Confused about singletons in servlets

Hello,
A DatabaseManager object is to be created within my RegistrationServlet. I wish to implement this DatabaseManager class as a singleton. I understand how the first client that invokes the RegistrationServlet will be able to create an instance of the DatabaseManager. However, what happens when a second client invokes the RegistrationServlet while the first client is still using the DatabaseManager instance? What is the best way to deal with this? Is an exception thrown?
Thanks.

Depends on how you implement the Singleton, of course.
A Singleton might be a bad idea. Sounds like a bottleneck waiting to happen.
That's a database isolation issue. It doesn't belong in a servlet. It belongs in a persistence layer.

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Hi all,
I have an customersBean which is inherit from customersRemote and my problem is i' am little confuse about injecting the entity(customer).
Where can you apply the EntityManagerFactory is it outside on EJB or Inside the EJB? means outside EJB is use the web application or java application. i have and example.
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To ragnic and other about Singleton class

Hi ragnic. Thanks for your reply. I posted the code wrong. Heres' my correct one.
I have a GUI first loaded information and the information is stored in a databse, I have some EJB classes..and my singleton class ABC has some method to access to the EJB..
so my first GUI will gather info using singleton class and later if I click on
a button in my first GUI class, will pop up another frame of another class , this class also need to class setPassword in my Singleton..
are my followign codes correctly??
iS my Class ABC a SINgleton class? thanks
Is my class ABC use as single correctly. And It is called from other classes is also correct?
I'm new to java and like to learn about Singleton class.
But I really dont' understand it clearly after reading many examples of it.
I have a project to convert my class abc to a singleton.
But I dont know how to do it.
In my class(soon will become a singleton) will have few methods that later I need to use it from another class A and class B.
I have a GUI application that first load my class A..and my class will call
class abc(singleton) to get some information from it.
and then in class A has a button, if I click on that button I will call SIngleton class again to update my password, in the singleton class has method calls updatePassword. But I dont know how to call a singleton from other class.
I have my code for them below:
1)public class ABC //attempt using a singleton
private static ABC theABC = null;
private ABC(){}
public synchronized static ABC getABC()
if(theABC == null)
theABC= new ABC();
return the ABC;
public void updateUserInfo(SimpleUser user)
throws UserNotFoundException, DelegateException
try
UserCollectionHome userCollectionHome = (UserCollectionHome)
EJBHomeFactory.getFactory().lookupHome("vista/UserCollection",
UserCollectionHome.class);
UserHome userHome = (UserHome)
EJBHomeFactory.getFactory().lookupHome("vista/User",UserHome.class);
UserCollection uc = userCollectionHome.create();
uc.updateUserInfo(user, userHome);
} catch(HomeFactoryException hfe) {
hfe.printStackTrace();
throw new DelegateException(hfe);
} catch(RemoteException re) {
re.printStackTrace();
throw new DelegateException(re);
} catch(CreateException ce) {
ce.printStackTrace();
throw new DelegateException(ce);
} catch(FinderException fe) {
fe.printStackTrace();
throw new UserNotFoundException();
public SimpleUser getID(String id)
throws UserNotFoundException, DelegateException
try
UserCollectionHome userCollectionHome = (UserCollectionHome)
EJBHomeFactory.getFactory().lookupHome("vista/UserCollection",
UserCollectionHome.class);
UserHome userHome = (UserHome)
EJBHomeFactory.getFactory().lookupHome("vista/User",UserHome.class);
UserCollection uc = userCollectionHome.create();
SimpleUser su = uc.getID(id, userHome);
return su;
} catch(HomeFactoryException hfe) {
throw new DelegateException(hfe);
} catch(RemoteException re) {
throw new DelegateException(re);
} catch(CreateException ce) {
throw new DelegateException(ce);
} catch(FinderException fe) {
throw new UserNotFoundException();
public void setPassword(String lname,String pw)
throws UserNotFoundException, DelegateException
try
UserCollectionHome userCollectionHome = (UserCollectionHome)
EJBHomeFactory.getFactory().lookupHome("vista/UserCollection",
UserCollectionHome.class);
UserHome userHome = (UserHome)
EJBHomeFactory.getFactory().lookupHome("vista/User",UserHome.class);
