Hi I have a question about best practices vs safe programming in building a JSF Web Applicaiton.
I have employee.xhtml page having backing Bean - EmployeeBean. All the variables that I declare in the backing bean are non static and have getter and setter methods. For example:
ArrayList <Employee> alEmployees = new ArrayList<Employee>();
int userId;
The constructor of the BackingBean loads the employees. I acheive this by calling a static method in delegate.
userId = //some value.
alEmployees = EmployeeDelegate.loadEmployees(userId);
The Delegate method calls a static method in DAO Class.
Will the static methods cause any data concurrency issues when n users are using the application at same time? I mean userId 56 seeing userId 75 list when both are using the application same time?
Is it really advisable to have static methods in Delegate and DAO layer?
Please let me know if I was not clear.
Thanks
If the EmployeeDelegate does not hold any class variables which is sensitive to changes caused by method calls and/or has influence on how methods behave, then it's safe to do so.
You however have another major problem with this approach. The delegate should be an interface so that you can easily substitute it with a different implementation. This approach suggests that the delegate is not an interface at all (since it can impossibly have static methods).
Related
I'm working on a JSF webapp which purpose is to wrap a command-line program.
One of its main functionality is the ability to share a session between users (eg. for courses purpose), so that when an input is sent to an instance of the application, the output sent to every subscriber for this session.
As a result of this design, the webapp is mainly composed of a view-scoped bean which will request a controller of the command-line application.
It has also been chosen to identify a session with the URL fragment (eg. mydomain/myapp/#SESSIONID), so that anyone using the URL with the same fragment will share inputs and outputs, using its own instance of the view-scoped bean but sharing the same controller
In order to push results to all subscribers, I'm using Primefaces Push. Results are primarily text that has to be appened to the webapp's terminal, but some commands lead to the programmatic creation of a JSF component.
In order to handle this, I just render these components to a string that I send to all subscribers.
Then, I realized that in order to handle ajax requests from components (and from every subscriber), the associated UIComponent needs to be added to the UIViewRoot in the context of (don't know how to express this) each view-scope bean.
As a matter of fact, I first tried to bind a "common container" (a UIForm) to a property of the view scoped bean, in which I would put the programmatically created components, but I obviously had to face the chicken/egg issue #BalusC talks about in his blog, because the component was added again on each ajax request. Setting javax.faces.PARTIAL_STATE_SAVING to false didn't help either (I'm using MyFaces 2.2.5)
So, as somewhat of a workaround, when the controller needs to create a new component, it basically adds the id of the component to the data pushed (in a HashMap converted to Json), and all subscribers will trigger (back) a remoteCommand to its own instance of the view-scoped bean, in order to update the "common container" from its own UIViewRoot.
This does work, but I don't like this way of doing it!
So:
would it be possible to handle this kind of sharing between view-scope beans (with the same name) which are stored in different HTTP sessions? I'm refering to this answer from #BalusC... maybe playing with javax.faces.ViewState - would it even be possible?
Is there a "magical" scope for my currently-view-scoped bean I could use?
Shall I rather use a completely different design?
Thanks!
If you want share data between all your application users you can use application scope.
If you still want to use view scope, you can connect your view scope with another application scope like this:
ApplicationView appView = BeanUtil.findBean("applicationView", FacesContext.getCurrentInstance());
import javax.faces.context.FacesContext;
public class BeanUtil {
#SuppressWarnings("unchecked")
public static <T> T findBean(String beanName, FacesContext context) {
return (T) context.getApplication().evaluateExpressionGet(context,
"#{" + beanName + "}", Object.class);
}
}
I am developing webapp where my MVC controller is JSF 2.1. I have several methods that are based on
FacesContext.getCurrentInstance()
I use this to
put/retrieve values from Flash scope
add messages on view
get request params map
examples:
public void addInfoMessage(String title, String description){
FacesContext.getCurrentInstance().addMessage(null, new FacesMessage(FacesMessage.SEVERITY_INFO,title, description));
}
and
public void putFlashMessage(String code, String value){
FacesContext.getCurrentInstance().getExternalContext().getFlash().put(code, value);
}
etc.
