Default JNDI Name for Resource or EJB Injection

When a resource or EJB reference is injected to a component class, not only can you directly use this variable, you can also lookup with JNDI. For example,

package demo;
public class FooServlet extends HttpServlet {
@Resource(name="jdbc/mysql-ds")
private DataSource dataSource;

protected void doGet(
  HttpServletRequest request,
  HttpServletResponse response)
  throws ServletException, IOException {
  Connection con = null;
  Connection conn = null;
  try {
    InitialContext ic = new InitialContext();
    DataSource ds =
      (DataSource) ic.lookup("java:comp/env/jdbc/mysql-ds");
  
    //the following 2 statements work the same:
    conn = dataSource.getConnection();    
    con  = ds.getConnection();
  } catch (NamingException ex) {
    throw new ServletException(ex);
  } catch (SQLException ex) {
    throw new ServletException(ex);
  } finally {
  //close con conn here
  }
}
}

If the name() field is not specified for @EJB or @Resource, the default jndi name is not the variable name; instead, it's in the form of fully-qualified-classname/variable-name. Therefore, using default jndi name, the above example needs to be rewrite as follows:

package demo;
public class FooServlet extends HttpServlet {
@Resource
private DataSource dataSource;

protected void doGet(
  HttpServletRequest request,
  HttpServletResponse response)
  throws ServletException, IOException {
  Connection con = null;
  Connection conn = null;
  try {
    InitialContext ic = new InitialContext();
    DataSource ds = (DataSource) ic.lookup(
      "java:comp/env/demo.FooServlet/dataSource");
  
    //the following 2 statements work the same:
    conn = dataSource.getConnection();  
    con  = ds.getConnection();
  } catch (NamingException ex) {
    throw new ServletException(ex);
  } catch (SQLException ex) {
    throw new ServletException(ex);
  } finally {
  //close con conn here
  }
}
}

Tags: javaee, resource injection, j2ee, jndi