UserCollection uc = userCollectionHome.create();
uc.setPassword(lname,pw, userHome);//assume that all lname are differents.
} catch(HomeFactoryException hfe) {
hfe.printStackTrace();
throw new DelegateException(hfe);
} catch(RemoteException re) {
re.printStackTrace();
throw new DelegateException(re);
} catch(CreateException ce) {
ce.printStackTrace();
throw new DelegateException(ce);
} catch(FinderException fe) {
fe.printStackTrace();
throw new UserNotFoundException();
}//Do I have my class as a Singleton correctly???
2)//Here is my First Frame that will call a Singleton to gather user information
public A(Frame owner)
super(owner, "User Personal Information",true);
initScreen();
loadPersonalInfo();
* This method instantiates all the GUI widgets and places them into panels and
* onto the frame.
private void initScreen()
txtFname = new JTextField(20);
txtLname=new JTextField(20);
btnsave =new JButton("Save");
btnChange= new JButton("Click here to change PW");//when you click this button there will be a frame pop up for you to enter informaton..this iwll call class B
JPanel pnlMain=new JPanel();
JPanel pnlFname= new JPanel();
pnlFname.setLayout(new BoxLayout(pnlFname, BoxLayout.X_AXIS));
pnlFname.setBorder(BorderFactory.createEmptyBorder(0,87,0,90));
pnlFname.add(new JLabel("First Name:"));
pnlFname.add(Box.createRigidArea(new Dimension(5,0)));
pnlFname.add(txtFname);
JPanel pnlLname= new JPanel();
pnlLname.setLayout(new BoxLayout(pnlLname, BoxLayout.X_AXIS));
pnlLname.setBorder(BorderFactory.createEmptyBorder(0,87,0,90));
pnlLname.add(new JLabel("Last Name:"));
pnlLname.add(Box.createRigidArea(new Dimension(5,0)));
pnlLname.add(txtLname);
pnlMain.add(pnlFname);
pnlMain.add(pnlLname);
pnlMain.add(btnsave);
pnlMain.add(btnChange");
btnSave = new JButton("Save");
btnSave.setActionCommand("SAVE");
btnSave.addActionListener(this);
btnCancel = new JButton("Cancel");
btnCancel.setActionCommand("CANCEL");
btnCancel.addActionListener(this);
JPanel pnlBottom = new JPanel();
pnlBottom.setLayout(new BoxLayout(pnlBottom, BoxLayout.X_AXIS));
pnlBottom.setBorder(BorderFactory.createEmptyBorder(25,55,0,0));
pnlBottom.add(btnSave);
pnlBottom.add(Box.createRigidArea(new Dimension(25,0)));
pnlBottom.add(btnCancel);
pnlMain.add(pnlBottom);
this.setContentPane( pnlMain);
setSize(500,500);
GraphicUtilities.center(this);
theABC=ABC.getABC();
//Do I call my ABC singleton class correctly??
private void loadPersonalInfo()
String ID= System.getProperty("user.name");
SimpleUser user = null;
try {
user = ABC.getID(ID);
//I tried to use method in ABC singleton class. IS this correctly call?
} catch(UserNotFoundException nfe)
JOptionPane.showMessageDialog(new JDialog(),"You have not yet registered.",
"User Not Found",JOptionPane.WARNING_MESSAGE);
System.exit(0);
} catch(DelegateException de) {
JOptionPane.showMessageDialog(new JDialog(),"You have not yet registered",JOptionPane.ERROR_MESSAGE);
System.exit(0);
currentUser = user;
txtFname.setText(currentUser.getFirstName());
txtLname.setText(currentUser.getLastName());
//This information will be display in my textfields Fname and Lname
//I can change my first and last name and hit button SAVE to save
public void actionPerformed(ActionEvent e)
if(e.getActionCommand().equals("SAVE")) submitChanges();
if(e.getActionCommand().equals("CHANGE_PASSWORD")) {
changepassword=new ChangePassword(new Frame(),name,badgeid);
public void submitChanges(){
String currentNTUsername = System.getProperty("user.name");
SimpleUser user =null;
try {
user = theABC.getID(ID);
user.setFirstName(txtFname.getText().trim());
user.setLastName(txtLname.getText().trim());
currentUser = user;
theABC.updateUserInfo(currentUser);
//IS this correctly if I want to use this method in singleton class ABC??
} catch(UserNotFoundException nfe)
JOptionPane.showMessageDialog(new JDialog(),"You have not yet registered",
"User Not Found",JOptionPane.WARNING_MESSAGE);
} catch(DelegateException de) {
JOptionPane.showMessageDialog(new JDialog(),"You have not yet registered",JOptionPane.ERROR_MESSAGE);
System.exit(0);
this.setVisible(false);
3) click on ChangePassword in my above GUI class A..will call this class B..and in this class B
I need to access method in a Singleton class- ABC class,,DO i need to inititates it agian, if not what should I do? thanks
package com.lockheed.vista.userinfo;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.border.*;
import javax.swing.table.*;
import javax.swing.tree.*;
import java.util.StringTokenizer;
import java.util.Vector;
import java.io.*;
import javax.swing.text.*;
import javax.swing.text.html.*;
import javax.swing.colorchooser.*;
