Singleton object in clustered enviornment

Hi,
          In my web application which is deployed in clustered enviornment, I am facing problem for singleton object.
          I need to share object among all servers in the clustered.
          I am using weblogic server 9.2. I have tried its Singleton services, but it doesnt work as expected.
          what could be other solution to solve the problem?

No. If you need this type of functionality, use Coherence.
          http://www.tangosol.com/coherence.jsp
          Peace,
          Cameron Purdy
          Tangosol, Inc.
          http://www.tangosol.com/coherence.jsp
          Tangosol Coherence: Clustered Replicated Cache for Weblogic
          "Ferruccio" <[email protected]> wrote in message
          news:[email protected]..
          > Hi,
          > I have a very basic question. In a WebLogic clustered
          > environment, is a Singleton replicated? In other words, if the
          > mySingleton on node A in a cluster is updated with a piece of data,
          > will this show in the mySingleton in node B?
          >
          > Thanks
          >
          > Ciao
          > Ferruccio

Similar Messages

Problem with lookup query in clustered enviornment!!!

Hi,
I have a lookup query in object form which will bring all users in OIM. It works fine on Standalone. But what I really dont understand is that when I use the same lookup in clustered enviornment(weblogic cluster and oracle DB cluster) it doesnt work. it brings up empty lookup.
My lookup query is configured with the following properties:
Defined field in object form
- LookupQuery, Select usr_login, usr_first_name, usr_last_name from usr
- Column options, User ID,First Name,Last Name
- Column Names,usr_login,usr_first_name,usr_last_name
- Lookup column name, usr_login
- Column width, 10,100
Thanks,
doki
Edited by: doki.prasad on Jun 9, 2009 11:25 AM

Did you resolve this issue? I see a similar problem
Thanks.

SingleTon object of WebServices (Please be specific as required and not be generic)

// Singleton Object of viewservice
private ViewService WorkListView = null;
ViewServiceObjectCreation viewstrWorkListView = ViewServiceObjectCreation.GetObject();
// Object Creation
public class ViewServiceObjectCreation
        private static ViewServiceObjectCreation singleTonObject=null;
        private static readonly object lockingObject = new object();
        private ViewServiceObjectCreation()
        public static ViewServiceObjectCreation GetObject()
            if(singleTonObject == null)
                 lock (lockingObject)
                      if(singleTonObject == null)
                           singleTonObject = new ViewServiceObjectCreation();
            return singleTonObject;
But this is not creating singleton object of webservice. How to create singleton object of webservice.
Vivek

Read my post again: Please describe your concrete problem which made you think you need a singelton.
A singelton only works per domain. Thus it will not help in your sketched scenario. Cause it cannot prevent an user or administrator for starting another domain (a.k.a. process).
In this case you should consider using a mutex, which is aquired when the web service is started and released when stopped.
While singeltons are a cool pattern per se, they are one of those evil ones. They are often not a correct solution and much worse, the kill testability cause the represent a global state.

ThreadSafeLazyLoading of a Singleton Object

Hi,
Do anyone know the mechanism and necessity of this ThreadSafe Lazy loading of a singleton object?
Thanks.

I know the mechanism (I believe Enum is the popular choice these days).
The necessity is dubious. Most people don't need lazy loading singletons, they just think it's a part of the Singleton pattern.

Multiple instances of a Singleton-Object by updaterule ?

Hi folks,
I'm trying to load > 1 Mio. records from an ODS into another InfoProvider. Every record gets some keyfigures out of a very very expensive table-join.
I tried creating this join in an ABAP-Singleton-Object to reduce uploading-time.
This object holds a private-static attribute 'instance' as a reference to a instance of the object and a public-static 'getInstance()'-method, which returns the 'instance'-value. This method is standard-Singleton-like designed.
Then I created a process-chain with:
- an ABAP-process, which calls the 'getInstance()'-method
of this Singleton.
At the first pass this method calls the constructor and
after that a private method, which creates the join and
holds the result in an internal table.
So the constructor is empty.
- after that the data should be transfered (by an Info-
Package) from the ODS to the other InfoProvider. In some
fields of the update-rule and in the startroutine of
the rule the 'getInstance()'-method of the Singleton is
been called and by this reference to the only (so I
thought) instance some other methods should return a
calculated value out of the join.
So theory .... the startroutine is been called for multiple datapackages (no problem) --- but for every package in the startroutine the 'getInstance()'-method calls the constructor, so I get multiple instances of a Singleton.
The time-gap between the package-calls is > 10 secs., so the static-attribute should been set immediately in the first pass of the 'getInstance()', since the constructor is empty.
Any ideas ???
Bye Ralf

