Standard flow control

Question

JSTL support for standard flow control.
what that means ?
I am aware of that JSTL can help in SQL processing , XML processing through Tag libraries.
But however, how the JSTL supports standard flow control ? is it the JSTL iterator we are talking about ?

Answer 1

Although you can apparently access a database on the JSP page using JSTL tags, it doesn't mean its a good idea. I suggest you use the MVC design. You separate the layers and not put database functionality in the presentation layer (JSP).
Hers is one MVC approach in which a single servlet acts as the control. There are other ways of doing it via Spring, Structs, etc. However, I suggest you master this approach before moving onto those.
presentation layer:
JSP, CSS, Javascript, and JSTL.
The JSP page and its supporting languages is responsible for displaying data and submitting user input back the controller. The Javascript is typically responsible for basic client side validation of user input. JSP gets its data that it is to display from request scope (and perhaps some from session scope). JSTL assists JSP in displaying data by doing such tasks as looping though a Java collection from the request scope and displaying it. The JSP page should not contain any logic from the other layers (below). The page will get complicated enough over time just displaying data without making it even more difficult to read by inserting business logic into it.
control layer:
A single servlet. This servlet takes in all url request and page submits coming from JSP pages. Avoid JSP to JSP page naviigation (there are exceptions to this rule). Go through the control layer. This servlet calls business logic to get data that the page requests. It puts it in request and/or session scope, and dispatches to the appropriate JSP page. Because all url request go through this servlet, the servlet can do centralized authentication (log in) and authorization (user assigned to a role). Dont generate presentation data (html) from this layer.
business layer:
Java classes that carry out requests from the control layer. It calls the database layer for raw data from the database and performs business logic on the data (if any) before sending it to the control layer.
database layer:
Takes in requests from the business layer. Queries the database via SQL. Is the only layer that has sql in it. Reads the resultSet from the database and puts the data in some kind of Java collection before returning it to the business layer. Never return the resultSet (a database concept) to the business layer.