Fundamental j2ee classpath question

hi folks --
I have a j2ee project with
- a WAR (which has among other things a servlet in it)
- a ejb project (which has a stateless session bean in it)
I need to call the session bean from the servlet and my servlet code gets a reference to the bean via jndi as follows
...skipping jndi stuff ...
LoadTimerTaskHome loadTimerTaskHome = (LoadTimerTaskHome)PortableRemoteObject.narrow( timerHomeObject, LoadTimerTaskHome.class);
However, at compile time, LoadTimerTaskHome (the home interface of the bean) can't be resolved in the servlet class. Which makes sense cuz how would the servlet class know about the bean class?
And that's the question: At compile time, how can i make classes in my WAR aware of classes in my EJB proj, which are deployed to the same EAR? There must be a very simple J2EE way of doing this...
I'm not an EJB person, so i'm just confused about what is probably extremely basic....
thx VERY much for any insights...

A brute force approach is to also package the ejb interface classes (and any classes needed by those interfaces etc.) in the .war. However, a cleaner solution is to put the shared classes within a utility .jar and package it within the .ear such they are visible by both .war and ejb-jar modules.
In Java EE 5, this is easily done by putting the shared .jar in "lib" directory at the top-level of the .ear. Java EE 5 guarantees that any .jars within that directory are visible to all component modules within the .ear.
Prior to Java EE 5, this was only possible by using the MANIFEST-CLASSPATH attribute within each module to refer to the utility .jar. That's very cumbersome and error-prone so I recommend the automatic "lib" directory approach.
--ken

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Hi Emily,
The solutions to your queries :
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Can you Pls tell me how to do ?
A. Ya. I assume that u have installed the software on C:
Find where the ejb.jar file is installed on ur system. Then Type the following at the command prompt :
SET CLASSPATH=C:\path\to\your\ejb.jar
For Servlets:
Find where the ejb.jar file is installed on ur system. Then Type the following at the command prompt :
SET CLASSPATH=C:\path\to\your\servlets.jar
The JSP does not require a CLASSPATH setting. The servlets CLASSPATH handles it for JSP also.
Q. In the program , it imports " import org.w3c.dom.* " because of using getXML method. when I
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Labview fundamentals test question

Hi,
I have attached a question from LV fundamentals test. Can't figure out the reasoning if the answer should be A or B. Any help appreciated?
Thanks,
ABM
Solved!
Go to Solution.
Attachments:
fundamental Q_8.doc ‏109 KB

Nono. The answer is B. The option A is incorrect.
Keep in mind that there are 25 points on graph. If the answer is A, there must be at least at one point with a value greater than 5 on the graph, since the possible outcome range from 0-10. The probabilty of getting a 6, 7, 8, 9, aor 10 is 5/11. That is a probability of about 50%.
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If you flip a coin 10 times, is it possible to not get a tail? We can think about it this way.
Yik
Kudos and Accepted as Solution are welcome!

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Hi Mark,
I'm sure I haven't understood your question, so the following may be useless to you (please excuse me if it is).
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The tooldocs Web page has details of how the JVM locates classes.
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Since the commons net 1.4.1 is compatible with jdk 1.3.1, I should only need to use loadjava on the .jar file. In fact, that works, given that there is no failure on load due to incompatible .jar or .class files structure.
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hi,
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Hi,
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Hello everybody,
In every J2EE instance there is a dispatcher and server0. This server0 could be up to server<n>, depending upon the load on the instance. When you add this server to J2EE then it basically adds more resources to instance.
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hi Sume
> I really wanted a quick starting tip about how to
> monitor that server is busy because of J2EE
> application.
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ak.
Message was edited by: Arun Kumar Ravi

