How to start a transaction in JDBC?

Question

Connection.setTransactionIsolation(int) warns:

Note: If this method is called during a transaction, the result is implementation-defined.

Answer 1

Maybe this will answer your question: You can only have one transaction per connection. If autocommit is on (default), every select, update, delete will automatically start and commit (or rollback) a transaction. If you set autocommit off, you start a "new" transaction (means commit or rollback won't happen automatically). After some statements, you can call commit or rollback, which finishes current transaction and automatically starts a new one. You cannot have two transactions actively open on one JDBC connection on pure JDBC.

Answer 2

I suggest you read this you'll see

Therefore, the first call of setAutoCommit(false) and each call of commit() implicitly mark the start of a transaction. Transactions can be undone before they are committed by calling

Edit:

Check the official documentation on JDBC Transactions

When a connection is created, it is in auto-commit mode. This means that each individual SQL statement is treated as a transaction and is automatically committed right after it is executed. (To be more precise, the default is for a SQL statement to be committed when it is completed, not when it is executed. A statement is completed when all of its result sets and update counts have been retrieved. In almost all cases, however, a statement is completed, and therefore committed, right after it is executed.)

The way to allow two or more statements to be grouped into a transaction is to disable the auto-commit mode. This is demonstrated in the following code, where con is an active connection:

con.setAutoCommit(false);

Source: JDBC Transactions