Re: replacement for useBean directive
-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1
Jonathan,
Jonathan Mast wrote:
class BeanBag {
private static AppleBean appleBean = null;
private static BananaBean bananaBean = null;
public static AppleBean getAppleBean() {
Might I recommend that you use a regular class instead of one with
static members and methods? I think you'll find it more flexible (for
instance, you will be able to extend the class and replace the object in
memory with the extended class, or you could wrap one object in another,
etc., neither of which are possible with static methods).
You could just create a new instance of this class (BeanBag) at app
startup and toss it into the application scope.
In the Servlet code, I just obtain a bean like this:
AppleBean appleBean = BeanBag.getAppleBean();
It would be a bit more complicated, but your new code would be:
BeanBag bb = (BeanBag)application.getAttribute(my.package.beanBag);
AppleBean appleBean = bb.getAppleBean();
If you're feeling sassy, you could implement a getAppleBean() method in
a superclass from which all of your servlets extend, and clean up your
code a little bit more. Tres' objectique!
My question is: where (or if) should I implement the synchronization?
Synchronize the methods of your BeanBag class (whether static or not).
But wouldn't making the methods in BeanBag synchronized be a better
approach?
In the example, the bean in question was an application-scoped bean,
which requires synchronization in the generated Java code itself
(because there is a null check for the reference and the possibility of
creating a new object and inserting it into the application scope). Your
solution will have a single object in the application scope (or will be
a static singleton) and therefore the synchronization can be handled
locally (in the class).
Hope that helps,
- -chris
-BEGIN PGP SIGNATURE-
Version: GnuPG v1.4.9 (MingW32)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org
iEYEARECAAYFAklufdIACgkQ9CaO5/Lv0PDV1ACfQMCD60vazQTz5xhJeRd8mCbh
rdIAnigXjKQ+z7XDFWC6jLdBUI79wzPh
=Vipb
-END PGP SIGNATURE-
-
To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org
For additional commands, e-mail: users-h...@tomcat.apache.org
replacement for useBean directive
OK I know this isn't Tomcat-specific, but my post on Sun Forums didn't get
much of a reply, so I thought I'd try it here.
I'm in the process of translating a series of JSPs into straightout servlets
and I have a question about how I should replicate the functionality of the
useBean directive in my Servlet.
I have a set of Beans that mediate between the JSP and a database (actually
btwn JSP and a class that accesses the db). These beans cache results from
the database, cutting back on back and forth traffic. They timeout after
varying periods of time, flush their memory (hashmaps) and then reload as
needed.
I've used the useBean directive with no problem, it's just that now the
project has grown in complexity to where it needs to be re-written as a set
Servlets.
My solution for replacing the useBean functionality has been a BeanBag class
with the following form:
class BeanBag {
private static AppleBean appleBean = null;
private static BananaBean bananaBean = null;
public static AppleBean getAppleBean() {
if (appleBean == null) {
appleBean = new AppleBean();
}
return appleBean;
}
. and so on
}
In the Servlet code, I just obtain a bean like this:
AppleBean appleBean = BeanBag.getAppleBean();
My question is: where (or if) should I implement the synchronization?
The generated servlets that Tomcat creates for the useBean directive uses
Synchronized Statements, like this:
synchronized (application) {
appleBean = (com.fruitsalad.AppleBean)
_jspx_page_context.getAttribute(appleBean, PageContext.APPLICATION_SCOPE);
if (appleBean == null){
appleBean = new com.fruitsalad.AppleBean();
_jspx_page_context.setAttribute(appleBean, appleBean,
PageContext.APPLICATION_SCOPE);
}
}
But wouldn't making the methods in BeanBag synchronized be a better
approach?
Thanks
RE: replacement for useBean directive
From: Jonathan Mast [mailto:jhmast.develo...@gmail.com] Subject: replacement for useBean directive wouldn't making the methods in BeanBag synchronized be a better approach? Definitely. Centralize the required synchronization rather than burdening each caller with it. - Chuck THIS COMMUNICATION MAY CONTAIN CONFIDENTIAL AND/OR OTHERWISE PROPRIETARY MATERIAL and is thus for use only by the intended recipient. If you received this in error, please contact the sender and delete the e-mail and its attachments from all computers. - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
Re: replacement for useBean directive
Thanks Chuck, just one more question: do I really need synchronization at
all?
These Beans basically work like this:
getApple(int appleID) {
purgeIfTimeout(); //calls appleMap.clear() if we've timed out
if (appleMap.containsKey(String.valueOf(appleID)) {
return (Apple)appleMap.get(String.valueOf(appleID);
} else {
Apple a = FruitDB.getApple(appleID); //this is where the database
interaction takes place
if (a != null) appleMap.put(String.valueOf(appleID), a);
return a;
}
}
Is synchronization really called for here, either around the getITEM()
methods inside the beans or around the methods in BeanBag that return the
bean?
On Tue, Jan 6, 2009 at 11:14 AM, Caldarale, Charles R
chuck.caldar...@unisys.com wrote:
From: Jonathan Mast [mailto:jhmast.develo...@gmail.com]
Subject: replacement for useBean directive
wouldn't making the methods in BeanBag synchronized be
a better approach?
Definitely. Centralize the required synchronization rather than burdening
each caller with it.
- Chuck
THIS COMMUNICATION MAY CONTAIN CONFIDENTIAL AND/OR OTHERWISE PROPRIETARY
MATERIAL and is thus for use only by the intended recipient. If you received
this in error, please contact the sender and delete the e-mail and its
attachments from all computers.
-
To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org
For additional commands, e-mail: users-h...@tomcat.apache.org
RE: replacement for useBean directive
From: Jonathan Mast [mailto:jhmast.develo...@gmail.com]
Subject: Re: replacement for useBean directive
do I really need synchronization at all?
Short answer: yes.
Is synchronization really called for here, either
around the getITEM() methods inside the beans or
around the methods in BeanBag that return the
bean?
Yes to both. Your example getApple() shows use of some form of Map, most forms
of which require external synchronization. Even if such Map objects
implemented internal synchronization, the logic that checks for the existence
of the key then retrieves the corresponding value requires that the state of
the Map not change between the containsKey() and get() calls.
BTW, you're creating a ton of throw-away objects by doing String.valueOf(int)
here; you may be better off to keep appleID as a String or Integer throughout.
Also, you don't need the containsKey() call, the get() will return null if the
key isn't present.
synchronized Apple getApple(int appleID) {
purgeIfTimeout(); //calls appleMap.clear() if we've timed out
Apple a = (Apple)appleMap.get(String.valueOf(appleID));
if (a != null) return a;
a = FruitDB.getApple(appleID);
if (a != null) appleMap.put(String.valueOf(appleID), a);
return a;
}
Also, your appleMap should be declared as HashMapString, Apple or
HashMapInteger, Apple (or whatever Map type you're using) so you can get rid
of the casting.
Your BeanBag class methods also need synchronization to close the window
between testing a field for null and then allocating an object for it. Failure
to do so runs the risk of two threads both seeing the field as null, and both
creating beans for the same item type.
- Chuck
THIS COMMUNICATION MAY CONTAIN CONFIDENTIAL AND/OR OTHERWISE PROPRIETARY
MATERIAL and is thus for use only by the intended recipient. If you received
this in error, please contact the sender and delete the e-mail and its
attachments from all computers.
-
To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org
For additional commands, e-mail: users-h...@tomcat.apache.org
