I'm trying to understand the concurrent model of each EJB session bean types.
The singleton is well documented and seems clear to me... Only one instance and many threads using it but each method by default is synchronized because @Lock is defaulted to WRITE. We can let multiple threads use on method with @Lock(READ).
The stateless beans are in a pool I think I read somewhere that the container will ensure only one thread is using one instance at a time but this instances are recycled/reused so many threads can use the same instance but one at a time.
Is this correct ? or is it possible that multi-threading occur in one instance of SLSB ?If in the client I obtain a single reference of a SLSB and share this "instance reference" in multiple threads is it true that all the threads could use different instances on the server side ?
The stateful instance I obtain in the client is linked to one server instance and any method call will target the same instace. If many threads are using the same reference, all method calls will be synchronized and waiting for a certain amount of time that can be defined in @AccessTimeout and if the timeout is reach will end with a ConcurrentAccessException.
Can we use @Lock(READ) and let many thread use the same method like in a singleton ?
Recently I discovered power of Java, I'm coming from Perl, Python world so I'm at very beginning. I have firm understanding of OOP and I'm ready for new challenges. I have question regarding writing to database performance and theory.
Basically as my personal project I'm trying to write some small program or addon which will enable me to write concurrently to database. Let's say that I have some software and that has FIFO output to database in single stream, but since the output interface is not fast enough congestion can occur if the input to the system is high.
I would like to extend that software with addon which will take that one output stream and create 2,3,4 concurrent input streams towards database. API from that software is provided so I can redirect output to third-party extensions and apps.
I put the code on pastebin.com because it is relatively long. How to improve this code that does not occur starvation and was ucziwy terms of writers and readers.
May be I did not understand the meaning and usage of attribute "session" in page directive. My understanding is if session=false, in page directive, then the JSP page will not participate in the session. However, I have my welcomepage as below:
Can I access the session object even session has been expired? I need to check whether session is expired or not for each request.The session invalidation is set null the session object. What I concluded, session time out I can access session object but session invalidation I can not access session object. How can I find the session time out by using session object?
1) From War A, I login to the application and then fetch some users that is a rest call. I get the response back from rest in json form that ui consumes and display the data on page.
2) Now I click on the logout link from ui jsp. This logs out the session from Ui. I use <form data-dojo-type="dijit/form/Form" based logout.
3) I then go to the proxy (using burp) and manually request the rest call which I made in step no 1), the rest gives the response back with the same json object returned in step no 1) This shows that the logout action on step 2) is invalidated the session from War A (ui war) but the session or cookie based from WAR B (rest war) is not invalidated.
Expected outcome:After I Logout from War A(ui war), the session must also get invalidated from war B (rest war) and manually request from proxy should not get the same response object as received in step 1)
I am developing a e-commerce college project, here i add the items in the cart(a div tag in the jsp page) via servlet by creating sessions,
flow control: shopping jsp (when user wants to add an item in the cart) --> item servlet (which is used to create session and synchronized it) --> cart servlet(which is used to add items in the arraylist and show them in the shopping.jsp's div tag + it also sets the total purchase amount in the session variable "totalpurchase")
now after that user wants to proceed to checkout, here i use the onclick event to check the minimumshopping amount must be less than the totalpurchase (totalpurchase which i had setted in the session),but my jsp page is unable to rechognise the updated value of the totalpurchase, yes, if i reload the page, it rechognises the new updated value of the totalpurchase? but i want it to rechognise the updated total purchase value, without reloading he jsp page..
This is a general question about best practices for handling persisted data in JSF. My JSF page is going to have several fields that map to a managed bean. Upon a button click the fields of this bean are going to be persisted in a database. Is it better to use another bean with application scope to handle the JDBC code, or should I have a method in the bean itself to handle that? Similarly I'll need a method to retrieve the information upon a user request.
I have a primefaces editable datatable with column filtering feature.The datatable has live scrolling feature.The problem that i am facing here is that both filtering and scrolling are happening correctly with Request scoped managed bean but when the scope of the same bean is changed to view scope(javax.faces.bean.ViewScoped) then the filtering happens but on removing the keyed in key word from filter box the table content is not reset to original state and also i am not able to scroll down to next set of records on reaching the end of scrolling.Cell editing feature is working perfectly.
One thing that i observed is ,currently i am querying 5000 odd records to load into datatable.But if the number of records is limited below 5000 scrolling is happening correctly but problem with filtering remains same.I even tested by upgrading to Primefaces 5.1 from 3.Code snippet of xhtml page
I'm wondering if there's a way to build a template for managed beans which could be extended by a constructor instead of re-writing beans for each entity. I can do that quite easily for Dao objects by creating facades and using those facades to create Dao implementations for specific entities. Not sure if the same concept works for managed beans and haven't really come accross any searches.
I wrote the following but I'm not sure how to implement or even if the concept of generics and templating can be applied to managed beans in the same way it can be applied to Dao classes:
public class BeanTemplate<T> { private ListDataModel<T> listModel; @EJB private GenDao dao; private Class<T> entityClass;
[Code] .....
The above assumes there's only one method needed in the bean. I thought of extending like this:
public class EmployeeBean extends BeanTemplate<Employee> { public EmployeeBean() { super(Employee.class); }
// how can the methods be called??
Is the same concept for creating dao templates possible for managed beans?