-/-

Singleton Object With Anonymouse Methods

I'm trying to create a singleton object using a GUI interface. The problem which I'm getting is that I can't find a way to create the object inside an .addActionListener() method while storing it for other .addActionListener() methods.
CreditCard.java
   public class CreditCard {
       private static CreditCard uniqueInstance = null;
      final String creditCardNumber;
      String name;
      float creditLimit;
      float creditBalance;
       private CreditCard(String creditCardNumber,String name,float creditLimit) {
           this.creditCardNumber = creditCardNumber;
           this.name = name;
           this.creditLimit = creditLimit;
       public static CreditCard getInstance(String creditCardNumber,String name,float creditLimit)
           if (uniqueInstance == null)
               uniqueInstance = new CreditCard (creditCardNumber, name, creditLimit);
           return uniqueInstance;
Here's some code
main class call
         CreditCard Student;
         JButton enterCardButton = new JButton("Edit Card");
         enterCardButton.addActionListener(
                new ActionListener() {
                   public void actionPerformed(ActionEvent ae) {
                     String cCNumber = creditCardNumberField.getText();
                     String cName = nameField.getText();
                     String cStringLimit = creditLimitField.getText();
                     float cLimit = Float.parseFloat(cStringLimit);
                     Student = CreditCard.getInstance(cCNumber, cName, cLimit);
         buttonPanel.add(enterCardButton);Of course the compiler error I get is that you must declare the CreditCard Student to be final. But if i make it final, I cannot create it in the method! I'm stuck :/

