Singleton and non singleton in webdynpro java

Hi All,
where we use singleton and non singleton in webdynpro application.please send me with any example (scenario).
Regards
Anand

Hello Anand,
I think that your question is for u201CWeb Dynpro Javau201D forum..
Please use the correct forum for your question.
In general:: http://wiki.sdn.sap.com/wiki/display/WDJava/SingletonandNon-Singleton+Nodes
There is example at : http://wiki.sdn.sap.com/wiki/display/WDJava/DynamicUIGeneration
u201CWelcome to Web Dynpro Java! u201C Wiki : http://wiki.sdn.sap.com/wiki/display/WDJava/WelcometoWebDynproJava%21
Thank you and best regards, Natalia Khlopina

Similar Messages

Singleton node and non singleton practical scenario

Hi Friends,
Iam totally confused with singleton and non singleton node implementation please explain practical implementation on singleton and nonsingle ton node . In which scenario non single ton node is used.
Thanks in advance
Prasad

Hi,
Singleton Node:
A singleton node contains only one instace of the node at runtime. And that instace contains multiple elements at runtime.
By default if we create a node under ROOT context node, it will be allways singleton true.
Non singleton node:
A non singeton node contains more then one node instance at runtime. And each instance contains multiple elements at runtime.
It is not possible to create NonSingletonNodes directly under ROOT context node. We can create under any node which is under ROOT context node.
Note: In terms of datastorage at runtime we can say if node is table then each elment of node instance is a row of that table.
When is it requried to create non singleton nodes?
For example if you have list of SalesOrders and each and every oder is having list of items. Then we can create this node structure in two ways:
Orders (singleton true)
> Items (singleton true)
Here in this case at any point of time the there will be only one instance of Items node exist for currently selected element of Orders node. And that instance contains multiple elements nothing but items of that order.
Orders (singleton true)
> Items (singleton false)
Here in this case at any point of time all the instances of Items node exist for all the elements(not only for currently selected element) of Orders node. And those instances contains multiple elements nothing but items of those corresponding orders.
I hope it helps.
Regards,
Vijay K

Connecting Non sap to webdynpro java

Hi All
My requirement is to connect a non sap (like mysql) to webdynpro java ..please can anyone provide me some document on this ..please help me
Thanks
Parameshwari

Hi,
If you are using NWDS 7.0 version, you have to create a Datasource in visual admin.
If you are using CE 7.1 version, you have to create a Datasource in NWA--Configuration Management->Infrastructure->Application Resources.
Step by step procedure how to create a Datasource in NWDS 7.0 and CE7.1 is given in this [PDF link|http://www.sdn.sap.com/irj/scn/go/portal/prtroot/docs/library/uuid/40db1ed9-b7c2-2b10-66b8-84f6954b6d2d?QuickLink=index&overridelayout=true]
MYSQL Server 2005
Driver/jar which you have to use --> sqljdbc.jar
Driver class --> com.microsoft.sqlserver.jdbc.SQLServerDriver
Connection URL --> jdbc:sqlserver://<host_name>:<port>;database=<db_name>
Hope this helps you..
Best Regards
Vijay K

Uploading and downloading files in webdynpro java

how to upload and download xl files in webdynpro java application .

Hi ,
Refer these links they maybe helpful to you
You can check this sampple example from SDN
https://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/library/uuid/40db4a53-41a9-2910-d4a2-9c28283f6658
Uploading and Downloading Files In Web Dynpro Java
https://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/library/uuid/00062266-3aa9-2910-d485-f1088c3a4d71
https://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/library/uuid/202a850a-58e0-2910-eeb3-bfc3e081257f
http://help.sap.com/saphelp_nw04/helpdata/en/43/85b27dc9af2679e10000000a1553f7/content.htm
Uploading and Downloading Files In Web Dynpro Tables
https://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/library/uuid/b0e10426-77ca-2910-7eb5-d7d8982cb83f
Some more links regarding Uploading and DownLoading Files
Uploading and downloading files
Upload and Download file through RFC called by java
Regards,
Saleem

