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Enterprise intermediate

EJB versus CDI

Replace heavyweight EJBs with lightweight CDI beans for dependency injection and transactions.

Code Comparison
✕ Java EE 
@Stateless
public class OrderEJB {
    @EJB
    private InventoryEJB inventory;

    public void placeOrder(Order order) {
        // container-managed transaction
        inventory.reserve(order.getItem());
    }
}
✓ Jakarta EE 8+ 
@ApplicationScoped
public class OrderService {
    @Inject
    private InventoryService inventory;

    @Transactional
    public void placeOrder(Order order) {
        inventory.reserve(order.getItem());
    }
}
Why the modern way wins
🪶

Lightweight

CDI beans are plain Java classes with no EJB-specific interfaces or descriptors.

💉

Unified injection

@Inject works for every managed bean, JAX-RS resources, and Jakarta EE components alike.

🧪

Easy unit testing

Plain classes without EJB proxy overhead are straightforward to instantiate and mock.

Old Approach
EJB
Modern Approach
CDI Bean
Since JDK
11
Difficulty
intermediate
JDK Support
EJB versus CDI
Available

Widely available since Jakarta EE 8 / Java 11

How it works

CDI (Contexts and Dependency Injection) provides the same dependency injection and transaction management as EJBs, but as plain Java classes with no container-specific interfaces or superclasses. Scopes like @ApplicationScoped and @RequestScoped control lifecycle, and @Transactional replaces mandatory EJB transaction semantics.

Related Documentation
Jakarta CDI Specification ↗ Jakarta Transactions — @Transactional ↗
Related patterns
Enterprise intermediate

Servlet versus JAX-RS

Java EE
@WebServlet("/users")
public class UserServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req,
                         HttpServletResponse res)
            throws ServletException, IOException {
        String id = req.getParameter("id");
        res.setContentType("application/json");
        res.getWriter().write("{\"id\":\"" + id + "\"}");
    }
}
Jakarta EE 8+
@Path("/users")
public class UserResource {
    @GET
    @Produces(MediaType.APPLICATION_JSON)
    public Response getUser(
            @QueryParam("id") String id) {
        return Response.ok(new User(id)).build();
    }
}
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JDK 11+ →
Enterprise intermediate

JDBC versus JPA

Java EE
String sql = "SELECT * FROM users WHERE id = ?";
try (Connection con = dataSource.getConnection();
     PreparedStatement ps =
             con.prepareStatement(sql)) {
    ps.setLong(1, id);
    ResultSet rs = ps.executeQuery();
    if (rs.next()) {
        User u = new User();
        u.setId(rs.getLong("id"));
        u.setName(rs.getString("name"));
    }
}
Jakarta EE 8+
@PersistenceContext
EntityManager em;

public User findUser(Long id) {
    return em.find(User.class, id);
}

public List<User> findByName(String name) {
    return em.createQuery(
        "SELECT u FROM User u WHERE u.name = :name",
        User.class)
        .setParameter("name", name)
        .getResultList();
}
Hover to see modern ➜
JDK 11+ →
Language beginner

Records for data classes

Java 8
public class Point {
    private final int x, y;
    public Point(int x, int y) { ... }
    public int getX() { return x; }
    public int getY() { return y; }
    // equals, hashCode, toString
}
Java 16+
public record Point(int x, int y) {}
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JDK 16+ →
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