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Use a ClassPath entry in your EJB jar module MANIFEST.MF file
Mark Cordobal
[email protected] (Frank LaRosa) wrote:
Hi,
I have a burning question regarding EJBs and classpaths.
Here is my situation:
- My application uses EJBs, Servlets and JSP pages
- My EJB remote interfaces and implementation classes extend common,
abstract base classes
- My EJB implementation classes use several utility classes, which are
also used by my servlets.
- Each EJB is deployed in a separate JAR file
The question I have is which classes should be included in the EJB JAR
files.
I'd like to put just the EJB implementation class in the EJB JAR, and
put everything else in a common JAR that is placed in my WEB-INF/lib
folder and shared by the rest of the application. However, if I do
that, Weblogic won't load the EJBs because it tries to do so before it
deploys my web app, and hence before it adds the JARs in the
WEB-INF/lib folder to its classpath.
I can explicitly add my jar to the Weblogic classpath on the
commandline (weblogic.class.path property). Now my EJBs load. However,
my servlets become unable to load any classes from any jar in
WEB-INF/lib. I read something about it being a bad idea to include a
jar from WEB-INF/lib in the classpath, so I'm probably seeing that
problem.
The third option is to include all the dependent classes in my EJB
jars themselves, in addition to deploying them in WEB-INF/lib. This
works, but it bothers me that there are multiple copies of the same
class files lying around.
I'm sure I'm not the first developer who's written an EJB that shares
classes with a servlet or JSP page. What's the proper way to do this?
Thanks.

J2EE Design Questions

Please forgive me, I am just getting into J2EE and, despite having a mountain of manuals on my desk, I'm having a little trouble figuring out how everything fits together...
Question 1.
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Question 2.
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http://java.sun.com/products/jndi/tutorial/getStarted/examples/naming.html
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I fully realize that this would imply (at best), in a distributed environment, the rather strange behavior of logging calls bouncing around to the first machine that happend to instantiate a logging bean...
regardless, I have the following broken code:
import javax.ejb.Stateless;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
@Stateless
public class LogEJB implements VCMarkWeb.log.LogEJBRemote {
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singletons are counter to the very concept of distributed computing, which EJB is of course liable to do.
So while you may have a class that behaves like a singleton inside its own enterprise application context, there is no guarantee it will behave like a singleton when seen from the perspective of a client.
In fact, when the enterprise application is run in a distributed environment it's guaranteed to not be a singleton anymore as each JVM instance will have its own instance of the class loaded.
It can get even worse depending on application server architecture, and you may end up having several instances of your "singleton" running inside the same server (possibly the same application) though that is more rare.
So the best thing to do with singletons is forget all about them.

Classpath question about the " . " notation

I try to run the class file from the /a/b/c/d directory using classpath:
java -classpath . MainClass
But so far this doesn't work. My current directory is /d which is the same as MainClass is in, and I use the " . " notation in -classpath to indicate a search in the current directory, and if I use the " . " then the full name of the class is not required (since I am in the same directory). But I know I am using classpath correctly because in my other try this works:
java -classpath /a b.c.d.MainClass, when my current directory is /a.
Thanks for any ideas.
My directory structure is as follows:
a
b
c
d
MainClass.class
package b.c.d;
public class MainClass {
public static void main(String[] args) {
System.out.println("Test");
}

So, basically no matter where I tell the classpath to look for a class, or what is my current directory I have to *always" include the full-qualified name for the class? Is that correct? I couldn't find that specific piece of information in the java tutorials...

Some J2EE Design Questions

Hello All,
1. How can a daemon process/service implemented in J2EE world? Any design pattern?
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I have the same problem.
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Suppose you have a distributed application consisting of a number (max 100) of webservers (Servlets/JSPs technology) which send information (e.g. a random number) to one central system (using EJBs). The central system receives the random numbers through a session facade and adds the contributions from the various webservers. When the total reaches a certain level, the central system needs to inform all contributing webservers of the new total.
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1. messaging (probably too complicated?)Actually quite easy, especially since your app server probably already has a JMS provider. And, if all of your Servlet servers are basically running the same application (e.g. same deployments), you'll only have to write one MessageListener to be placed in the application.
2. polling from the webservers (too much traffic?)Too much traffic, threading issues, wasteful of processing power - a whole host of problems with that approach.
3. central system invoking a Servlet on each webserver
(is this practical?)Then your main EJB application would have to "know" the address of each and every webserver - which gets you into a maintenance nightmare. Not practical at all...

J2EE Design Question -- Am I On The Right Track?

