Re: AW: Multiple users share java bean?

[camccuk]

You guys are confusing me...

At 10:52 27/03/2002 +0100, you wrote:
> Great, that's what I thought.  But here's why I'm getting confused. The
> servlet tutorial says that a servlet is created once and once
> only (that's
> when the init() is run).
> http://java.sun.com/docs/books/tutorial/servlets/lifecycle/index.html
> If the servlet class is created only once, how does Tomcat then create
> multiple instances of the class ?

>In that case, I think Sun might be right ;-) As I said, I have never done
>servlets, the above is just what I suspected...

Yes, this had alarm bells ringing for me - I'm pretty sure the tutorial is
correct. As I understand it, each user request is serviced by a thread and
these threads will all access the *same* instance of the class - this is
precisely why we have to be careful of threading issues and use synchronised
code blocks. From the tutorial:

"HTTP servlets are typically capable of serving multiple clients concurrently.
If the methods in your servlet that do work for clients access a shared
resource, then you can handle the concurrency by creating a servlet that
handles only one client request at a time. (You could also synchronize access
to the resource, a topic that is covered in this tutorial's lesson on threads.)


To have your servlet handle only one client at a time, have your servlet
implement the SingleThreadModelinterface in addition to extending the
HttpServlet class. "

Various scoping mechanisms, such as those pointed out for beans, are available
through various user, request, session and application data structures - see my
book suggestions below.

Eric wrote:

>If I comment out the init() method in my servlet do I get an instance of it
>for each request?
>
>Do people commonly do this?

I suspect that if you do this Eric, it won't compile...

If you'd prefer books written in English, I'd suggest you could do a lot worse
than Hunter & Crawford's Java Servlet Programming (2nd ed) from O'Reilly. As
usual for O'R, its about as good a text as you'll get for the big picture and
covers thread basics.

More 'heavy duty' concurrency stuff (though not specifically related to
servlets), based upon his book 'Concurrent Programming - the Java Programming
Language' is available from Steven Hartley's site:

http://www.mcs.drexel.edu/~shartley/ConcProgJava/

HTH
cam

__
Do You Yahoo!?
Yahoo! Movies - coverage of the 74th Academy Awards®
http://movies.yahoo.com/

--
To unsubscribe:   
For additional commands: 
Troubles with the list: 

Re: AW: Multiple users share java bean?

[Joel Rees]

Chenming Zhao elucidated:

> In fact I output the loginname. But here, when the problem happened, still
> the loginname was updated. So the problem is that the loginname was
updated,
> then the username cannot get the right value. But when I tested it on
> different computer, it's correct.
   ^^
> So I wonder why there is the problem when
> I open windows for multiple users.

This is just a guess, but try using two separate browsers (ergo, Netscape
and Opera) on the same machine, too.

Looking at your code, it is not clear whether numEvents is coming from some
database owned by the server or from a variable in the browser's
"environment".

I'm not sure what the terminology in Tomcat/JSP, but the "environment"
variables from the browser are not necessarily flushed unless you shut the
browser application program itself down. It's not even good enough to close
one window if you have other windows of the same browser open. Since you are
trying to access simultaneously, there is no way you would be able to shut
the browser down before logging in as the second user.

Browsers don't know much about sessions except for the cookie or query part
of the URL in the link that the server might build.

HTH.