You do need to call getInstance on a
singleton. The compiler doesn't treat them specially.
So, outside of the singleton itself you need
something like
String ccNumber =
CreditCard.getInstance().getCreditCardNumber();(and it's probably best to define accessor methods
for singleton fields).I actually do this for my other methods, thank you malcolmmc :). But the problem right now is the inablity to create the class using the ActionListener. I'm goign to Paste my whole code segment this time to try to provide a better picture.
*          MAIN CLASS
package Project2;
   import java.awt.BorderLayout;
   import java.awt.GridLayout;
   import java.awt.event.ActionEvent;
   import java.awt.event.ActionListener;
   import javax.swing.DefaultListModel;
   import javax.swing.JButton;
   import javax.swing.JFrame;
   import javax.swing.JLabel;
   import javax.swing.JList;
   import javax.swing.JPanel;
   import javax.swing.JScrollPane;
   import javax.swing.JTextField;
   import java.io.*;
   import java.lang.*;
   import java.util.*;
    public class Project2TestFrame {
      // public enum transactionType { LIMIT_CHANGE, CHARGE, PAYMENT}
       public static JFrame getTestFrame() {
         JFrame testFrame = new JFrame("Project 2 Tester");
      // Build the data portion of the frame
         final JTextField creditCardNumberField = new JTextField(15);
         final JTextField nameField = new JTextField(15);
         final JTextField creditLimitField = new JTextField(15);
         final JTextField chargeAmountField = new JTextField(15);
         JPanel dataPanel = new JPanel();
         dataPanel.setLayout(new GridLayout(4,2));
         dataPanel.add(new JLabel("Credit Card Number"));
         dataPanel.add(creditCardNumberField);
         dataPanel.add(new JLabel("Name"));
         dataPanel.add(nameField);
         dataPanel.add(new JLabel("Credit Limit"));
         dataPanel.add(creditLimitField);
         dataPanel.add(new JLabel("Charge Amount"));
         dataPanel.add(chargeAmountField);
         testFrame.add(dataPanel, BorderLayout.CENTER);
      // Add the buttons to the frame. Note only the Exit button is
      // given here. You should add other buttons.
         JPanel southPanel = new JPanel();
         southPanel.setLayout(new GridLayout(2,1));
         JPanel buttonPanel = new JPanel();
         southPanel.add(buttonPanel);
      // Add the messageField and
         String[] sarray = {"", "", "", "", ""};
         DefaultListModel dlm = new DefaultListModel();
         dlm.copyInto(sarray);
         final JList messageList = new JList(dlm);
         final JScrollPane jsp = new JScrollPane(messageList);
         southPanel.add(jsp);
         testFrame.add(southPanel, BorderLayout.SOUTH);
      // Add your buttons here.
         //Main Class Instance of CreditCard class.
         CreditCard Student;
         JButton enterCardButton = new JButton("Edit Card");
         enterCardButton.addActionListener(
                new ActionListener() {
                   public void actionPerformed(ActionEvent ae) {
                     String cCNumber = creditCardNumberField.getText();
                     String cName = nameField.getText();
                     String cStringLimit = creditLimitField.getText();
                     float cLimit = Float.parseFloat(cStringLimit);
                     //***Compile Error** Needs to be final, but if final still complains
                     Student = CreditCard.getInstance(cCNumber, cName, cLimit);
         buttonPanel.add(enterCardButton);
         JButton chargeButton = new JButton("Charge Credit Card");
         chargeButton.addActionListener(
                new ActionListener() {
                   public void actionPerformed(ActionEvent ae) {
                       String cStringCharge = chargeAmountField.getText();
                       float cAmount = Float.parseFloat(cStringCharge);
         buttonPanel.add(chargeButton);
         JButton paymentButton = new JButton("Payment");
         paymentButton.addActionListener(
                new ActionListener() {
                   public void actionPerformed(ActionEvent ae) {
         buttonPanel.add(paymentButton);
         JButton dummyButton = new JButton("Transactions");
         buttonPanel.add(dummyButton);
         dummyButton.addActionListener(
                new ActionListener() {
                   public void actionPerformed(ActionEvent ae) {
                     DefaultListModel messageData = (DefaultListModel)messageList.getModel();
                     messageData.clear();
                     messageData.addElement("String1");
                     messageData.addElement("String2");
                     messageData.addElement("String3");
         JButton exitButton = new JButton("Exit");
         buttonPanel.add(exitButton);
         exitButton.addActionListener(
                new ActionListener() {
                   public void actionPerformed(ActionEvent ae) {
                     System.exit(0);
      // Finish and return data.
         return testFrame;
    * @param args
       public static void main(String[] args) {
         JFrame p2tf = getTestFrame();
         p2tf.pack();
         p2tf.setVisible(true);
    class Transaction {
      public enum transactionType { LIMIT_CHANGE, CHARGE, PAYMENT}
    //enum transactionType;
      int date;
      int amount;
       public Transaction(int date, int amount)
        //this.transactionType = transactionType;
         this.date = date;
         this.amount = amount;
* CreditCard.java
* Created on June 21, 2006, 9:27 AM
* To change this template, choose Tools | Options and locate the template under
* the Source Creation and Management node. Right-click the template and choose
* Open. You can then make changes to the template in the Source Editor.
package Project2;
   import java.io.*;
   import java.lang.*;
   import java.util.*;
   public class CreditCard {
       private static CreditCard uniqueInstance = null;
      final String creditCardNumber;
      String name;
      float creditLimit;
      float creditBalance;
      ArrayList<String> transactionHistory;
       private CreditCard(String creditCardNumber,String name,float creditLimit) {
           this.creditCardNumber = creditCardNumber;
           this.name = name;
           this.creditLimit = creditLimit;
       public static CreditCard getInstance(String creditCardNumber,String name,float creditLimit)
           if (uniqueInstance == null)
               uniqueInstance = new CreditCard (creditCardNumber, name, creditLimit);
           return uniqueInstance;
       public void setName(String name)
         this.name = name;
       public String getName()
         return this.name;
       public String getCreditCardNumber()
         return this.creditCardNumber;
       public float getCreditLimit()
         return this.creditLimit;
       public void setCreditLimit(float creditLimit)
         this.creditLimit = creditLimit;
       public float getAvailableCredit()
         return this.creditBalance;
       public void addCharge(float chargeAmount)
        this.creditBalance -= chargeAmount;
       public void paymentReceived(float paymentAmount)
        this.creditBalance += paymentAmount;
    //public String[] getTransactions()
    //    return this.transactionHistory.toArray();
   class NumberOutOfBoundsException extends Exception {
    private int number;
    public NumberOutOfBoundsException() {
        number = 0;
    public NumberOutOfBoundsException(String Message) {
        super(Message);
    public NumberOutOfBoundsException(int number) {
        this.number = number;
    public NumberOutOfBoundsException(String Message, int number) {
        super(Message);
        this.number = number;
    public int getNumber() {
        return number;
}

What is the role of singleton property in clustered environment.

