Ok I know scope questions come up all the time but I'm interested in a slightly different approach to the solution. The #ViewScope is a fantastic bridge between the #RequestScope and the #SessionScope.
However there is still a common use case (at least for me) where I really don't want to use #SessionScope but I need the data over a couple of views. A really simple case is when I have multiple datatables chained together each one depending on previous selections.
It's perfectly possible to use <f:paramView> and pass a single or even a couple of pieces of data as params in the address and then retrieve everything from the database again. I am more interested in finding a way of creating a 'snapshot' of the beans state / variables, creating the new #ViewScope and then 'restoring' the 'snapshot state' to the new bean.
Does such a thing exist? Ideas? Opinions?
I don't know if this is the 'accepted solution' but I've implemented an idea that works for me. (Feedback appreciated!)
So I have created a #SessionScoped class with a couple of static maps:
private static Map<String, Object> objectVariableMap;
// Getters, setters and methods etc. are omitted for simplicity
The idea being that I have specified a map that accepts a String as the key and an Object as the value. I've specifically not set the type of object to allow me to store any type of object in there. The caveat is that you need to be sure of the type of object when retrieving it so you can cast it back into its original type.
Now comes the time to set the data from the first #ViewScoped. I generate a random UUID (or what ever you want) as the Map key and then set the value to the object I'm working with (ie. this, or indeed any other objects you might want to pass to the next view). Save the key, value into the map and set the URL param to the key.
I'm never keen on passing data like user id's etc. in URL params (even when its encrypted). This idea has the added benefit of offering disposable URL values that have a specifiable life span.
On the receiving end (ie. The new #ViewScoped bean, or any other scope for that matter) you read in the URL param (the map key) using <f:paramView> and then use a preRenderView event to retrieve and set the Object where working with.
At this point you can choose to remove the key pair from the Map and invalidate the ability to retrieve that object or you can keep keep the key pair for a longer duration by simply updating the object if there are any changes.
UPDATE: Conceptually this has been really successful (for me at least). I've created a handfull of useful methods and classes surrounding the concept to make it more universal. If anybody wants more specific instructions or I might even create a small library if anybody wants.
You can use the CDI "Conversation Scope" for this. This is narrower than the session scope but wider than the view scope.
If the pages between which you pass parameters are a unit, you can also make them a flow in JSF 2.2 and use the flow scope.
Projects like CODI offer various other scopes that can be used between pages.
Related
I have a general JSF problem, I found no nice solution for yet. See the picture for a general idea. I have a workaround solution (sorry for the typo in the image) in place that solves the problem by a listbox. However the desired solution is to display all existing versions next to each other (probably always around 1-3).
I have a view with a tree and picklist. There is a complex flow regarding the interaction between list and tree, e.g. you can only move models to subgroups, not top-level-groups and much more. I created a handler class that manages this behavior and translates it to service calls.
Now, a new requirement came up. There are several versions of this tree that should be displayed all together on one page. My gut feeling is that managing n versions in one handler is a big mess as I need to store several things in the handler already for one version.
In React, I would create a component that wraps the tree and all of the interaction. However, in JSF I'm not so sure what is the best practice here?
I would be happy about suggestions and ideas, I'm not expecting Code :)
I found a solution that fits my needs and I post it here hoping that it might help other people as well :)
So on my view I have several tree views with complex interactions. For example, if an item within the tree is moved, the operation is immediately reflected in the database. As I use JPA, I need to translate this to an entitymanager call.
The views are either displayed in a list or just one-at-a-time via a dropdown select.
Anyway, the idea is that every complex view component has its own controller with a reference to an entitymanager and a transaction, while having just one JSF handler class. If JSF would allow to create multiple handlers (like #{handler_1}, {handler_2}), the problem could be solved in a different way. But as JSF works name based and the name {#handler} always refers to the same container managed thing, this is no option.
The handler class is ViewScoped (or SessionScoped, if you prefer). For each tree component it has a ComponentController class that receives the EntityManager and the UserTransaction as well as the related data form the handler via constructor injection. This way, the handler can delegate all commands to the Controller while being DRY.
With this solution, the controller logic can be re-used regardless how many tree components exist. Each view elements binds a specific controller via handler.controllers.get(id).
All other solutions did not work for me as they are not able to perform database operations on view interactions.
Good day
This question is more of a meta question than a specific problem based question.
It is always a good idea to separate any and all DB code from view related code and view files, correct?
