如何在Play中实施流量控制？

Question

We are trying to implement some flow control in Play, kind of a wizard with several steps. What is the best practice to do it in Play?

Requirements we have:

1. Should allow multi-step flows, like step1 -> step2 -> step3 -> step4 -> finish
2. Should be able to change order or steps depending on context, so if user selects a checkbox on step2, flow should be step1 -> step2 -> warningStep -> step5 -> finish
3. Ideally needs support for "Back" button to return between steps

The problem we have is that any single step in flow doesn't know where it should redirect next and since Play session is very simple, it won't help here much.

Here is the solution we currently have:

1. Store Flow steps in database in user object with @OneToMany public List<FlowStep> flowSteps
2. Provide methods in user model to add/remove/skip and change order of flow steps stored for this user
3. Implement steps normally, with form action leading to "doStep3" controller etc
4. Implement "Flows" controller that uses @Before and @After interceptors to correctly redirect to next step after current step is processed and no validation errors found
5. Added Flows.next() controller that redirects to next step (used for "Skip" button href)

What are the disadvantages of this solution? Is there any better way (maybe some Play built-in methods) to improve it?

Answer 1

What you want is a finite state machine . To implement it, you'll need a class that knows all the possible transitions between steps. Then you can provide to it the current step and any relevant input, and it will return the output (where the output is the view to render next).

Then you use render to redirect the user, as in:

render("my/view/path.html", myparams);

This is not the only option, and storage of the transitions will depend on how complex you need them (can be hardcoded for simple scenarios, maybe stored in database for more complex ones), but it should work.

As Play is stateless you'll need to keep the information in the database (for complex scenarios where you need to take in account information for several steps) or, if the relevant togles are just a few, store them in the cookie itself.

I would avoid using @Before/@After as you are coupling the state machine to the controller. Ideally you want them to be idnependent, with the state machine returning only transitions that you can translate later into view paths. That will simplify changing transitions.

If the scenario is not extremely complex, I would not even bother to store them in the database. If you want it reusable and extremely flexible, then do it, otherwise it may be simpler to just "hardcode it".

Answer 2

Did you check this section in the Play documentation (a very quick read):
http://www.playframework.org/documentation/1.2.4/model#stateless

It lists the options you have for exactly what you are asking.

Answer 3

You can try to use Play Cache mechanism as pseudo session to store the validated steps instead of handling in the database. Using Play Cache would be a simpler solution