Drag and Drop functionality in webdynpro java

Hi,
Please check this article
[https://www.sdn.sap.com/irj/scn/go/portal/prtroot/docs/library/uuid/f0fec52a-abad-2b10-48b8-cbdfd0dbca62]
Thanks and Regards

Hi raman,
Such kind of drag and drop feture is only supported with CE 7.1 Eph1 onwards. if you have CE 7.1 Eph1 then you will also see these 'dragsourceinfo' and 'droptargetinfo'.
Please check teh version of your installation.
If you dont have CE 7.1 then I am afraid that you cannot implement any such feature using webDynpro. At maximum what you can do is create a browse and collect pattern, which will allow you to select multiple values from one table(Browse Table) and transfer that to other table (Collect Table). We also have many such screens which require multiple selection from one item list to other. And we follow the same technique.
I hope this solves your issue. Please revert back if you require any other help or kindly close the thread.
Thanks and Regards,
Pravesh

Context Mapping for Non-Singleton Node

Hi ,
I have following context structure
Node_A
| attr 1
|________ Node_B
 attr2
 attr3
Node_B is the child of Node_A. NOde_B has attributes attr2 and attr3.
Node_B is a Non SIngleton Node.
Node_B is mapped to Node_View of the View Controller.
Node_A had 2 elements. Initially Element 1 is the Lead selection Element for Node A. I get the reference for Node_B using the Lead Selection Path
NodeA_element1 = Node_A->GET_ELEMENT( ).
Node_B = NodeA_element1->GET_CHILD_NODE( 'NODE_B' ).
Node_B is filled with elements, lets say attr2 = 'Dallas', attr3 = 'Detroit'
Node_View shows the values Dallas and Detrait since its mapped to Node_B
Now the Lead selection of Node_A changes to 2.
I again gett he reference for NOde_B usign the Lead Selection Path (index 2)
NodeA_element2 = Node_A->GET_ELEMENT( ).
Node_B = NodeA_element2->GET_CHILD_NODE( 'NODE_B' ).
Node_B is now filled with, lets say attr2 = 'Mexico', attr3 = 'Canada'
Since element 2 is Lead selection for Node A, now, and NodeB is mapped to Node_View, I expect the contents of Node_View to be attr2 = 'Mexico', attr3 = 'Canada' since this is along the Lead Selection of Node_A
But it stays attr2 = 'Dallas', attr3 = 'Detroit'
So in a nut shell, the Context Mapping of the Non Singleton Node DOES NOT map the Lead selection Path when its parent , changes in Lead Selection.
Is this a BUG ?
Thanks

Hi Anand,
There is no bug. See when you are saying
"Node_B is now filled with, lets say attr2 = 'Mexico', attr3 = 'Canada' "
I am just not sure how you have filled the data in node B. Because the way u populate node data that way only you can get the data. The way you want to get data you must populate data in this way:
1. Get Node A instance let say in lv_node_A.
2. Get Node A element instance (lead selection) in your case lets say in lv_elem_A.
3. Now get node B instance by lv_elem_A->get_child_node( 'B' ) lets say in lv_node_B.
4. Create element of lv_node_B and bind it to the node B and also populate the value of attributes.
Repeat the steps as per your requirement. Also Singleton and Non singleton has nothing to do with this it is all about how the instances will be manged in the memory.
Look at this sample code and will help you while populating data in nested nodes:
 DATA lo_nd_a TYPE REF TO if_wd_context_node.
 DATA lo_el_a TYPE REF TO if_wd_context_element.
 DATA lo_nd_b TYPE REF TO if_wd_context_node.
 DATA lo_el_b TYPE REF TO if_wd_context_element.
 DATA ls_a TYPE wd_this->element_a.
 DATA lv_test LIKE ls_a-test.
 data lv_btest type string.
navigate from <CONTEXT> to <A> via lead selection
 lo_nd_a = wd_context->get_child_node( name = wd_this->wdctx_a ).
@TODO handle not set lead selection
 IF lo_nd_a IS INITIAL.
 ENDIF.
 data count type c.
 data count_i type i value 1.
 do 2 times.
 lo_el_a = lo_nd_a->create_element( ).
 lo_el_a->set_attribute(
 EXPORTING
 name = `TEST`
 value = count_i ).
 lo_nd_a->bind_element( new_item = lo_el_a
 SET_INITIAL_ELEMENTS = abap_false ).
 lo_nd_b = lo_el_a->get_child_node( 'B' ).
 lo_el_b = lo_nd_b->create_element( ).
 move count_i to count.
 concatenate count 'in node b' into lv_btest.
 lo_el_b->set_attribute(
 EXPORTING
 name = `BTEST`
 value = lv_btest ).
 lo_nd_b->bind_element( new_item = lo_el_b
 SET_INITIAL_ELEMENTS = abap_false ).
 count_i = count_i + 1.
 enddo.
This code will set value 1 and 2 in node A's test attribute. and on change of lead selection between 1 and 2 it will show value of attribute BTEST in node B as 1 in node B and 2 in node B...
Regards,
Neha