Joel Rees
Alps Giken Kansai Systems Develoment
Suita, Osaka


> Is it the problem of the server or
> setting?
>
> - Original Message -
> From: "Wagoner, Mark" <[EMAIL PROTECTED]>
> To: "'Tomcat Users List'" <[EMAIL PROTECTED]>
> Sent: Tuesday, March 26, 2002 3:28 PM
> Subject: RE: AW: Multiple users share java bean?
>
>
> > Are your sure loginname is getting set properly?  Try including the
value
> in
> > your JSP output (right before the call to mb.test()) just to make sure.
> >
> > -----Original Message-
> > From: Chenming Zhao [mailto:[EMAIL PROTECTED]]
> > Sent: Tuesday, March 26, 2002 3:05 PM
> > To: Tomcat Users List
> > Subject: Re: AW: Multiple users share java bean?
> >
> >
> >
> >
> > ----- Original Message -
> > From: "Wagoner, Mark" <[EMAIL PROTECTED]>
> > To: "'Tomcat Users List'" <[EMAIL PROTECTED]>
> > Sent: Tuesday, March 26, 2002 2:12 PM
> > Subject: RE: AW: Multiple users share java bean?
> >
> >
> > > Are you sure you really want independent instances of the bean, or
just
> > the
> > > ability to keep the variable values separate by user?  If it is the
> > latter,
> > > then just use local variables in your bean methods.
> > >
> >
> > It seems that couldn't work. The value of such variables can be updated
by
> > another user's when there are two or more users calling the same java
bean
> > almost at the same time. Here is my main work. First jsp write uname
(when
> a
> > user login the website, there is a user name "uname") to the bean and
> > activate it, and get the result  or save it to the database.
> >  Jsp file:
> > 
> > ???How about the scope value? session or request or page?
> > 
> > The result is:
> > <%= mb.test() %>
> >
> > Bean code:
> > public class test
> > {
> > String uname= "";
> >
> > public synchronized int test()
> > {
> > int real=0;
> > int eventCounter=0;
> > int numEvents;
> >
> > // connect to the database and get the numEvents according to
the
> > uname.
> > .;
> >
> > while(eventCounter<=numEvents)
> > {
> > real=eventCounter;
> >
> > // wait for 0.01 second
> > try{wait(10);}
> > catch(InterruptedException e){};
> > eventCounter++;
> > }
> > return real;
> > }
> >
> > public synchronized void setUname(String sec)
> > {
> > uname= sec;
> > }
> > }
> >
> > For user1, numEvents=100; and user2, it's 120. So I want to run them at
> the
> > same time, and hope to get resuls 100 and 120 respectively. But in fact
I
> > got both 100 or 120. Have any idea? If my description is not clear, tell
> me
> > please.




--
To unsubscribe:   <mailto:[EMAIL PROTECTED]>
For additional commands: <mailto:[EMAIL PROTECTED]>
Troubles with the list: <mailto:[EMAIL PROTECTED]>

Re: AW: Multiple users share java bean?

[Chenming Zhao]

In fact I output the loginname. But here, when the problem happened, still
the loginname was updated. So the problem is that the loginname was updated,
then the username cannot get the right value. But when I tested it on
different computer, it's correct.  So I wonder why there is the problem when
I open windows for multiple users. Is it the problem of the server or
setting?

- Original Message -
From: "Wagoner, Mark" <[EMAIL PROTECTED]>
To: "'Tomcat Users List'" <[EMAIL PROTECTED]>
Sent: Tuesday, March 26, 2002 3:28 PM
Subject: RE: AW: Multiple users share java bean?


