JNDI, session beans and JBoss

4 Message(s) by 2 Author(s) originally posted in java beans

From: cold80

Date: Friday, February 02, 2007

I was trying the first EJB

<specification, business, programming> (EJB) A {server}-side
	{component architecture} for writing reusable {business logic}
	and {portable} {enterprise} applications.  EJB is the basis of
	{Sun}'s {Java 2 Platform, Enterprise Edition} (J2EE).

	Enterprise JavaBean components are written entirely in {Java}
	and run on any EJB compliant server.  They are {operating
	system}, {platform}, and {middleware} independent, preventing
	vendor {lock-in}.

	EJB servers provide system-level services (the "plumbing")
	such as {transactions}, security, {threading}, and
	{persistence}.

	The EJB architecture is inherently transactional,
	{distributed}, {multi-tier}, {scalable}, secure, and {wire
	protocol} neutral - any {protocol} can be used: {IIOP},
	{JRMP}, {HTTP}, {DCOM} etc.  EJB 1.1 requires {RMI} for
	communication with components.  EJB 2.0 is expected to require
	support for RMI/IIOP.

	EJB applications can serve assorted clients: {browsers}, Java,
	{ActiveX}, {CORBA} etc.  EJB can be used to wrap {legacy
	systems}.

	EJB 1.1 was released in December 1999.  EJB 2.0 is in
	development.

	Sun claims broad industry adoption.  30 vendors are shipping
	server products implementing EJB.  Supporting vendors include
	{IBM}, {Fujitsu}, {Sybase}, {Borland}, {Oracle}, and
	{Symantec}.

	An alternative is Microsoft's MTS ({Microsoft Transaction
	Server}).

	{Home (http://java.sun.com/products/ejb/)}.

	{FAQ (http://java.sun.com/products/ejb/faq.html)}.

	(2000-04-20)

example of the book "Mastering Enterprise
JAVA Beans". After building the bean

<programming> A {component architecture} for the {Java}
	programming language, developed initially by {Sun}, but now
	available from several other vendors.  JavaBeans components
	are called "{beans}".

	JavaBeans allows developers to create reusable software
	components that can then be assembled together using visual
	application builder tools including {Sybase}'s {PowerJ},
	{Borland}'s {JBuilder}, {IBM}'s {Visual Age for Java},
	{SunSoft}'s {Java Workshop} and {Symantec}'s {Visual Cafe}.

	JavaBeans support Introspection (a builder tool can analyze
	how a Bean works), Customisation (developers can customise the
	appearance and behaviour of a Bean), Events (Beans can
	communicate), Properties (developers can customise and program
	with Beans(?)) and Persistence (customised Beans can be stored
	and reused).

	{Home (http://www.javasoft.com/beans/)}.

	(1997-11-20)

and deploying it successfully I
had many problems making the client

<programming> A computer system or process that requests a
	service of another computer system or process (a "{server}")
	using some kind of {protocol} and accepts the server's
	responses.  A client is part of a {client-server} software
	architecture.

	For example, a {workstation} requesting the contents of a file
	from a {file server} is a client of the file server.

	(1997-10-27)

work. The client code

<software> Instructions for a computer in some programming
	language, often {machine language}.  The word "code" is often
	used to distinguish instructions from {data} (e.g. "The code
	is marked 'read-only'") whereas "{software}" is used in
	contrast with "{hardware}" and may consist of more than just
	code.

	(2000-04-08)

is very
simple

public class

1. <programming> The prototype for an {object} in an
	{object-oriented language}; analogous to a {derived type} in a
	{procedural language}.  A class may also be considered to be a
	set of objects which share a common structure and behaviour.
	The structure of a class is determined by the {class
	variables} which represent the {state} of an object of that
	class and the behaviour is given by a set of {methods}
	associated with the class.

	Classes are related in a {class hierarchy}.  One class may be
	a specialisation (a "{subclass}") of another (one of its
	"{superclasses}") or it may be composed of other classes or it
	may use other classes in a {client-server} relationship.  A
	class may be an {abstract class} or a {concrete class}.

