Spring Boot MCQ Questions – Page 3 of 49

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

A) Service is null in static context.. Spring's `@Autowired` mechanism is designed for instance fields and methods, not static fields. The annotation on the static `service` field is ignored, leaving `service` as `null` and resulting in 'Service is null in static context.'

Q: What is the output of this code when the `main` method of `MyApplication` is executed?

A) MyService found: Service initialized from other package.. The `@ComponentScan(basePackageClasses = {MyMarkerClass.class})` annotation instructs Spring to scan the package of `MyMarkerClass` (which is `com.example.other`). This allows `MyService` to be discovered, autowired, and its method called by the `CommandLineRunner`.

Q: What is the output when accessing `/items?item=apple&item=banana&item=orange`?

A) Selected items: [apple, banana, orange]. Spring can automatically bind multiple query parameters with the same name into a `List` or array type parameter in the handler method.

Q: When are 'Aware' interfaces (e.g., BeanNameAware, BeanFactoryAware) typically called within the Spring bean lifecycle?

C) After property population but before any initialization callbacks.. Aware interfaces allow beans to be notified of their containing environment. They are invoked after properties have been set but before the main initialization callbacks begin.

Q: What is the HTTP status code and response body when a GET request is sent to `/service/status` given the following Spring Boot code?

A) Status: 503 SERVICE_UNAVAILABLE, Body: Error: Service is temporarily down. The `StatusController` throws `ServiceUnavailableException`. The `CustomErrorHandler` catches this exception, and the `@ResponseStatus(HttpStatus.SERVICE_UNAVAILABLE)` annotation sets the HTTP status to 503. The method's returned `String` becomes the response body.

Q: What is the primary use case for `@Value` compared to `@ConfigurationProperties`?

B) `@Value` is for injecting single primitive values or simple strings, whereas `@ConfigurationProperties` is better for binding multiple related properties to a POJO.. `@Value` is ideal for injecting individual values (primitives, strings). `@ConfigurationProperties` is designed for binding a group of related properties into a type-safe configuration bean (POJO).

Q: How can you make a `@RequestBody` parameter optional in a Spring Boot controller method?

C) By setting `@RequestBody(required = false)`.. The `required` attribute of `@RequestBody` can be set to `false` (i.e., `@RequestBody(required = false)`) to make the request body optional. If the body is then missing, the parameter will be `null`.

Q: What is printed to the console when the following Spring Data JPA code is executed?

A) Product saved with ID: 1. When `GenerationType.IDENTITY` is used, the database auto-increments the ID upon insertion. After `save()`, the entity's ID field is populated with the generated value, typically starting from 1 for the first record.

Q: What happens when Spring Boot tries to inject 'myService' into 'MyComponent'?

B) The application starts successfully, but 'getServiceMessage()' will return 'Service not injected' because static fields are not autowired.. Spring's @Autowired mechanism is designed for instance fields and methods within Spring-managed beans. It does not support static fields, so 'myService' will remain null. When 'getServiceMessage()' is called, it will access a null field, leading to the specified output, assuming no NullPointerException is immediately triggered.

Q: What is the output printed to the console when a simple `@Service` method is called in a Spring Boot application? (Assume standard Spring Boot application setup and necessary imports.)

A) 8. The `@Service` annotation simply marks the class as a service component. Its methods behave like regular Java methods. The `add` method performs integer addition and returns the sum of 5 and 3, which is 8.

Q41 medium code output

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

java

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

@Component
class RegularService {
    public String getName() { return "Regular Service"; }
}

@Component
class StaticAutowiredBean {
    @Autowired 
    private static RegularService service; // Autowiring on a static field is ignored

    public String useService() {
        return service != null ? service.getName() : "Service is null in static context.";
    }
}

@Component
class MyRunner implements CommandLineRunner {
    @Autowired
    private StaticAutowiredBean bean;

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

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

Q42 medium code output

What is the output of this code when the `main` method of `MyApplication` is executed?

java

// src/main/java/com/example/mainapp/MyApplication.java
package com.example.mainapp;

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

// Dummy class in other package to reference
import com.example.other.MyMarkerClass;