> Are your sure loginname is getting set properly?  Try including the value
in
> your JSP output (right before the call to mb.test()) just to make sure.
>
> -Original Message-
> From: Chenming Zhao [mailto:[EMAIL PROTECTED]]
> Sent: Tuesday, March 26, 2002 3:05 PM
> To: Tomcat Users List
> Subject: Re: AW: Multiple users share java bean?
>
>
>
>
> - Original Message -
> From: "Wagoner, Mark" <[EMAIL PROTECTED]>
> To: "'Tomcat Users List'" <[EMAIL PROTECTED]>
> Sent: Tuesday, March 26, 2002 2:12 PM
> Subject: RE: AW: Multiple users share java bean?
>
>
> > Are you sure you really want independent instances of the bean, or just
> the
> > ability to keep the variable values separate by user?  If it is the
> latter,
> > then just use local variables in your bean methods.
> >
>
> It seems that couldn't work. The value of such variables can be updated by
> another user's when there are two or more users calling the same java bean
> almost at the same time. Here is my main work. First jsp write uname (when
a
> user login the website, there is a user name "uname") to the bean and
> activate it, and get the result  or save it to the database.
>  Jsp file:
> 
> ???How about the scope value? session or request or page?
> 
> The result is:
> <%= mb.test() %>
>
> Bean code:
> public class test
> {
> String uname= "";
>
> public synchronized int test()
> {
> int real=0;
> int eventCounter=0;
> int numEvents;
>
> // connect to the database and get the numEvents according to the
> uname.
> .;
>
> while(eventCounter<=numEvents)
> {
> real=eventCounter;
>
> // wait for 0.01 second
> try{wait(10);}
> catch(InterruptedException e){};
> eventCounter++;
> }
> return real;
> }
>
> public synchronized void setUname(String sec)
> {
> uname= sec;
> }
> }
>
> For user1, numEvents=100; and user2, it's 120. So I want to run them at
the
> same time, and hope to get resuls 100 and 120 respectively. But in fact I
> got both 100 or 120. Have any idea? If my description is not clear, tell
me
> please.
>
>
> > -Original Message-
> > From: Chenming Zhao [mailto:[EMAIL PROTECTED]]
> > Sent: Tuesday, March 26, 2002 2:06 PM
> > To: Tomcat Users List
> > Subject: Re: AW: Multiple users share java bean?
> >
> >
> > What's the meaning of JMS? I'm not sure my problem is just what you
said.
> I
> > want to get independent instance or the same bean for each user. So they
> can
> > work independently, and won't influence with each other. Thanks.
> >
> > - Original Message -
> > From: "peter lin" <[EMAIL PROTECTED]>
> > To: "Tomcat Users List" <[EMAIL PROTECTED]>
> > Sent: Tuesday, March 26, 2002 1:32 PM
> > Subject: Re: AW: Multiple users share java bean?
> >
> >
> > >
> > > One common technique to solve this is to use JMS. All beans that are
> > > instances of the same user listen to the same topic. when one instance
> > > of the user's bean is updated, the other instances are notified. Each
> > > bean then goes to the database to refresh itself.
> > >
> > > peter lin
> > >
> > >
> > > Chenming Zhao wrote:
> > > >
> > > > In fact, it's a good and difficult topic. Now I haven't still
> understood
> > it
> > > > completely. I have a question about my application.
> > > >
> > > > I describe the work what I need to finish.
> > > > First the jsp file gets a user name, then pass it to java bean. And
> the
> > bean
> > > > get some values from the database accoding to the user name, then
get
> a
> > > > result and save it to da

RE: AW: Multiple users share java bean?

[Wagoner, Mark]

Are your sure loginname is getting set properly?  Try including the value in
your JSP output (right before the call to mb.test()) just to make sure.

-Original Message-
From: Chenming Zhao [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, March 26, 2002 3:05 PM
To: Tomcat Users List
Subject: Re: AW: Multiple users share java bean?




- Original Message -
From: "Wagoner, Mark" <[EMAIL PROTECTED]>
To: "'Tomcat Users List'" <[EMAIL PROTECTED]>
Sent: Tuesday, March 26, 2002 2:12 PM
Subject: RE: AW: Multiple users share java bean?


> Are you sure you really want independent instances of the bean, or just
the
> ability to keep the variable values separate by user?  If it is the
latter,
> then just use local variables in your bean methods.
>

It seems that couldn't work. The value of such variables can be updated by
another user's when there are two or more users calling the same java bean
almost at the same time. Here is my main work. First jsp write uname (when a
user login the website, there is a user name "uname") to the bean and
activate it, and get the result  or save it to the database.
 Jsp file:

???How about the scope value? session or request or page?

