Java Reference
In-Depth Information
For example:
<jsp:useBean id="myAccount" class="bank.Account"
scope="session" />
Recall that Tomcat has a folder called classes. For each bean that we wish to use
with a JSP, we should create a sub-folder of classes that has the same name as the
package that is to hold the bean. For instance, in the above example, directory bank
holds a bean called Account (within package bank ) and directory bank is placed
inside classes . Once a bean has been placed inside a JSP, the 'get' and 'set' methods
of the bean may be used.
There is a great deal of scope for things to go wrong when using JavaBeans from
JSPs, so you should get used to seeing error pages. In addition to this, re-compilation
by the server (necessary after any change to the JSP, of course) is slow ! Re-loading
of a pre-compiled JSP is fi ne, though. In addition, recall that it is not necessary
to stop and restart the server every time a change is made to a JSP (as it was with
servlet changes in Chap. 8 ).
Calling a Bean's Methods Directly
This is a modifi cation of one of our JDBC examples ( ) from Chap. 7 .
It is advisable to specify an error page, of course, since several things can go wrong
when accessing a database that could be remote.
There are several changes that need to be made to the original program, as listed
￿ Remove all references to GUI elements (substantially reducing the code in so
Remove all exception-handling code (since we shall be using a JSP error page).
Since class ResultSet has no constructor and does not implement Serializable ,
introduce a Vector for transferring query results.
Introduce a 'get' method for retrieving the contents of the Vector object.
The numeric values retrieved from the database and stored in a Vector will need
to be typecast into objects of the type Integer and Float when the Vector is received
by the JSP. Due to auto-unboxing, these values may be assigned directly to variables
of type int and fl oat .
Here is the code for the bean…
package jdbc;
import java.sql.*;
import java.util.Vector;
public class JDBCBean
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