I am using following code for registering and listening to Oracle database change notifications. This code is working fine when i run it as a standalone java program. It is receiving the notification from the database and printing as expected.
public class DBChangeNotification {
static final String USERNAME = "XXX";
static final String PASSWORD = "YYY";
static String URL = "jdbc:oracle:thin:@xxxx:xxxx:xxxx";
public static void main(String[] args) {
DBChangeNotification demo = new DBChangeNotification();
try {
demo.run();
} catch (SQLException mainSQLException) {
mainSQLException.printStackTrace();
}
}
public void run() throws SQLException {
OracleConnection conn = connect();
Properties prop = new Properties();
prop.setProperty(OracleConnection.DCN_NOTIFY_ROWIDS, "true");
prop.setProperty(OracleConnection.DCN_QUERY_CHANGE_NOTIFICATION, "true");
prop.setProperty(OracleConnection.DCN_BEST_EFFORT, "true");
DatabaseChangeRegistration dcr = conn.registerDatabaseChangeNotification(prop);
try {
// add the listenerr:
DCNDemoListener list = new DCNDemoListener(this);
dcr.addListener(list);
// second step: add objects in the registration:
Statement stmt = conn.createStatement();
// associate the statement with the registration:
((OracleStatement) stmt).setDatabaseChangeRegistration(dcr);
ResultSet rs = stmt.executeQuery("select * from xxxxxxxx where yyyy='zzzzz'");
while (rs.next()) {
}
String[] tableNames = dcr.getTables();
for (int i = 0; i < tableNames.length; i++) {
System.out.println(tableNames[i] + " is part of the registration.");
}
rs.close();
stmt.close();
} catch (SQLException ex) {
// if an exception occurs, we need to close the registration in order
// to interrupt the thread otherwise it will be hanging around.
if (conn != null) {
conn.unregisterDatabaseChangeNotification(dcr);
}
ex.printStackTrace();
throw ex;
} finally {
try {
// Note that we close the connection!
conn.close();
} catch (Exception innerex) {
innerex.printStackTrace();
}
}
}
/**
* Creates a connection the database.
*/
OracleConnection connect() throws SQLException {
OracleDriver dr = new OracleDriver();
Properties prop = new Properties();
prop.setProperty("user", DBChangeNotification.USERNAME);
prop.setProperty("password", DBChangeNotification.PASSWORD);
return (OracleConnection) dr.connect(DBChangeNotification.URL, prop);
}
}
/**
* DCN listener: it prints out the event details in stdout.
*/
class DCNDemoListener implements DatabaseChangeListener {
DBChangeNotification demo;
DCNDemoListener(DBChangeNotification dem) {
System.out.println("DCNDemoListener");
demo = dem;
}
@Override
public void onDatabaseChangeNotification(DatabaseChangeEvent e) {
Thread t = Thread.currentThread();
System.out.println("DCNDemoListener: got an event (" + this + " running on thread " + t + ")");
System.out.println(e.toString());
synchronized (demo) {
demo.notify();
}
}
}
My requirement is to use this feature in a web application. Web application when started in the server, has to listen to data change notifications (may be on a separate thread) and notify the application through a websocket client. I have added the following code in contextInitialized method of servlet context listener, so that it will start as soon as the application starts.
public class MyServletContextListener implements ServletContextListener {
DBChangeNotification demo;
@Override
public void contextDestroyed(ServletContextEvent arg0) {
//Notification that the servlet context is about to be shut down.
}
@Override
public void contextInitialized(ServletContextEvent arg0) {
demo = new DBChangeNotification();
try {
demo.run();
} catch (SQLException mainSQLException) {
mainSQLException.printStackTrace();
}
}
}
I did not see any notifications received by the web application when database change event occurs in the registered table. Please help me in resolving the issue. I do not know whether this is a correct approach or not.... may please suggest any alternative except continuous polling. I need to start something in the server as soon as i receive notification from database. Thank you.