The result is:
<%= mb.test() %>

Bean code:
public class test
{
String uname= "";

public synchronized int test()
{
int real=0;
int eventCounter=0;
int numEvents;

// connect to the database and get the numEvents according to the
uname.
.;

while(eventCounter<=numEvents)
{
real=eventCounter;

// wait for 0.01 second
try{wait(10);}
catch(InterruptedException e){};
eventCounter++;
}
return real;
}

public synchronized void setUname(String sec)
{
uname= sec;
}
}

For user1, numEvents=100; and user2, it's 120. So I want to run them at the
same time, and hope to get resuls 100 and 120 respectively. But in fact I
got both 100 or 120. Have any idea? If my description is not clear, tell me
please.


> -Original Message-
> From: Chenming Zhao [mailto:[EMAIL PROTECTED]]
> Sent: Tuesday, March 26, 2002 2:06 PM
> To: Tomcat Users List
> Subject: Re: AW: Multiple users share java bean?
>
>
> What's the meaning of JMS? I'm not sure my problem is just what you said.
I
> want to get independent instance or the same bean for each user. So they
can
> work independently, and won't influence with each other. Thanks.
>
> - Original Message -----
> From: "peter lin" <[EMAIL PROTECTED]>
> To: "Tomcat Users List" <[EMAIL PROTECTED]>
> Sent: Tuesday, March 26, 2002 1:32 PM
> Subject: Re: AW: Multiple users share java bean?
>
>
> >
> > One common technique to solve this is to use JMS. All beans that are
> > instances of the same user listen to the same topic. when one instance
> > of the user's bean is updated, the other instances are notified. Each
> > bean then goes to the database to refresh itself.
> >
> > peter lin
> >
> >
> > Chenming Zhao wrote:
> > >
> > > In fact, it's a good and difficult topic. Now I haven't still
understood
> it
> > > completely. I have a question about my application.
> > >
> > > I describe the work what I need to finish.
> > > First the jsp file gets a user name, then pass it to java bean. And
the
> bean
> > > get some values from the database accoding to the user name, then get
a
> > > result and save it to database. The idea of synchronized objects
cannot
> > > work. I want to acitvate independent instance of java bean for any
user.
> How
> > > can I do? Is there any good book or material? Or maybe you can show me
> some
> > > simple example?
> > >
> > > Thanks.
> > >
> > > --
> > > To unsubscribe:   <mailto:[EMAIL PROTECTED]>
> > > For additional commands: <mailto:[EMAIL PROTECTED]>
> > > Troubles with the list: <mailto:[EMAIL PROTECTED]>
> >
> > --
> > To unsubscribe:   <mailto:[EMAIL PROTECTED]>
> > For additional commands: <mailto:[EMAIL PROTECTED]>
> > Troubles with the list: <mailto:[EMAIL PROTECTED]>
> >
> >
>
>
> --
> To unsubscribe:   <mailto:[EMAIL PROTECTED]>
> For additional commands: <mailto:[EMAIL PROTECTED]>
> Troubles with the list: <mailto:[EMAIL PROTECTED]>
>
> --
> To unsubscribe:   <mailto:[EMAIL PROTECTED]>
> For additional commands: <mailto:[EMAIL PROTECTED]>
> Troubles with the list: <mailto:[EMAIL PROTECTED]>
>
>


--
To unsubscribe:   <mailto:[EMAIL PROTECTED]>
For additional commands: <mailto:[EMAIL PROTECTED]>
Troubles with the list: <mailto:[EMAIL PROTECTED]>

--
To unsubscribe:   <mailto:[EMAIL PROTECTED]>
For additional commands: <mailto:[EMAIL PROTECTED]>
Troubles with the list: <mailto:[EMAIL PROTECTED]>

Re: AW: Multiple users share java bean?

[Chenming Zhao]

- Original Message -
From: "Wagoner, Mark" <[EMAIL PROTECTED]>
To: "'Tomcat Users List'" <[EMAIL PROTECTED]>
Sent: Tuesday, March 26, 2002 2:12 PM
Subject: RE: AW: Multiple users share java bean?