Webdynpro Java Portal Eventing

Hi All,
From my VC application, i want to pass 1 parameter value to webdynpro iview field. From the "signal out" of my vc iview, i have taken the "EPCM event", and "name". and have mentioned in webdynpro Java iview.
public void wdDoInit()
    //@@begin wdDoInit()
    WDPortalEventing.subscribe("urn:com.sap.vc:epcm", "Filter1",
   wdThis.wdGetReactPortalEventingAction() );
    //@@end
public void onActionReactPortalEventing(com.sap.tc.webdynpro.progmodel.api.IWDCustomEvent wdEvent, java.lang.String dataObject )
     wdContext.currentContextElement().setName(dataObject);
    //@@end
How can i make the webdynpro iview take up the parameter from VC iview? Can anyone please help me out in solving this issue?
Regards,
Divya

answered

Future for webdynpro-java

Hi Everyone ,
This is not a technical query just in general .
I am basically a java developer and got into this webdynpro-java development . Now as the news that- "webdynpro-java will be no more after few years " making me to think abou my career. I am just thinking wheather to go back to java or stayback in this webdynpro. Can someone suggest me on this .
Thanks

Hi,
You can read this blog by Mr.Wolfgang, Chief Product Owner for BPM & ESB -
The death of Web Dypro Java has been greatly exaggerated
This topic is blown out of proportion and you can get a clear understanding of the disputed topic.
Arun is right, its like any other product in market which is driven by demand and supply. You cannt deny a product which is wanted by the customer.
Regards,
Ganesh N

