About httpsession concept

Hi,ALL
I get confused something about HttpSession.Please help to clear it up.
When Server receives HttpServeletRequest, we always do getSession.
If there is no session in it,it creates one depending on parameter setting.
The question is: if server creates a httpsession and response to the client. Does it also send all the information to client with response?
My understanding is that the information only saved in server.
however, how does it manager those information with thousands of users request?
Thanks in advanced

if server creates a httpsession and response to the client. Does it also send all the information to client with response?The answer is no. You can, of course, set cookies on the client from your servlet to store certain data on the client.
What's more, the client has no way of accessing any java code residing on the web server.
how does it manager those information with thousands of users request?There is always a session id. This id is a long string of numbers and characters. They are unique for the web server. You can use session.getId() to find out what it is.
-S

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Hi !!
have a look on the given link for more details
Leveraging Service Oriented Architecture (SOA)
for Business Model Innovation
https://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/library/uuid/408c5726-ef5b-2910-26a9-9d5b58075700
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https://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/library/uuid/403fd993-56d9-2910-eaa4-9c52bcd1b82d
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About rfc concept

hi gurus,
Can any body explain me about the rfc concept.
Thanks.

Hi Rangamma,
Check this info.
These are the types of RFC
Asynchronous RFC (aRFC)
Synchronous RFC (sRFC)
Transactional RFC (tRFC)
Queued RFC (qRFC)
Parallel RFC (pRFC)
Asynchronous RFC :
This is used when you need to increase the performance of ABAP program by having system call more than one function module in parallel than forcing the program to wait for results .
Transactional RFC
This let you group one or more function module call together o tRFC LUW and ensure that fucnction module within LUW is called once . In contrast to aRFC and sRFC the tRFC belonging to tRFC LUW are executed in order .
tRFC is always used if a function is executed as a Logical Unit of Work (LUW). Within a LUW, all calls are
1.Executed in the order in which they are called
2.Executed in the same program context in the target system
3.Run as a single transaction: they are either committed or rolled back as a unit.
Implementation of tRFC is recommended if you want to guarantee that the transactional order of the calls is preserved
Asynchronous remote function calls (aRFCs) are similar to transactional RFCs, in that the user does not have to wait for their completion before continuing the calling dialog. There are three characteristics, however, that distinguish asynchronous RFCs from transactional RFCs:
When the caller starts an asynchronous RFC, the called server must be available to accept the request.
The parameters of asynchronous RFCs are not logged to the database, but sent directly to the server.
Asynchronous RFCs allow the user to carry on an interactive dialog with the remote system.
The calling program can receive results from the asynchronous RFC.
You can use asynchronous remote function calls whenever you need to establish communication with a remote system, but do not want to wait for the functions result before continuing processing. Asynchronous RFCs can also be sent to the same system. In this case, the system opens a new session (or window). You can then switch back and for between the calling dialog and the called session
RECEIVE RESULTS FROM FUNCTION Remotefunction is used within a FORM routine to receive the results of an asynchronous remote function call. The following receiving parameters are available:
IMPORTING
TABLES
EXCEPTIONS
The addition KEEPING TASK prevents an asynchronous connection from being closed after receiving the results of the processing. The relevant remote context (roll area) is kept for re-use until the caller terminates the connection.
Transactional RFC (tRFC) and Queued RFC (qRFC).
tRFC is used mainly to transfer ALE Intermediate Documents (IDocs).
Transactional RFC:
If an error occurs during a synchronous remote function call, the system cannot tell at what point the error occurred (most crucially, whether the function module was actually processed in R/3 before the operation failed). Restarting a failed call is therefore a dangerous thing to do, since you risk duplicating a completed function call.
To alleviate this problem, you can use transactional RFC, which guarantees that each function call you issue will only be executed once, even if you submit it repeatedly to the R/3 System. The system implements this safeguard by assigning a unique transaction ID (TID) to each transaction that you submit. When you attempt to process the transaction, the system checks whether that TID has already been processed. If it has, the transaction is ignored.
Disadvantages of tRFC
- tRFC processes all LUWs independent of one another. Due to the amount of activated tRFC processes, this procedure can reduce performance significantly in both the send and the target systems.
- In addition, the sequence of LUWs defined in the application cannot be kept. Therefore, there is no guarantee that the transactions are executed in the sequence dictated by the application. The only guarantee is that all LUWs are transferred sooner or later.
Queued RFC:
When you use transactional RFC, you cannot guarantee the order in which the function calls will be processed in the system (it is quite possible that one call might overtake another). For cases where you need to specify a particular processing order, you can use queued RFC, which is an extension of transactional RFC. In qRFC, you place each function call in a logical queue. A function call cannot be executed until all of its predecessors in the queue have been processed. Queued RFC calls are processed asynchronously
Therefore, Queued RFC is better than Transactional RFC.
Remote Function Call:
RFC is an SAP interface protocol. Based on CPI-C, it considerably simplifies the programming of communication processes between systems.
RFCs enable you to call and execute predefined functions in a remote system - or even in the same system.
RFCs manage the communication process, parameter transfer and error handling.
http://help.sap.com/saphelp_47x200/helpdata/en/22/042860488911d189490000e829fbbd/frameset.htm.
Remote Function Call (RFC) is the standard SAP interface for communication between SAP systems. The RFC calls a function to be executed in a remote system.
Synchronous RFC:
The first version of RFC is synchronous RFC (sRFC). This type of RFC executes the function call based on synchronous communication, which means that the systems involved must both be available at the time the call is made.
Transactional RFC (tRFC) and Queued RFC (qRFC). tRFC is used mainly to transfer ALE Intermediate Documents (IDocs).
Transactional RFC:
If an error occurs during a synchronous remote function call, the system cannot tell at what point the error occurred (most crucially, whether the function module was actually processed in R/3 before the operation failed). Restarting a failed call is therefore a dangerous thing to do, since you risk duplicating a completed function call.
To alleviate this problem, you can use transactional RFC, which guarantees that each function call you issue will only be executed once, even if you submit it repeatedly to the R/3 System. The system implements this safeguard by assigning a unique transaction ID (TID) to each transaction that you submit. When you attempt to process the transaction, the system checks whether that TID has already been processed. If it has, the transaction is ignored.
Queued RFC:
When you use transactional RFC, you cannot guarantee the order in which the function calls will be processed in the system (it is quite possible that one call might overtake another). For cases where you need to specify a particular processing order, you can use queued RFC, which is an extension of transactional RFC. In qRFC, you place each function call in a logical queue. A function call cannot be executed until all of its predecessors in the queue have been processed. Queued RFC calls are processed asynchronously
For more information on RFC, please go through the link.
http://help.sap.com/saphelp_nw04/helpdata/en/6f/1bd5b6a85b11d6b28500508b5d5211/content.htm
Have a look at this link.
http://help.sap.com/printdocu/core/Print46c/en/data/pdf/BCFESDE2/BCFESDE2.pdf
http://help.sap.com/saphelp_47x200/helpdata/en/22/042860488911d189490000e829fbbd/frameset.htm.
Rewards some points if it is helpful.
Rgds,
P.Naganjana Reddy

