How to inject a Datasource in your Enterprise applications

To inject a Datasource in your Enterprise applications you can use the javax.annotation.Resource annotation to declare a reference to that resource.

The @Resource can decorate a class, a field, or a method. The container will inject the resource referred to by @Resource into the component either at runtime or after its initialization.

In the following example, we can see how to inject a DataSource object into a Class field:

@WebServlet("/demo")
public class DemoServlet extends HttpServlet {

   @Resource(lookup="java:/PostGreDS")
   private DataSource ds;


    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html");
        PrintWriter out = resp.getWriter();
        out.write("<h1>Datasource example</h1>");

        try (Connection con = ds.getConnection();
             PreparedStatement ps = createPreparedStatement(con);
             ResultSet rs = ps.executeQuery()) {

            while(rs.next()) {
                out.write("Time from Database: " +rs.getString(1));
            }

        } catch (SQLException e) {
            e.printStackTrace();
        }


    }
    private PreparedStatement createPreparedStatement(Connection con) throws SQLException {
        String sql = "SELECT NOW();";
        PreparedStatement ps = con.prepareStatement(sql);
        return ps;
    }
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

By deploying the above Servlet, you will be able to check the current time on a PostgreSQL Datasource which needs to be available on the application server:

To learn how to configure PostgreSQL Database on WildFly we recommend checking this tutorial: Configuring a datasource with PostgreSQL and JBoss/WildFly