Using H2 database server how to notify changes to clients (JMS messaging)

Question

I am successfully using H2 database in AUTO_SERVER mode so that a database file is shared among a number of desktop clients on a network transparently. This way a server is

Answer 1

H2 does not implement JMS (in fact I don't know of a database that does). However, you could build a simple notify mechanism within H2, using a trigger and a user defined function, as follows. Please note this would require the multi-threaded mode in H2, which is not fully tested yet. Because of that, it might make sense to use a separate database for messaging than the database you use for your data.

import java.sql.*;
import java.util.concurrent.atomic.AtomicLong;
import org.h2.tools.TriggerAdapter;

public class TestSimpleDb {

    public static void main(String[] args) throws Exception {
        final String url = "jdbc:h2:mem:test;multi_threaded=true";
        Connection conn = DriverManager.getConnection(url);
        Statement stat = conn.createStatement();
        stat.execute("create alias wait_for_change for \"" + 
                TestSimpleDb.class.getName() + 
                ".waitForChange\"");
        stat.execute("create table test(id identity)");
        stat.execute("create trigger notifier " + 
                "before insert, update, delete, rollback " +
                "on test call \"" + 
                TestSimpleDb.Notifier.class.getName() + "\"");
        new Thread() {
            public void run() {
                try {
                    Connection conn = DriverManager.getConnection(url);
                    for (int i = 0; i < 10; i++) {
                        conn.createStatement().execute(
                                "call wait_for_change(10000)");
                        System.out.println("Receiver: event received");
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }.start();
        Thread.sleep(500);
        for (int i = 0; i < 10; i++) {
            System.out.println("Sender: I change something...");
            stat.execute("insert into test values(null)");
            Thread.sleep(1000);
        }
        conn.close();
    }

    static AtomicLong modCount = new AtomicLong();

    public static void waitForChange(long maxWaitMillis) {
        synchronized (modCount) {
            try {
                modCount.wait(maxWaitMillis);
            } catch (InterruptedException e) {
                // ignore
            }
        }
    }

    public static class Notifier extends TriggerAdapter {
        public void fire(Connection conn, ResultSet oldRow, ResultSet newRow)
                throws SQLException {
            modCount.incrementAndGet();
            synchronized (modCount) {
                modCount.notifyAll();
            }
        }
    }

}