Blog do projektu Open Source JavaHotel

piątek, 7 września 2012

DB2, HADR and J2EE

HADR works perfectly with stand alone Java application using Driver Manager interface. But what about Web applications where common practice is a connection by means of DataSource ?
Sample application
 To check it I created a simple GWT application (running on Tomcat container) connecting to HADR enabled DB2 and doing several simple actions like before. Full source code is available here. I reused the whole interface and implementation of IJDBCAction without changing any single line.
The application itself looks like (I did not pay too much attention to GUI design)

It is nothing more but Web (GWT) interface to IJDBCAction.
The only difference is of course the method of obtaining JDBC Connection.

  private class GetConnection implements IGetConnection {

                public Connection getCon() throws SQLException, ClassNotFoundException {
                        InitialContext ic;
                        DataSource ds;
                        try {
                                ic = new InitialContext();
                                ds = (DataSource) ic.lookup("java:comp/env/jdbc/SAMPLE");
                                Connection c = ds.getConnection();
                                return c;
                        } catch (NamingException e) {
                                throw new ClassNotFoundException(e.getLocalizedMessage());


The most important thing is defining the data source (server.xml for Tomcat)
<Resource auth="Container" driverClassName="" name="jdbc/SAMPLE" password="db2had1" 
username="db2had1" >
The crucial point is adding additional connection parameters describing alternative DB2 server participating in HADR configuration. Beside that there is nothing specific in this application.
Additional remarks
  • I reused IJDBCAction implementation from JavaHadr project by means of Eclipse "source link". The only disadvantage that I was unable to use PersonRecord bean as a transient object in GWTHadr application. The nice feature of GWT is the possibility to share code between server and client part. It is possible to achieve that but it requires to decompose JavaHadr application into two parts.
  • Adding additional parameters to URL is not the only method to create DataSource connection HADR enabled. The second method is to create an instance of DB2ClientRerouteServerList and pass it to DataSource as a JNDI entry. It is described here in more detail.

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