Chain of Responsibility Design Pattern

Is there any java api which helps in implementing Chain of Responsibility Design pattern by parsing a XML file?. Can I use XML file to do this in Apache Commons Chain API?

A quick look at the javadocs for that project suggest that, yes, indeed they do provide a way to specify a chain of command using XML.
In fact I'm kind of confused why you even asked this question, since you already seem to know the answer.
I've never heard of such a thing in the standard API, if that's what you're asking, probably because it's a simple pattern to implement, and most of the pain of any implementation is likely to be due to details specific to the problem domain, not the pattern.
If you're really eager to use XML, you might want to check out Spring. You could configure a bunch of beans in a chain, if you like.

Similar Messages

Design Patterns that are used in standard j2se/j2ee classes/interfaces

Hi All,
I am understanding following design patterns (used within standard j2se/j2ee):
Adapter
Facade
Composite
Bridge
Singleton
Observer
Mediator
Proxy
Chain of Responsibility
Flyweight
Builder
Factory Method
Abstract Factory
Prototype
Memento
Template Method
State
Strategy
Command
Interpreter
Decorator
Iterator
Visitor
I want to see if/where these design patterns are used in j2se/j2ee classes/interfaces. i am looking for few examples of standard java classes/interfaces/cases where these design patterns are used by jdk developers.
for e.g.
WindowAdapter class is an example of Adapter DP.
JOptionPane is an exmple of Facade DP.
MouseListener is an example of Observer DP.
Similarly, where can find examples of jdk classes/interfaces of the remaining DPs.
I searched a lot of books, but they explain the DPs by creating their own classes/interfaces.
I would like to see where these DPs are already utilised in std j2se/j2ee
thanks,
Madhu_1980

877316 wrote:
I searched a lot of books, but they explain the DPs by creating their own classes/interfaces.
I would like to see where these DPs are already utilised in std j2se/j2eeWell, you can go through the javadocs first, they sometimes mention the pattern used.
Then you can get the sources for the jdk and go through the classes yourself, identifying the patterns.

What is the best design pattern for this problem?

No code to go with the question. I am trying to settle on the best design pattern for the problem before I code. I want to use an Object Oriented approach.
I have included a basic UML diagram of what I was thinking so far.
Stated simply, I have three devices; Module, Wired Modem, and Wireless Modem.
In the Device Under Test parent class, I have put the attributes that are variable from device to device, but common to all of them.
In the child classes, I have put the attributes that are not variable to each copy of that device. The attributes are common across device types. I was planning to use controls in the class definition that have the data set to a default value, since it doesn't change for each serial number of that device. For example, a Module will always have a Device Type ID of 1. These values are used to query the database.
An example query would be [DHR].[GetDeviceActiveVersions] '39288', 1, '4/26/2012 12:18:52 PM'
The '1' is the device type ID, the 39288 is the serial number, and the return would be "A000" or "S002", for example.
So, I would be pulling the Serial Number and Device Type ID from the Device Under Test parent and child, and passing them to the Database using a SQL string stored in the control of the Active Versions child class of Database.
The overall idea is that the same data is used to send multiple queries to the database and receiving back various data that I then evaluate for pass of fail, and for date order.
What I can't settle on is the approach. Should it be a Strategy pattern, A Chain of Command pattern, a Decorator pattern or something else.
Ideas?

elrathia wrote:
Hi Ben,
I haven't much idea of how override works and when you would use it and why. I'm the newest of the new here.
Good. At least you will not be smaking with a OPPer dOOPer hammer if I make some gramatical mistake.
You may want to look at this thread in the BreakPoint where i trie to help Cory get a handle on Dynamic Dispatching with an example of two classes that inherit from a common parent and invoke Over-ride VIs to do the same thing but with wildly varying results.
The example uses a Class of "Numeric" and a sibling class "Text" and the both implement an Add method.
It is dirt simple and Cory did a decent job of explaining it.
It just be the motivation you are looking for.
have fun!
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

