"Craig R. McClanahan" wrote:
> Christopher Cobb wrote:
>
> >
> > How do you specify an entity that you want to be global across applications?
> >
>
> The standard Java approach of using a class with public static methods is the usual
> technique for accomplishing this. This is often referred to as the "singleton"
> pattern. An example of this approach is the DateFormat.getDateInstance() method,
>which
> returns you a DateFormat object. Because this is a static method, you can call it
>from
> anywhere (including from any servlet-based application).
>
> However, you must be aware of class loader issues to ensure that this works the way
>you
> intended. If everything in the servlet container is loaded by a single ClassLoader
> instance (as is the case with JSWDK and the current version of Jakarta Tomcat, but
>*not*
> the case for many existing servlet engines), the standard approach works fine.
>However,
> if your servlet container supports automatic reloading of servlets when you change
>the
> class files, you have to make sure that the class containing the static methods is
> loaded by a class loader in common (usually the system class loader that reads from
>the
> CLASSPATH).
>
> The reason for this is that classes (and therefore the static methods and variables
>they
> contain) are unique per class loader, not per JVM. It is entirely possible to have a
> class like this:
>
> import java.sql.Connection;
>
> public class MyClass {
>
> private static Connection conn = null;
>
> public static Connection getConnection() {
> return (conn);
> }
>
> public static void setConnection(Connection conn) {
> this.conn = conn;
> }
>
> }
>
> to share a JDBC connection globally (you would really want to use a connection pool
>for
> this, but I'm illustrating the class loader issue here). The idea is that you'd
>have an
> initialization call somewhere:
>
> Connection conn = ....; // Create a JDBC connection
> MyClass.setConnection(conn);
>
> and every servlet, in every application, could share this connection, like so:
>
> Connection conn = MyClass.getConnection();
>
> However, if the MyClass class is loaded by the class loader for a particular web
> application (in servlet containers that support class reloading), it will *not* be
> shared. The answer to this, as mentioned above, is to ensure that MyClass is loaded
>by
> the system class loader instead. The details of how class loading is configured
>vary by
> servlet container, so you need to check the docs for yours.
>
> Craig McClanahan
Thanks for the insightful explanation. It seems like
scope="global"
would be easier...
:)
===========================================================================
To unsubscribe: mailto [EMAIL PROTECTED] with body: "signoff JSP-INTEREST".
FAQs on JSP can be found at:
http://java.sun.com/products/jsp/faq.html
http://www.esperanto.org.nz/jsp/jspfaq.html
