How to Prevent Multiple entries stored in database

Consider am using java , struts, hibernate and oracle. How can i prevent duplicate entries stored in
database. One way is to make field as Unique . For example i am entering name "prakash" in jsp page ,
prakash is already available means how can i prevent it.

What is wrong with making it unique in the database?

How to prevent duplicate entries programmatically , not in DB.

You'd need to check before each insert whether or not there is a conflicting entry in the database.

Rajendra Prakash wrote:How to prevent duplicate entries programmatically , not in DB.

read a field one by one and compare it with our new entry using loops... But wait a minute... this is very vague idea...let us wait for some ones better solution..

Yes i want to check before each insert whether or not there is a conflicting entry in the database.

Of course, that is not going to be a 100% guaranteed mechanism. How do you prevent another process inserting duplicate data after your check but before your insert without pessimistically locking the table? And why use pessimistic locking when databases provide a mechanism already in the form of unique indexes?

its ok . I also want to know ,how can we do after inserting a record

You can't anymore, because the uniqueness is already violated.

To check is there is a double you need all the information so you have two options:

Hold all the information in memory (then what's the use of the database?)
Contact the database to check if the element already exists.

If you use one of these options you'll need to check for concurrent access and exposure of your datastructure.
The best solution is to set a constraint on the database.