Design Pattern / Best Practice Question

Hi,
I have been using Flex for a while now, but there is a
scenario which I still have not found a solution I'm entirely happy
with. I'm wondering if anyone else out there might have suggestions
on a design pattern or best practice.
Suppose I have a view which depends on model data which
resides in some back end systems. That model data may or may not
have been loaded (e.g. via a web service or remote object call) at
the time the view is displayed.
I don't know if the user will ever visit this part of the
application so I would prefer to defer retrieval of the data until
the user actually navigates to this view. Or I want to retrieve the
data each time the view is displayed because the data is dynamic
and could change between one presentation of the view and the next.
Because the data comes from several systems, I cannot simply
make one service call and display the view when it completes and
all the data is available. I need to call several services which
could complete in any order but I only want to display my view
after I know all of them have completed and all of the model data
is available. Otherwise, I can present the user an incomplete view
(e.g. some combo boxes are empty until the corresponding service
call to get the data completes).
The solution I like best so far is to dispatch a single event
(I am using Cairngorm) handled by a single command which acts as
the caller and responder for all of the services. This command then
remembers which responses it has received and dispatches another
event to navigate to the view once all the results have returned.
If the services being called are used in different
combinations on different screens, this results in proliferation of
events and commands. An event and command for each service and
additional events and commands to bundle the services and the
handling of their responses in the right combinations for each of
the views.
Another approach is to have some helper class listen for all
of the model changes and only display the view when the model
enters some state that is acceptable. It is sometimes difficult to
determine just by looking at the model whether it is in the right
state (e.g. how can I tell that a collection is the new collection
that should just have been requested versus an old one lingering
from a previous call). The logic required can get kind of
convoluted and brittle.
Basically, all of the solutions I've come up with so far seem
less than ideal and a little hackish. I keep thinking there is some
elegant solution out there that I am just missing ... but so far,
no luck finding it. Thoughts?
Thanks.
Bill

i think a service class is right - to coordinate your calls.
i would have 1 event per call (so you could listen to individual
responses if you wanted to).
then i would use a flag. if you want to check for staleness,
you would probably want two objects to map your service flag to
lastRequested and lastCompleted. when you check, check if it's
completed, and if it's not stale and that your lastRequested is
less than lastCompleted (meaning that you're not currently waiting,
i.e. you've returned since making a request). then make the request
and update your lastRequested.
here's a snippet of what i mean.
./paul
public static const SVC1_LOADED:int = 1;
public static const SVC2_LOADED:int = 2;
public static const SVC3_LOADED:int = 4;
public static const SVCALL_LOADED:int = 7;
private var completedFlag:int = 0;
then each call would have it's own callback.
private function onSvc1Complete( evt:Event):void {
completedFlag |= SVC1_LOADED;
lastCompleted[ SVC1_LOADED ] = getTimer();
dispatchEvent( new Event("svc1complete") );
checkDone();
private function checkDone():void{
if( completedFlag == SVCALL_LOADED )
dispatchEvent(new Event( "allLoaded" ));

ANN: New Design Pattern (DAO)

Hello,
Thanks for your overwhelming response to our previous sample applications demonstrating various [url http://www.oracle.com/technology/sample_code/tech/java/j2ee/designpattern/index.html]design patterns.
Continuing with the series, this month we have showcased the [url http://www.oracle.com/technology/sample_code/tech/java/j2ee/designpattern/dataaccesstier/index.html]Data Access Object (DAO) Design Pattern which is considered as a best practice for applications accessesing the database or the underlying persistence layer from the business tier.
The DAO implements the access mechanism required to work with the data source. The data source could be a persistent store like an RDBMS, an external service like a B2B exchange, a repository like an LDAP database, or an XML Repository. Using the scenario of web based News Application, this sample application demonstrates the effective use of this pattern.
[url http://www.oracle.com/technology/sample_code/tech/java/j2ee/designpattern/dataaccesstier/index.html]Download the sample application to learn more about this pattern.
More Sample Applications are available at [url http://www.oracle.com/technology/sample_code/index.html]
http://www.oracle.com/technology/sample_code/index.html
Thanks,
Rajat
OTN Team

Hi
This is because you are not using the latest jdbc driver version. Either use the latest ojdbc14.jar downloadable from the location given in the readme(Oracle Database 10g (10.1.0.2.0) drivers),
Or simply comment this part in the code.
Also you may just replace the close method call with ods=null;
Hope this helps
Shrinivas

What is command design pattern? what is the problem that it solves?