> Are you sure you really want independent instances of the bean, or just
the
> ability to keep the variable values separate by user?  If it is the
latter,
> then just use local variables in your bean methods.
>

It seems that couldn't work. The value of such variables can be updated by
another user's when there are two or more users calling the same java bean
almost at the same time. Here is my main work. First jsp write uname (when a
user login the website, there is a user name "uname") to the bean and
activate it, and get the result  or save it to the database.
 Jsp file:

???How about the scope value? session or request or page?

The result is:
<%= mb.test() %>

Bean code:
public class test
{
String uname= "";

public synchronized int test()
{
int real=0;
int eventCounter=0;
int numEvents;

// connect to the database and get the numEvents according to the
uname.
.;

while(eventCounter<=numEvents)
{
real=eventCounter;

// wait for 0.01 second
try{wait(10);}
catch(InterruptedException e){};
eventCounter++;
}
return real;
}

public synchronized void setUname(String sec)
{
uname= sec;
}
}

For user1, numEvents=100; and user2, it's 120. So I want to run them at the
same time, and hope to get resuls 100 and 120 respectively. But in fact I
got both 100 or 120. Have any idea? If my description is not clear, tell me
please.


> -Original Message-
> From: Chenming Zhao [mailto:[EMAIL PROTECTED]]
> Sent: Tuesday, March 26, 2002 2:06 PM
> To: Tomcat Users List
> Subject: Re: AW: Multiple users share java bean?
>
>
> What's the meaning of JMS? I'm not sure my problem is just what you said.
I
> want to get independent instance or the same bean for each user. So they
can
> work independently, and won't influence with each other. Thanks.
>
> - Original Message -----
> From: "peter lin" <[EMAIL PROTECTED]>
> To: "Tomcat Users List" <[EMAIL PROTECTED]>
> Sent: Tuesday, March 26, 2002 1:32 PM
> Subject: Re: AW: Multiple users share java bean?
>
>
> >
> > One common technique to solve this is to use JMS. All beans that are
> > instances of the same user listen to the same topic. when one instance
> > of the user's bean is updated, the other instances are notified. Each
> > bean then goes to the database to refresh itself.
> >
> > peter lin
> >
> >
> > Chenming Zhao wrote:
> > >
> > > In fact, it's a good and difficult topic. Now I haven't still
understood
> it
> > > completely. I have a question about my application.
> > >
> > > I describe the work what I need to finish.
> > > First the jsp file gets a user name, then pass it to java bean. And
the
> bean
> > > get some values from the database accoding to the user name, then get
a
> > > result and save it to database. The idea of synchronized objects
cannot
> > > work. I want to acitvate independent instance of java bean for any
user.
> How
> > > can I do? Is there any good book or material? Or maybe you can show me
> some
> > > simple example?
> > >
> > > Thanks.
> > >
> > > --
> > > To unsubscribe:   <mailto:[EMAIL PROTECTED]>
> > > For additional commands: <mailto:[EMAIL PROTECTED]>
> > > Troubles with the list: <mailto:[EMAIL PROTECTED]>
> >
> > --
> > To unsubscribe:   <mailto:[EMAIL PROTECTED]>
> > For additional commands: <mailto:[EMAIL PROTECTED]>
> > Troubles with the list: <mailto:[EMAIL PROTECTED]>
> >
> >
>
>
> --
> To unsubscribe:   <mailto:[EMAIL PROTECTED]>
> For additional commands: <mailto:[EMAIL PROTECTED]>
> Troubles with the list: <mailto:[EMAIL PROTECTED]>
>
> --
> To unsubscribe:   <mailto:[EMAIL PROTECTED]>
> For additional commands: <mailto:[EMAIL PROTECTED]>
> Troubles with the list: <mailto:[EMAIL PROTECTED]>
>
>


--
To unsubscribe:   <mailto:[EMAIL PROTECTED]>
For additional commands: <mailto:[EMAIL PROTECTED]>
Troubles with the list: <mailto:[EMAIL PROTECTED]>

RE: AW: Multiple users share java bean?

