What levels of transaction isolation are supported in JDBC?

The following transaction isolation levels are supported in JDBC:

1. TRANSACTION_NONE: The connection does not support transactions.
2. TRANSACTION_READ_UNCOMMITTED: Allows reading uncommitted data from other transactions (dirty read).
3. TRANSACTION_READ_COMMITTED: The transaction only sees data committed by other transactions. Dirty reads are prevented, but non-repeatable reads are possible.
4. TRANSACTION_REPEATABLE_READ: The transaction sees the same data during repeated reads unless it was changed by the transaction itself. It prevents dirty reads and non-repeatable reads but allows phantom reads.
5. TRANSACTION_SERIALIZABLE: The highest level of isolation. Transactions are executed as if they were sequential. It prevents dirty reads, non-repeatable reads, and phantom reads. It provides maximum consistency but may reduce performance.

The isolation level can be set for a connection using the method Connection.setTransactionIsolation(int level). Example:

// Set the isolation level to Repeatable Read
connection.setTransactionIsolation(Connection.TRANSACTION_REPEATABLE_READ);

The default value depends on the specific DBMS.

To get the current isolation level, use the method Connection.getTransactionIsolation():

int isolationLevel = connection.getTransactionIsolation();
// Check the current level
if (isolationLevel == Connection.TRANSACTION_READ_COMMITTED) {
    System.out.println("Current isolation level is READ_COMMITTED");
}

It is important to choose the appropriate isolation level, balancing data consistency and application performance.