import javax.swing.filechooser.*;
import javax.accessibility.*;
import java.beans.*;
import java.applet.*;
import java.net.*;
import org.apache.log4j.*;
import com.lockheed.common.gui.GraphicUtilities;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.border.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import vista.user.UserServicesDelegate;
import vista.user.SimpleUser;
import vista.user.UserNotFoundException;
import vista.user.*;
import com.lockheed.common.ejb.*;
import com.lockheed.common.gui.*;
import com.lockheed.vista.publish.*;
* This program allow users to change their Vista Web Center's password
public class ChangePassword extends JDialog
implements ActionListener{
protected final Logger log = Logger.getLogger(getClass().getName());
private UserServicesDelegate userServicesDelegate;
private User currentUser = null;
private JPasswordField txtPasswd, txtVerifyPW;
private JButton btnSubmit,btnCancel;
private JLabel lblName,lblBadgeID;
private String strBadgeID="";
* This is the constructor. It creates an instance of the ChangePassword
* and calls the method to create and build the GUI.
public ChangePassword(Frame owner,String name,String badgeid)
super(owner, "Change Password",true);
initScreen(name,badgeid);//build the GUI
* This method instantiates all the GUI widgets and places them into panels and
* onto the frame.
private void initScreen(String strname,String strBadgeid)
txtPasswd = new JPasswordField(20);
txtVerifyPW=new JPasswordField(20);
txtPasswd.setEchoChar('*');
txtVerifyPW.setEchoChar('*');
JPanel pnlMain=new JPanel();
pnlMain.setLayout(new BoxLayout(pnlMain, BoxLayout.Y_AXIS));
pnlMain.setBorder(BorderFactory.createEmptyBorder(20,0,20,0));
JPanel pnlPW=new JPanel();
pnlPW.setLayout(new BoxLayout(pnlPW, BoxLayout.X_AXIS));
pnlPW.setBorder(BorderFactory.createEmptyBorder(0,96,0,30));
pnlPW.add(new JLabel("Password:"));
pnlPW.add(Box.createRigidArea(new Dimension(5,0)));
pnlPW.add(txtPasswd);
JPanel pnlVerifyPW=new JPanel();
pnlVerifyPW.setLayout(new BoxLayout(pnlVerifyPW, BoxLayout.X_AXIS));
pnlVerifyPW.setBorder(BorderFactory.createEmptyBorder(0,63,0,30));
pnlVerifyPW.add(new JLabel("Verify Password:"));
pnlVerifyPW.add(Box.createRigidArea(new Dimension(5,0)));
pnlVerifyPW.add(txtVerifyPW);
JPanel pnlTop= new JPanel();
pnlTop.add(pnlPW);
pnlTop.add(Box.createRigidArea(new Dimension(0,10)));
pnlTop.add(pnlVerifyPW);
pnlMain.add(pnlTop);
btnSubmit = new JButton("Submit");
btnSubmit.setActionCommand("SUBMIT");
btnSubmit.addActionListener(this);
btnCancel = new JButton("Cancel");
btnCancel.setActionCommand("CANCEL");
btnCancel.addActionListener(this);
JPanel pnlBottom = new JPanel();
pnlBottom.setLayout(new BoxLayout(pnlBottom, BoxLayout.X_AXIS));
pnlBottom.setBorder(BorderFactory.createEmptyBorder(25,55,20,30));
pnlBottom.add(btnSubmit);
pnlBottom.add(Box.createRigidArea(new Dimension(25,0)));
pnlBottom.add(btnCancel);
pnlMain.add(pnlBottom);
this.setContentPane( pnlMain);
setSize(350,230);
setVisible(true);
public void actionPerformed(ActionEvent e)
if(e.getActionCommand().equals("CANCEL")) this.setVisible(false);
if(e.getActionCommand().equals("SUBMIT")) submitPW();
* This method is called when the submit button is clicked. It allows user to change
* their password.
public void submitPW(){
myABC= ABC.getABC();//Is this correct?
char[] pw =txtPasswd.getPassword();
String strPasswd="";
for(int i=0;i<pw.length;i++){
strPasswd=strPasswd+pw;
char[] vpw =txtVerifyPW.getPassword();
String strVerifyPW="";
for(int i=0;i<vpw.length;i++){
strVerifyPW=strVerifyPW+pw;
if((strPasswd==null)||(strPasswd.length()==0)) {
JOptionPane.showMessageDialog(new JDialog(),"You have not enter a password. Please try again.",
"Invalid Password",JOptionPane.ERROR_MESSAGE);
if((!strPasswd.equals(strVerifyPW)))
//password and verify password do not match.
JOptionPane.showMessageDialog(new JDialog(),"Your passwords do not match. Reenter and try again.",
"Invalid Password",JOptionPane.ERROR_MESSAGE);
try
myABC.setUserPassword(strPasswd);//try to use a method in Singleton class
txtPasswd.setText("");
txtVerifyPW.setText("");
this.setVisible(false);
} catch(DelegateException e) {
JOptionPane.showMessageDialog(new Frame(),
"Error.",
"Unable to change password information.",JOptionPane.WARNING_MESSAGE);
} catch(UserNotFoundException e) {
JOptionPane.showMessageDialog(new Frame(),
"Error.",
"Unable to change password information.",JOptionPane.WARNING_MESSAGE);
And ofcourse I have other EJB classes to work with these classes.
***It compiles okey but when I ran, it say "NullPointerException"
I think I call my Singleton wrong.
Please help me.thanks