Static and non-static variables and methods

Hi all,
There's an excellent thread that outlines very clearly the differences between static and non-static:
http://forum.java.sun.com/thread.jsp?forum=54&thread=374018
But I have to admit, that it still hasn't helped me solve my problem. There's obviously something I haven't yet grasped and if anyone could make it clear to me I would be most grateful.
Bascially, I've got a servlet that instatiates a message system (ie starts it running), or, according to the action passed to it from the form, stops the message system, queries its status (ie finds out if its actually running or not) and, from time to time, writes the message system's progress to the browser.
My skeleton code then looks like this:
public class IMS extends HttpServlet
 public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
 doPost(request, response);
 public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
 //get the various parameters...
 if (user.equalsIgnoreCase(username) && pass.equalsIgnoreCase(password))
 if(action.equalsIgnoreCase("start"))
 try
 IMSRequest imsRequest = new IMSRequest();
 imsRequest.startIMS(response);
 catch(IOException ex)
 catch(ClassNotFoundException ex)
 else if(action.equalsIgnoreCase("stop"))
 try
 StopIMS stopIMS = new StopIMS();
 stopIMS.stop(response);
 catch(IOException ex)
 else if(action.equalsIgnoreCase("status"))
 try
 ViewStatus status = new ViewStatus();
 status.view(response);
 catch(IOException ex)
 else
 response.sendRedirect ("/IMS/wrongPassword.html");
public class IMSRequest
//a whole load of other variables
public PrintWriter out;
 public int messageNumber;
 public int n;
 public boolean status = false; //surely this is a static variable?
 public String messageData = ""; // and perhaps this too?
 public IMSRequest()
 public void startIMS(HttpServletResponse response) throws IOException, ClassNotFoundException
 try
 response.setContentType("text/html");
 out = response.getWriter();
 for(n = 1 ; ; n++ )
 getMessageInstance();
 File file = new File("/Users/damian/Desktop/Test/stop_IMS");
 if (n == 1 && file.exists())
 file.delete();
 else if (file.exists())
 throw new ServletException();
 try
 databaseConnect();
 catch (ClassNotFoundException e)
//here I start to get compile problems, saying I can't access non-static methods from inside a static method
 out.println(FrontPage.displayHeader());
 out.println("</BODY>\n</HTML>");
 out.close();
 Thread.sleep(1000);
 catch (Exception e)
 }OK, so, specifially, my problem is this:
Do I assume that when I instantiate the object imsRequest thus;
IMSRequest imsRequest = new IMSRequest();
imsRequest.startIMS(response); I am no longer in a static method? That's what I thought. But the problem is that, in the class, IMSRequest I start to get compile problems saying that I can't access non-static variables from a static method, and so on and so on.
I know I can cheat by changing these to static variables, but there are some specific variables that just shouldn't be static. It seems that something has escaped me. Can anyone point out what it is?
Many thanks for your time and I will gladly post more code/explain my problem in more detail, if it helps you to explain it to me.
Damian

Can I just ask you one more question though?Okay, but I warn you: it's 1:00 a.m., I've been doing almost nothing but Java for about 18 hours, and I don't do servlets, so don't take any of this as gospel.
If, however, from another class (FrontPage for
example), I call ((new.IMSRequest().writeHTML) or
something like that, then I'm creating a new instance
of IMSRequest (right?)That's what new does, yes.
and therefore I am never going
to see the information I need from my original
IMSRequest instance. Am I right on this?I don't know. That's up to you. What do you do with the existing IMS request when you create the new FrontPage? Is there another reference to it somewhere? I don't know enough about your design or the goal of your software to really answer.
On the other hand, IMSRequest is designed to run
continuously (prehaps for hours), so I don't really
want to just print out a continuous stream of stuff to
the browser. How can I though, every so often, call
the status of this instance of this servlet?One possibility is to pass the existing IMSRequest to the FrontPage and have it use that one, rather than creating its own. Or is that not what you're asking? Again, I don't have enough details (or maybe just not enough functioning brain cells) to see how it all fits together.
One thing that puzzles me here: It seems to me that FP uses IMSReq, but IMSReq also uses FP. Is that the case? Those two way dependencies can make things ugly in a hurry, and are often a sign of bad design. It may be perfectly valid for what you're doing, but you may want to look at it closely and see if there's a better way.

When a context node use non-singleton, how to invoke the supply funtion eve

when a context node use non-singleton, how to invoke the supply funtion everytime the lead selection is changed ?

Hi wei,
Non-singleton nodes:
Web Dynpro allows you to define non-singleton nodes. Each non-singleton node has one node instance for each node element of the parent collection at runtime. The advantage is that each instance can be accessed directly. When using non-singleton nodes, the nodes are only created when the node values are retrieved. This can save resources that otherwise would slow down the performance of the application.
Supply function:
The Web Dynpro tools also automatically enhance the corresponding controller class with a supply function including the user coding area contained in it
Supply functions are implemented as methods of type
public void supplyChildNodeElements(SomeChildNode node,
SomeParentNodeElement)
in a Web Dynpro controller (view controller or custom controller). Supply functions and context nodes have a 1..1 relationship, that is, supply functions are specific for individual context nodes. Under certain conditions, supply functions are called by pages in the Web Dynpro runtime environment.
Hope this helps u,
Regards,
Nagarajan.