Hi i have been reading few articles on command design pattern but was unable to understand what it is and what problem does it solve. As far as my understanding goes if there is a pre specified method in an object that could execute and perform the necessary activities then it is called as command design pattern. Why is it named as command design pattern, it is because in a shell we use commands to retrieve output. For example when we type "dir" in dos command prompt it returns the list of files. so here we have to remember a preexisting exe file named "dir" which does something when used. So here like we call it command because when "dir" is passed to the computers it returns something that is expected. may be the computer obeys the command issued and return something back. So like wise if there is a method that is defined as as the command, for example in struts framework the action class must have a method "execute()" which is called by the framework to execute the necessary action mapped to it. So if there is a predefined method like "execute" in struts then the object is said to be followed command design pattern. So what actually does it solve?
What ever i have written is my understanding from the articles i have read about the design pattern. So kindly correct me if i am wrong. Help me understanding what actual problem does this pattern solves. Thanking you in advance.

This is really off-topic for these forums. You might do better on StackOverflow.com. I'll just say that although the first Design Patterns book came as a revelation to me, it was more for (a) the nomenclature (decorator, factory, facade, etc) which is still with us and (b) about five of the original patterns, which told me things I didn't already know. I've never used any of the others, including Command, and the whole design patterns thing quickly degenerated into farce with what seemed like a sustained attempt to reduce the whole of computer science to design patterns, which really isn't the point. As an example, there is one in another book called Type Object, which is nothing but 3rd normal form, which can be defined roughly in a couple of sentences. This pattern went on for dozens of pages with a very artificial example. I wrote to the mailing list about it: 'Type Object considered hilarious'. I got a rude reply from the original author, which I guess I expected, but also an incredible response from the list owner, saying I should recast my objections in the form of a design pattern. That lost it for me. True story. Moral: don't take this religion, or any IT religion, too seriously. They come around every 18 months or so with the regularity of the next bit of Moore's Law. I've seen dozens of them come and go since 1971, all with something to say, all 90% nonsense.
See here for a longer version of this incident.

Design pattern

Hi all
I am developing a enterprise application using Struts 1.2,Spring 2.0 and Hibernate 3.0.Now i am concentrating in design pattern of my application. I read many article, there I Could find many pattern like session facade, business delegate, service locator, layered pattern ,etc. I came to know that business delegate and session facade are useful for EJB based application with distributed environment. My application does not need distributed environment. I have a plan to implement design pattern as follows
Presentation layer -Struts
Data Transfer object or Value object -with support from Struts form Bean
Business layer - Spring ,Transaction management with spring AOP ,
Persistence layer -Hibernate with spring support.
Service locator - implemented by Spring application context file.
IN the above, layers orders may change, pls ignore that.
Please suggest ,it is a correct design or any enhancement can be given to this pattern.
Any with relevant examples are really appreciated
Thanks in advance

For Data Access layer you will be having a Query or stored procedure defined which will be in Sync with your Orchestration . So whenever there is request coming from UI you need to call this Orchestration through schema or Orchestration exposed as web service.
So there are two pointers.
1) consume your Query or Stored procedure inside your Orchestration (with WCF SQL or WCF Oracle adapter). various articles exist to implement it
http://msdn.microsoft.com/en-us/library/dd787968.aspx
http://btsguru.blogspot.in/2011/08/wcf-sql-adapter-stored-procedure.html
2) Once done you can expose your request response schema as web service
http://msdn.microsoft.com/en-us/library/bb246047.aspx
Thanks
Abhishek

Design Patterns in Dynamic Programming

I mentioned this on a thread some time ago - that many of the GoF patterns disappear in languages such as Lisp, but didn't have the reference handy. Came across it again today so I thought I'd post the link:
http://www.norvig.com/design-patterns/
Pete

hi sourdi
Below are the list of Design pattern in abap .
Singleton: ensuring single class instantiation
Adapter: making class interfaces compatible
Factory: encapsulating object creation
MVC: decoupling business logic from the view
Facade: providing a simplified interface
Composite: treating individual objects and compositions uniformly
Decorator: forming a dynamic chain of components to be used as one by the client
regards
chinnaiya P

Design Patterns in ABAP.