There are multiple tables in my database. Each table has a primary key, and the table that relates to other tables has foreign keys. I have to match the primary key and foreign key to go from one table to another. The specifics are spelled out below:
The first table has login, pwd, and a primary key as fields, the second table contains completely different fields plus a primary key and foreign keys. The fields in the third table are different from those in the first and second tables plus its primary key. Queries to the third table can be made only if the user login and pwd are found in the first table, and through the second table's relation to the first table and the third table�s relation to the second table.
The fields of all those tables may be accessed concurrently, but the fields are read-only (for the time being).
I have a servlet to handle browser interactions. And I have a session bean to handle the workflow and business logic. However, I am confused with the choices between VO and entity beans.
I first thought that I should use value objects to represent the data fields of the specific rows I looked for in those tables. Here is what I read about Value Object:
"If a business object merely represents a structure to hold data fields, and the only behavior it provides are get and set method for the fields, then it would be wasteful of system resources to implement it as an enterprise bean. To avoid expensive remote methods calls (system resources and network bandwidth) to get the value of entity object fields, a value object is used to represent the details of the entity object. Only one remote call is required to retrieve the value object and then a client�s request to query the state of the object can then be met via local get methods on this details object."
On my second thought, I think I should use entity beans to represent the specific rows I am looking for in those tables because I must use primary key and foreign key relations to go from one table to another.
I do not use DAO because I am using CMP. The first call is within the session bean. It is a remote call to look for a specific row in the first table in my database. Subsequently, the mapping of the row in the first table to the second table, and the mapping of the row in the second table to the third table are all invoked on the �local" interfaces of those entity beans.
client(browser)-->front controller(servlet)-->session facade(session ejb)-->entity ejb-->entity ejb -- > entity ejb
Please advise if this is the right design. Am I on the right track? Is there improvement to be made?

I might not explain my question well in my previous post -- there is no business logic involved in what I am doing to go from the first entity bean to the second entity bean and to go from the second entity bean to the third entity bean.
Based on the login information, I have to go through those entity beans to find the very specific row in the third table in order to get the data field I need. That is to say, only thing involved is searching for rows.
In my view, session bean -- > 1st entity bean -- > 2nd entity bean -- > 3rd entity bean
1. session bean -- > 1st entity bean: remote call and returns the key to the 1st entity bean for locating the 2nd entity bean
2. 1st entity bean -- > 2nd entity bean: local call and returns the key to the 2nd entity bean for locating the 3rd entity bean
3. 2nd entity bean -- > 3rd entity bean: local call and then returns the value of the specific field to the session bean
The alternative approach is:
session bean
|
+ + +
1st entity bean 2nd entity bean 3rd entity bean
1. session bean -- > 1st entity bean: remote call and returns the key to the session bean for locating the 2nd entity bean
2. session bean -- > 2nd entity bean: remote call
and returns the key to the session bean for locating the 3rd entity bean
3. session bean -- > 3rd entity bean: remote call and the session bean can get the value of the specific field from the 3rd entity bean
I do not know which approach to go for. Please provide guidance. Thanks.

Setting CLASSPATH question

Hi,
          I'm evaluating Weblogic 5.1. My evaluation requires me to write an
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          server, and have an HTML page call into the EJB through a servlet. The
          servlet is also sitting on the server. I've managed to prove that this
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          I've set my HTML page to have a link to the servlet I need to hit
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          wasn't found in classpath."
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          registered that location in my wl.props and it shows on the server. I'm
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          Thanks, 'Soli


[email protected] (Chris Basoli) wrote in
          <[email protected]>:
          >Hi,
          >"weblogic.servlet.ServletName" is my location on the server. I've
          >registered that location in my wl.props and it shows on the server. I'm
          >running Win2K and have the location of my EJB and location of the
          >servlet in both the User CLASSPATH and the System CLASSPATH.
          I'm having a little trouble understanding "my location on the server". The
          registration is for associating names with classfiles. Thus, in order for
          what it seems like you're saying here to work, you'd need (assuming a
          default installation of WLS):
          in weblogic.properties:
          weblogic.httpd.servlet.classpath=c:/weblogic/myserver/servletclasses
          weblogic.httpd.register.ServletName=weblogic.servlet.ServletName
          on the filesystem:
          c:\weblogic\myserver\servletclasses\weblogic\servlet\ServletName.class
          >
          >Can anyone help me out? Where can I find the exact meaning of error
          >"10.5.1.500 Internal Server Error"?
          From this error, I can determine that you do have the register part of the
          properties file properly set up. Either the class file is not there (see
          filesystem statement) or it does not have the proper package statement.
          The error is actually "500 Internal Server Error". The 10.5.1 might be a
          documentation reference (Cameron? BEA?), but the 500 error is sufficient.
          It means the web server you're talking to had a processing error that it
          couldn't recover from and thus could not return the response you requested.
          You'll usually get in in servlet failures, or app server failures.
          Jesse

Fundamental j2ee classpath question

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