package foo;



import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.Statement;



import javax.naming.Context;

import javax.naming.InitialContext;

import javax.sql.DataSource;

import javax.transaction.UserTransaction;



public class DBTest{



    int foo = -1;

    // value stored in DB



    public void init(String completion) {

        try{

            Context ctx = new InitialContext();



            // JDBC stuff

            DataSource ds =

                (DataSource)ctx.lookup("java:comp/env/jdbc/myDB");



            UserTransaction ut = (UserTransaction)ctx.lookup("java:comp/UserTransaction");



            java.sql.Connection conn = ds.getConnection();



            System.out.println("<<< beginning the transaction >>>");

            ut.begin();



             // JDBC statements

             Statement stmt = conn.createStatement();

             ResultSet rst =

                 stmt.executeQuery("select id, foo from testdata");

             if(rst.next()) {

                 foo=rst.getInt(2);

             }

             System.out.println("foo = "+ foo +" (before completion)");



             PreparedStatement pstmt = conn.prepareStatement("update testdata set foo=? where id=1");

             pstmt.setInt(1,++foo);

             pstmt.executeUpdate();



              if (completion != null && completion.equals("commit")) {

                  System.out.println("<<< committing the transaction >>>");

                  ut.commit();

              } else {

                  System.out.println("<<< rolling back the transaction >>>");

                  ut.rollback();

              }



             // we set foo to the value stored in the DB

             rst =

                 stmt.executeQuery("select id, foo from testdata");

             if(rst.next()) {

                 foo=rst.getInt(2);

             }

             System.out.println("foo = "+ foo +" (after completion)");



             conn.close();

             System.out.println("<<< done >>>");

        }catch(Exception e) {

            System.out.print("DBTest >> ");

            e.printStackTrace();

        }

    }



    public String getFoo() { return ""+foo; }

}