Hi
Could anyone suggest links or tutorials explaining the singleton property and its importance in clustered environment(both active-active and active-passive).
Please anyone explain this .
I've googled and couldn't understand the explanations which I've gone through.
Appreciate your help.
Regards,
Dev...

HI,
click on ur node and on the singleton proprty click F1. u will get the full detail.
The property "Singleton" specifies the number of instances that can exist in a dependent context node (that does not belong directly to the root node).
If the property "Singleton" is set, exactly one instance of the node exists. Its content changes when the lead selection of the parent node changes.
If the property "Singleton" is not set, one instance per parent instance exists. The content of the instances does not change when the lead selection of the parent changes.

How to create more kinds of singleton objects?

Hello,
in my application I need to create more objects. Every object does during its creation same actions (they differ only in one parameter) and add some own methods.
These all objects should behave as a singleton pattern.
Could you help me (different design pattern) how to achieve this?
Thank you.

I have such slightly modified Multiton pattern class.
Now I want create a method that returns database server IP address from database setting type - try to tell me (exactly) how to write this method.
public class Setting {
     public enum Type {
          database, application, mail
     private static final Map<Object, Setting> instances = new HashMap<Object, Setting>();
     protected PropertiesFile file = null;
     private Setting(Setting.Type key) throws IOException {
          file = new PropertiesFile(key.toString() + ".properties");
     public static Setting getDatabase() throws IOException {
          return Setting.getInstance(Setting.Type.database);
     public static Setting getApplication() throws IOException {
          return Setting.getInstance(Setting.Type.application);
     public static Setting getMail() throws IOException {
          return Setting.getInstance(Setting.Type.mail);
     private static Setting getInstance(Setting.Type key) throws IOException {
          Setting instance = instances.get(key);
          if (instance == null) {
               instance = new Setting(key);
               instances.put(key, instance);
          return instance;
}

Singleton behaviour in clustered environment

Hi,
          I have a very basic question. In a WebLogic clustered
          environment, is a Singleton replicated? In other words, if the
          mySingleton on node A in a cluster is updated with a piece of data,
          will this show in the mySingleton in node B?
          Thanks
          Ciao
          Ferruccio


No. If you need this type of functionality, use Coherence.
          http://www.tangosol.com/coherence.jsp
          Peace,
          Cameron Purdy
          Tangosol, Inc.
          http://www.tangosol.com/coherence.jsp
          Tangosol Coherence: Clustered Replicated Cache for Weblogic
          "Ferruccio" <[email protected]> wrote in message
          news:[email protected]..
          > Hi,
          > I have a very basic question. In a WebLogic clustered
          > environment, is a Singleton replicated? In other words, if the
          > mySingleton on node A in a cluster is updated with a piece of data,
          > will this show in the mySingleton in node B?
          >
          > Thanks
          >
          > Ciao
          > Ferruccio

How can we destroy the instance of a singleton object?

I think by writing a method like getInstance and making null in that method will not the correct answer of this. Can someone tell me what should I do.

why do you need to destroy the singleton?
normally..it should live for the duration of the application.
most singleton i've worked with are used by sevarals different classes.
if you're singleton use by only one class...refactor your code to make the singleton an inner class. so the singleton will be destroy when that class is no longer references 9and gc kick in)
if the singleton is share among several class...you can have a destroy method...like destroyInstance() where you null the singleton. keep in mind about synchronization of the method as well as the instance ... example createInstance() and destroyInstance() get call at the same time.. Also, make sure you have condition to check to determine if your singleton class is null or not
example
MySingleton s = MySingleton.createInstance();
Object obj = s.getData(); // what happen when another thread call MySingleton.destroyInstance() you're s.getData would result in NullPointerException
so..it's not wise to destroy a singleton.
I think what is better for your app is an Object Pool that create new instance (if none exist) and hand it out to any requester...and recycle the object...or null it after use)

Light memory singleton object.