[Dahnke, Eric]

Referring to this point:

>Great, that's what I thought.  But here's why I'm getting confused. The 
>servlet tutorial says that a servlet is created once and once only (that's 
>when the init() is run).

If I comment out the init() method in my servlet do I get an instance of it
for each request?

Do people commonly do this?

--
To unsubscribe:   
For additional commands: 
Troubles with the list: 

Re: AW: Multiple users share java bean?

[peter lin]

I misunderstood. You want many users to use the same bean to get common
information, kind of like a message board. each user works
independently, but they are using a common bean.

someone else said "If it is the latter, then just use local variables in
your bean methods."

more information about the requirements would help. there are a variety
of ways to solve this type of problem, but they depend on the kind of
persistence required. If they never get persisted, than anything old
bean will do.

peter lin


Chenming Zhao wrote:
> 
> What's the meaning of JMS? I'm not sure my problem is just what you said. I
> want to get independent instance or the same bean for each user. So they can
> work independently, and won't influence with each other. Thanks.
> 
> -

--
To unsubscribe:   
For additional commands: 
Troubles with the list: 

RE: AW: Multiple users share java bean?

[Wagoner, Mark]

Are you sure you really want independent instances of the bean, or just the
ability to keep the variable values separate by user?  If it is the latter,
then just use local variables in your bean methods.

-Original Message-
From: Chenming Zhao [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, March 26, 2002 2:06 PM
To: Tomcat Users List
Subject: Re: AW: Multiple users share java bean?


What's the meaning of JMS? I'm not sure my problem is just what you said. I
want to get independent instance or the same bean for each user. So they can
work independently, and won't influence with each other. Thanks.

- Original Message -
From: "peter lin" <[EMAIL PROTECTED]>
To: "Tomcat Users List" <[EMAIL PROTECTED]>
Sent: Tuesday, March 26, 2002 1:32 PM
Subject: Re: AW: Multiple users share java bean?


>
> One common technique to solve this is to use JMS. All beans that are
> instances of the same user listen to the same topic. when one instance
> of the user's bean is updated, the other instances are notified. Each
> bean then goes to the database to refresh itself.
>
> peter lin
>
>
> Chenming Zhao wrote:
> >
> > In fact, it's a good and difficult topic. Now I haven't still understood
it
> > completely. I have a question about my application.
> >
> > I describe the work what I need to finish.
> > First the jsp file gets a user name, then pass it to java bean. And the
bean
> > get some values from the database accoding to the user name, then get a
> > result and save it to database. The idea of synchronized objects cannot
> > work. I want to acitvate independent instance of java bean for any user.
How
> > can I do? Is there any good book or material? Or maybe you can show me
some
> > simple example?
> >
> > Thanks.
> >
> > --
> > To unsubscribe:   <mailto:[EMAIL PROTECTED]>
> > For additional commands: <mailto:[EMAIL PROTECTED]>
> > Troubles with the list: <mailto:[EMAIL PROTECTED]>
>
> --
> To unsubscribe:   <mailto:[EMAIL PROTECTED]>
> For additional commands: <mailto:[EMAIL PROTECTED]>
> Troubles with the list: <mailto:[EMAIL PROTECTED]>
>
>


--
To unsubscribe:   <mailto:[EMAIL PROTECTED]>
For additional commands: <mailto:[EMAIL PROTECTED]>
Troubles with the list: <mailto:[EMAIL PROTECTED]>

--
To unsubscribe:   <mailto:[EMAIL PROTECTED]>
For additional commands: <mailto:[EMAIL PROTECTED]>
Troubles with the list: <mailto:[EMAIL PROTECTED]>

Re: AW: Multiple users share java bean?

