Transaction Management in JDBC

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Savepoint;
import java.sql.Statement;
 
public class Transfer {
    static void show(Connection con, String when) throws SQLException {
        try (Statement st = con.createStatement();
             ResultSet rs = st.executeQuery(
                 "SELECT owner, balance FROM account ORDER BY owner")) {
            StringBuilder line = new StringBuilder(when + ":");
            while (rs.next()) {
                line.append(" ").append(rs.getString(1)).append("=")
                    .append(rs.getInt(2));
            }
            System.out.println(line);
        }
    }
 
    static void transfer(Connection con, String from, String to, int amount)
            throws SQLException {
        String take =
            "UPDATE account SET balance = balance - ? WHERE owner = ?";
        String give =
            "UPDATE account SET balance = balance + ? WHERE owner = ?";
        con.setAutoCommit(false);
        try (PreparedStatement debit = con.prepareStatement(take);
             PreparedStatement credit = con.prepareStatement(give)) {
            debit.setInt(1, amount);
            debit.setString(2, from);
            debit.executeUpdate();
 
            credit.setInt(1, amount);
            credit.setString(2, to);
            if (credit.executeUpdate() != 1) {
                throw new SQLException("No account for " + to);
            }
            con.commit();
            System.out.println("Committed: " + amount + " from " + from
                + " to " + to);
        } catch (SQLException e) {
            con.rollback();
            String state = e.getSQLState();
            String why = state != null && state.startsWith("23")
                ? "a constraint was violated (SQLState " + state + ")"
                : e.getMessage();
            System.out.println("Rolled back: " + why);
        } finally {
            con.setAutoCommit(true);
        }
    }
 
    public static void main(String[] args) throws Exception {
        try (Connection con =
                 DriverManager.getConnection("jdbc:h2:mem:bank")) {
            try (Statement st = con.createStatement()) {
                st.execute("CREATE TABLE account (owner VARCHAR(30) "
                    + "PRIMARY KEY, balance INT CHECK (balance >= 0))");
                st.executeUpdate("INSERT INTO account VALUES "
                    + "('Navika', 5000), ('Srihitha', 1000)");
            }
            show(con, "Start");
 
            transfer(con, "Navika", "Srihitha", 2000);
            show(con, "After 1");
 
            // The receiver doesn't exist: the debit must be undone.
            transfer(con, "Navika", "Advitha", 500);
            show(con, "After 2");
 
            // More than the balance: the CHECK constraint refuses it.
            transfer(con, "Srihitha", "Navika", 9000);
            show(con, "After 3");
 
            // Savepoint: undo part of a transaction, keep the rest.
            con.setAutoCommit(false);
            try (Statement st = con.createStatement()) {
                st.executeUpdate("UPDATE account SET balance = balance + 100 "
                    + "WHERE owner = 'Navika'");
                Savepoint bonus = con.setSavepoint("bonus");
                st.executeUpdate("UPDATE account SET balance = balance + 999 "
                    + "WHERE owner = 'Srihitha'");
                con.rollback(bonus);
                con.commit();
            }
            con.setAutoCommit(true);
            show(con, "After savepoint");
        }
    }
}