Points and discussion about the concepts behind making a 2D game

Hi all. I'm currently trying my hand at a 2D RPG style game. I have a few questions open for discussion, however, regarding the general points of implementation behind it.
1. Tiles vs static background argument aside, am I right in the thinking the best way of implementing movement across a big background map is actually to move the background and other sprites in relation to the player, giving the illusion of player movement although he in fact never moves from the center of the screen? Is there a way of actually creating a large map, populating it with sprites, and then moving the player across it and panning the screen after him?
2. Collision detection. If we go with the idea of moving everything in relation to the player rather than the player himself, woudln't this mean a large amount of calculations when collision detection occurs. Example, u want the player to stop moving when he hits a brick wall so you have to tell every entity sprite to stop moving in response to key presses (because remember, pressing up moves everything else up, not the player character).
3. Isometric. Is the easiest way of implementing an isometric style game just to develop isometric graphics and sprites?
4. Tiles. I've been doing a lot of reading into tiles but I'm not sure what's a better implementation: a tile system which consists of the entire background and things like houses split into tiles or a simple big background which can be scrolled around and is populated by house sprites which are all moved in relation to the player and their collision detections done individually. Tiles certainly seem like a nice innovation but I feel like the graphics suffer as a consequence and u end up with a 8bit NES looking game!
I'm just getting to grips with the concepts behind a lot of game design and all of this are some interesting points which I thought would be insightful to discuss. Opinions please!
Cheers.