Hi,
I want to know about the Design Patterns in ABAP.
Regards,
Sourav

hi sourdi
Below are the list of Design pattern in abap .
Singleton: ensuring single class instantiation
Adapter: making class interfaces compatible
Factory: encapsulating object creation
MVC: decoupling business logic from the view
Facade: providing a simplified interface
Composite: treating individual objects and compositions uniformly
Decorator: forming a dynamic chain of components to be used as one by the client
regards
chinnaiya P

Common Design Patterns For Webservices

Hi All,
I am creating a webservice which generate the result by iterating multiple webservices serially(Workflow) or parallel(Aggregator).
What are the common Design patterns I can apply here ? Currently my application flow is
WebserviceEndpoint-> WebserviceDelegate(POJO) -> Helper Classes ->Aggregator/Workflow Impl which uses WSClients(JAX-WS Stub)
Do we need to maintain separate DTO for passing Request to the Inner layers ?
Please share your comments.
Thanks,
Paul

Thanks for your valuable time
I have 3 Webservices A(Provider),B,C. Service 'A' is a consumer of service 'B' and 'C'.
A - is exposed to Consumers, A act as a proxy layer for service B and abstract 'C' from users ,Service 'A' only do the service orchestration .Service 'A' using data from Service 'B' and 'C'
B – is of same specification as that of Service A (Service B contains All operation defined on A +Internal operation for service A).Internal Webservice which act as active datasource.Request and response structure is same as that of Service 'A'.
C – is different external service ,requests for Invoking Service 'C' need to be generated from Consumer Request and operations exposed in Service 'B'. External Webservice act as active Data source. Enrich the service 'B' output using service 'C' ,This is done by Service 'A'
I have done this using following components.
WebserviceEndpoint-> WebserviceFacade(POJO) -> Helper Classes ->Aggregator/Workflow Impl which uses WSClients(JAX-WS Stub)
It will be great If some of you can suggest a good logical separation for Service 'A' ? Is above logical separation is correct?
Thanks,
Paul

When I use SmartSync Notifier/ Observer design pattern

Hi all,
I have development a simple SmartSync Application with S01 syncBO type.
I not use SmartSync Notifier/ Observer design pattern for read the local syncbo and local delta.
When I have to use and I have to implement the SmartSync Notifier/ Observer design pattern ?

Hi Rocco,
<b>SmartSync uses Notifier/Observer design pattern for applications to access inbox/outbox. Application has a read-access to the passed SyncBoOutDelta instance during the notification</b>
The usage of this API depending upon your custom requirement. If u want to monitor the number of new records(for example sales or like thAT) u have created in the client device , then that delta records will be there in the Smart Sync Outbox. If u want to monitor this new records then u have to use the API related with (Outbox - SyncBoOutDelta)..
Then comes the Inbox.The new records came from the Server will be there in the inbox of the MI client. This new records may be the response of number of new records u ahve created in the client device . If u want to monitor the number of new records that has downloaded to the MI client , then u have to make use of the SmartSyncInboxDelta..
Using this APIs , u can also find out the errors happened during the particular synchronization. For this APIs are also available...
refer these helps also..
SyncBoChange
This interface is the base interface to describe SyncBo delta change. Application should not use the interface directly, instead, use its sub interfaces - SyncBoInDelta, SyncBoOutDelta.
http://media.sdn.sap.com/public/html/submitted_docs/MI/MDK_2.5/content/javadoc/com/sap/ip/me/api/smartsync/SyncBoChange.html
SyncBoInDelta
http://media.sdn.sap.com/public/html/submitted_docs/MI/MDK_2.5/content/javadoc/com/sap/ip/me/api/smartsync/SyncBoInDelta.html
SyncBoInDelta is used to apply SyncBo delta data from backend to client. The SyncBoInDelta could may be a delta data from either the backend or other devices, or a response to the previously uploaded SyncBoOutDelta from the client, which can be distinguisehd by the SyncReply information included within the SyncBoInDelta
SyncBoOutDelta
SmartSync uses Notifier/Observer design pattern for applications to access inbox/outbox. Application has a read-access to the passed SyncBoOutDelta instance during the notification
http://media.sdn.sap.com/public/html/submitted_docs/MI/MDK_2.5/content/javadoc/com/sap/ip/me/api/smartsync/SyncBoOutDelta.html
Regards
Kishor Gopinathan

