements Inversion of Control?

Q291 medium

You have an optional dependency that might not always be present in the `ApplicationContext`. How can you configure `@Autowired` to prevent an error if the dependency is not found?

Q292 medium code error

A client sends a DELETE request to `/api/orders/123`. What error will this code produce?

java

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

@RestController
@RequestMapping("/api/orders")
public class OrderController {

    private OrderService orderService; // Assume injected

    @DeleteMapping("/{id}")
    public ResponseEntity<Void> deleteOrder(@RequestParam("id") Long orderId) {
        orderService.deleteOrder(orderId);
        return ResponseEntity.noContent().build();
    }
}

Q293 medium code error

Consider the following Spring Boot application setup. What error will occur when this application attempts to start?

java

package com.example.app;

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

class MyDependency {
    public String getData() {
        return "Data from dep";
    }
}

@Component
class MyService {
    private final MyDependency dependency;

    @Autowired
    public MyService(MyDependency dependency) {
        this.dependency = dependency;
    }
}

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

Q294 medium code error

What is the result when Spring Boot attempts to start this application?

java

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import java.util.List;

@Component
class MyDataProcessor {
    @Autowired
    private List<String> stringList;

    public void process() {
        // Uses stringList
    }
}

Q295 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.ApplicationContext;
import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;

@Component @Scope("prototype")
class ScopedBean {
    private static int counter = 0;
    public ScopedBean() { counter++; }
    public int getInstanceCount() { return counter; }
}

@SpringBootApplication
public class App8 {
    public static void main(String[] args) {
        ApplicationContext ctx = SpringApplication.run(App8.class, args);
        ScopedBean b1 = ctx.getBean(ScopedBean.class);
        ScopedBean b2 = ctx.getBean(ScopedBean.class);
        System.out.println(b1.getInstanceCount() + "," + b2.getInstanceCount());
    }
}

Q296 medium code error

Given the Spring Boot application structure below, what error will occur when running the `main` method and trying to retrieve `externalMessage`?

java

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

@Configuration
public class ExternalConfig {
    @Bean
    public String externalMessage() {
        return "Hello from external config!";
    }
}

// In a separate package: com.example.app
package com.example.app;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;

@SpringBootApplication // Assumes base package is com.example.app
public class MyApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(MyApplication.class, args);
        String message = context.getBean("externalMessage", String.class); 
        System.out.println(message);
    }
}

Q297 medium code output

Given `application.properties` contains `app.greeting=Hello Spring!` and the following Java code, what does it print?

java

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

@Component
public class GreetingService {
    @Value("${app.greeting}")
    private String greetingMessage;

    public String getGreeting() {
        return greetingMessage;
    }
}
// In a Spring Boot application, if this component is scanned:
// GreetingService service = applicationContext.getBean(GreetingService.class);
// System.out.println(service.getGreeting());

Q298 medium code error

Given the following Spring Boot configuration, what is the consequence when `ReportGenerator` attempts to use `DataSourceManager`?

java

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

@Configuration
public class AppConfig {

    @Bean
    public DataSourceManager dataSourceManager() {
        return null; // Explicitly returning null
    }

    @Bean
    public ReportGenerator reportGenerator(@Autowired DataSourceManager dsm) {
        return new ReportGenerator(dsm);
    }
}

class DataSourceManager {}
class ReportGenerator {
    public ReportGenerator(DataSourceManager dsm) {}
}

Q299 medium code error

What error will occur when accessing `/api/items?page=abc&size=10` with the following Spring Boot controller?

java

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

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

    @GetMapping("/items")
    public String getItems(
            @RequestParam(defaultValue = "0") int page,
            @RequestParam int size) {
        return "Fetching items - Page: " + page + ", Size: " + size;
    }
}

Q300 medium code output

What is the HTTP status and body returned by the `processPayload` method when a POST request is made to `/payload` with `Content-Type: application/json` and the JSON body `{"id": "not-an-int"}`?

java

import org.springframework.web.bind.annotation.*;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.http.converter.HttpMessageNotReadableException;

class DataPayload {
    private int id;
    public int getId() { return id; }
    public void setId(int id) { this.id = id; }
}

@RestController
@RequestMapping("/payload")
class PayloadController {
    @PostMapping
    public ResponseEntity<String> processPayload(@RequestBody DataPayload payload) {
        return new ResponseEntity<>("Processed ID: " + payload.getId(), HttpStatus.OK);
    }

    @ExceptionHandler(HttpMessageNotReadableException.class)
    public ResponseEntity<String> handleHttpMessageNotReadable(HttpMessageNotReadableException ex) {
        return new ResponseEntity<>("Invalid request body format: " + ex.getMessage().split(":")[0].trim(), HttpStatus.BAD_REQUEST);
    }
}

🌱 Spring Boot MCQ Questions – Page 15