[Vijay Shinde]

JMS - Javs Messaging Service

Chenming Zhao wrote:

> What's the meaning of JMS? I'm not sure my problem is just what you said. I
> want to get independent instance or the same bean for each user. So they can
> work independently, and won't influence with each other. Thanks.
>
> - Original Message -
> From: "peter lin" <[EMAIL PROTECTED]>
> To: "Tomcat Users List" <[EMAIL PROTECTED]>
> Sent: Tuesday, March 26, 2002 1:32 PM
> Subject: Re: AW: Multiple users share java bean?
>
> >
> > One common technique to solve this is to use JMS. All beans that are
> > instances of the same user listen to the same topic. when one instance
> > of the user's bean is updated, the other instances are notified. Each
> > bean then goes to the database to refresh itself.
> >
> > peter lin
> >
> >
> > Chenming Zhao wrote:
> > >
> > > In fact, it's a good and difficult topic. Now I haven't still understood
> it
> > > completely. I have a question about my application.
> > >
> > > I describe the work what I need to finish.
> > > First the jsp file gets a user name, then pass it to java bean. And the
> bean
> > > get some values from the database accoding to the user name, then get a
> > > result and save it to database. The idea of synchronized objects cannot
> > > work. I want to acitvate independent instance of java bean for any user.
> How
> > > can I do? Is there any good book or material? Or maybe you can show me
> some
> > > simple example?
> > >
> > > Thanks.
> > >
> > > --
> > > To unsubscribe:   <mailto:[EMAIL PROTECTED]>
> > > For additional commands: <mailto:[EMAIL PROTECTED]>
> > > Troubles with the list: <mailto:[EMAIL PROTECTED]>
> >
> > --
> > To unsubscribe:   <mailto:[EMAIL PROTECTED]>
> > For additional commands: <mailto:[EMAIL PROTECTED]>
> > Troubles with the list: <mailto:[EMAIL PROTECTED]>
> >
> >
>
> --
> To unsubscribe:   <mailto:[EMAIL PROTECTED]>
> For additional commands: <mailto:[EMAIL PROTECTED]>
> Troubles with the list: <mailto:[EMAIL PROTECTED]>


--
To unsubscribe:   <mailto:[EMAIL PROTECTED]>
For additional commands: <mailto:[EMAIL PROTECTED]>
Troubles with the list: <mailto:[EMAIL PROTECTED]>

Re: AW: Multiple users share java bean?

[Chenming Zhao]

What's the meaning of JMS? I'm not sure my problem is just what you said. I
want to get independent instance or the same bean for each user. So they can
work independently, and won't influence with each other. Thanks.

- Original Message -
From: "peter lin" <[EMAIL PROTECTED]>
To: "Tomcat Users List" <[EMAIL PROTECTED]>
Sent: Tuesday, March 26, 2002 1:32 PM
Subject: Re: AW: Multiple users share java bean?


>
> One common technique to solve this is to use JMS. All beans that are
> instances of the same user listen to the same topic. when one instance
> of the user's bean is updated, the other instances are notified. Each
> bean then goes to the database to refresh itself.
>
> peter lin
>
>
> Chenming Zhao wrote:
> >
> > In fact, it's a good and difficult topic. Now I haven't still understood
it
> > completely. I have a question about my application.
> >
> > I describe the work what I need to finish.
> > First the jsp file gets a user name, then pass it to java bean. And the
bean
> > get some values from the database accoding to the user name, then get a
> > result and save it to database. The idea of synchronized objects cannot
> > work. I want to acitvate independent instance of java bean for any user.
How
> > can I do? Is there any good book or material? Or maybe you can show me
some
> > simple example?
> >
> > Thanks.
> >
> > --
> > To unsubscribe:   <mailto:[EMAIL PROTECTED]>
> > For additional commands: <mailto:[EMAIL PROTECTED]>
> > Troubles with the list: <mailto:[EMAIL PROTECTED]>
>
> --
> To unsubscribe:   <mailto:[EMAIL PROTECTED]>
> For additional commands: <mailto:[EMAIL PROTECTED]>
> Troubles with the list: <mailto:[EMAIL PROTECTED]>
>
>


--
To unsubscribe:   <mailto:[EMAIL PROTECTED]>
For additional commands: <mailto:[EMAIL PROTECTED]>
Troubles with the list: <mailto:[EMAIL PROTECTED]>

Re: AW: Multiple users share java bean?

