I was wondering how I could create “component-scoped” beans, or so-to-say, “local variables inside a composite component” that are private to the instance of the composite component, and live as long as that instance lives.
Below are more details, explained with an example:
Suppose there is a “calculator” component – something that allows users to type in a mathematical expression, and evaluates its value. Optionally, it also plots the associated function.
I can make a composite component that has:
- a text box for accepting the math expression
- two buttons called “Evaluate”, and “Plot”
- another nested component that plots the function
It is evidently a self-contained piece of function; so that somebody who wants to use it may just say <math:expressionEvaluator />
But obviously, the implementation would need a java object – something that evaluates the expression, something that computes the plot points, etc. – and I imagine it can be a bean – scoped just for this instance of this component, not a view-scoped or request-scoped bean that is shared across all instances of the component.
How do I create such a bean? Is that even possible with composite components?
There is no “per-component instance” scope. But you can still achieve your desired effect.
Use a ViewScoped bean to do the evaluating and plotting – these functions are “stateless” and so are fed by your input.
Your input would be backed by a user supplied bean – in the same way a text box or calendar widget needs an input box bound to a user supplied bean. This holds the data that your “stateless” viewscoped bean acts on.
If you really wanted to keep everything contained in the component, I guess you could back the input with a ViewScoped bean that contains a map keyed by the input id. Not sure if that would work though.