Data Transfer Objects

Data Transfer Objects

• DTOs - Data Transfer Objects
• DTOs are simple Java POJOs
• DTOs are data structures, generally should NOT have behavior
• DTOs are objects used to transfer data between producers and consumers
• Controller models are typically DTOs

Why Not Entities?

• Database Entities are also POJOs, why can’t we use those?
• For simple applications you can
• Spring Data REST exposes database entities directly
• Database entities can “leak” data to client tier
• As applications become more complex, having the separation becomes more  important
• The needs of the consumers are different than the needs of persistence
• DTOs can be optimized for JSON serialization and deserialization

Type Conversions

• Type Conversions are often done within methods
• Best practice is to use dedicated converters
• Single Responsibility Principle
• Spring Framework provides an Interface called “Converter” with generics
• Can be used with conjunction with Conversion service
• MapStruct is a code generator which automates generation of type converters

MapStruct

• MapStruct is a code generator
• You provide the interface, MapStruct generates the implementation
• Works like Lombok via annotation processing during code compile
• Has good Spring integration - can generate Spring Converters or Spring Components
• You can use Mapstruct Components for injection into services