I'm just wondering where is proper place to put this methods if I use this on every single managed bean? I consider two options:
a) create class "JSFUtils", where all method are public and static
b) create super class "ManagedBean" with no declared scope and no declared #ManagedBean annotation, but with these public methods. Every managed bean should be child of these class so it will have inherited these methods.
An utility class is the recommended approach. Instead of reinventing your own, you can use an existing JSF utility library, such as OmniFaces which has Faces and Messages utility classes for the purpose.
String foo = Faces.getRequestParameter("foo");
Messages.create(summary).detail(detail).add();
Messages.addGlobalInfo(summary); // Without detail.
Faces.setFlashAttribute(key, value);
You can indeed also abstract it away as a "super bean", but this is not reusable and you would keep repeating yourself in every JSF project. Also, a class can extend from only one class. So if your bean happen to need to extend from another super class, then you're lost.
I would recommend a utility class for the purpose simply because you allow the flexibility to extend other useful classes, such as those that have some common logic that you'd like to share across other beans.
Having said that, a JSFUtils class can grow quite cluttered with time with many many methods and can become very unmanageable. It would be better to categorize the util methods and put them in separate static utility classes.
I've first seen annotating Seam entity classes here
http://www.developer.com/java/ejb/article.php/10931_3715171_5/Introducing-JBossreg-Seam.htm
and for whatever reason I've been doing so ever since:
#Entity
#Table (name= "GADGET")
#Name("gadget")
public class GadgetBean implements Serializable {
private String mDescription = "";
private String mType = "";
...
}
However, I do not use "entity components" like this anywhere in my views. Can anyone explain the use of this and what this gains? Is it a non-practice?
If you are not using any of these entity components in your views, you should remove the #Name annotation.
Seam is great, but seam components come with overhead in the way of interceptors firing every time you access a method in that class. Since you are not accessing these attributes in your view, there is no need to make them into seam components. You are incurring the interceptor overhead every time you use a getter or setter from your entity beans.
Seam-gen, the tool used to create seam projects, can also generate entities that are reverse-engineered from your database tables. By default, the seam-gen entity generator does NOT add the #Name annotation to these classes. That should tell you something!
Hope this helps.
During testing a weakness was exposed in how our app builds f:selectItems lists, specifically, entering really long names on some of our entities screws page alignment by making really wide selects.
Many of these selectItem lists are duplicated in multiple views and backing beans, so I'd like to consolidate their creation.
We already have an application scoped bean that provides List<SelectItem> for enums, and my initial thought was to place them there.
I have some questions, though. We're using jsf 1.2 (if that matters)
1) My understanding is that application scoped beans are singleton simply because a single instance is instantiated and placed in session context. They are not like EJB3 singletons in that only one thread can access any method, so multiple requests won't block trying to access different methods. Is that correct?
2) I suspect each method would have to be synchronized to prevent multiple threads calling the same method from clobbering each other. Is that the case even if the only class member accessed in the method is a threadsafe stateless #EJB?
Following is an implementation of one of them that would be used in 20 views. The implementations for 10 other entities would be similar. Also, the appropriate converters are registered.
public synchronized List<SelectItem> getAccountSelect(){
List<Account> list = new ArrayList<Account>(pemEJB.list(Account.class));
Collections.sort(list, new AccountByActiveByName());
List<SelectItem> result=new ArrayList<SelectItem>(list.size());
for(Account row : list){
result.add(new SelectItem(row,
StringUtil.prefixTruncate(row.getName(), MAX_ACCT_LENGTH, row.isActive())));
}
return result;
}
Any advice appreciated
If it's really mandatory to do the data loading in a getter instead of in the constructor/postconstruct, then there's definitely no point of making it an application scoped bean. Just make it a request scoped one where you do the data loading job in the constructor/postconstruct.
In the jsf applications I work on we load almost all of our reference data (values for selectOneMenues primarily) in Application scope beans and we set up the values in the Constructor of those beans. The data is then available to other managed beans and views via getters but is globalized and centralized for the application. Since the values are only read via getters there is no need for synchronization.
We then expose the beans as mbeans through jmx with a reload method so that they can be updated as needed. The reload method(s) are synchronized so as to block during the short reloads.
