Similarly, when returning all the authors in the database you might not be interested in providing all the data on the books they wrote. If you are a Gradle >= 4.6 user, add these dependencies to your build. The latter will be used by MapStruct to generate the mapper implementations during build-time. This is the list of all the prerequisites for the demo application you are going to build:įirst, you need to add mapstruct and mapstruct -processor to your project’s dependencies. Let’s see how to integrate MapStruct into a Spring Boot and Java project to map JPA entities into DTOs with no extra effort. In other words, MapStruct is plugged into the Java compiler and can automatically generate mappers at build-time. The generated mapping code uses plain method invocations and thus is fast, type-safe, and easy to understand. MapStruct is a code generator tool that greatly simplifies the implementation of mappings between Java bean types based on a convention over configuration approach. This involves boilerplate code and introduces overheads that might not be overlooked, especially when dealing with large data. As mentioned earlier, the DTO pattern depends on mappers aimed at converting data into DTOs and vice versa. As a consequence, you get a more concise class with a reduced number of required methods.Īll these examples share the same major drawback, which is part of the DTO pattern itself. For example, by using DTO objects you can define DAO (Data Access Object)-layer methods handling many parameters or return highly-structured data. You can also use DTOs as both input and output in method calls. Plus, the server is sending only the minimum amount of data across the wire. This way, the client application can get all the desired data in a single API call. When contacted by the client, the server application collects all the requested data, stores it in a custom-defined DTO, and sends it back. For example, in client-server applications, they are especially useful when employed to send data to a client application, such as an Angular or React Single-Page Application (SPA). The DTO pattern can be employed in many different ways, and as I have already shown, the most common approach to exploiting DTOs is to use them to transfer data between different layers of multi-layered architectures. Martin Fowler introduced the concept of a Data Transfer Object (DTO) as an object that carries data between processes in order to reduce the number of method calls. Then, you will see how to create a demo REST services application aimed at showing how to harness the DTO pattern with MapStruct in Spring Boot in Java. Thankfully, there is MapStruct, a Java library aimed at avoiding this boilerplate code by automating the mapping process as much as possible.įirstly, you will dive into the DTO pattern and MapStruct. The main issue that comes with this approach is that it requires writing a large amount of mapping code, which is an error-prone and tedious task. This can be avoided by harnessing the DTO pattern, which involves defining simple classes to transfer data between layers, thus simplifying communication. In such architectures, communicating between layers may become cumbersome. For example, this is what usually happens in client-server applications. In multi-layered architectures, data is usually represented differently at each layer.
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