Let's say you wanna build singleton but you want it to be kept in memory as long as someone is using it. This is possible if the instance static object is maintained via Soft or Weak reference. Here is how it is done:
class MySingleton
private static Object objLock = new Object();
private static WeakReference instance = null;
   * Gets the instance of this class.
   * @return MySingleton
public static MySingleton getInstance()
    synchronized (objLock)
      if (instance == null || instance.get() == null)
        instance = new WeakReference(new MySingleton());
    return (MySingleton)instance.get();
}

Once you create the instance of the Sibgleton the GC
CANNOT clear it because of the static refernec to it.
If you don't know that fact first read more. I do understand what you want to do. I have been programming in Java for 10 years and have never heard about a person who has needed what you are trying to do, and I don't think that it is a good idea.
I can of course be 100% wrong on this since there are many different environments.
With the
weak or soft reference the GC can clear it anytime it
goes or needs memory (depending whether is weak or
soft). I know what weak a soft references do, but I don't understand why you want to use them. Your singleton will not be a singleton since instances will be created and destroyed. Creating your "heavy" object many times is worse than creating it one time.
That's the usefulness. It isn't useful. It's a singleton which isn't a singleton, and it's only good for read only data.
Let's say you have a
module that operates with huge objects and that
module is singleton. Once the application gets the
singleton it's created and never destroyed until the
app goes away. This way you ensure that this memory
is released after you don't use the singleton. Haven't you considered that you might create that huge object many many times with your design?
Kaj

Singleton Object

Hi all,
is it possible to create systemwide unique objects?
I know of the singleton class, but I do not want to create a unique class instance,
but I want to create some kind of factory class which gives unique objects.
For instance I want to create delivery objects and I do not want multiple users
to create the same delivery object (you can imagine why).
How can I achieve this?
Greetings Fred.

What you are doing here is as you've found out is to try and get round the limits of using OO in a " Classic Relational Database" system.
When SAP starts using OBDBMS (Object database system) and can geuninely save objects as "persistent" in this type of database system then it probably can be done.
However in the current SAP system complex objects can only be built from data held in large numbers of different tables which may have a complex relationship (by virtue of the RDBMS - relational data base system) so "Locking" this stuff system wide is not really (AFAIK) an option.
A possibility is to use the JDO in JAVA where you can create genuine persistant objects which are held in a type of "OBDBMS" or Object data base management system as opposed to the traditional RDBMS (Relational model) that SAP uses.
The JAVA JDO handles the actual SAP data base updates and maintains Data integrity between the JAVA object and the various SAP tables.
Classic ABAP currently isn't really geared to handle this yet. OO Abap is a HUGE improvement but still essentially limited by use of the underlying RDBMS (relational data base system) and (internal) SQL queries to retrieve the data from various tables when "constructing" / instantiating your object.
Graham's suggestion seems to be the nearest you can get to answering this problem.
However if anybody does have an answer to this I'll also be interested so please post on this thread.

