add postgresql listener

jdbc-postgresql/src/main/java/module-info.java

@@ -4,6 +4,7 @@ import org.xbib.jdbc.postgresql.Postgresql;
 module org.xbib.jdbc.postgresql {
     requires org.xbib.jdbc.query;
     requires java.sql;
+    requires org.postgresql.jdbc;
     uses Flavor;
     exports org.xbib.jdbc.postgresql;
     provides Flavor with Postgresql;

jdbc-postgresql/src/main/java/org/xbib/jdbc/postgresql/Listener.java

@@ -0,0 +1,53 @@
+package org.xbib.jdbc.postgresql;
+
+import org.postgresql.PGNotification;
+
+import java.sql.Connection;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.sql.Statement;
+import java.util.function.Consumer;
+
+public class Listener implements Runnable {
+
+    private final Connection connection;
+
+    private final org.postgresql.PGConnection pgConnection;
+
+    private final Consumer<PGNotification> notificationConsumer;
+
+    private final Consumer<Throwable> errorConsumer;
+
+    public Listener(Connection connection,
+                    Consumer<PGNotification> notificationConsumer,
+                    Consumer<Throwable> errorConsumer) throws SQLException {
+        this.connection = connection;
+        this.pgConnection = (org.postgresql.PGConnection) connection;
+        this.errorConsumer = errorConsumer;
+        this.notificationConsumer = notificationConsumer;
+        try (Statement stmt = connection.createStatement()) {
+            stmt.execute("LISTEN event");
+        }
+    }
+
+    @Override
+    public void run() {
+        while (true) {
+            try (Statement stmt = connection.createStatement();
+                 ResultSet rs = stmt.executeQuery("SELECT 1")) {
+            } catch (SQLException e) {
+                errorConsumer.accept(e);
+            }
+            try {
+                PGNotification[] notifications = pgConnection.getNotifications();
+                if (notifications != null) {
+                    for (PGNotification notification : notifications) {
+                        notificationConsumer.accept(notification);
+                    }
+                }
+            } catch (SQLException e) {
+                errorConsumer.accept(e);
+            }
+        }
+    }
+}