Code to implement H2's ";AUTO_SERVER=true" functionality for HSQLDB

HsqlAutoserverManager.java

package hsql_test;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintStream;
import java.net.ServerSocket;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Optional;

import org.hsqldb.Server;
import org.hsqldb.persist.HsqlProperties;
import org.hsqldb.server.ServerAcl.AclFormatException;

/**
 * Code to implement H2's ";AUTO_SERVER=true" functionality for HSQLDB.
 */
public class HsqlAutoserverManager {
    private static final String AUTOSTART_SERVER_FILE_LOCK_POSTFIX = "_autoserver_lock";
    private final String databaseFileName;
    private Optional<Server> ownedServer = Optional.empty();

    /**
     * Constructor.
     * @param databaseFileName file to create connection to, eq. "D:\\\\dbtest\\database.db" (\ needs escaping)
     */
    public HsqlAutoserverManager(String databaseFileName) {
        this.databaseFileName = databaseFileName;
    }

    /**
     * Starts a connection either by starting a new server and connect to it, or find the running server for the given file and connect to it.
     * TODO proper exception handling
     * @return JDBC connection, make sure to close it
     */
    public synchronized Connection createConnection() {
        System.out.println("Starting Database");
        try {
            String portToConnect;
            File databasePortFile = new File(databaseFileName + AUTOSTART_SERVER_FILE_LOCK_POSTFIX);
            if (!databasePortFile.exists()) {
                portToConnect = startNewServer();
                writeServerPortToFile(databasePortFile, portToConnect);
            } else {
                portToConnect = readServerPortFromFile(databasePortFile);
            }
            return createJdbcHsqlConnectionToPort(portToConnect);
        } catch (Exception e) {
            throw new RuntimeException("Unable to create DB connection", e);
        }
    }

    /**
     * If this JVM started the server, the server will be shut down, otherwise no operation.
     */
    public synchronized void shutdown() throws SQLException {
        if (ownedServer.isPresent()) {
            ownedServer.get().shutdown();
            File file = new File(databaseFileName + AUTOSTART_SERVER_FILE_LOCK_POSTFIX);
            file.delete();
            System.out.println("Database shutdown");
        }
    }

    private String startNewServer() throws IOException, AclFormatException, FileNotFoundException {
        String randomPortToStartServerServerOn = String.valueOf(findRandomOpenPort());
        HsqlProperties properties = createHsqlProperties(randomPortToStartServerServerOn);
        startServer(properties);
        return randomPortToStartServerServerOn;
    }

    private HsqlProperties createHsqlProperties(String port) {
        HsqlProperties properties = new HsqlProperties();
        properties.setProperty("server.database.0", "file:" + databaseFileName + ";hsqldb.write_delay=false");
        properties.setProperty("server.dbname.0", "mydb");
        properties.setProperty("server.port", port);
        return properties;
    }

    private void startServer(HsqlProperties p) throws IOException, AclFormatException {
        Server dserver = new Server();
        dserver.setProperties(p);
        dserver.setLogWriter(null); // can use custom writer
        dserver.setErrWriter(null); // can use custom writer
        dserver.start();
        ownedServer = Optional.of(dserver);
    }

    private String readServerPortFromFile(File file) throws FileNotFoundException, IOException {
        String portToConnect;
        BufferedReader is = new BufferedReader(new InputStreamReader(new FileInputStream(file)));
        portToConnect = is.readLine();
        is.close();
        return portToConnect;
    }

    private void writeServerPortToFile(File file, String port) throws IOException, FileNotFoundException {
        file.createNewFile();
        PrintStream fs = new PrintStream(new FileOutputStream(file));
        fs.print(port);
        fs.close();
    }

    private Integer findRandomOpenPort() throws IOException {
        try (ServerSocket socket = new ServerSocket(0)) {
            return socket.getLocalPort();
        }
    }

    private Connection createJdbcHsqlConnectionToPort(String portToConnect) throws SQLException {
        String connectionUri = "jdbc:hsqldb:hsql://localhost:" + portToConnect + "/mydb";
        System.out.println("Connecting to server: " + connectionUri);
        return DriverManager.getConnection(connectionUri, "SA", "");
    }
}