How to instantitate a non-singleton node

I need to instantitate the non-singleton node which has the following properties
Collection cardinallity of 0..n
and
Selection Cardinallity of 0..1
But when I try to get this node using wdContext.nodeA().nodeB()
where
nodeA is singleton
nodeB is non-singleton whose properties are given below
I always get nodeB as null . it seems nodes are initialized only if set to singleton
I need non-singleton node for using the TableRowGrouping element
If any one can please help that will be great

Hi Gaurav,
You have not mentioned nodeA properties.If it's cardinality is 1..x then no need to initialize A otherwise you must initialize A first then initialize nodeB.
Try like this:
//If cardinality of A is not 1...1
IPrivateTrstView.IAElement ele = wdContext.createAElement();
//Set if there are any attributes
ele.setXXX();
wdContext.nodeA().addElement(ele);
IPrivateTrstView.IBElement ele = wdContext.createBElement();
ele.setXXX();
wdContext.nodeB().addElement(ele);
The singleton property refers the relationship between the node and its parent but not between the node its child as for as I know.
Regards,
Siva

"requires unreachable" warning emitted when using static variables and the singleton pattern

I'm implementing code contracts on an existing code base and I've come across this situation in a few places. Wherever we have additional logic with code contracts where a singleton instance is instantiated, all code contracts emit a "reference use
unreached", or "requires unreachable" warning.
The code below demonstrates this.
static string instance = null;
static string InstanceGetter()
if (instance == null)
instance = "initialized";
AdditionalLogic(instance); // requires unreachable warning on this line
return instance;
static void AdditionalLogic(string str)
Contract.Requires(str != null);
Console.WriteLine(str);

Would the class get unloaded even if the Singleton object has some valid/reachable references pointing to it?
On a different note, will all the objects/instances of a class get destroyed if the class gets unloaded.That's the other way round, really: instances cannot be garbage-collected as long as they are strongly reachable (at least one reference pointing to them), and classes cannot be unloaded as long as such an instance exists.
To support tschodt's point, see the JVM specifications: http://java.sun.com/docs/books/jvms/second_edition/html/Concepts.doc.html#32202
*2.17.8 Unloading of Classes and Interfaces*
A class or interface may be unloaded if and only if its class loader is unreachable. The bootstrap class loader is always reachable; as a result, system classes may never be unloaded.
Will the same case (Custom ClassLoader getting unloaded) occur if I write the singleton using the code wherein we lazily initialize the Singleton (and actually create a Singleton instance rather than it being a Class/static variable).You should check the meaning of this vocabulary ("object", "instance", "reference"): http://download.oracle.com/javase/tutorial/java/javaOO/summaryclasses.html
The difference between the lazy vs eager initializations is the time when an instance is created. Once it is created, it will not be garbage collected as long as it is reachable.
Now I'm wondering, whether being referenced by a static attribute of a class guarantees being reachabe. I'm afraid not (see the JLS definition of reachable: http://java.sun.com/docs/books/jls/third_edition/html/execution.html#44762). That is, again, unless the class has been loaded by the system class loader.

When not using EJBs can I make BD a Singleton and cache facade instances?

Hi,
In an application which does not use EJBs can I make BD(Business Delegate) a singleton?
I was very sure about doing this but when I tried Google on the same subject the answers were'nt supportive of this but that was in the context of applications which used EJBs. And also item 4 in Effective Java isnt very supportive of caching Objects at the drop of a hat.
When not using EJBs would it be an unnecessary thing to make BD a singleton and cahce Facade instances in a BD and DAO instances in a Facade? I am planning to use a array based blocking bounded buffer for the purposes of caching. Or would it be better to make both BD and a facade as SIngletons and just cache DAOs in a Facade?
Any suggestion would be of good help to me.
Thanks a lot.

