Spring Boot general concepts

Inversion of control

Spring-boot particularly is focused on using a pattern design called inversion of control, in which the programming is less imperative and explicit, and becomes declarative and aspect-oriented.

Basically one of the most used features is the automatic dependency injection. When annotating a class with @Component we are telling Spring-Boot that a class can be auto-injected in places where the @Autowired annotation is present.

This is useful because we do not need to initialize or instantiate the classes of our program.

Annotations

@Converter

A converter is a class that defines two methods to interchange the format between two classes A and B. It is particularly used transparently when in need to convert a memory object to a serializable type when introducing it into the DB and vice-versa.

The @Converter annotation can receive a parameter autoApply = bool so it performs automatic translation between types implicitly, there is no need to call directly the methods. Spring will call it for you when needed.

In the following example the converter is used to convert Paths to String (Serializable) and vice-versa:

@Converter(autoApply = true)  
public class PathConverter implements AttributeConverter<Path, String>, Serializable {

    @Override
    public String convertToDatabaseColumn(Path path) {
        return path == null ? null : path.toString();
    }

    @Override
    public Path convertToEntityAttribute(String s) {
        return s == null ? null : Paths.get(s);
    }
} 

@Component and its specialized @Service, @Controller, @RestController, @Repository

All classes marked with these annotations are converted automatically into components that Spring Boot is able to inject in runtime. The specializations provide some useful effects if we are actually using a specialized component annotation:

• @Repository: Marks all method as transactional and handles the session automatically inside them. Repository is used in classes that are responsible for communicating with a DB.
• @Service: The class provides a service inside the application.
• @Controller: Handles the serialization and deserialization of data coming in and out of the methods of the class. Controller provides endpoints that our clients are connected to, and as such they are the first and last piece of code executed when handling a request.
• @RestController: The same as a controller, but provides support for the typical CRUD operations.

@Autowired

This annotation is used to annotate a property of a class, setter of a property or constructor. This tells Spring Boot that a field needs to be automatically injected. Then, we do not need to initialize or call the constructor of that class.

Access Control List permissions

We use the default permission evaluator of Spring Security, which does not do bitwise operations to check the permissions against something. So the default with this code is the following:

• 1 means “READ”
• 2 means “Write”
• 4 means “Create”
• 8 means “Delete”
• 16 means “Administer”