	See also {signature}.

	2. <programming> See {type class}.

	3. <networking> One of three types of {Internet addresses}
	distinguished by their most significant bits.

	3. <language> A language developed by the {Andrew Project}.
	It was one of the first attempts to add {object-oriented}
	features to {C}.

	(1995-05-01)

Main {
public static void main(String[] args) throws Exception{
Context ctx=new InitialContext();

Hello hello=(Hello)ctx.lookup("HelloBean");
System.out.println(hello.hello());
}
}

But I found many problems using the lookup method. Using the full
"path" for the interface

<jargon> A boundary across which two systems communicate.  An
	interface might be a hardware connector used to link to other
	devices, or it might be a convention used to allow
	communication between two software systems.  Often there is
	some intermediate component between the two systems which
	connects their interfaces together.  For example, two {EIA-232}
	interfaces connected via a serial cable.

	See also {graphical user interface}, {Application Program
	Interface}.

	(1996-05-22)

"examples.session.stateless.Hello", as
specified in the book, I got

Exception in thread

1. See {multithreading}.

	2. See {threaded code}.

	3. {topic thread}.

	[{Jargon File}]

"main" JAVAx.naming.NameNotFoundException:
examples.session.stateless.Hello not bound

Otherwise, using the line

Hello hello=(Hello)ctx.lookup("HelloBean");

I got the error

Exception in thread "main" JAVA.lang.ClassCastException:
org.jnp.interfaces.NamingContext cannot be cast to
examples.session.stateless.Hello

So I think I was grabbing the wrong object

<object-oriented> In {object-oriented programming}, an
	instance of the data structure and behaviour defined by the
	object's {class}.  Each object has its own values for the
	{instance variables} of its class and can respond to the
	{methods} defined by its class.

	For example, an object of the "Point" class might have
	instance variables "x" and "y" and might respond to the "plot"
	method by drawing a dot on the screen at those coordinates.

	(2004-01-26)

from JBoss. Looking on many
posts and web pages I found that using

Hello hello=(Hello)ctx.lookup("HelloBean/remote");

I can get the right object. Why? It's really difficult for me to
understand the way JNDI is naming my resources...can you give me
informations about that? It'd be really appreciated...

Cold

From: Per Newgro

Date: Saturday, February 03, 2007

Hallo cold80@xxxxxxxxxxx,

I was trying the first EJB example of the book "Mastering Enterprise
JAVA Beans". After building the bean and deploying it successfully I
had many problems making the client work. The client code is very
simple
public class Main {
public static void main(String[] args) throws Exception{
Context ctx=new InitialContext();
Hello hello=(Hello)ctx.lookup("HelloBean");
System.out.println(hello.hello());
}
}

I expect

<language, tool> A {Unix} tool written in {Tcl} and a {script
	language} for automating the operation of {interactive}
	applications such as {telnet}, {FTP}, {passwd}, {fsck},
	{rlogin}, {tip}, etc..  Expect can feed input to other
	programs and perform {pattern matching} on their output.  It
	is also useful for testing these applications.  By adding
	{Tk}, you can also wrap interactive applications in {X11}
	{GUIs}.

	{Home (http://expect.nist.gov/)}.

	["expect: Scripts for Controlling Interactive Tasks", Don
	Libes, Comp Sys 4(2), U Cal Press Journals, Nov 1991].

	(1997-06-09)

Hello ist your BusinessInterface. But the lookup only returns the
HomeInterface. AFAIK

<chat> as far as I know.

you've to do the following
Object o = new InitialContext().lookup("HelloBean");
HelloHome home = (HelloHome) PortableRemoteObject.narrow(o,
HelloHome.class);
HelloRemote remote = home.create();

With this I expect you deployed your bean under the name "HelloBean".

But I found many problems using the lookup method. Using the full
"path" for the interface "examples.session.stateless.Hello", as
specified in the book, I got
Exception in thread "main" JAVAx.naming.NameNotFoundException:
examples.session.stateless.Hello not bound

Because the bean isn't bound under that name (see META-INF/ejb-jar.xml for
details).