Not sure I understand all your design, but you seem
to describe an architecture where requests are queued
and handled serially.Sorry if I messed up while explaining it. No, it will not be handled serially. Since the BD is a singleton multiple threads can pass messages to it simulteanously, a bit like an object of the Action class in Struts. Since I dont see having any synchronized methods in a BD requests will be handled simulteanously.
The impact on throughput of handling requests
serially (as opposed to parallelizing them) probably
outweights by far the cost of instantiating one more
object per request...Yes, I understand that but as I explained above the reqests wont be handled serially.
To be more clear, I am thinking of using any one of these two things:
1) BD(Singleton)-->Facade(Singleton, caches DAOs in a thread safe data structure)
2)1) BD(Singleton, caches Facade instances in a thread safe data structure)-->Facade(caches DAOs in a thread safe data structure).
the thread safe data structure I am planning to have is a array based bounded buffer which blocks using wait and notify mechanism.
Thank you for the reply.

Singletons and multithreading question

Hi, I had a class created as a singleton as it was only used in one place. However since Ive now multithreaded the part of the program that calls the singleton code so it could be called twice at the same time.
If the method being called initializes all its variables within the method, is that method safe to be called in a mutli-threaded env or not ?
If it in my situation all variables are declared within the method except a precompiled javax.xml.XPathExpression class, the same one is used to parse an Input Source, the input source itself is created within the method. I
think I am having concurrency problems , (SAXParser Exceptions) and I think it is because of this XPathExpression class but cannot clearly understand why.
What is the correct solution, I dont want to initilize the XPathExpression within the method because the method is called many times always for the same expression, dropping the singleton and creating new instances of the class on every call would be even worse. I require multithreading to improve concurrency is there a safe Multi Singleton pattern that i should be using ?

There are two issues:
a) is the singleton object safe for multithreaded use
b) how do I safely create a singleton in a multi-threaded application
The answer to (a) depends on the class. It sounds from your description that you are using an object (the XPathExpression) that might not be thread-safe. I can't tell you if it is or not. Assuming it is not you either need to synchronize this method so that all threads will go through it (and use the expression) one at a time - which may defeat the purpose of multi-threading - or else you need a way to use multiple instances of these expressions in different threads. As I'm not familiar with these classes I can't tell you what you can and can't do concurrently.
There are a number of answers to (b). Construction via static initialization is the simplest and safest. If you want lazy initialization and the class that holds the reference to the singleton must be loaded even if the singleton isn't needed, then lookup the initialize-on-demand-holder-class idiom (see Josh Bloch's "Effective Java" item 48)

What's the differences between a singleton and a class with static methods

Hi everybody.
My question is in the subject. Perhaps "differences" is not the good word. The positive and negative points ?
Imagine you have to write a connection pool, sure you gonna choose a singleton but why ?
Thank you very much.

A class is a class. Java doesn't have (and I wish it
did) a static outer class. Any class can extend
another class or implement an interface.A Class object cannot extend or implement anything - it is not under programmer control in any way. You can create a class which implements interfaces, but calling static methods is completely unrelated. Interfaces only affect instance methods, not class ones. I think all of your comparison to C++ is actually confusing you more. In Java, there is a real class object at runtime, as opposed to C++.
YATArchivist makes a good point about being able to
serialize, altho I've not met that desire in practice.
Maybe a concrete example would help.
mattbunch makes another point that I don't understand.
A class can implement an interface whether it sticks
its data in statics or in a dobject, so I guess I
still don't get that one.See my comment above. Static methods are free from all contractual obligations.
I prefer instance singletons to singleton classes because they are more flexible to change. For instance I created a thread pool singleton which worked by passing the instance around, but later I needed two thread pools so I made a slight modification to the class and poof! no more singleton and 99% of my code compiled cleanly against it.
When possible, I prefer to hand the instance off from object to object rather than have everything call Singleton.instance() since it makes changes like I mentioned earlier more feasible.

Singleton and non singleton in webdynpro java

Similar Messages

Maybe you are looking for