@SpringBootApplication
@ComponentScan(basePackageClasses = {MyMarkerClass.class})
public class MyApplication {
    @Autowired(required = false)
    private MyService myService;

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

    @Bean
    public CommandLineRunner run() {
        return args -> {
            if (myService != null) {
                System.out.println("MyService found: " + myService.getMessage());
            } else {
                System.out.println("MyService not found.");
            }
        };
    }
}

// src/main/java/com/example/other/MyMarkerClass.java
package com.example.other;
// This class is just a marker, not a component itself.
public class MyMarkerClass {}

// src/main/java/com/example/other/MyService.java
package com.example.other;

import org.springframework.stereotype.Service;

@Service
public class MyService {
    public String getMessage() {
        return "Service initialized from other package.";
    }
}

Q43 medium code output

What is the output when accessing `/items?item=apple&item=banana&item=orange`?

java

import org.springframework.web.bind.annotation.*;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import java.util.List;

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

    @GetMapping("/items")
    public String getItems(@RequestParam List<String> item) {
        return "Selected items: " + item.toString();
    }
}

Q44 medium

When are 'Aware' interfaces (e.g., BeanNameAware, BeanFactoryAware) typically called within the Spring bean lifecycle?

Q45 medium code output

What is the HTTP status code and response body when a GET request is sent to `/service/status` given the following Spring Boot code?

java

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

class ServiceUnavailableException extends RuntimeException {
    public ServiceUnavailableException(String message) { super(message); }
}

@RestController
class StatusController {
    @GetMapping("/service/status")
    public String getServiceStatus() {
        throw new ServiceUnavailableException("Service is temporarily down");
    }
}

@RestControllerAdvice
class CustomErrorHandler {
    @ExceptionHandler(ServiceUnavailableException.class)
    @ResponseStatus(HttpStatus.SERVICE_UNAVAILABLE)
    public String handleServiceUnavailable(ServiceUnavailableException ex) {
        return "Error: " + ex.getMessage();
    }
}

Q46 medium

What is the primary use case for `@Value` compared to `@ConfigurationProperties`?

Q47 medium

How can you make a `@RequestBody` parameter optional in a Spring Boot controller method?

Q48 medium code output

What is printed to the console when the following Spring Data JPA code is executed?

java

import jakarta.persistence.*;

@Entity
public class Product {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;

    public Product() {}
    public Product(String name) { this.name = name; }
    public Long getId() { return id; }
}

// Assume productRepository is injected and available
// Assume transaction context is active
Product newProduct = new Product("Laptop");
productRepository.save(newProduct);
System.out.println("Product saved with ID: " + newProduct.getId());

Q49 medium code error

What happens when Spring Boot tries to inject 'myService' into 'MyComponent'?

java

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

@Component
class MyService {
    public String getMessage() { return "Hello"; }
}

@Component
class MyComponent {
    @Autowired
    private static MyService myService;

    public static String getServiceMessage() {
        return myService != null ? myService.getMessage() : "Service not injected";
    }
}

Q50 medium code output

What is the output printed to the console when a simple `@Service` method is called in a Spring Boot application? (Assume standard Spring Boot application setup and necessary imports.)

java

import org.springframework.stereotype.Service;

@Service
class CalculatorService {
    public int add(int a, int b) {
        return a + b;
    }
}

// In a @SpringBootApplication's CommandLineRunner, after autowiring:
// System.out.println(calculatorService.add(5, 3));

Q51 medium code output

Given the `TestController` and the MockMvc test, what is the output of the test after calling `andDo(print())`?

java

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
import org.springframework.test.web.servlet.MockMvc;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultHandlers.print;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;

@WebMvcTest(controllers = TestController.class)
class TestControllerTest {
    @Autowired
    private MockMvc mockMvc;

    @Test
    void testDebugEndpoint() throws Exception {
        mockMvc.perform(get("/debug/info"))
               .andDo(print())
               .andExpect(status().isOk())
               .andExpect(content().string("Debug Info"));
    }
}

// Assuming TestController has:
// @RestController
// class TestController {
//    @GetMapping("/debug/info")
//    public String debugInfo() { return "Debug Info"; }
// }

Q52 medium

To automatically deserialize the JSON or XML payload of an HTTP POST request into a Java object parameter in a Spring Boot controller method, which annotation must be used?