1. When replying, use <reply>, don't post a new topic.
2. Implementing a singleton is a frequently asked question. Search before you post.
3. This is not a question about Swing. A more appropriate forum would be "New To Java Technology" or perhaps "Java Programming", but see point 1.
4. When posting code, keep it short. It increases the chance of readers looking at it. And in composing your shorter version for the forum, you just may solve your problem.

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ThanksPass by value implies that the actual parameter is copied and that copy is used as the formal parameter (that is, the method is operating on a copy of what was passed in)
Pass by reference means that the actual parameter is the formal parameter (that is, the method is operating on the thing which is passed in).
In Java, you never, ever deal with objects - only references to objects. And Java always, always makes a copy of the actual parameter and uses that as the formal parameter, so Java is always, always pass by value using the standard definition of the term. However, since manipulating an object's state via any reference that refers to that object produces the same effect, changes to the object's state via the copied reference are visible to the calling code, which is what leads some folk to think of java as passing objects by reference, even though a) java doesn't pass objects at all and b) java doesn't do pass by reference. It passes object references by value.
I've no idea what you're talking about wrt PreparedStatement, but String is immutable, so you can't change its state at all, so maybe that's what's tripping you up?
Good Luck
Lee
PS: I will venture a guess that this is the 3rd reply. Let's see...
Ok, second. Close enough.
Yeah, good on yer mlk, At least I beat Jos.
Message was edited by:
tsith

PSE 7 confusion about folder location, help needed

Here's some background: I'm using PhotoShop Elements 7 on Win XP. I have an external firewire hard drive I use for overflow/backups. Originally, this showed up as a K: drive on my system.
I added a RAID controller and two more drives to stripe as a single drive for temp space rendering movies. This ended up as a K: drive and the external moved to L: However, when I did this there were some pictures from my catalog that I had on the external drive. I have used File > reconnect missing files to handle the moves, but PSE is still confused (very).
PSE has started to mix up the RAID (K:) and external (L:) content. If I move a set of pictures (e.g. a folder of them) onto the external drive (L:) via drag and drop in the folder location view, the folder will show up empty on the L: heirarchy, but will show up as a gray folder icon in the K: RAID drive hierarchy. If I open up windows explorer, the RAID drive will appear empty. In other cases (I'm not sure when/how yet), pictures physically end up on the RAID drive itself instead of the external. I have uninstalled both the external drive and the RAID drive and reinstalled them both, but they are still getting confused in the folder view by PSE. I've also tried moving content outside of PSE and just reconnecting missing files, but it still wants to put things under the K: RAID drive instead of the external L:.
I've searched everywhere I can think of for a description of what gray folder icons in the folder location view means and can find none. I'm not sure how to convince PSE that there's nothing on the RAID K: drive and it shouldn't try to connect the two. Any suggestions?
Thanks,
Jim