In your example above it seems like you could just return a Collection of selectItems so as long as the values are setup in advance you can use this method and still serve multiple threads just fine:
public List<SelectItem> getAccountSelectItems() {
return this.accountSelectItems;
}
Just add this private member to your bean:
private List<SelectItem> accountSelectItems;
and set it up in the constructor:
public AccountBean() {
List<Account> list = new ArrayList<Account>(pemEJB.list(Account.class));
Collections.sort(list, new AccountByActiveByName());
this.accountSelectItems = new ArrayList<SelectItem>(list.size());
for(Account row : list) {
this.accountSelectItems.add(new SelectItem(row, StringUtil.prefixTruncate(row.getName(), MAX_ACCT_LENGTH, row.isActive())));
}
}
If on the other hand this is data that is constantly changing and needs to be updated you might be better off just loading it per session or per request, though you can reload it periodically in application scope using Quartz or some other timer to keep the data reads from your data source down if real time is not an essential requirement for this data in your app. If you are reloading the data then you will want to synchronize those operations if you're using application scope.
I'm new to JSF and am wondering if I got things right. Let's say I have a simple CMS that makes it possible to write pages.
First, I define a JPA entity called Page:
#Entity
public class Page {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column
private Long id;
#Column private String title;
#Column private String content;
// getters & setters ...
}
Then I would like in a view to create Page-s. For that, it looks like I need a page bean of some sort. For now I handled things like this:
#Model
public class PageBean {
private Page page = new Page();
public String getTitle() {
return page.getTitle();
}
public void setTitle(String title) {
page.setTitle(title);
}
// rest of properties & getters & setters ...
public void save() {
// persist using EntityManager
}
}
My question is the following one: given that my JPA entity model and the model I want to use in the views are most of the time exactly the same, is there a way of avoiding to have to create a batch of getters & setters in the PageBean?
I read somewhere that you should not use a same bean as JPA entity and JSF model bean (because JSF does repeated calls to getters that may affect JPA), yet I do wonder if there is not a simpler way that would help avoiding this kind of code duplication. Especially when you've got an application with a large model and in many instances do not require anything special in the view beans, it looks like this can get quite cumbersome.
[...] given that my JPA entity model and the model I want to use in the views are most of the time exactly the same, is there a way of avoiding to have to create a batch of getters & setters in the PageBean?
I don't see the point of using a wrapper around an Entity and adding such a layer is indeed duplication. Just use the entity from your JSF page. Yes, this introduce some sort of coupling between the view and the domain but, in general, modifying the database usually means adding or removing fields on the view. In other words, I don't buy the "decoupling" argument and I've written enough extra layers, mapping code, boilerplate code, etc to favor the simple approach when possible.
I read somewhere that you should not use a same bean as JPA entity and JSF model bean (because JSF does repeated calls to getters that may affect JPA)
I'd be interested if you could provide a reference but a wrapper class (delegating calls to the entity) is not going to change anything if there is a problem somewhere.
Just in case, some additional resources:
EclipseLink/Examples/JPA/JSF Tutorial
It's not code duplication. The are no algorithms duplicated. The business logic is still in one place.
What your bean is doing is just connecting the View to the Domain model. This is good, it's part of the MVC pattern.
If you were using your JPA entity as your backing bean, you would be breaking the MVC pattern. For example, if one day instead of displaying a plain String you would need to add a Date to this String because the view requires so (i.e. interface requirements), are you going to write this view logic inside the JPA class? That does not make sense, mixing domain model and view model.
On the other hand, why the view has to know about how the domain is implemented? What if the domain values format change? (For example you save a timestamp String instead a date class in de Database for performance reasons). All you would need to do is just rewrite the method in the backing bean, it would take the timestamp and adapt it to a Date so everything would work as it was before. Just one change outside the JPA class. If you had it in the JPA class you would end up maintaining both logics in just one class (interface logic and domain logic).
What if you want to develop a new view (for example for mobile version)? Are you gonna add even more code to the JPA class? It would be better to keep the JPA as it was and create another Bean (that extends a common bean for both views) for the mobile version.
If after all this, you still want to not to write the getters and setters, you can do
#{myBean.page.title}
all you need is a getPage() inside the backing bean.