Cor design pattern

I use cor design pattern little different than what I see in google.
here is m y cor
     public static abstract class CORHandler    {
          CORHandler nextHandler;
          public void process(){
               if(canHandleRequest()){
                    handleRequest();
               }else {
                    if(nextHandler!=null) nextHandler.process();
          protected abstract boolean canHandleRequest();
          protected abstract void handleRequest();
          public void setNextHandler(CORHandler corHandler){
               nextHandler=corHandler;
     }this serves most of my need and also I can override process method for change behaviour .
this code helps me save lots of if/else conditions , I am not passing any object to the method here reason is I use this always as inner class inside a method so I can access all final fields
advice me is this right when applying cor pattern?

Making it a base class increases connectivity to no good purpose.
It violates the concept of inheritance by making the objects COR classes which is not what they are.
It violates the principal of COR in that the intent is to handle a responsibility not all responsibilities. This same problem obscures the pattern as well by eliminating the objects to be acted upon.

Suggest what design pattern is applicable for my case

I have an object called GrantAward , these awards I have to show to the user for selection
1. I call a web service to get list of GrantAwards.
2.for each GrantAward check if this is present in my database
a. if not there insert
3.for each GrantAward check some conditions
a if satisfied add to the list to show to user
b if not satisfied do not add to list .
these are the steps involved before I can show the GrantAwards to user for selection , please suggest me what design pattern can I use ?

I'm not sure you want to hunt for patterns when you already know what you are implementing. A lot of people have pattern fever. Patterns are useful constructs for communicating design ideas and enforcing best practices. But I rarely go out and hunt for a specific pattern (or name my objects after patterns). If you are doing a heavyweight methodology with RUP or something similar, I could see stereotyping your UML with patterns.
That having been said, you already have a Facade with your service. You are undoubtedly using DataAccessObject to fetch your records. Your conditions could be implemented with a ChainOfResponsibility and/or Strategy pattern. What you return could be a Composite. Potentially the request and response are a Command. And your overall architecture could be MVC.
But IMO that is overkill.
- Saish

Design pattern for quiz module

Hello fellow developers.
I am making/refactoring a module in a jee mobileplatform. It's a quiz module where the enduser participates via sms. Now, I am trying to redesign the module and I am thinking about using the state pattern for this, where the user can be in i.e the following states: StartQuizState(welcomemessage and first question), NextQuestionState, NoAnswerState(the user sent an empty or no valid response), QuizFinishedState(sum up the points etc), and maybe a BonusState if the user makes x points within a specific time limit.
I was wondering if anyone had any comments on my choice of pattern for this module :)
Thanks in advance for any comments,
Best regards,
Eivind

Good morning Saish, sorry for my late response.
First of all - thanks again for showing such interest in my "discussion", and my deepest apologies for my grammatical error hehe, I was tired and wrote a little bit too fast. Normally I take great pride in writing correctly :)
I would also like to say that many, many times before, these forums, and others, have helped me when stuck in a programming problem or other problems related to software. So without all those people out there willing to spend their free time answering questions from people like me, a lot of us wouldn't be able to solve whatever problem we might have, and basically the general experience amongst inexperienced programmers would evolve much slower. So Saish, thanks to people like you there are a lot of happy programmers out there. It is very important for those of us working with development, to share whatever knowledge we might have.
Anyway back to the discussion:)
I totally agree, the state is absolutely the Quiz, not the contestant of the quiz. I just read a Head first design patterns (a great book by the way!), and I was a bit to hung up on using patterns instead of looking for a solution that works. So what I have done so far, refactoring my solution:
I have the following models:
- Quiz
- Contestant
- Answer
- QuizManager
Quiz Object
The Quiz model that represents the actual quiz, which contains a list of Question objects, and Answer objects. The quiz has a int constant QUIZ_STATE, and the possible states:
private static final int START_QUIZ_STATE = 0;
private static final int FINISH_QUIZ_STATE = 1;
private static final int NEXT_QUESTION_STATE = 2;
private static final int REPEAT_QUESTION_STATE = 3;
private int quizState = START_QUIZ_STATE;
As you can see the quizState defaults to START_QUIZ_STATE. The first thing I do when the contestant enters, is to check the state of the quiz, if he already is an contestant, if the quiz is finished etc.
Then I continue and process the quiz based on the state of the quiz (this time everything in one class - a quizmanager).
Contestant Object
Contestant model containing what questions are already answered, number of points and so on.
Answer Object
The Answer object is created if the contestant sends an answer and his answer corresponds with the alternatives in the Answer object. E.g if the answer alternatives are a) 100 kilometers and b) 20 kilometers, and the contestant sends an answer c, it is considered as no answer, and the last question is repeated, if the contestant sends a, or b, his answered is compared with the current Answer alternative, and a new question is sent him.
I have some database tables for managing this module, and basically a Quiz is configured as an XML, where 1 xml is a quiz, and 1 quiz xml can contain many question and answer tags. These are read upon quiz start, and Quiz, Answer, and Question objects are created. Every time a new contestant enters, a new Contestant object is ofcoursed created.
All the logic takes place in the previously mentioned QuizManager. Any comments on the solution so far would be greatly appreciated.
If interesting to anyone I can post the classes when I am finished with the module, as a standalone java application without a database.
Regards,
Eivind