Everything I'm about to say is based off of a tile-based Maze game I made.
1. Using a big background map is a bit lazy if you ask me, but graphically it would be easier to create a nice-looking game. You also have to think about memory. Let's say you manage to get an 800x600 background image at the size of 200kb with JPEG compression. That 200kb jpg image you use as a background is not 200kb when loaded into memory. I dont remember exactly how much bigger it gets in memory, so this next statement is probably wrong. But I heard that: 4bytes per pixel for the ARGB data, and there are 800x600 (480,000) pixels. That's 480000*4 (1920000) bytes if that statement is right. But it's probably wrong, so hopefully Abuse or someone will correct it :)
2. Move EVERYTHING up? I think you're a little mixed up. When the background (and all objects with it) is scrolled, their actual X,Y data is not changed. It is simply drawn according to the scroll offset. The only thing that is being calclulated for movement is the character/scroll offset. Think of it as a camera. The entire world is not moving, just the location of where you're viewing it. Quick example:
You have a Tree who's location is (10,10). If the scroll offset is (0,0), then that Tree will be drawn at (10,10). But let's say your character moves up 5 pixels. You say you want him centered, so the scroll offset also moves up 5 pixels, making the offset (0,-5). When it's time to draw again, that Tree can't be at the same place it was, because the character moved. If the character moved up, the Tree would appear as if it moved DOWN. So you'd draw it like:
g.drawImage(tree.getImage(),tree.x-scrollOffsetX,tree.y-scrollOffsetY,null);With that math, the Tree is actually drawn at (10,15), which is lower than before the character moved. You don't actually loop through all of your objects and change each and every X and Y value, you just change the global scroll offset
Speaking of collision detection, this is where TileMaps have a large advantage. In a TileMap, you don't have to check through each and every object in the world for collision. You can just grab the 4 surrounding tiles (north,west,east,south) from the Tile array. This means there are only 4 collision detections no matter where the character is in any situation on the map.
If you used an image for background instead of tiles, you'd have to check each object in the world for collision because it's harder to tell how close it is to the character. One thing you could do is just grab all of the object currently visible on screen and check their collision, but, depending on where you are on the map, this could easily cause an inconsistent frame rate (you could be in a field of grass that has no collision or a forest of 50 trees each screen- LOTS of collision!).
3. I dont got much to say about isometric :P
4. an 8bit NES game, eh? That is the common misconception that you have to use images that are the same size of the tiles. Have you seen the game "The Legend of Zelda: Four Swords"? That's a tile-based game, but on several occasions you see trees that are 10 times bigger than the 20x20 tiles. They mixed it up, they used a TileMap for the basic ground, and put good looking large images on top. The large images (such as a large tree) uses 4 or 5 "base" tiles that are used for collision. That way the character will only collide with the bottom-half of the tree, giving the appearance of going "behind" the tree when the Y value is above the middle line of the tree. This is far away from looking like an 8bit NES game :)
I hope that was more helpful than it was confusing, but I tend to babble, so.. anyway. Hope it helps :o

Question about the concept of RMI reverse calls.

Hello guys.
I'd appreciate if someone could clarify something to me. As far as I understand , RMI reverse call in concept, is the mean thought witch a server can remotely call a method belonging to the client.
I've done that like this: the client called a method from to the server(classic rmi) , method that had the particularity to received as a parameter an instance of a serialized .class belonging to client. Through that received remote object it seems the server can call specific methods belonging to the client .class.
I'm not sure it's the correct way to do reverse calls, but what puzzles me is that shouldn't the server be able to call a client method without first needing to receive that instance of the client's .class and implicitly being dependent on that client initial call (maybe to get that .class in a different way)?

I'm not sure it's the correct way to do reverse callsIt's not. If the object passed to the server is serializable, the server can call methods on it, but they will execute at the server.
The object you pass to the server must be an exported remote object. Then the server callbacks will execute at the client.
but what puzzles me is that shouldn't the server be able to call a client method without first needing to receive that instance of the client's .classNo, why?
and implicitly being dependent on that client initial call (maybe to get that .class in a different way)?When you get the exported remote object part right, the remote method via which the client passes the callback to the server will declare the callback as a remote interface, not as the implementing class at the client.

