Java beans and PJC's

can any one give me the differences of java beans and pluggable java components.

Pluggable Java Components (PJCs) are JavaBeans that are either embedded in the form as a separate object (Bean Area on the Layout Editor toolbar) or that act as a substitute for a Forms object such as an item or button. Incorporating PJCs will allow you to extend the capabilities of Forms and solve problems such as how to read and write to the client's file system, how to provide a Java spell checker for a Web form, how to implement timers that fire only on the client.
You could find some examples at:
http://otn.oracle.com/products/ids/daily/mar04.html
Thanks,
Rashmi.

Similar Messages

Hi frnds i want to help in servlet,java bean and JSP

hi friends i'm right now in M.SC(IT) and i want to do project in SERVLET,,JAVA BEANS and JSP ,
so pls give me a title about that
NOTE: I develop a project in group(2 persons there)
my email id is : [email protected] , [email protected] , [email protected]

You cannot pair your iPod to a cell phone, so forget about it.
The only way you can get free WiFi is to hang out at a Denny's, a Starbucks, or a truck stop, and I don't think your parents would approve....

Java Beans and JSP Arrays

Hi..
I am trying to pass a 2D String array to a Java Bean and i am getting
"java.lang.NoSuchMethodError"
Any Ideas?
Thanks
Joe
Jsp Call
Sorts s = new Sorts();
s.getTotal(items);
"items[][]" is a 2 dimentional arrays and size can vary..
Java Bean
public class Sorts implements Serializable {
public double getTotal(String sItems[][]){
double aSum=0;
for(int i=0;i<sItems[0].length;i++){
aSum=aSum+(Double.parseDouble(sItems[1])*Double.parseDouble(sItems[2][i]));
return aSum;

Can someone show me how to pass a 2 Dimentional Array to a Java Bean method? obviously i am doing something wrong.
Joe
Hi..
I am trying to pass a 2D String array to a Java Bean
and i am getting
"java.lang.NoSuchMethodError"
Any Ideas?
Thanks
Joe
Jsp Call
Sorts s = new Sorts();
s.getTotal(items);
"items[][]" is a 2 dimentional arrays and size can
vary..
Java Bean
public class Sorts implements Serializable {
public double getTotal(String sItems[][]){
double aSum=0;
for(int i=0;i<sItems[0].length;i++){
aSum=aSum+(Double.parseDouble(sItems[1])*Double.pars
Double(sItems[2][i]));
return aSum;

Question about main difference between Java bean and Java class in JSP

Hi All,
I am new to Java Bean and wonder what is the main difference to use a Bean or an Object in the jsp. I have search on the forum and find some post also asking the question but still answer my doubt. Indeed, what is the real advantage of using bean in jsp.
Let me give an example to illustrate my question:
<code>
<%@ page errorPage="errorpage.jsp" %>
<%@ page import="ShoppingCart" %>

<jsp:useBean id="cart" scope="session" class="ShoppingCart" />
<html>
<head><title>Shopping Cart</title></head>
<body bgcolor="#FFFFFF">
Your cart's ID is: <%=cart.getId()%>.
</body>
<html>
</code>
In the above code, I can also create a object of ShoppingCart by new operator then get the id at the following way.
<code>
<%
ShoppingCart cart = new ShoppingCart();
out.println(cart.getId());
%>
</code>
Now my question is what is the difference between the two method? As in my mind, a normal class can also have it setter and getter methods for its properties. But someone may say that, there is a scope="session", which can be declared in an normal object. It may be a point but it can be easily solved but putting the object in session by "session.setAttribute("cart", cart)".
I have been searching on this issue on the internet for a long time and most of them just say someting like "persistance of state", "bean follow some conventions of naming", "bean must implement ser" and so on. All of above can be solved by other means, for example, a normal class can also follow the convention. I am really get confused with it, and really want to know what is the main point(s) of using the java bean.
Any help will be highly apprecaited. Thanks!!!
Best Regards,
Alex