Design Pattern for execution queue

Anyone know of any good design patterns for using a JMS Queue and MDB's
          as async
          execution queue which maintains execution order by some key


Enforced ordering on redelivery will be supported in the
          next release, but only if the application clamps the pipe-line
          size down to its minimum and the MDB pool size down to one.
          I don't think enforced ordering is supported in the current release.
          We are looking at least partially addressing the general design
          pattern below in the release after next. I don't think I can
          get away with being more specific. (Sorry.) Currently, I
          think something along the line of Larry's solution is the only way to
          accomplish it. Interestingly, the recent thread started
          by "[email protected]" on correlating requests and responses
          seems to be somewhat related.
          Tom, BEA
          Larry Presswood wrote:
          > Well you are both correct however we have something which works
          > however it does involve some threading primitives which generally is not
          > a good idea
          > inside wlas but seems to work.
          >
          >
          > Generally have a singleton on the server which has slots for each key
          > with message
          > numbering for each message and force a wait if message for key is out of
          > order
          > during fifo processing rules. IE do what things you can do in parallel
          > but gate for
          > the last step.
          >
          > I think there is a general remote execution pattern out there.
          >
          > The general problem to solve is this:
          >
          > In a messaging system you want to process messages for each key/session
          > in order however
          > with a large number of sessions its possible to parallel messages for
          > different sessions
          >
          > Otherewise you can either create custom queues or a topic with a
          > selector and then
          > create custom consumers which does not behave as well from a resource
          > perspective
          > as MDB's do.
          >
          >
          >
          >
          >
          >
          >
          > Nick Minutello wrote:
          >
          >>I may be completely wrong - but I think that Larry is referring to the inherant
          >>out-of-order message consumption that you get when using MDB pools to consume
          >>from a Queue.
          >>
          >>In short, the only design pattern here is to deploy the MDB to only one machine
          >>in the cluster - and set the pool size to 1.
          >>
          >>In-order execution is incompatible with the parallel execution that MDB's give
          >>you.
          >>
          >>-Nick
          >>
          >>
          >>
          >>Tom Barnes <[email protected]> wrote:
          >>
          >>
          >>>Hi Larry,
          >>>
          >>>Generally, I think it is best to have a seperate queue per key if the
          >>>
          >>>number of keys is small. This prevents starvation of a particular
          >>>message. For example when handling message-priority, low priority gets
          >>>
          >>>an MDB pool of size 1, high priority gets and MDB pool of size 10.
          >>>
          >>>Note that WebLogic JMS allows a queue to specify a sort-order keys based
          >>>on arbitrary message fields. Note that the in-flight message pipe-line
          >>>
          >>>between server and asynchronous clients is unsorted.
          >>>
          >>>Tom, BEA
          >>>
          >>>Larry Presswood wrote:
          >>>
          >>>
          >>>>Anyone know of any good design patterns for using a JMS Queue and MDB's
          >>>>
          >>>>
          >>>>as async
          >>>>execution queue which maintains execution order by some key
          >>>>
          >>>>
          >>>>
          >>
          >>
          >>
          >

Chain of Responsibility Design Pattern

Similar Messages

Maybe you are looking for