Thank you! I ran psedbtool and the output shows the catalog has the wrong drive letter for the L: drive.
Is there a way to make PSE forget about the K: and L: drives that it is so confused about so that it can relearn of their existence? If I use the drive letter reassignment to fix PSE, it will break other apps that are now dependent on the current drive letter assignments. I've tried removing all files from the L: drive, but it's still remembered as part of the catalog.
Thanks,
Jim
psedbtool version 1.07
Opening catalog C:\Documents and Settings\All Users\Application Data\Adobe\Photoshop Elements\Catalogs\Moms pics\catalog.pse7db
Photoshop Elements version:      7
Total files               :   4833
Total files missing       :      0
Total files offline       :    278
Total files wrong volume :      0
****** Volumes with warnings: 1
PSE Volume Table
Path used by PSE        : F:
Type                    : builtin_drive
Status                  : online
Total files             : 0
Total files missing     : 0
Total files wrong volume: 0
Description             : MEDIA
Serial                  : 1C2F-9805
Drive_path_if_builtin   : F:
Id                      : 32520
Path used by PSE        : M:
Type                    : builtin_drive
Status                  : online
Total files             : 938
Total files missing     : 0
Total files wrong volume: 0
Description             : FreeAgent Drive
Serial                  : 7830-2970
Drive_path_if_builtin   : M:
Id                      : 93626
Path used by PSE        : E:
Type                    : builtin_drive
Status                  : online
Total files             : 0
Total files missing     : 0
Total files wrong volume: 0
Description             : GAMES
Serial                  : 025A-4B70
Drive_path_if_builtin   : E:
Id                      : 93625
Path used by PSE        : L:
Type                    : builtin_drive
Status                  : online
Total files             : 114
Total files missing     : 0
Total files wrong volume: 0
Description             : FreeAgent Drive
Serial                  : 60AE-A816
Drive_path_if_builtin   : K:
Id                      : 31354
***** WARNING *****     : Wrong drive letter in catalog
Path used by PSE        : \\dmzhost\media
Type                    : network_drive
Status                  : offline
Total files             : 278
Total files missing     : 0
Total files wrong volume: 0
Description             : //dmzhost/media
Serial                  : //dmzhost/media
Drive_path_if_builtin   :
Id                      : 26948
Path used by PSE        : J:
Type                    : builtin_drive
Status                  : online
Total files             : 3503
Total files missing     : 0
Total files wrong volume: 0
Description             : MEDIA2
Serial                  : BAC0-B5A3
Drive_path_if_builtin   : J:
Id                      : 108
Path used by PSE        : C:\Documents and Settings\All Users\Application Data\Adobe\Photoshop Elements\Catalogs\Moms pics
Type                    : database_relative_drive
Status                  : online
Total files             : 0
Total files missing     : 0
Total files wrong volume: 0
Description             : database relative
Serial                  : amoc:database_relative_volume
Drive_path_if_builtin   :
Id                      : 2
Windows Drives
Drive Type             Serial     Path
A:     removable_drive 0000-0000
C:     builtin_drive    9088-07F9
D:     builtin_drive    F408-1CB0
E:     builtin_drive    025A-4B70
F:     builtin_drive    1C2F-9805
G:     builtin_drive    242D-15ED
H:     readonly_drive   0000-0000
I:     builtin_drive    427D-3F6B
J:     builtin_drive    BAC0-B5A3
K:     builtin_drive    64E8-9846
L:     builtin_drive    60AE-A816
M:     builtin_drive    7830-2970
Thanks so much for your help!
Jim

Confused about schema..

I'm currently working on a project using VB 2010 Express and Oracle 11g XE. On my Oracle My SQL Developer, I am currently logged on as 'user X' and I created three tables. All of which are just listed on the 'tables' tree. Does it mean that 'user X' is like a schema when compared to MySQL?
I have already integrated my database to my vb project and is working fine ATM. I'm just really confused about schemas in Oracle 11g XE.

