FND MESSAGES:
Here i am Explaining  how to create Fnd Messages  via  E-Business suite  and the implementation of message retrieval via the pl/sql API package provided with Oracle Applications.
Creating an Oracle E-Business Suite Message

To create a message in the E-Business suite message library you will need the “Application Developer” responsibility.
Navigate to Application Developer > Application > Messages. This will launch a form

Enter a unique name for your message
Eg: XX_CUSTOMER_MSG
Select the language that your message is written in and the application that the message belongs
Enter the message text in the “Current Message Text” box.
Eg: This is my first message
Click the save icon.

Retrieving a message using PL/SQL:

In order to retrieve the message from the database we need to use a standard API’s in the FND_MESSAGE package.
An E-Business suite message should be retrieved as follows:
1. Clear the current session of any message variables that may already be set
2. Tell E-Business suite which message you wish to retrieve
3. Retrieve the actual message string
4. Clear the session (Optional)

Below is the PL/SQL Block to retrive the message

DECLARE
 my_message VARCHAR2(100);

 BEGIN

  –Initialize Apps Session
  fnd_global.apps_initialize( user_id      => 1234
                             ,resp_id      => 1235
                             ,resp_appl_id => 1236
                           );
                         
  /*–Note: You will get the uer_id, resp_id and Resp_appl_id using below Query
    select fnd.user_id ,
         fresp.responsibility_id,
         fresp.application_id
  from   fnd_user fnd,
         fnd_responsibility_tl fresp
  where  fnd.user_name = ‘OEAG’
  and    fresp.responsibility_name = ‘Custom HRMS Responsibility‘;
  */
 
  –Clear the existing session
  FND_MESSAGE.CLEAR;

  –Tell e business suite which message you want (custom application short name/message name) 
  FND_MESSAGE.SET_NAME(‘XXERP’,’XX_CUSTOMER_MSG’);

  –Retrieve the message
  my_message := FND_MESSAGE.GET;  

  –Output the message
  DBMS_OUTPUT.PUT_LINE(my_message);
 END;

Output for the Above Block Is : This is my first message

Using Tokens in the message:

The Oracle E-Business suite allows the substitution of tokens within a message string to enable the programmer to add dynamic content to the message at run time.
Open the E-Business Suite message create a New Message
Navigate to Application Developer > Application > Messages. This will launch a form

Enter a unique name for your message
Eg: XX_UNAME_TOKEN_MSG
Select the language that your message is written in and the application that the message belongs
Enter the message text in the “Current Message Text” box.
Eg: This is my second message and the Token User name is &USERNAME
Click the save icon.
Note: In order to insert a token into a message it is necessary to prefix the token with a ampersand e.g. &USERNAME
Retrieving message With Token Substitution
Here USERNAME is called as TOKEN, we will Add the value dynamically

Example Block  is below:

DECLARE
 my_message VARCHAR2(100);
BEGIN
 –Initialize Apps Session
 fnd_global.apps_initialize( user_id      => 1234
                            ,resp_id      => 1235
                            ,resp_appl_id => 1236
                           );
                         
  /*–Note: You will get the uer_id, resp_id and Resp_appl_id using below Query
    select fnd.user_id ,
         fresp.responsibility_id,
         fresp.application_id
  from   fnd_user fnd,
         fnd_responsibility_tl fresp
  where  fnd.user_name = ‘OEAG’
  and    fresp.responsibility_name = ‘Custom HRMS Responsibility’;
  */
 
 –Clear the existing session
 FND_MESSAGE.CLEAR;

 –Tell e business suite which message you want (Application short name/message name)
 FND_MESSAGE.SET_NAME(‘XXERP‘,’XX_UNAME_TOKEN_MSG’);

  –Set the username message token with the current applications user
 FND_MESSAGE.SET_TOKEN(‘USERNAME’,FND_GLOBAL.USER_NAME);

 –Retrieve the message
 my_message := FND_MESSAGE.GET;

 –Output the message
 DBMS_OUTPUT.PUT_LINE(my_message);
END;

Out put for above block is : 

This is my second message and the Token User name is IAMKRISHNA

Downloading and Uploading Messages using the Generic Loader

To download our example message we would use the following command at the Unix prompt on the mid-tier:
 
FNDLOAD apps/apps 0 Y DOWNLOAD $FND_TOP/patch/115/import/afmdmsg.lct XX_UNAME_TOKEN_MSG.ldt
FND_NEW_MESSAGES APPLICATION_SHORT_NAME=’PER’ MESSAGE_NAME=”XX_UNAME_TOKEN_MSG”

To Upload our example message we would use the following command at the Unix prompt on the mid-tier:

FNDLOAD apps/apps 0 Y UPLOAD $FND_TOP/patch/115/import/afmdmsg.lct XX_UNAME_TOKEN_MSG.ldt