Doubt about the concept of HashSet and LinkedHashSet

I read one of the SCJP 6 exam book, when talking about Set, it gives one definition:
When using HashSet or LinkedHashSet, the objects you add to them must override hashCode(). If they don't override hashCode(), the default Object. hashCode() method will allow multiple objects that you might consider "meaningfully equal" to be added to your "no duplicates allowed" set.
What I am getting confused is that IF the objects we add to them must override hashCode(), we must override equals() method also! Isn't it?
Edited by: roamer on 2009?10?23? ??10:29

jverd wrote:
endasil wrote:
When using HashSet or LinkedHashSet, the objects you add to them must override hashCode(). If they don't override hashCode(), the default Object. hashCode() method will allow multiple objects that you might consider "meaningfully equal" to be added to your "no duplicates allowed" set.This really is completely wrong. Duplicates being added to your set has nothing to do with not overriding hashCode, and everything to do with not overriding equals. No, if you override equals but not hashCode, you can get dupes. That is, two items that your equals method says are equal can make it into the Set.Sorry, to clarify, what I meant by that was that to avoid duplicates of meaningfully equal objects, you must override equals, and overriding hashCode is just a consequent of overriding equals (to maintain the equal objects have equal hashcodes invariant). Overriding hashCode alone will not, and cannot, prevent meaningfully equal duplicates if you don't first define meaningfully equal by overriding equals.
In summary, it's wrong because
1) You don't have to override hashCode() if you don't override equals (or rather, don't deviate from the default "two objects are equal if and only if they are the same object").
2) If you have any other definition of meaningfully equal that you want enforced in a Set, you must override equals to correspond to that definition.
3) If you override equals, you must override hashCode by the contract of hashCode and equals.
That's why I was saying that the statement was completely wrong. It's taking a backwards approach.
By not overriding equals, you're saying that no two separate instances can be meaningfully equal, so the default hashCode is fine. Yeah, I kind of figured for the statement to be meaningful, it is assumed that you have already overridden equals. Otherwise what's the point of even mentioning something two objects "meaningfully equal"?All this talk of "meaningfully equal" makes me think the opposite: that they haven't overridden equals, or haven't discussed it yet. Otherwise you could just say that the objects are equal, or are equal according to equals().
I would question the authority of the source that said that.I would quesiton the source's ability to express himself clearly. :-)Yeah, maybe that's all it is. In that case, I suggest (to the OP) reading [Effective Java, Chapter 3|http://java.sun.com/developer/Books/effectivejava/Chapter3.pdf]. Best source I've seen for beginners to make sense of all this.
Edited by: endasil on 26-Oct-2009 1:11 PM

Not clear about some concepts.

I'm a newbie on installing Oracle8i.
I 'm confused with some concepts in installation.
A.Listener Name
B.Service Name
C.Net Service Name
Question:
1.Does one A listen on only one port?
2.Can one A commuticate with several db instance?
3.Does B stand for a db instance's name?
4.Is B the same as ORACLE_SID?
5.If the host I'm running Oracle has the name as "xxx.yyy.com",then can I give B the form as "db1.xxx.yyy.com"?
6.Does C have the similiar meaning as all entries defined in /etc/services?
7.Shoud I add some entry in /etc/services for any of A\B\C?
Thank you!
null

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Q:
1. No, you can configure your listener so that it listens to more than one port
2. Yes, it can. Just add your databases to your listener.ora using netasst
3. It doesn't need to be the same
4. It doesn't need to be the same
5. No, it has nothing to do with what you do in /etc/services
6. No, you can leave /etc/services alone<HR></BLOCKQUOTE>
Thanks,and some other questions:
8.Does ORACLE_SID stands for a db instance's name.
9.What's the relation between B and a db instance's name and ORACLE_SID?
10.What's the relation between A and C.

About some concepts.

can anybody describs definition and relation in detail about business object,idoc type,message type,segment type.,filter object type and so on?
thanks a lot.