I'm just really confused about schemas in Oracle 11g XE.http://docs.oracle.com/cd/E11882_01/server.112/e25789/intro.htm#CEGJFFFD

I am confused about Icloud. I have a 5 year old Macbook, a 2 year old macbook and a 5 year old mac mini. What exactly do I need to do to get all this connected via Icloud. I also have an Iphone 3G. Help please!

I am confused about Icloud. I have a 5 year old Macbook, a 2 year old macbook and a 5 year old mac mini. What exactly do I need to do to get all this connected via Icloud. I also have an Iphone 3G. Help please! Also, I still don't understand exactly what the benefits are. At the moment it seems a lot of hassle to change a system that's been working perfectly well and that I'm very happy with. I'm not at all sure whether the mac mini (1.66 GHz INtel Core Duo) can be brought up to the relevant spec to run ICloud. Any thoughts?

There are two aspects to iCloud. One is simply getting an account, or migrating a mobileme account to iCloud. The second part is using the various features of iCloud to sync contacts, calendars, use music match or photo sharing, and store iWorks documents.
First to get an iCloud account:
If you have a mobileme account, you can migrate by simply logging onto www.icloud.com (ignore any references to Lion and just click through to complete the migration). If you have OS X Lion or an iOS 5 mobile device, you can create an iCloud account on that device using any valid AppleID.
Once you have an account, you can use JUST the mail account if you wishi - it is a standard IMAP account so you would set it up like any other IMAP email account you have, in whatever client program you use to read email.
To use the OTHER feautes of iCloud, your computers will have to be running OS X Lion (10.7). Your iPhone 3G will never be able to use iCloud as it cannot run iOS 5 (you need a min. of an iPhone 3GS to run iOS 5).
The requirements for OS X Lion are here - http://www.apple.com/macosx/specs.html You need a min. of a Core 2 duo processor so you mini is not capable of running Lion.
So, in your case, the single reasons for iCloud would be if you have a mobileme account, then use the online www.icloud.com to migrate your account so you do not lose your @me.com email address. You can use iCloud email (without using any other iCloud features) by setting it up as IMAP mail with these settings - http://support.apple.com/kb/HT4864
If you want an iCloud account and do NOT already have a mobileme account, you will need to upgrade one machine at least to Lion in order to be able to create an iCloud account.

Confuse about Configuring Oracle Warehouse Builder

newbie here... i am abit confuse on how to configure the Oracle Warehouse builder...
I have 2 database... 1 source and 1 new one...
I understand that i have to install the Runtime Repository in the database computer and the Target Schema through the client's computer...
so all this while... i am just confuse about what to install into the source database and what to install into the new database...
Please help...

Location is a logical entity in your OWB design that can be either a database schema, a flat file location, an SAP application location etc. Once you complete your design and are ready to deploy the design into the runtime environment, you will have to 'register' the locations by providing the physical details of your location to OWB (user name/password, database, hostname etc.).
I am a bit confused by your configuration - are the source and the target in two separate schemas or in the same schema? Your posts are somewhat contradictory.
If they are in two different schemas, you should:
1. Create a source module pointing to a source schema (you can then import data object structures from the source schema - i.e. you don't have to create source tables manually in OWB, but you can import them into the module automatically). This module will have a source location (for example SRC_LOC).
2. Create a target module where all your target objects will be (i.e. where the data will be loaded). This module will have a different location (TGT_LOC). In your target module you will also create the mappings.
3. When deploying, you will register SRC_LOC with the physical details of your source schema, while the target location will be registered with the physical details of the target schema. The code generated by OWB during deployment will make sure that the data is extracted from the source schema and inserted into the target schema (either by generating and using DB links or by qualifying the schemas in the extraction queries if source and target are in the same database instance).
On the other hand, if both source and target objects are in the same db schema, you can have all your objects in the same target module and you will only have to register the location of this target module when deploying (LOC_TGT).
That said, there can be a variety of reasons why there is no data in the target after you run the extract mapping that have nothing to do with locations, such as logical errors in the mapping (an inappropriate filter or a wrong join), insufficient privileges etc. I suggest you take a look in the runtime audit browser that should contain the error messages relative to your mapping.
Regards:
Igor

Confused about singletons in servlets

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