DTO pattern for data transfer in Spring Boot - Performance & Optimization

Performance: DTO pattern for data transfer

MEDIUM IMPACT

This pattern affects the amount of data sent over the network and the processing time on both client and server during data transfer.

Sending data from server to client in a Spring Boot application

Spring Boot

public class UserDTO {
    private String username;
    private String email;
    // getters and setters
}

@GetMapping("/users/{id}")
public UserDTO getUser(@PathVariable Long id) {
    User user = userRepository.findById(id).orElse(null);
    if (user == null) return null;
    UserDTO dto = new UserDTO();
    dto.setUsername(user.getUsername());
    dto.setEmail(user.getEmail());
    return dto;
}

Only necessary fields are sent, reducing payload size and avoiding sensitive data exposure.

📈 Performance GainReduces payload size by 30-50%, speeds up JSON parsing and rendering.

Sending data from server to client in a Spring Boot application

Spring Boot

public class User {
    private Long id;
    private String username;
    private String password;
    private String email;
    private Date createdAt;
    // getters and setters
}

@GetMapping("/users/{id}")
public User getUser(@PathVariable Long id) {
    return userRepository.findById(id).orElse(null);
}

Sending the entire entity including sensitive and unnecessary fields increases payload size and risks exposing sensitive data.

📉 Performance CostIncreases payload size by 30-50%, blocks rendering longer due to larger JSON parsing.

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Sending full entity as JSON	N/A	N/A	High due to large JSON parsing	[X] Bad
Sending DTO with minimal fields	N/A	N/A	Low due to smaller JSON parsing	[OK] Good

Rendering Pipeline

The DTO pattern reduces the data size sent from server to client, which decreases network transfer time and parsing time in the browser.

→Network Transfer

→Parsing

→Rendering

⚠️ BottleneckNetwork Transfer and Parsing stages are most expensive due to large payloads.

Core Web Vital Affected

LCP

This pattern affects the amount of data sent over the network and the processing time on both client and server during data transfer.

Optimization Tips

1Always send only the data needed by the client using DTOs.

2Avoid sending sensitive or unnecessary fields in API responses.

3Smaller JSON payloads improve load speed and reduce parsing time.

Performance Quiz - 3 Questions

How does using a DTO pattern improve web app performance?

A By reducing the size of data sent over the network

B By increasing the number of database queries

C By adding more fields to the JSON response

D By delaying the server response

DevTools: Network

How to check: Open DevTools, go to Network tab, reload the page, and inspect the size of the JSON response payload.

What to look for: Look for smaller payload size and faster load times indicating efficient data transfer.

Practice

1. What is the main purpose of using a DTO (Data Transfer Object) in a Spring Boot application?

easy

A. To manage application configuration settings

B. To store data permanently in the database

C. To handle user authentication and authorization

D. To safely transfer only necessary data between different parts of the application

Solution

1. Step 1: Understand the role of DTOs

   DTOs are simple objects designed to carry data between layers or parts of an application without exposing sensitive or unnecessary details.

2. Step 2: Identify the correct purpose

   Unlike entities or configuration classes, DTOs focus on safe and clean data transfer, not storage or security management.

3. Final Answer:

   To safely transfer only necessary data between different parts of the application -> Option D

4. Quick Check:

   DTO purpose = safe data transfer [OK]

Hint: DTOs move data safely without exposing all details [OK]

Common Mistakes:

• Confusing DTOs with database entities
• Thinking DTOs handle security
• Assuming DTOs store data permanently

2. Which of the following is the correct way to define a simple DTO class in Spring Boot using Java records?

easy

A. public record UserDTO(String name, String email) {}

B. public class UserDTO { private String name; private String email; }

C. public interface UserDTO { String getName(); String getEmail(); }

D. public enum UserDTO { NAME, EMAIL }

Solution

1. Step 1: Recognize Java record syntax

   Java records provide a concise way to create immutable data carriers with automatic getters and constructors.

2. Step 2: Match the correct syntax

   public record UserDTO(String name, String email) {} uses the correct record declaration with fields inside parentheses and empty body braces.

3. Final Answer:

   public record UserDTO(String name, String email) {} -> Option A

4. Quick Check:

   Java record syntax = public record UserDTO(String name, String email) {} [OK]

Hint: Java records use 'record Name(fields) {}' syntax [OK]

Common Mistakes:

• Using class without constructors/getters
• Confusing interface with DTO class
• Using enum for data transfer

3. Given this Spring Boot code snippet, what will be the output when the getUserDTO() method is called?

public record UserDTO(String name, int age) {}

public UserDTO getUserDTO() {
    UserDTO user = new UserDTO("Alice", 30);
    return new UserDTO(user.name(), user.age() + 5);
}

medium

A. UserDTO[name=Alice, age=5]

B. UserDTO[name=Alice, age=35]

C. UserDTO[name=Alice, age=30]

D. Compilation error due to missing constructor

Solution

1. Step 1: Understand record instantiation and methods

   The record UserDTO has fields name and age with automatic accessor methods name() and age().

2. Step 2: Analyze the returned object

   The method creates a UserDTO with name "Alice" and age 30, then returns a new UserDTO with the same name and age increased by 5 (30 + 5 = 35).

3. Final Answer:

   UserDTO[name=Alice, age=35] -> Option B

4. Quick Check:

   Age incremented by 5 = 35 [OK]

Hint: Records have automatic getters like name() and age() [OK]

Common Mistakes:

• Forgetting to add 5 to age
• Confusing method calls with field access
• Assuming default toString format

4. Identify the error in this DTO usage code snippet:

public record ProductDTO(String name, double price) {}

public ProductDTO createProduct() {
    ProductDTO product = new ProductDTO("Book");
    return product;
}

medium

A. Missing second argument for price in ProductDTO constructor

B. Records cannot be used as DTOs

C. Method createProduct should return void

D. ProductDTO fields must be private

Solution

1. Step 1: Check record constructor parameters

   The ProductDTO record requires two parameters: a String name and a double price.

2. Step 2: Identify constructor call mistake

   The constructor call provides only one argument "Book", missing the price argument, causing a compile-time error.

3. Final Answer:

   Missing second argument for price in ProductDTO constructor -> Option A

4. Quick Check:

   Constructor args must match record fields [OK]

Hint: Record constructors need all fields in order [OK]

Common Mistakes:

• Passing fewer arguments than fields
• Thinking records can't be DTOs
• Ignoring method return types

5. You want to create a DTO that hides the user's password when sending data to the client. Given the entity:

public class User {
    private String username;
    private String password;
    private String email;
    // getters and setters
}

Which DTO definition best achieves this goal?

hard

A. public class UserDTO { private String password; }

B. public record UserDTO(String username, String password, String email) {}

C. public record UserDTO(String username, String email) {}

D. public record UserDTO(String password) {}

Solution

1. Step 1: Understand the goal to hide password

   The DTO should exclude the password field to avoid exposing it to clients.

2. Step 2: Choose DTO fields accordingly

   public record UserDTO(String username, String email) {} includes only username and email, omitting password, which meets the requirement.

3. Final Answer:

   public record UserDTO(String username, String email) {} -> Option C

4. Quick Check:

   Exclude sensitive fields in DTO [OK]

Hint: Exclude sensitive fields from DTO to hide them [OK]

Common Mistakes:

• Including password in DTO fields
• Using DTO with only password
• Confusing entity with DTO