Nested DTOs in Spring Boot - Performance & Optimization

Performance: Nested DTOs

MEDIUM IMPACT

Nested DTOs affect the data serialization and deserialization time during API calls, impacting response time and client rendering speed.

Sending complex data structures in API responses

Spring Boot

public class OrderDTO {
  private String customerName;
  private String customerCity;
  private List<String> productNames;
  // getters and setters
}

Flattening DTOs reduces nesting, lowers payload size, and simplifies serialization.

📈 Performance GainSingle serialization pass, reduces payload size by 30-50%, improves LCP and client render speed.

Sending complex data structures in API responses

Spring Boot

public class OrderDTO {
  private CustomerDTO customer;
  private List<ProductDTO> products;
  // getters and setters
}

public class CustomerDTO {
  private AddressDTO address;
  // getters and setters
}

public class AddressDTO {
  private String street;
  private String city;
  private CountryDTO country;
  // getters and setters
}

public class CountryDTO {
  private String name;
  private String code;
  // getters and setters
}

Deep nesting causes large JSON payloads and complex serialization, increasing response time and client parsing cost.

📉 Performance CostTriggers multiple serialization passes and increases payload size by 30-50%, blocking rendering longer.

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Deeply Nested DTOs	High due to complex data binding	Multiple reflows possible if UI updates per nested data	High paint cost from large DOM updates	[X] Bad
Flattened DTOs	Lower DOM operations	Single reflow after data binding	Lower paint cost with simpler DOM	[OK] Good

Rendering Pipeline

Nested DTOs increase JSON size and complexity, causing longer parsing and rendering time on the client side.

→Network Transfer

→JSON Parsing

→DOM Update

⚠️ BottleneckJSON Parsing and DOM Update due to large payload and complex data structure

Core Web Vital Affected

LCP

Nested DTOs affect the data serialization and deserialization time during API calls, impacting response time and client rendering speed.

Optimization Tips

1Avoid deep nesting in DTOs to reduce JSON payload size.

2Flatten DTOs to simplify serialization and speed up client parsing.

3Monitor API payload size and parsing time to optimize LCP.

Performance Quiz - 3 Questions

How do deeply nested DTOs affect API response performance?

A Increase payload size and serialization time

B Reduce payload size and speed up serialization

C Have no impact on performance

D Only affect server CPU usage, not client

DevTools: Network

How to check: Open DevTools, go to Network tab, inspect API response payload size and timing for JSON data.

What to look for: Look for large JSON payload size and long transfer or parsing times indicating nested DTO overhead.