Jaybird 2.1 JDBC driver Java Programmer's Manual - Firebird

PreparedStatement updateSales = null;
String updateString = "update COFFEES " +
"set SALES = ? where COF_NAME like ?";
updateSales = con.prepareStatement(updateString);
try {
int [] salesForWeek = {175, 150, 60, 155, 90};
String [] coffees = {"Colombian", "French_Roast",
"Espresso", "Colombian_Decaf",
"French_Roast_Decaf"};
int len = coffees.length;
for(int i = 0; i < len; i++) {
}
updateSales.setInt(1, salesForWeek[i]);
updateSales.setString(2, coffees[i]);
try {
updateSales.executeUpdate();
} catch(SQLException ex) {
}
} finally {
}
if (ex.getErrorCode() == ...)
// do something
else
throw new BusinessDBException(ex);
updateSales.close();
Illustration 3.1.: Typical resource allocation and error handling patterns
The nested try/catch block shows you an example of handling a deadlock error if
it happens (first scenario according to our classification), otherwise the exception
is converted and passed to the upper layers (second scenario). As you see, there is
no special treatment to the third scenario.
A possible bug in the JDBC driver could have generated runtime exception in the
PreparedStatement.executeUpdate() method, which would lead to the
statement handle leakage if no try/finally block is used to do the resource cleanup.
As a rule of thumb, the “try” keyword should go right after the resource was
allocated and the “finally” keyword should be placed right before the resource is
freed.
Such coding practice might look weird, because on the first sight the whole
purpose of using the PreparedStatement is neglected – statement is prepared,
used only once and then deallocated. However, when this practice is combined
with the connection and statement pooling, it brings enormous advantage to the
application code. The code becomes much more manageable – resource
allocations and deallocations happen in the same method and software developer
must not remember the places where the same prepared statement might be used –
statement pool will either reuse the statement or it will prepare a new one, if it
detects that all pooled prepared statements are currently in use. As a side effect,
Chapter 3. Handling exceptions 25