Jakarta EE

• Jakarta Servlet: defines how to manage HTTP requests, in a synchronous or asynchronous way. It is low level and other Jakarta EE specifications rely on it;
• Jakarta WebSocket: API specification that defines a set of APIs to service WebSocket connections;
• Jakarta Server Faces: a technology for constructing user interfaces out of components;
• Jakarta Expression Language (EL) is a simple language originally designed to satisfy the specific needs of web application developers. It is used specifically in Jakarta Server Faces to bind components to (backing) beans and in Contexts and Dependency Injection to name beans, but can be used throughout the entire platform.

• Jakarta RESTful Web Services provides support in creating web services according to the Representational State Transfer (REST) architectural pattern;
• Jakarta JSON Processing is a set of specifications to manage information encoded in JSON format;
• Jakarta JSON Binding provides specifications to convert JSON information into or from Java classes;
• Jakarta XML Binding allows mapping XML into Java objects;
• Jakarta XML Web Services can be used to create SOAP web services.

• Jakarta Contexts and Dependency Injection (CDI) is a specification to provide a dependency injection container;
• Jakarta Enterprise Beans (EJB) specification defines a set of lightweight APIs that an object container (the EJB container) will support in order to provide transactions (using JTA), remote procedure calls (using RMI or RMI-IIOP), concurrency control, dependency injection and access control for business objects. This package contains the Jakarta Enterprise Beans classes and interfaces that define the contracts between the enterprise bean and its clients and between the enterprise bean and the ejb container.
• Jakarta Persistence (JPA) are specifications about object-relational mapping between relation database tables and Java classes.
• Jakarta Transactions (JTA) contains the interfaces and annotations to interact with the transaction support offered by Jakarta EE. Even though this API abstracts from the really low-level details, the interfaces are also considered somewhat low-level and the average application developer in Jakarta EE is either assumed to be relying on transparent handling of transactions by the higher level EJB abstractions, or using the annotations provided by this API in combination with CDI managed beans.
• Jakarta Messaging (JMS) provides a common way for Java programs to create, send, receive and read an enterprise messaging system's messages.

• Validation: This package contains the annotations and interfaces for the declarative validation support offered by the Bean Validation API. Bean Validation provides a unified way to provide constraints on beans (e.g. JPA model classes) that can be enforced cross-layer. In Jakarta EE, JPA honors bean validation constraints in the persistence layer, while JSF does so in the view layer.
• Jakarta Batch provides the means for batch processing in applications to run long running background tasks that possibly involve a large volume of data and which may need to be periodically executed.
• Jakarta Connectors is a Java-based tool for connecting application servers and enterprise information systems (EIS) as part of enterprise application integration (EAI). This is a low-level API aimed at vendors that the average application developer typically does not come in contact with.

To assist the view, Jakarta EE uses a concept called a "Backing Bean". The example below uses Contexts and Dependency Injection (CDI) and Jakarta Enterprise Beans (EJB).

@Named
@ViewScoped
public class UserEdit {

    private User user;

    @Inject
    private UserDAO userDAO;

    public String saveUser() {
        userDAO.save(this.user);
        addFlashMessage("User " + this.user.getId() + " saved");

        return "users.xhtml?faces-redirect=true";
    }

    public void setUser(User user) {
        this.user = user;
    }

    public User getUser() {
        return user;
    }
}

To implement business logic, Jakarta Enterprise Beans (EJB) is the dedicated technology in Jakarta EE. For the actual persistence, JDBC or Jakarta Persistence (JPA) can be used. The example below uses EJB and JPA. Not explicitly shown is that JTA is used under the covers by EJB to control transactional behavior.

@Stateless
public class UserDAO {

    @PersistenceContext
    private EntityManager entityManager;

    public void save(User user) {
        entityManager.persist(user);
    }

    public void update(User user) {
        entityManager.merge(user);
    }

    public List<User> getAll() {
        return entityManager.createNamedQuery("User.getAll", User.class)
                            .getResultList();
    }

}

For defining entity/model classes Jakarta EE provides the Jakarta Persistence (JPA), and for expressing constraints on those entities it provides the Bean Validation API. The example below uses both these technologies.

@Entity
public class User {

    @Id
    @GeneratedValue(strategy = IDENTITY)
    private Integer id;

    @Size(min = 2, message="First name too short")
    private String firstName;

    @Size(min = 2, message="Last name too short")
    private String lastName;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

}