Synchronizing Creation of a Singleton Object

I've encountered a synchronization issue I haven't seen covered in the material I've read so far. My server app uses message driven beans that maintain a variety of lookup tables (maps, actually), to do data validation. Each map is a singleton, and is created with lazy instantiation (i.e., not created until requested the first time). The problem is this: I want to prevent one thread from trying to read the map while another is creating it. Until the map is created, there's nothing to synchronize, but after it's created, there's no point in synchronizing either, because it will never change. The only time I need synchronization is during the one time the map is created. I don't want to synchronize later accesses to the map, for performance reasons. The code examples I've seen so far don't address this particular issue. Here's a code snippet of how I'm thinking of implementing this. Any comments or criticisms would be greatly appreciated.
This code is from the the superclass of my data validation classes. The design is that a thread/bean needing map access would call getMapIfNeeded(), then do the lookup. The buildMap() method calls a separate, unsynchronized database class
* Builds the lookup map if it doesn’t already exist.
* @param attribute Name of the attribute in table <span class="oracle">efm_accp_valu</span>.
* @param map Map against which we’ll validate values. If non-null, nothing is done.
* @return The map (newly created if the input argument was <code>null</code>).
* @throws APISystemException If a serious system error occurs.
* @see #getListIfNeeded(String, List)
protected static Map getMapIfNeeded(final String attribute, Map map)
   throws APISystemException
   if (map == null)
      map = buildMap(attribute);
   return map;
* Builds the lookup map if it doesn’t already exist.
* @param attribute Name of the attribute in table <span class="oracle">efm_accp_valu</span>.
* @param map Map against which we’ll validate values. If non-null, nothing is done.
* @return The map (newly created if the input argument was <code>null</code>).
* @throws APISystemException If a serious system error occurs.
* @see #getListIfNeeded(String, List)
protected static synchronized Map buildMap(final String attribute)
   throws APISystemException
   return AcceptableValueDAO.getMap(attribute);
{code}

After doing some more research, I've concluded that, in my scenario at least, a better solution is to create the maps in static blocks. This avoids synchronization issues altogether, with the disadvantage being that if a database exception is thrown in the static block, I can't do much except print the stack trace. If anyone knows better, don't be shy about speaking up!

Clarification needed on JDBC Connection Pool in Clustered enviornment

Hi All,
          Although I went through the bea online documentation , its not clear how
          JDBC connection pool works in clustered environment.
          If anyone can please answer following questions, it would be a great help.
          1) Do I need to create identical connection pools (with identical ACLs) on
          each WebLogic Server in the cluster ?
          2) Online documentation says " If you create an identical JDBC DataSource in
          each clustered WebLogic Server instance and configure those DataSources to
          use different connection pools, the cluster can support load balancing for
          JDBC connections. " what actually this means
          3) What's the use of "JDBC MultiPools " ? Is it same as "JDBC metapool "
          Thanks
          Regards
          Nalika


See comments inline...
          Nalika wrote:
          > Hi All,
          >
          > Although I went through the bea online documentation , its not clear how
          > JDBC connection pool works in clustered environment.
          > If anyone can please answer following questions, it would be a great help.
          >
          > 1) Do I need to create identical connection pools (with identical ACLs) on
          > each WebLogic Server in the cluster ?
          I don't believe that it is strictly necessary to do this but it is certainly the
          most common configuration and probably the preferred one as well. WLS is smart
          enough to automatically use its Type 3 driver to route requests to a connection
          on another server but this type of server-to-server communication can have an
          impact on performance and scalability.
          > 2) Online documentation says " If you create an identical JDBC DataSource in
          > each clustered WebLogic Server instance and configure those DataSources to
          > use different connection pools, the cluster can support load balancing for
          > JDBC connections. " what actually this means
          Don't read too much into this. All that this is saying is that application
          components in each server will "prefer" to use their local DataSource (all other
          things being equal) and since other clustering technology (or things like
          hardware load balancers) are spreading the load across the servers, you will
          also spread the load across the different connection pools.
          > 3) What's the use of "JDBC MultiPools " ? Is it same as "JDBC metapool "
          Yes, these are one and the same.
          Hope this helps,
          Robert

Singletons and clusters

Hi,
Does anyone have any idea on what to do with singletons on a cluster ?
Right now we have 3 singleton, main business objects that handle core
method calls.
If we decide to cluster , how do we deal with singletons across clusters
-Sam

Does anyone have any idea of the performance implications of moving singleton
objects to RMI objects for clustering ?
We have an Environment Object that is encapsulated in a Servlet so that PageObjects
can be loaded at startup. I could easily make the Environment Object an RMI object
but I would be creating extra network traffic from each cluster participant.
thanks
Joe Ryan
Don Ferguson wrote:
Rickard Öberg wrote:
Hey
Bytecode wrote:
My point exactly.
A singleton replicated ?? Isnt that a conradiction in terms ??
What state are these different instances going to be in ?? Excatly identical
at all points of time ??If I understood Don right it's the stub that will be replicated. Not
the RMI-object. So all stubs in the clustered JNDI-tree will point to
the same RMI-object.
/RickardYes, that's the idea.
-Don

Singleton object in clustered enviornment

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