What is a DTO in spring Boot?

DTO, which stands for Data Transfer Object, is a design pattern conceived to reduce the number of calls when working with remote interfaces.the main reason for using a Data Transfer Object is to batch up what would be multiple remote calls into a single one. For example, lets say that we were communicating with a RESTful API that exposes our banking account data. In this situation, instead of issuing multiple requests to check the current status and latest transactions of our account, the bank could expose an endpoint that returned a DTO summarizing everything. As one of the most expensive operations in remote applications is the round-trip time between the client and the server, this coarse-grained interface can help improving performance by a great deal. ModelMapper Introduction To avoid having to write cumbersome/boilerplate code to map DTOs into entities and vice-versa, we are going to use a library called ModelMapper. The goal of ModelMapper is to make object mapping easy by automatically determining how one object model maps to another. This library is quite powerful and accepts a whole bunch of configurations to streamline the mapping process, but it also favors convention over configuration by providing a default behavior that fits most cases. The user manual of this library is well written and can be a valuable resource if time comes where we need to tweak the mapping process. To give a little taste of what this library can do, let's say that we had a User like that:

// assume getters and setters

class User {

long id;

String firstName;

String lastName;

String email;

String password;

String securitySocialNumber;

boolean isAdmin;

}

And wanted to expose just the id, firstName, and email. By using ModelMapper we would have to create a DTO like this:

// assume getters and setters

class UserDTO {

long id;

String firstName;

String email;

}

And then call ModelMapper as follows:

ModelMapper modelMapper = new ModelMapper();

// user here is a prepopulated User instance

UserDTO userDTO = modelMapper.map(user, UserDTO.class);

That is, only by defining the structure that we want to expose and by calling modelMapper.map, we achieve our goal and hide what is not meant to be exposed. One might argue that libraries like Jackson provide annotations to ignore some properties when serializing objects, but this solution restrict developers to a single way to express their entities. By using DTOs and ModelMapper, we can provide as many different versions (with different structures) of our entities as we want. A data transfer object (DTO) is an object that is used to encapsulate data, and send it from one subsystem of an application to another. DTOs are commonly used in n-tiered web applications to transfer data between model and view. A DTO differs to the model and DAOs (which persist and retrieve data from the database) in that a DTO does not have contain any business logic except for storage and retrieval of its own data. A DTO’s data can be aggregated from several database tables or other data sources. The main benefit of using DTOs is that they can reduce the amount of data that needs to be sent across the wire in web applications. The following text describes a simple example of a DTO in a Java-based library-like web application. The model of the application consists of two simple classes, Person and Book. The main class is Person which has the following attributes: private int personId; private String name; private String address; private String telephone; private String email; private ArrayList books The Book class includes a bookId, title, author and a personId which serves as a foreign key between the tables of the database which form a typical 1:M relationship. In this application, a servlet named AdminMemberships calls page adminMembership.jsp to allow library members and their books to be displayed and deleted by librarians. AdminMembershipDTO (illustrated below) is a simple Java class with instance variables for a Person and a boolean attribute hasBooks which tests if that Person has any Books on loan.