Database locking using JSP and Oracle database

Question

Dear All
I am reading about how to do database locking in general and i want to implement these mechanisms using JSP pages and oracle database, but i have the following questions:-
1.If i write a “select for update” quesry in the JSP page will it locks the record ? or it will not lock the record because the connection between the JSP pages and the server will be stateless in most online systems?
2.If i write all my jave code in transaction , something like this:-
• Begin transaction
• Commit or
• Rollback
Then should i be worried about the locking issues or the database manger will handle the locking mechanisms to insure data integrity(and what the default mechanism (if any) that the oracle database manger use to do the locking)?
3. If the answer for question 2 is no, then how can i handle the optimistic and the pentemistic locking using JSP pages?
BR

Answer 1

One way to solve this issue is as follows:
* You add a new column to each database table called 'version' which is of int type.
* Each time you alter any field in a record, you increament the version number.
* When you read a record and display it, you store the version number in your code
* when you go to update the record, you write your sql something like this:
update person set firstName=? where personId=? and version=?
Where the version is whatever you stored locally. If someone altered the record in the database while your
end user was looking at it, the version numbers will not match and the sql statement will
return zero as the number of records it altered. If its zero, inform the end user someone altered the record
while he was looking at it and weather or not he wants to proceed.
The chances of two people altering the same record in a table while both are logged in and viewing the same set of data is small so such collisions will be few.
You only need transactions if you are updating more than one record at a time (in the same table or multiple tables).
You dont need it for reading records if you use a single sql statement to read (for example: to join multiple tables).
In general, you get a (pooled) connection, use it, and close it as quickly as possible in a try/catch/finally block. You dont hold onto it for the duration of the user's session. A book on JDBC should help clarify this.