Q53 medium code output

What is the HTTP status code and response body for a PUT request to `/api/documents/10` with the JSON body `{"title": "My New Doc"}`?

java

import org.springframework.web.bind.annotation.*;
import org.springframework.http.ResponseEntity;
import org.springframework.http.HttpStatus;
import java.util.HashMap;
import java.util.Map;
import javax.validation.Valid;
import javax.validation.constraints.NotNull;

// Assume Document class has Long id, @NotNull String title, String content.
// And @Valid is enabled globally for Spring Boot.

class Document {
    private Long id;
    @NotNull
    private String title;
    private String content;
    // Getters, Setters, Constructor
    public Document(Long id, String title, String content) { this.id = id; this.title = title; this.content = content; }
    public Long getId() { return id; }
    public void setId(Long id) { this.id = id; }
    public String getTitle() { return title; }
    public void setTitle(String title) { this.title = title; }
    public String getContent() { return content; }
    public void setContent(String content) { this.content = content; }
}

@RestController
@RequestMapping("/api/documents")
public class DocumentController {
    private Map<Long, Document> documents = new HashMap<>();

    public DocumentController() {
        documents.put(10L, new Document(10L, "Old Title", "Some content"));
    }

    @PutMapping("/{id}")
    public ResponseEntity<Document> updateDocument(@PathVariable Long id, @Valid @RequestBody Document docDetails) {
        if (!documents.containsKey(id)) {
            return ResponseEntity.status(HttpStatus.NOT_FOUND).build();
        }
        docDetails.setId(id);
        documents.put(id, docDetails);
        return ResponseEntity.ok(docDetails);
    }
}

Q54 medium code error

What error will be reported when Spring Boot tries to instantiate `MyService`?

java

package com.example.app;

import org.springframework.stereotype.Service;

@Service
public class MyService {
    private final int value;

    public MyService(int value) {
        this.value = value;
    }

    public String getInfo() {
        return "Value: " + value;
    }
}

Q55 medium code output

What is the output of this code?

java

import org.springframework.security.access.prepost.PreAuthorize;
import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;
import org.springframework.security.core.authority.SimpleGrantedAuthority;
import org.springframework.security.core.context.SecurityContextHolder;
import java.util.Collections;

public class SecureService {
    @PreAuthorize("hasAuthority('ADMIN')")
    public String getRestrictedInfo() { return "Restricted Info"; }
}

public class TestRunner {
    public static void main(String[] args) {
        SecurityContextHolder.getContext().setAuthentication(
            new UsernamePasswordAuthenticationToken("admin", "pass", Collections.singletonList(new SimpleGrantedAuthority("ROLE_ADMIN")))
        );
        SecureService service = new SecureService();
        try { System.out.println(service.getRestrictedInfo()); }
        catch (Exception e) { System.out.println(e.getClass().getSimpleName()); }
    }
}

Q56 medium

To handle a specific exception type (e.g., `ResourceNotFoundException`) that might be thrown *within a particular controller*, which annotation would you use on a method inside that controller?

Q57 medium

Given `application.properties` contains `app.servers=server1,server2,server3`, how can you inject these values as a `List<String>` into a field?

Q58 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);
        String message = context.getBean("myGreeting", String.class);
        System.out.println(message);
    }
}

@Configuration
class AppConfig {
    @Bean(name = "myGreeting")
    public String greetingBean() {
        return "Hello from Spring Boot Bean!";
    }
}

Q59 medium

When an incoming JSON request body contains fields that are not present in the target Java object (DTO) annotated with `@RequestBody`, what is the default behavior in Spring Boot (using Jackson)?

Q60 medium

If a `@RequestParam` is marked as required (either by default or explicitly `required=true`) and the client does not provide the parameter in the request, what HTTP status code will Spring Boot typically return?

🌱 Spring Boot MCQ Questions – Page 3