[peter lin]

One common technique to solve this is to use JMS. All beans that are
instances of the same user listen to the same topic. when one instance
of the user's bean is updated, the other instances are notified. Each
bean then goes to the database to refresh itself.

peter lin


Chenming Zhao wrote:
> 
> In fact, it's a good and difficult topic. Now I haven't still understood it
> completely. I have a question about my application.
> 
> I describe the work what I need to finish.
> First the jsp file gets a user name, then pass it to java bean. And the bean
> get some values from the database accoding to the user name, then get a
> result and save it to database. The idea of synchronized objects cannot
> work. I want to acitvate independent instance of java bean for any user. How
> can I do? Is there any good book or material? Or maybe you can show me some
> simple example?
> 
> Thanks.
> 
> --
> To unsubscribe:   
> For additional commands: 
> Troubles with the list: 

--
To unsubscribe:   
For additional commands: 
Troubles with the list: 

Re: AW: Multiple users share java bean?

[Soefara Redzuan]

First of all, thank you so much Alexander for taking the time to explain 
this so thoroughly.


> > First, am I correct in saying that the default behaviour for a
> > Javabean is that each servlet or JSP that uses it will create > a new 
>instance of that Javabean ?  For example, if we have > Register.jsp which 
>uses a Javabean called memberData.java then > if 2 people were to submit 
>data to Register.jsp
> > at exactly the same time, each page would actually create and use
> > a separate instance of the bean memberData.java. Is this correct?
>
>Nice answer: That depends :-)
>a) 
>The bean is created for exactly this page executed by this user
>
>b) 
>The bean is created for this page and all pages you  in this 
>request.
>
>c) 
>The bean is created and accessible by all pages of this application
>(You must include this line into all pages)
>p.ex.: You create a session bean that accesses a database. The database
>connection will be made once and will stand until the session runs out.
>There is a seperate bean for every user, though.
>
>d) 
>The bean is created the first time a user accesses a page in your
>application. From then on, every user and every page will have the same
>bean!

Lovely concise answer. I've printed this out as a cheat sheet :-)

Now, since each JSP is essentially a servlet, how does the servlet perform 
the sharing of the javabean ? Does a servlet that shares a javabean (similar 
to the JSP case [d] above, where scope="application"), is actually creating 
the javabean as a *static* variable so that it is shared by all members of 
the class ?


> > Third, I'm getting confused and starting to doubt my understanding of
> > servlets within the Tomcat servlet container. If we have a simple 
>servlet
> > using the helloWorld.class and it just prints "hello world" to
> > the web page,
> > then if 10 people were to requsest the servlet at the same time, am I
> > correct in assuming that 10 different instances of the class are
> > created to
> > handle these requests ?
>
>true


Great, that's what I thought.  But here's why I'm getting confused. The 
servlet tutorial says that a servlet is created once and once only (that's 
when the init() is run).
http://java.sun.com/docs/books/tutorial/servlets/lifecycle/index.html
If the servlet class is created only once, how does Tomcat then create 
multiple instances of the class ?

>I could recommend a german book here, but I think that wouldn't be of
>great use for you...

Good guess. Learning German through Java would surely be a challenge :)

Thank you again, Soefara.


_
MSN Photos is the easiest way to share and print your photos: 
http://photos.msn.com/support/worldwide.aspx


--
To unsubscribe:   
For additional commands: 
Troubles with the list: