How to show error messages on the form that are coming from the constructors

[Dhamayanthi Karuppanan]

I have a form which is bound to a managed bean (say:apply). In the bean constructor, Im talking to DB and getting some data to the form based on some conditions. The problem is, if i get into some error, im trying to show it in the form. I have add message to the form, in which case, the form is null. I hope ,as this is in constructor. Could any one please suggest me a way to do this. I hope i explained my problem in understandable way.

Appreciate your time and help.

[Tim Holloway]

It doesn't work very well to do database operations in a JSF backing bean constructor, I'm sorry to say. For one thing, JSF backing beans are created using a no-arguments constructor, so if you want a professional-grade data object where the database parameters and search arguments aren't hard-coded into the bean, you're out of luck, since the property injectors don't get called uniitl AFTER the constructor has finished.

One solution is to use the @PostConstruct annotation, instead, although not all JSF implementations honor that.

For things like dropdown menus, however, I just defer the database operation until the first reference of the items that require database lookup. Like so:

public List<SelectItem> getMenuList() {
  if ( this.menuList == null ) {
    this.menuList = loadMenuListSelectItems();
  }
  return this.menuList;
}

An advantage of this scheme is that I can request a refresh of the list by simply setting "this.menuList" to null.

[Dhamayanthi Karuppanan]

I understand this. but still I have some doubts: I may not designed in great way.
The scenario is like this:
I get request parameter "uid" and I pass this DB to get whether this uid is a supervisor or not. and based on the result i show one link, else i will not show it.
the jsp page is below:

		<f:view>
			<h:form id="loadEmployee" binding="#{loadEmp.form}" >
				<h:outputLink value="leaveform.faces">
					<h:outputText value="Apply Leave" />
				</h:outputLink>
				<f:verbatim>
					<BR>
				</f:verbatim>
				<h:outputLink value="viewleavebalance.faces">
					<h:outputText value="View Leave Balanace" />
				</h:outputLink>
				<f:verbatim>
					<BR>
				</f:verbatim>
				<h:outputLink value="leavelist.faces"
					rendered="#{loadEmp.empHrAssignment.showManagersView}">
					<h:outputText value="Approve / Reject Leave" />
				</h:outputLink>
				<f:verbatim>
					<BR>
					<a href="javascript:window.close();">Close Window</a>
				</f:verbatim>
			</h:form>
		</f:view>

the corresponding managed bean for the above page:

public class EmpLoggedOnFrom extends AbstractLeaveForm
{
    // Properties
    // ---------------------------------------------------------------------------------
    protected EmployeeHrAssignmentDTO empHrAssign = new EmployeeHrAssignmentDTO();

    protected final EmployeeHrAssignmentDAO empHrAssignDAO = Config.getInstance()
        .getDAOFactory().getEmployeeHrAssignmentDAO();

    static Logger logger = Logger.getLogger(EmpLoggedOnFrom.class);

    public EmpLoggedOnFrom()
    {
        emp.setEmployeeId(JsfUtility.getEmpIdFromSesion());

        logger.info("Logged in user is : " + emp.getEmployeeId());
        
        LoadEmployeePersonal();
        
        LoadEmployeeHR();

    }

    /**
     * Get Logged in Employee details
     */
    public void LoadEmployeePersonal()
    {
        try
        {
            logger.info("Calling empDAO with employee id: " + emp.getEmployeeId());
            emp = empDAO.find(emp.getEmployeeId());
            if (emp != null)
            {
                logger.info("emp id: " + emp.getEmployeeId());    
            }
            else
            {
                logger.info("emp is null");
            }
            
        }
        catch (DAOException e)
        {
            logger.debug(e);
            setErrorMessage(e);
        }
    }

    /**
     * Get Logged in Employee details
     */
    public void LoadEmployeeHR()
    {
        try
        {
            logger.info("Calling empHrAssignDAO with employee id: " + emp.getEmployeeId());
            empHrAssign = empHrAssignDAO.find(emp.getEmployeeId());
            
            logger.info("User Grade is : " + empHrAssign.getGrade());

            if (empHrAssign.getGrade() != null
                && empHrAssign.getGrade().equals("L1"))
            {
                logger.info("Set Managers View to True");
                
                empHrAssign.setShowManagersView(true);
            }
            else
            {
                logger.info("Set Managers View to False");
                
                empHrAssign.setShowManagersView(false);
            }

        }
        catch (DAOException e)
        {
            logger.debug(e);
            setErrorMessage(e);
        }
    }

    public EmployeeHrAssignmentDTO getEmpHrAssignment()
    {
        return empHrAssign;
    }

}

The problem I explained the post is this. If i get some error from DB, the setErrorMessage will try to log in the facesmessage. But everything is in constructor, the form has not been created.

I realize I have not designed it in proper way. Any help.

[Tim Holloway]

The Backing Bean (Model) is constructed by the JSF Controller as it builds the View, so yes, there is a "form" (View) being assembled. In JSF, the View controls the code, not the other way around.

However, like I said, database operations in constructors are awkward at best.

A more JSF-friendly way of doing what you want is to attach the operation to the actual item being controlled. Like so:

<h:commandLink action="#{myNean.doAdmin}" rendered="#{myBean.admin}"/>

Back this view component with the following Model logic in myBean:

public boolean isAdmin() {
   if ( ! this.securityChecked ) {
     checkSecurity();
   }
   return (userLevel == SECURITY_ADMIN);
}

private void checkSecurity() {
  // code to load from database, set userLevel
  //....
  securityChecked = true;
}

The caching of the userLevel variable (indicated by "securityChecked") is important, since getter methods are often called multiple times on a single page request, and at best, the multiple database hits would be a big (and unnecessary) slowdown.

[Dhamayanthi Karuppanan]

Thanks a lot for your kind reply.

I will do the coding in same way as you explained. Looks like long way to go for me in JSF.