If I have the next request scoped JSF bean for example:
public class UserBean { private String name; private String surname; public String saveUser(){ //service is called to save a user } public String updateUser(){ //service is called to update a user
[Code] ....
1.In struts for example the Action classes are singletons and I think is the way it has to be because they contain business logic and is the same logic for every user but in JSF because of you mix properties from a form and methods with business logic, these beans have to be request scoped like the above one but is very wierd that a bean which contains business logic(saveUser()....) be request scoped;I dont see it effective, is like creating a new servlet each time you want to save a user but I think is the way JSF works, right?
2 To avoid the mixing of form properties in a bean with business logic, some people say to have the form beans request scoped and actions beans session scoped.
- Is this right? - How then can you get the request form bean in the action bean? - The scopes in JSF are request, session and view so you cannot create singleton action beans, the best you can get is a session action bean, right?. Once again I dont see the point of creating action beans with session scoped,they should be application scoped if it existed
I've spent almost 3 hours on googling about java beans and where it is usable. What I've figured out is that a bean has a public non-arg constructor, properties and getters/setters to manipulate them. I also know that a bean contains no logic, only fields. However, I don't fully understand why I need to use beans instead of normal classes even if a class can do the same things like a bean? Are beans used to store data or what?
I have seen in some examples like URL... a good design is to have the model and the action methods in one just single bean and the model not to be a separated class but a few properties like this:
public class CustomerBean implements Serializable{ //DI via Spring CustomerBo customerBo; [b]public String name;[/b] [b]public String address;[/b] //getter and setter methods
[code]...
Some questions:
1. If you are using hibernate or any other ORM like the above example(URL...), why not to use the hibernate pojo bean directly like it represented the form instead of using properties?:
public class CustomerBean implements Serializable{ //DI via Spring CustomerBo customerBo; [b]Customer customer;[/b] //represents the properties of a form //getter and setter methods public void setCustomerBo(CustomerBo customerBo) { this.custom
2. Why is it said that JSF represents the purest MVC? Spring separates the model from the view too and Struts does too. I dont really understand it
I have an in-cell editable data table with a viewscoped managed bean.I found that the control never goes to the ajax event method onCellEdit when the scope of the bean is @Viewscoped but it works when the scope is changed to request scope.how to get this feature work with viewscope.Below is my code snippet
private String displayFormat = "%02d:%02d:%02d";// produces 00:00:00 hour:min:seconds public void timerHasChanged() { currentTime = System.currentTimeMillis(); // How long has been taken so far? long secsTaken = (currentTime - startTime) / 1000; long minsTaken = secsTaken / 60; secsTaken %= 60; long hoursTaken = minsTaken/60; minsTaken %= 60;
Formatter fmt = new Formatter(); fmt.format(displayFormat, hoursTaken, minsTaken, secsTaken); timerJbl.setText(fmt.toString());
How would i code the get and set method for format, so in property tab a user can choose if they want the timer shown in seconds, or minutes or hours or seconds&minutes
I have tried this example ([URL].../) with CarDao extending the BaseDao, it works like a charm.However, from the CarDao class, my NetBeans underlined the class name “CarDao” with the error message “A session bean must not extend another session bean.” But I can compile, deploy and run the application without any problem.
I have also heard that a session bean cannot extend another session bean, but why it works here?
I am using Java EE 6, NetBeans 8.0.1 and WebLogic 12c for this code testing.
Viewing this example of pagination [URL] and other similar beans for pagination, why do they do these beans view scoped? These beans dont contain any properties for a form so they could be application scoped, right?
I am using JSF2 with Primefaces. Here is my business requirement-Hidden field on JSF page should take the value from the session object that is set in managed bean. Session object is updated every time when the user submits the page. I am able to update the session object in the managed bean and able to get the value in the hidden field first time and after that i see the same value in the hidden field even though session object has different value. Here is the hidden field: <h:inputHidden id="xyz" value="xyz"/> i tried using sessionScope but still didn't work.
I have set the session timeout in web.xml to 60 but when I start on the home page and begin to enter any data I immediately get redirected to the timeout page.From the timeout page I can click a link that takes me to the home page. Now I get the 60 minutes before another timeout occurs. Changing the timeout only results in a change to the timeout after going back to the home page..why I am seeing an immediate timeout?
I'm trying to go back to basic and strengthen some of my foundation. I'm wondering what kind of data would be appropriate to be stored inside a session? My app is a web app where all the users are the employee of a company. So it's an web-based app that keeps track of stock movements, purchasing and sales order (standard distributor company). The web app interacts strictly with employees, so no public facing app (yes, that's right, no shopping cart). So, in this kind of web app, what kind of data that by storing it to session.
I am new to JSP and I'm having a problem with captcha containing a value in the field when toggling from the first page to another and clicking submit on the second page before entering data to validate the fields and the code just falls through and returns the error "Please enter the correct code". The values returned are (captcha)96043 (code)null, captcha is not null because it is retrieved from session which is the last value captured from the page I'm assuming.
I've used request.getSession().removeAttribute( "captcha" ); before building the page to clear out the values, resetting captcha to null etc.; nothing is working.
Is it a good idea to use the date and time with the first or last few values of the session ID. Or should I just use the complete session ID value for my "unique id"?
I've already tested with disabled="false", too, but only the Session attribute is saved as NULL, though it appears in the form field. The other fields are saved properly.