Otherwise, using the line
Hello hello=(Hello)ctx.lookup("HelloBean");
I got the error
Exception in thread "main" JAVA.lang.ClassCastException:
org.jnp.interfaces.NamingContext cannot be cast to
examples.session.stateless.Hello

Because you do not get a Hello instance. It's a home interface you get.

So I think I was grabbing the wrong object from JBoss. Looking on many
posts and web pages I found that using
Hello hello=(Hello)ctx.lookup("HelloBean/remote");
I can get the right object. Why? It's really difficult for me to
understand the way JNDI is naming my resources...can you give me
informations about that? It'd be really appreciated...

JNDI is a way to bind a name to a class and get a remote (or local) instance
of this class. The EJB spec requires the definition of a deployment
descriptor file

<file system> An element of data storage in a {file system}.

	The history of computing is rich in varied kinds of files and
	{file systems}, whether ornate (e.g., {Macintosh file system}
	for a well-known case) or deficient (e.g., many simple
	pre-1980s file systems don't allow {directories}).

	However, the prototypical file has these characteristics:

	* It is a single sequence of bytes (but consider {Macintosh}
	{resource forks}).

	* It has a finite length, unlike, e.g. a {Unix} {device}.

	* It is stored in a {non-volatile storage} medium (but see
	{ramdrive}).

	* It exists (nominally) in a {directory}.

	* It has a name that it can be referred to by in file
	operations, possibly in combination with its {path}.

	Additionally, a file system may associate other information
	with a file, such as {permission} bits or other {file
	attributes}; timestamps for file creation, last revision, and
	last access; revision numbers (a` la VMS), and other kinds of
	{magic}.

	Compare: {document}.

	(1997-04-08)

ejb-jar.xml. Here you can define the bean environment
(jndi-name, home class, remote class etc.). The container reads this file
and configures your beans. So you've a defined way for accessing your
beans.

Cheers
Per

From: cold80

Date: Monday, February 05, 2007

I did not mentioned that my example is developed using EJB 3.0. Maybe
the container is defining the local and remote interfaces for me, but
I just define a interface as

package examples.session.stateless;

public interface Hello {
public String hello();
}

and a class implementation

package examples.session.stateless;

import JAVAx.ejb.Stateless;
import JAVAx.ejb.Remote;

@xxxxxxxxxxx
@xxxxxxxxxxx(Hello.class)
public class HelloBean implements Hello{
public String hello(){
System.out.println("hello()");
return "Hello world!!!";
}
}

So, as you see, I'm not using ejb-jar.xml file to define the
informations needed by the container. Intead I'm writing annotation

1. <programming, compiler> Extra information associated with a
	particular point in a document or program.  Annotations may be
	added either by a {compiler} or by the programmer.  They are
	not usually essential to the correct function of the program
	but give hints to improve performance.

	2. <hypertext> A new commentary {node} linked to an existing
	node.  If readers, as well as authors, can annotate nodes,
	then they can immediately provide feedback if the information
	is misleading, out of date or plain wrong.

	(1995-11-26)

s
on the code. Do you think I've to write

1. <chat> {Unix}'s simple {talk} command and {protocol}.
	write has been largely superseded by {talk} and then {irc}.

	An enhancement, {RWP}, has been proposed.

	2. <tool> A simple {text editor} for {Windows}.

	(1998-04-28)

the ejb-jar.xml file as
well? I mean, is it because I did not write it that I can not access it?
Do you know where I can find informations about this matter on the
Internet (specific for Jboss, actually)?

Thank you again for your help

Cold

Per Newgro ha scritto:

Hallo cold80@xxxxxxxxxxx,
> I was trying the first EJB example of the book "Mastering Enterprise
> JAVA Beans". After building the bean and deploying it successfully I
> had many problems making the client work. The client code is very
> simple
>
> public class Main {
> public static void main(String[] args) throws Exception{
> Context ctx=new InitialContext();
>
> Hello hello=(Hello)ctx.lookup("HelloBean");
> System.out.println(hello.hello());
> }
> }
I expect Hello ist your BusinessInterface. But the lookup only returns the
HomeInterface. AFAIK you've to do the following
Object o = new InitialContext().lookup("HelloBean");
HelloHome home = (HelloHome) PortableRemoteObject.narrow(o,
HelloHome.class);
HelloRemote remote = home.create();
With this I expect you deployed your bean under the name "HelloBean".
> But I found many problems using the lookup method. Using the full
> "path" for the interface "examples.session.stateless.Hello", as
> specified in the book, I got
>
> Exception in thread "main" JAVAx.naming.NameNotFoundException:
> examples.session.stateless.Hello not bound
Because the bean isn't bound under that name (see META-INF/ejb-jar.xml for
details).
> Otherwise, using the line
>
> Hello hello=(Hello)ctx.lookup("HelloBean");
>
> I got the error
>
> Exception in thread "main" JAVA.lang.ClassCastException:
> org.jnp.interfaces.NamingContext cannot be cast to
> examples.session.stateless.Hello
Because you do not get a Hello instance. It's a home interface you get.
> So I think I was grabbing the wrong object from JBoss. Looking on many
> posts and web pages I found that using
>
> Hello hello=(Hello)ctx.lookup("HelloBean/remote");
>
> I can get the right object. Why? It's really difficult for me to
> understand the way JNDI is naming my resources...can you give me
> informations about that? It'd be really appreciated...
JNDI is a way to bind a name to a class and get a remote (or local) instance
of this class. The EJB spec requires the definition of a deployment
descriptor file ejb-jar.xml. Here you can define the bean environment
(jndi-name, home class, remote class etc.). The container reads this file
and configures your beans. So you've a defined way for accessing your
beans.
Cheers
Per

From: Per Newgro

Date: Monday, February 05, 2007

Hallo cold80@xxxxxxxxxxx,

I did not mentioned that my example is developed using EJB 3.0.
Aha.

Maybe the container is defining the local and remote interfaces for me,
but I just define a interface as
package examples.session.stateless;
public interface Hello {
public String hello();
}

In ejb-3.0 spec the "default" for the business interface (here Hello) is
@xxxxxxxxxxx U have to specify it as @xxxxxxxxxxx

and a class implementation
package examples.session.stateless;
import JAVAx.ejb.Stateless;
import JAVAx.ejb.Remote;
@xxxxxxxxxxx
@xxxxxxxxxxx(Hello.class)
public class HelloBean implements Hello{
public String hello(){
System.out.println("hello()");
return "Hello world!!!";
}
}

The @xxxxxxxxxxx annotation is afaik not required if you added it to Hello.

So, as you see, I'm not using ejb-jar.xml file to define the
informations needed by the container. Intead I'm writing annotations
on the code. Do you think I've to write the ejb-jar.xml file as
well?

Nope. Benefit of EJB3 is afaik the simplification of deployment to. SO
ejb-jar.xml isn't required (but possible)

I mean, is it because I did not write it that I can not access it?
Do you know where I can find informations about this matter on the
Internet (specific for Jboss, actually)?

I strongly recommend you to read the ejb-3.0 spec. It's realy simple to
read. After this much of the new concepts are clear. Trust me.
You can download

<jargon> To transfer data from one computer to another.
	Downloading usually refers to transfer from a larger "host"
	system (especially a {server} or {mainframe}) to a smaller
	"client" system, especially a {microcomputer} or specialised
	peripheral, and "{upload}" usually means from small to large.

	Others hold that, technically, download means "receive" and
	upload means "send", irrespective of the size of the systems
	involved.

	Note that in communications between ground and space,
	space-to-earth transmission is always "down" and the reverse
	"up", regardless of size.  So far the in-space machines have
	invariably been smaller; thus the upload/download distinction
	has been reversed from its usual sense.

	[{Jargon File}]

	(2003-11-04)

it here:
http://jcp.org/aboutJAVA/communityprocess/final/jsr220/index.html

Tell me if problems still occur.

Cheers
Per

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