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import book.util.JDBCUtil; import book.util.InputUtil; class DemoOptLockingBySavingOldValues { public static void main(String args[]) throws Exception { Connection conn = null; Object[] empDetails = null; try { conn = JDBCUtil.getConnection( "scott", "tiger", "ora10g" ); We initialize the variable empno with Martin s employee number, and then we invoke the method _displayEmpDetails. The method _displayEmpDetails prints out Martin s salary and name information, and also returns the current employee name and salary in an object array: int empNo = 7654; empDetails = _displayEmpDetails( conn, empNo ); We then introduce an artificial pause in our program by invoking InputUtil.waitTill UserHitsEnter() (discussed in section A Utility to Pause in a Java Program of 1) to simulate the time the end user takes to change the employee details before issuing the final update. This enables us to sneak in a conflicting update in our experimental runs: InputUtil.waitTillUserHitsEnter("Row has been selected but is not locked."); We invoke the _updateEmpInfo() method to update the employee information (we retain the old name but bump up the salary by $100, from $1,350 to $1,450): String oldEmpName = (String) empDetails[0]; int oldSalary = ((Integer) empDetails[1]).intValue(); _updateEmpInfo( conn, empNo, oldEmpName, oldSalary, "MARTIN", 1450 ); } finally { JDBCUtil.close ( conn ); } }// end of main The _displayEmpDetails method simply invokes the opt_lock_save_old_val_demo.get_ emp_details method to retrieve the employee details to be modified: private static Object[] _displayEmpDetails( Connection conn, int empNo ) throws SQLException { Object[] result = new Object[2]; CallableStatement cstmt = null; int salary = 0; String empName = null; try

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Note Individual patterns cannot bind the same variables twice. For example, a pattern (x,x) is not

This page is now ready to go. The results are quite different from similar functionality provided by postbacks. The lists populate quickly, the UI remains responsive while the address is looked up in the background, and the browser is not clicking and running its status bar for refreshes. Even on a LAN, this interface is more responsive and usable than it would be using postbacks. One of the greatest things about this feature is that it s cross-browser compatible. In Figure 4-13 you see the Pool Hall Address Lookup page running in the Firefox browser.

{ cstmt = conn.prepareCall( "{call opt_lock_save_old_val_demo.get_emp_details( , , )}" ); cstmt.setInt( 1, empNo ); cstmt.registerOutParameter( 2, OracleTypes.VARCHAR ); cstmt.registerOutParameter( 3, OracleTypes.NUMBER ); cstmt.execute(); empName = cstmt.getString( 2 ); salary = cstmt.getInt( 3 ); System.out.println( "empno: " + empNo + ", name: " + empName + ", salary: " + salary ); result[0] = empName; result[1] = new Integer( salary ); } finally { JDBCUtil.close( cstmt ); } return result; } Toward the end of the class, we define the method _updateEmpInfo() that invokes the method opt_lock_save_old_val_demo.update_emp_info to update the employee details. Notice that we print an appropriate message depending on the number of rows successfully updated: private static void _updateEmpInfo( Connection conn, int empNo, String oldEmpName, int oldSalary, String newEmpName, int newSalary ) throws SQLException { CallableStatement cstmt = null; try { cstmt = conn.prepareCall( "{call opt_lock_save_old_val_demo.update_emp_info( , , , , , )}" ); cstmt.setInt( 1, empNo ); cstmt.setString( 2, oldEmpName ); cstmt.setInt( 3, oldSalary ); cstmt.setString( 4, newEmpName ); cstmt.setInt( 5, newSalary ); cstmt.registerOutParameter( 6, OracleTypes.NUMBER ); cstmt.execute(); int numOfRowsUpdated = cstmt.getInt( 6 ); if( numOfRowsUpdated <= 0 ) { System.out.println( "Sorry. Someone else changed the data that" + " you were trying to update. Please retry." ); }

permitted, though (x,y) when x = y is permitted. Furthermore, each side of an or pattern must bind the same set of variables, and these variables must have the same types.

else { System.out.println( "You have successfully updated the " + "employee information." ); } } finally { JDBCUtil.close( cstmt ); } } }// end of program To run the program, I opened two windows (you need to use command-line windows in Windows and an xterm or its equivalent in UNIX). I then executed the following command in window 1: B:\>java DemoOptLockingBySavingOldValues URL:jdbc:oracle:thin:@(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp) (PORT=1521)(HOST=rmenon-lap))(CONNECT_DATA=(SID=ora10g))) empno: 7654, name: MARTIN, salary: 1350, checksum: 12858 Row has been selected but is not locked. Press Enter to continue... With the pause still on in window 1, I executed the same command in window 2: B:\>java DemoOptLockingBySavingOldValues URL:jdbc:oracle:thin:@(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp) (PORT=1521)(HOST=rmenon-lap))(CONNECT_DATA=(SID=ora10g))) empno: 7654, name: MARTIN, salary: 1350, checksum: 12858 Row has been selected but is not locked. Press Enter to continue... I then pressed Enter in window 1. The update went through successfully, and I got the following message: You have successfully updated the employee information. When I pressed Enter in window 2, though, the update would not work since the same row was changed by the process in window 1 during its pause time. Hence I got the following message: Sorry. Someone else changed the data that you were trying to update. Please retry. This shows that the optimistic locking technique has successfully prevented a lost update.