Transaktionen

package at.aydin.lab.transactions.legacy;

import java.math.BigDecimal;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

// Design Pattern: Transaction Script
// Zweck: Ein kompletter fachlicher Ablauf wird explizit in einer Methode transaktional ausgeführt.
public final class LegacyTransferService {
    private final String url;
    public LegacyTransferService(String url) {
        this.url = url;
        initialize();
    }

    private Connection connection() throws SQLException {
        return DriverManager.getConnection(url, "sa", "");
    }

    private void initialize() {
        try (Connection c = connection(); Statement s = c.createStatement()) {
            s.executeUpdate("create table if not exists account(id bigint primary key, balance decimal(15,2))");
            s.executeUpdate("merge into account key(id) values (1,1000.00),(2,200.00)");
        } catch (SQLException e) {
            throw new IllegalStateException(e);
        }
    }

    public void transfer(long from, long to, BigDecimal amount, boolean simulateFailure) {
        try (Connection c = connection()) {
            c.setAutoCommit(false);
            try {
                update(c, from, amount.negate());
                if (simulateFailure) throw new IllegalStateException("Simulierter Fehler");
                update(c, to, amount);
                c.commit();
            } catch (Exception e) {
                c.rollback();
                throw new IllegalStateException("Überweisung zurückgerollt", e);
            }
        } catch (SQLException e) {
            throw new IllegalStateException(e);
        }
    }

    private void update(Connection c, long id, BigDecimal delta) throws SQLException {
        try (PreparedStatement ps = c.prepareStatement("update account set balance=balance+? where id=?")) {
            ps.setBigDecimal(1, delta);
            ps.setLong(2, id);
            if (ps.executeUpdate() != 1) throw new SQLException("Konto fehlt: " + id);
        }
    }

    public BigDecimal balance(long id) {
        try (Connection c = connection(); PreparedStatement ps = c.prepareStatement("select balance from account where id=?")) {
            ps.setLong(1, id);
            try (ResultSet rs = ps.executeQuery()) {
                if (!rs.next()) throw new IllegalArgumentException();
                return rs.getBigDecimal(1);
            }
        } catch (SQLException e) {
            throw new IllegalStateException(e);
        }
    }
}

package at.aydin.lab.transactions.modern;

import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import java.math.BigDecimal;

@Service
// Design Pattern: Service Layer + declarative Transaction Boundary
// Zweck: Rollback-Regeln werden vom Framework statt durch manuelles JDBC gesteuert.
public class TransferService {
    private final AccountRepository repository;
    public TransferService(AccountRepository repository) {
        this.repository = repository;
    }

    @Transactional
    public void transfer(long from, long to, BigDecimal amount, boolean simulateFailure) {
        repository.changeBalance(from, amount.negate());
        if (simulateFailure) throw new IllegalStateException("Simulierter Fehler");
        repository.changeBalance(to, amount);
    }
}

package at.aydin.lab.transactions.modern;

import org.springframework.jdbc.core.simple.JdbcClient;
import org.springframework.stereotype.Repository;
import java.math.BigDecimal;

@Repository
public class AccountRepository {
    private final JdbcClient jdbc;
    public AccountRepository(JdbcClient jdbc) {
        this.jdbc = jdbc;
    }

    public void changeBalance(long id, BigDecimal delta) {
        int count = jdbc.sql("update account set balance=balance+:delta where id=:id").param("delta", delta).param("id", id)
                .update();
        if (count != 1) throw new IllegalArgumentException("Konto fehlt: " + id);
    }

    public BigDecimal balance(long id) {
        return jdbc.sql("select balance from account where id=:id").param("id", id).query(BigDecimal.class).single();
    }
}

package at.aydin.lab.transactions.legacy;

import java.math.BigDecimal;

public final class TransactionsLegacyApplication {
    private TransactionsLegacyApplication() {
    }

    public static void main(String[] args) {
        LegacyTransferService service = new LegacyTransferService("jdbc:h2:mem:txlegacy;DB_CLOSE_DELAY=-1");
        service.transfer(1, 2, new BigDecimal("50.00"), false);
        System.out.println("Konto 1: " + service.balance(1));
        System.out.println("Konto 2: " + service.balance(2));
    }
}

package at.aydin.lab.transactions.modern;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class TransactionsModernApplication {
    public static void main(String[] args) {
        SpringApplication.run(TransactionsModernApplication.class, args);
    }
}