follow the links.
business objects
http://help.sap.com/saphelp_nw04/helpdata/en/7c/3ce3c065ba11d395fe00a0c94260a5/frameset.htm
http://www.erpgenie.com/abap/bor.htm - 40k
http://www.sap-img.com/abap/reading-attribute-of-a-business-object-in-abap.htm - 8k -
http://diamond.businessobjects.com/sdn - 25k
publib.boulder.ibm.com/infocenter/wbihelp/v6rxmx/topic/com.ibm.wbia_adapters.doc/doc/mysap4/mysap4146.htm - 4k -
IDOC
ALE/ IDOC
http://help.sap.com/saphelp_erp2004/helpdata/en/dc/6b835943d711d1893e0000e8323c4f/content.htm
http://www.sapgenie.com/sapgenie/docs/ale_scenario_development_procedure.doc
http://edocs.bea.com/elink/adapter/r3/userhtm/ale.htm#1008419
http://www.netweaverguru.com/EDI/HTML/IDocBook.htm
http://www.sapgenie.com/sapedi/index.htm
http://www.sappoint.com/abap/ale.pdf
http://www.sappoint.com/abap/ale2.pdf
http://www.sapgenie.com/sapedi/idoc_abap.htm
http://help.sap.com/saphelp_erp2005/helpdata/en/0b/2a60bb507d11d18ee90000e8366fc2/frameset.htm
http://help.sap.com/saphelp_erp2005/helpdata/en/78/217da751ce11d189570000e829fbbd/frameset.htm
http://www.allsaplinks.com/idoc_sample.html
http://www.sappoint.com/abap.html
http://help.sap.com/saphelp_erp2004/helpdata/en/dc/6b835943d711d1893e0000e8323c4f/content.htm
http://www.sapgenie.com/sapgenie/docs/ale_scenario_development_procedure.doc
http://edocs.bea.com/elink/adapter/r3/userhtm/ale.htm#1008419
http://www.netweaverguru.com/EDI/HTML/IDocBook.htm
http://www.sapgenie.com/sapedi/index.htm
http://www.allsaplinks.com/idoc_sample.html
cheers,
sharad.

Clear me about package concept?

While executing packages at first time the entire package loaded into memory then 2nd time execution it will executed from local memory.
if in case any update happened in any schema object then how the execution happened?
its from server or local memory?

The package is cached in shared memory on the server, not local memory on your desktop. The state of package variables is also held in the private memory area associated with each session that is using it (e.g. if you set somepackage.var := 3, that is held in your session's private memory and nobody else can see it).
If the package is invalidated by changes to underlying objects, the cached version is also invalidated and must be reloaded by the next session to use it.

A doubt about mailing concept

Hi i just ended up completing mail servlet from where i can send mail through a SMTP and recieve at
my POP account.Attachments too can be included/downloaded in both cases.
1>
The problem is that when i login to pop account and see the messages after it is retrieved
, i get only new messages and not the ones which have been viewed already as we do in
Outlook express.When i see them through outlook express first and then go to inbox from my servlet,those messages are not there and i get Empty.
2>Every time retrieval process starts to show same messages again.
How to handle this ?.I find illustration of codes in java-mail working in same way .

If this is the limitation of Javamail as i have not
seen a single code either in demo or anywhere then i
would say it is good for nothingIt's not a limitation of Java. You need to understand the POP protocol. I don't think there's a way with POP to read a message and leave it on the server. As far as I know, once you read a message, it comes off the server. You need to manage its storage after that. The IMAP protocol allows you to read a message but leave it on the server. Read up on these protocols, and to through the [url http://java.sun.com/developer/onlineTraining/JavaMail/]JavaMail tutorial

Noob question about HttpSession's

Hey all, I've been scripting in jsp for awhile but most recently started using struts.
I have a class (User) created with values for Username, First name, Last name, etc.
When a user logs into the application I want to hold these values in a Session, so that I can use my getter and setter methods on it.
I have a class that stores the object in the session
session.setAttribute("User", ValidUser);
[ValidUser being an Object of type User]
Now in a jsp I'd like to use something like
mypack.User myNewUser = (mypace.User)session.getAttribute("User");
and then be able to use
myNewUser.getUsername();

Thanks, that works, but is there a better way to store information in a session?
For instance a way that I can get around declaring a User variable on every page.
like:
session.getAttribute("User").getUsername();
Or should I be declaring this object as a bean with a scope of session?
and then use
<%@ taglib uri="/tags/struts-bean" prefix="bean" %>
<bean:write name="myUserBean" property="Username">
I'm just looking for the cleanest way to do it, thanks.

HELP About HttpSession ?

Hello All,
i have a website which is online, and so many user daily
come on my website.
i made that website by java servlets.
my problem is that i want to know at any time i can check
how many users are online on my site.
if any example code or any help.
please any body help me, i m thanksfull.
onlyforjava.

If you are using a ServletContainer that conforms to the 2.3 spec, you can use the HttpSessionListener. There is an example here that does what you're looking for:
http://www.stardeveloper.com/articles/display.html?article=2001111901&page=1
This will not be precise as it will depend on what your session timeout is set to. It should do the trick though.
I hope this helps,
Mike Dalrymple

About httpsession concept

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