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.
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:
An advantage of this scheme is that I can request a refresh of the list by simply setting "this.menuList" to null.
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Joined: Oct 20, 2009
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:
the corresponding managed bean for the above page:
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.
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:
Back this view component with the following Model logic in myBean:
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.
Joined: Oct 20, 2009
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.