Thus is my assumption when using JSF correct in that:
The xhtml file forms part of the view in the MVC.
The #Named backing beans also forms part of the view.
To ensure that one can relatively painlessly migrate away from JSF to another type of tech, one would ensure to not have ANY DB code inside the #Named backing beans.
All DB code should reside in a controller / service class.
The controller / service class will contain all the DB access code and business logic. This thus forms the controller of the MVC.
The #Entity classes are used to map the DB to JPA and this thus forms the model of the MVC.
Now, if my understanding of the above is correct, what would best methods and methodologies be when handling the following scenario:
I have an XHTML file displaying JSF components (Primefaces). The lists and component linked members that link the JSF components to the Java code all resides in the #Named backing bean.
Now for argument sake, let's say that the specific form is used to CRUD a supplier's information, which of the following methods is recommended as best practices (while attemping to maintain as much seperation of concern between the View and the Controller Java code) when for instance edits were made on the XHTML form:
Enforce ZERO DB code (thus never defining or using the Entity Manager) in the #Named backing bean file). The code to persist the changes after all input validation was successfully done, will reside in the Controller. To get these values to the Controller, we will have a function looking perhaps like this (basically send all the components on the xhtml form as parameters to a function in the Controller):public void supplierService (String supName, String SupAddress, String supTel....) The problem with this of course is that one may end up running into methods that takes tens of parameters. Very ugly and difficult to maintain.
Accept that separating some DB code is not possible and every #Named file must have the required JPA DB code to persist and or merge changes to the models (however if this is considered best practice, what is the use of having Controller classes?).
Create a temporary object of the same type as the model and set the attributes of this temporary object to the values obtained from the XHTML mapped components. Then only pass this temporary object to a method in the Controller. This method in the Controller will then persist and or merge the passed object's info. However I feel this may introduce unnecessary object instantiation overhead. Also I am not 100% sure what exactly happens 'behind the scenes' when I have a model named SupplierEntity.java that is mapped via JPA to a PostgreSQL DB and I call this code: SupplierEntity tempSup = new SupplierEntity(); Will JPA via Hibernate on Wildfly actually at this point create a new entity (record in the DB), and as such I cannot use this to create a temporary object to hold the values I am passing to the Controller as a temp instance of the underlying JPA entity, or will Hibernate (using JPA 2.1) ONLY create a new record when I do em.persist(mySupplier); and thus it is safe to use this method to pass objects to the controller's persisting method, instead of passing tens of parameters to the persisting method.
Something completely different than what I mentioned above is considered to be the best practice for separating the MVC components in JSF as much as possible, while still preventing having to pass 50 parameters to the Controller.
Please as said right in the start, this is a meta question regarding best practices. If Stackoverflow is not the right forum for these questions, instead of down voting this into oblivion, please let me know where I should ask instead and I will gladly delete the question from here and create it on the right forum.
To not have to keep repeating some validations, for example, who can see a button in a certain status of a document in the worlflow, I'm using session, scope, and session variables to store the user roles and application variable to store the Status related to each area.
I was evaluating whether it would be better from a performance and build point of view to implement a managed bean, to return the user roles and the possible statuses of each participating workflow area. Would it be the best structure in fact? What do you think? I do not have much experience in java. How could I construct the structure in java, several methods, one for roles and the other for set of status associated with the area that would name the related method? You could return the results of this method in arrays, or there is a better return structure.
Thanks a lot!
My best suggestion is to adopt the pageController Methodology. Then it's more like true MVC. This has been talked about on NotesIn9 screencast many times but basically you have a java object that's bound to your XPage. In effect it's a viewScoped bean that holds all your page logic. Then you can have methods like isGroupMember(), hasRole() etc and calculate that on the pageInit. There's little need to hold onto that in sessionScope in my opinion. So for example I have this in my pageController :
public boolean isGroupMember(String groupName) {
return JSFUtil.getXSPContext().getUser().getGroups().contains(groupName);
}
So that's available to each page. BUT I don't need to copy that snippet onto every page controller. In Java you can have your page controllers extend a more generic class. so I have a "base.pageController" class. All the specific page controllers extend that. So this isGroupMember() code goes into the base and then it's available to be used on every XPage. Doing it this way gives you the ability to have generic functions like this and then hold more specific function that are only for the individual page.
You can also have a hasRole() function etc...
