Spring Boot | Dependency Injection | Transactions | REST | SQL | Programming

Duration: 20 Minutes

Experience: 4–8 Years

This assessment evaluates Spring Boot fundamentals and production-ready backend concepts frequently used in enterprise applications.

---

Section A – Spring Boot MCQs (5 Questions)

---

Question 1 – Dependency Injection

Consider the following code:

interface NotificationService {
    void send();
}

@Service
class EmailService implements NotificationService {
    public void send() {}
}

@Service
class SmsService implements NotificationService {
    public void send() {}
}

@Service
class AlertService {

    @Autowired
    private NotificationService notificationService;

}

What happens when the application starts?

A. EmailService is injected automatically

B. SmsService is injected automatically

C. Spring throws NoUniqueBeanDefinitionException

D. Compilation Error

---

Question 2 – @Qualifier

Assume the same classes as above.

Which annotation resolves the ambiguity?

A.

@Qualifier("emailService")

B.

@Order(1)

C.

@PrimaryBean

D.

@BeanName

---

Question 3 – Bean Scope

What is the default scope of a Spring Bean?

A. prototype

B. singleton

C. request

D. session

---

Question 4 – @Transactional

Which statement is TRUE?

A. It always starts a new transaction.

B. It rolls back only checked exceptions by default.

C. It rolls back on unchecked (RuntimeException) exceptions by default.

D. It cannot be used on service methods.

---

Question 5 – REST API

Which HTTP method is most appropriate for updating an existing resource completely?

A. GET

B. POST

C. PUT

D. DELETE

---

Section B – SQL Challenge

Question 6

Tables

CUSTOMER

ID	NAME
1	Alice
2	Bob
3	Charlie

ORDERS

ORDER_ID	CUSTOMER_ID	AMOUNT
101	1	500
102	1	200
103	2	1000

Query

SELECT C.NAME,
       SUM(O.AMOUNT)
FROM CUSTOMER C
LEFT JOIN ORDERS O
ON C.ID = O.CUSTOMER_ID
GROUP BY C.NAME;

Which statement is correct?

A. Charlie is excluded

B. Charlie appears with NULL total amount

C. Query throws an error

D. Only Alice and Bob appear

---

Section C – Programming Questions

---

Question 7 – Group Employees by Department

Given

class Employee {

    String name;
    String department;

}

Using Java 8 Streams, group employees by department.

Expected Output

IT -> [John, Steve]

HR -> [Mary]

Finance -> [David]

---

Question 8 – Highest Salary Per Department

Given

class Employee {

    String department;
    int salary;

}

Using Java 8 Streams, print the highest salary for each department.

Expected Output

IT -> 90000

HR -> 70000

Finance -> 85000

---

Question 9 – Longest Word

Write a Java program to find the longest word in a sentence.

Example

Java Spring Boot Microservices

Expected Output

Microservices

Bonus

Solve using Java 8 Streams.

---

Answer Key & Detailed Explanations

---

Question 1

Correct Answer: C

Explanation

Spring finds two beans implementing NotificationService:

• EmailService
• SmsService

Since no bean is marked as preferred and no qualifier is provided, dependency injection becomes ambiguous.

Spring throws:

NoUniqueBeanDefinitionException

Interview Follow-up

• How can this be resolved?
• Difference between @Primary and @Qualifier.

---

Question 2

Correct Answer: A

Explanation

@Qualifier("emailService") explicitly tells Spring which bean to inject.

Example:

@Autowired
@Qualifier("emailService")
private NotificationService notificationService;

Alternative solution:

Annotate one implementation with:

@Primary

---

Question 3

Correct Answer: B

Explanation

Unless specified otherwise, Spring creates a single shared instance of each bean.

Default scope:

singleton

Other common scopes include:

• prototype
• request
• session
• application

---

Question 4

Correct Answer: C

Explanation

By default, Spring rolls back transactions only for unchecked exceptions (RuntimeException and Error).

Checked exceptions require explicit configuration:

@Transactional(rollbackFor = Exception.class)

---

Question 5

Correct Answer: C

Explanation

REST guidelines:

Method	Purpose
GET	Read
POST	Create
PUT	Replace entire resource
PATCH	Partial update
DELETE	Remove resource

---

Question 6

Correct Answer: B

Explanation

LEFT JOIN returns every customer.

Charlie has no matching orders.

SUM(O.AMOUNT) therefore evaluates to NULL for Charlie.

Result

Alice    700

Bob      1000

Charlie  NULL

Interview Follow-up

How would you return 0 instead of NULL?

Expected Answer:

COALESCE(SUM(O.AMOUNT),0)

---

Question 7 – Sample Solution

employees.stream()

.collect(Collectors.groupingBy(
Employee::getDepartment,
Collectors.mapping(
Employee::getName,
Collectors.toList())))
.forEach((k,v)->
System.out.println(k+" -> "+v));

Concepts Tested

• groupingBy
• mapping
• Method References

---

Question 8 – Sample Solution

employees.stream()

.collect(Collectors.groupingBy(
Employee::getDepartment,
Collectors.maxBy(
Comparator.comparingInt(
Employee::getSalary))))
.forEach((k,v)->
System.out.println(k+" -> "+v.get().getSalary()));

Alternative:

Use Collectors.collectingAndThen() to avoid calling get() on the Optional.

---

Question 9 – Sample Solution

Traditional

String longest = "";

for(String word : sentence.split(" ")){

    if(word.length() > longest.length()){

        longest = word;

    }

}

System.out.println(longest);

Java 8

Arrays.stream(sentence.split(" "))

.max(Comparator.comparingInt(String::length))

.ifPresent(System.out::println);

Complexity

Time: O(n)

Space: O(1) (excluding the array created by split())

---

Evaluation Guide

Score	Recommendation
9/9	Excellent – Strong Spring Boot Developer
7–8	Good – Recommended for Technical Round
5–6	Average – Needs Further Evaluation
Below 5	Not Recommended

---

Interviewer’s Notes

This set evaluates practical Spring Boot knowledge expected from backend developers.

A strong candidate should be able to explain:

• Why Spring fails when multiple beans implement the same interface.
• When to use @Qualifier versus @Primary.
• Why singleton is the default bean scope.
• How @Transactional behaves with checked and unchecked exceptions.
• Appropriate HTTP methods for REST APIs.
• How LEFT JOIN interacts with aggregate functions such as SUM().
• How Java 8 collectors (groupingBy, mapping, maxBy) simplify business logic.

Candidates who answer the follow-up questions confidently are typically ready for deeper discussions on Spring Boot architecture, transactions, and microservices.