Transaktionen

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>at.aydin.academy</groupId>
        <artifactId>05transactions-pair</artifactId>
        <version>1.0.0</version>
        <relativePath>../pom.xml</relativePath>
    </parent>
    <artifactId>transactions-legacy</artifactId>
    <packaging>jar</packaging>
    <name>Transactions Legacy (JDBC)</name>
    <dependencies>
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
            </plugin>

        </plugins>
    </build>
</project>

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.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.legacy;

import org.junit.jupiter.api.Test;
import java.math.BigDecimal;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertThrows;

class LegacyTransferServiceTest {
    @Test
    void rollsBackBothUpdates() {
        LegacyTransferService service = new LegacyTransferService("jdbc:h2:mem:txrollback;DB_CLOSE_DELAY=-1");
        assertThrows(IllegalStateException.class, () -> service.transfer(1, 2, new BigDecimal("50.00"), true));
        assertEquals(new BigDecimal("1000.00"), service.balance(1));
        assertEquals(new BigDecimal("200.00"), service.balance(2));
    }
}