Recommend you check out this video : http://www.notesin9.com/2016/08/25/notesin9-196-no-dependency-page-controllers/
Also for a question like this, I recommend you just use the xpages tag. Adding others like javabeans can bring people in who know nothing about XPages and XPages is unique enough of a beast that outsiders can cause some confusion on occasion.
What's the difference? When should I prefer one over another?
And some minor questions related to this:
if I have object data, when is saveObject called?
it looks like garbage collector recycles all my domino handles. I tried to downcast then clone it, but it didn't help (how does it know its still a domino object?). Is there a workaround?
if I create "var tmpVar = new package.TestClass()" from xPages, it gets recycled on update. But if I create java object from bean it stays there. Correct?
Managed beans are exactly that, managed by the XPages runtime. They are created as and when there is a first call to them. Although they have an empty constructor, managed-properties elements in the faces-config allow you to define values (and I believe you can add SSJS code to the faces-config to compute the values).
Object data sources allow you to handle what's created when, and it means they can be scoped to a smaller level than viewScope - to a Panel or Custom Control. The saveObject method is called by a Save All Datasources event. In reality, if you're coding object data sources, you'll code a button and call the relevant method rather than use a simple action.
Java variables can get recycled, but Domino objects are only recycled via two methods. The first is calling recycle() methods, the second is at the end of each request, when the session gets recycled. Because recycle() calls recycle all child elements, everything gets recycled at the end of a request. Which is why you can't store Domino objects in scoped variable or any other persisted object (i.e. a bean). Note that objects like DateTimes, RichTextStyles etc are children of the session, not of any more granular Domino object like a NotesItem or NotesRichTextItem.
var tmpVar = new package.TestClass() will only get persisted beyond the current request if you store tmpVar somewhere. If you're using that code in a crerateObject method, return tmpVar will pass that instance of TestClass into the Data Object.
I go back and forth on pure Managed Beans vs. Data Object. I was using a lot of Data Objects for a while but then ran into some issue with the JSF lifecycle I think that I just couldn't make work. Not sure if a repeat or custom control was involved. So I pretty much have gone back and given up on them for now.
Other then that problem I had I'm not sure there's a ton of difference. I think dataObject can tend to be a little more confusion. Since you can set it on an XPage - but you can change the scope of it to session or application I believe. But if you do then that seems messier and hard to find then making the bean in the faces-config.
I'm not sure about the saveObject part of your question.
You never want to put a pure domino object inside a bean, or scoped variable because they are not serializable and will be tossed by the garbage collector at some point that will likely be most inconvenient to you.
if you just do "var tmpVar = new package.TestClass()" then yeah that will get killed pretty quick because of limited life of that variable. if you want to create an object that way and keep it around longer put it in a true scope: viewScope.put("myObject", tmpVar);
I have a video where I tried to give examples of I think 4 ways to use java Objects. In the blog posting are some really good comments by Tim Tripcony which might give you further information.
http://www.notesin9.com/2013/08/01/notesin9-122-working-with-java-objects-in-xpages/
I've written a new back-end Java component (extending UIComponentBase) as an alternative for the ExtLib Application Layout control. The control needs to show a collection of data that is looked up from another Notes application. The data is user dependant and doesn't change from page to page so, to avoid repeatedly doing a lookup to the other application, I want to store it in the session scope. (Note that because this is a layout control, there will only ever be one per page.)
I know I could use a session-scoped maanged bean (and have done in previous iterations) but the data only needs to be used in this control and shouldn't be used elsewhere on the page which it could be with a bean. So my question is, what's the best practice approach I should take here? Should I just directly store the data in the sessionMap or am I missing a trick with the component stateHolder? Or am I stuck with using a bean?
Thanks
(Edited for clarification)
It looks like you're talking about your own back-end Java components rather than Custom Controls within a single NSF.
I'm not sure at what level, when you write your own native XPages components, the properties are cached by the stateHolder when calling saveState(). I would presume no higher than View, for the reasons Frantisek says, that otherwise it would be unclear which instance to update if you had multiple on one XPage but one on another. It couldn't update both at the same time on the same page, so I would guess that each is a separate instance. As a result, the same component on multiple pages would be a separate discreet instance.
But there's nothing stopping you, in specific setters of the component, writing to sessionScope as well as the private property, and then doing the reverse on the getter. I'm not sure if you'd want to try the internal property before trying sessionScope or vice versa. It would depend how you wanted to handle the situation of the same sessionScope being updated from multiple pages (if the collection could change).