JDBC Transaction let you control how and when a transaction should commit into database.

//transaction block start
//SQL insert statement
//SQL update statement
//SQL delete statement
//transaction block end

In simple, JDBC transaction make sure SQL statements within a transaction block are all executed successful, if either one of the SQL statement within transaction block is failed, abort and rollback everything within the transaction block.

See below two examples to understand how JDBC transaction works.

1. Without JDBC Transaction

By default, data will be committed into database when executeUpdate() is called.

String insertTableSQL = "INSERT INTO DBUSER"
			+ "(USER_ID, USERNAME, CREATED_BY, CREATED_DATE) VALUES"
			+ "(?,?,?,?)";
String updateTableSQL = "UPDATE DBUSER SET USERNAME =? "
			+ "WHERE USER_ID = ?";
preparedStatementInsert = dbConnection.prepareStatement(insertTableSQL);
preparedStatementInsert.setInt(1, 999);
preparedStatementInsert.setString(2, "mkyong101");
preparedStatementInsert.setString(3, "system");
preparedStatementInsert.setTimestamp(4, getCurrentTimeStamp());
preparedStatementInsert.executeUpdate(); //data COMMITTED into database.
preparedStatementUpdate = dbConnection.prepareStatement(updateTableSQL);
preparedStatementUpdate.setString(1, "A very very long string caused DATABASE ERROR");
preparedStatementUpdate.setInt(2, 999);
preparedStatementUpdate.executeUpdate(); //Error, value too big,  ignore this update statement,
                                                //but user_id=999 is inserted

When this code is executed, the USER_ID = ‘999’ is inserted but the username is not update.

2. With JDBC Transaction

To put this in a transaction, you can use

1. dbConnection.setAutoCommit(false); to start a transaction block.
2. dbConnection.commit(); to end a transaction block.

See code snippets :

dbConnection.setAutoCommit(false); //transaction block start
String insertTableSQL = "INSERT INTO DBUSER"
			+ "(USER_ID, USERNAME, CREATED_BY, CREATED_DATE) VALUES"
			+ "(?,?,?,?)";
String updateTableSQL = "UPDATE DBUSER SET USERNAME =? "
			+ "WHERE USER_ID = ?";
preparedStatementInsert = dbConnection.prepareStatement(insertTableSQL);
preparedStatementInsert.setInt(1, 999);
preparedStatementInsert.setString(2, "mkyong101");
preparedStatementInsert.setString(3, "system");
preparedStatementInsert.setTimestamp(4, getCurrentTimeStamp());
preparedStatementInsert.executeUpdate(); //data IS NOT commit yet
preparedStatementUpdate = dbConnection.prepareStatement(updateTableSQL);
preparedStatementUpdate.setString(1, "A very very long string caused DATABASE ERROR");
preparedStatementUpdate.setInt(2, 999);
preparedStatementUpdate.executeUpdate(); //Error, rollback, including the first insert statement.
dbConnection.commit(); //transaction block end

When this code is executed, update statement is hits error, and make both insert and update statements rollback together.

Full JDBC Transaction example

See a complete JDBC transaction example.

package com.mkyong.jdbc;
import java.sql.DriverManager;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
public class JDBCTransactionExample {
	private static final String DB_DRIVER = "oracle.jdbc.driver.OracleDriver";
	private static final String DB_CONNECTION = "jdbc:oracle:thin:@localhost:1521:MKYONG";
	private static final String DB_USER = "user";
	private static final String DB_PASSWORD = "password";
	public static void main(String[] argv) throws SQLException {
		Connection dbConnection = null;
		PreparedStatement preparedStatementInsert = null;
		PreparedStatement preparedStatementUpdate = null;
		String insertTableSQL = "INSERT INTO DBUSER"
				+ "(USER_ID, USERNAME, CREATED_BY, CREATED_DATE) VALUES"
				+ "(?,?,?,?)";
		String updateTableSQL = "UPDATE DBUSER SET USERNAME =? "
				+ "WHERE USER_ID = ?";
		try {
			dbConnection = getDBConnection();
			dbConnection.setAutoCommit(false);
			preparedStatementInsert = dbConnection.prepareStatement(insertTableSQL);
			preparedStatementInsert.setInt(1, 999);
			preparedStatementInsert.setString(2, "mkyong101");
			preparedStatementInsert.setString(3, "system");
			preparedStatementInsert.setTimestamp(4, getCurrentTimeStamp());
			preparedStatementInsert.executeUpdate();
			preparedStatementUpdate = dbConnection.prepareStatement(updateTableSQL);
			// preparedStatementUpdate.setString(1,
			// "A very very long string caused db error");
			preparedStatementUpdate.setString(1, "new string");
			preparedStatementUpdate.setInt(2, 999);
			preparedStatementUpdate.executeUpdate();
			dbConnection.commit();
			System.out.println("Done!");
		} catch (SQLException e) {
			System.out.println(e.getMessage());
			dbConnection.rollback();
		} finally {
			if (preparedStatementInsert != null) {
				preparedStatementInsert.close();
			}
			if (preparedStatementUpdate != null) {
				preparedStatementUpdate.close();
			}
			if (dbConnection != null) {
				dbConnection.close();
			}
		}
	}
	private static Connection getDBConnection() {
		Connection dbConnection = null;
		try {
			Class.forName(DB_DRIVER);
		} catch (ClassNotFoundException e) {
			System.out.println(e.getMessage());
		}
		try {
			dbConnection = DriverManager.getConnection(DB_CONNECTION, DB_USER,
					DB_PASSWORD);
			return dbConnection;
		} catch (SQLException e) {
			System.out.println(e.getMessage());
		}
		return dbConnection;
	}
	private static java.sql.Timestamp getCurrentTimeStamp() {
		java.util.Date today = new java.util.Date();
		return new java.sql.Timestamp(today.getTime());
	}
}