Hi All,
I am new to Java Bean and wonder what is the main
difference to use a Bean or an Object in the jsp. The first thing to realize is that JavaBeans are just Plain Old Java Objects (POJOs) that follow a specific set of semantics (get/set methods, etc...). So what is the difference between a Bean and an Object? Nothing.
<jsp:useBean id="cart" scope="session" class="ShoppingCart" />
In the above code, I can also create a object of
ShoppingCart by new operator then get the id at the
following way.
ShoppingCart cart = new ShoppingCart();
out.println(cart.getId());
...Sure you could. And if the Cart was in a package (it has to be) you also need to put an import statement in. Oh, and to make sure the object is accessable in the same scope, you have to put it into the PageContext scope. And to totally equal, you first check to see if that object already exists in scope. So to get the equivalant of this:
<jsp:useBean id="cart" class="my.pack.ShoppingCart"/>Then your scriptlet looks like this:
<%@ page import="my.pack.ShoppingCart %>
<%
ShoppingCart cart = pageContext.getAttribute("cart");
if (cart == null) {
    cart = new ShoppingCart();
    pageContext.setAttribute("cart", cart);
%>So it is a lot more work.
As in my mind, a normal class can also
have it setter and getter methods for its properties.True ... See below.
But someone may say that, there is a scope="session",
which can be declared in an normal object.As long as the object is serializeable, yes.
It may be
a point but it can be easily solved but putting the
object in session by "session.setAttribute("cart",
cart)".Possible, but if the object isn't serializable it can be unsafe. As the point I mentioned above, the useBean tag allows you to check if the bean exists already, and use that, or make a new one if it does not yet exist in one line. A lot easier than the code you need to use otherwise.
I have been searching on this issue on the internet
for a long time and most of them just say someting
like "persistance of state", "bean follow some
conventions of naming", "bean must implement ser" and
so on. Right, that would go along the lines of the definition of what a JavaBean is.
All of above can be solved by other means, for
example, a normal class can also follow the
convention. And if it does - then it is a JavaBean! A JavaBean is any Object whose class definition would include all of the following:
1) A public, no-argument constructor
2) Implements Serializeable
3) Properties are revealed through public mutator methods (void return type, start with 'set' have a single Object parameter list) and public accessor methods (Object return type, void parameter list, begin with 'get').
4) Contain any necessary event handling methods. Depending on the purpose of the bean, you may include event handlers for when the properties change.
I am really get confused with it, and
really want to know what is the main point(s) of
using the java bean.JavaBeans are normal objects that follow these conventions. Because they do, then you can access them through simplified means. For example, One way of having an object in session that contains data I want to print our might be:
<%@ page import="my.pack.ShoppingCart %>
<%
ShoppingCart cart = session.getAttribute("cart");
if (cart == null) {
    cart = new ShoppingCart();
    session.setAttribute("cart", cart);
%>Then later where I want to print a total:
<% out.print(cart.getTotal() %>Or, if the cart is a JavaBean I could do this:
<jsp:useBean id="cart" class="my.pack.ShoppingCart" scope="session"/>
Then later on:
<jsp:getProperty name="cart" property="total"/>
Or perhaps I want to set some properties on the object that I get off of the URL's parameter group. I could do this:
<%
ShoppingCart cart = session.getAttribute("cart");
if (cart == null) {
    cart = new ShoppingCart();
    cart.setCreditCard(request.getParameter("creditCard"));
    cart.setFirstName(request.getParameter("firstName"));
    cart.setLastName(request.getParameter("lastName"));
    cart.setBillingAddress1(request.getParameter("billingAddress1"));
    cart.setBillingAddress2(request.getParameter("billingAddress2"));
    cart.setZipCode(request.getParameter("zipCode"));
    cart.setRegion(request.getParameter("region"));
    cart.setCountry(request.getParameter("country"));
    pageContext.setAttribute("cart", cart);
    session.setAttribute("cart", cart);
}Or you could use:
<jsp:useBean id="cart" class="my.pack.ShoppingCart" scope="session">
<jsp:setProperty name="cart" property="*"/>
</jsp:useBean>The second seems easier to me.
It also allows you to use your objects in more varied cases - for example, JSTL (the standard tag libraries) and EL (expression language) only work with JavaBeans (objects that follow the JavaBeans conventions) because they expect objects to have the no-arg constuctor, and properties accessed/changed via getXXX and setXXX methods.
>
Any help will be highly apprecaited. Thanks!!!
Best Regards,
Alex

JAVA beans and JAVA related services require Oracle client to be installed?

Can you please advice whether an application server that make use of JAVA beans and JAVA related services require Oracle client to be installed? For an example if the solution build based on Java and JBOSS to be used as application server, do we still require oracle client to be installed and configure the tnsnames in order to communicate to database server?

SHANOJ wrote:
Can you please advice whether an application server that make use of JAVA beans and JAVA related services require Oracle client to be installed? For an example if the solution build based on Java and JBOSS to be used as application server, do we still require oracle client to be installed and configure the tnsnames in order to communicate to database server?Oracle client is not required when JDBC is used to connect to the remote DB

First use of jsp and java bean and "Unable to compile class for JSP" error

Hi,
I am trying to create my first jsp + java bean and I get a basic error (but I have no clue what it depends on exactly). Tomcat seems to cannot find my class file in the path. Maybe it is because I did not create a web.xml file. Did I forgot to put a line in my jsp file to import my bean?
Thank you very much for your help.
Here is my error:
An error occurred at line: 2 in the jsp file: /login.jsp
Generated servlet error:
[javac] Compiling 1 source file
/usr/local/tomcat/jakarta-tomcat-5/build/work/Catalina/localhost/test/org/apache/jsp/login_jsp.java:43: cannot resolve symbol
symbol : class CMBConnect
location: class org.apache.jsp.login_jsp
CMBConnect test = null;
I only have this in my directory:
test/login.jsp
test/WEB-INF/classes/CMBConnect.java
test/WEB-INF/classes/CMBConnect.class
Do I need to declare another directory in classes to put my class file in it and package my bean differently?
Here is my login.jsp:
<%@ page errorPage="error.jsp" %>
<jsp:useBean id="test" type="CMBConnect" scope="session" />
<html>
<head>
<title>my test</title>
</head>
<body>
<h3>Login information</h3>
<b><%=session.getValue("customerinfo.message")%></b>
<form> ....... </form>
</body>
</html>
and here is my CMBConnect.java:
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
public class CMBConnect
public CMBConnect () { }
public String openConnection(String id, String password) {
String returnText = "";
try {
Connection con = null;
DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());
con = DriverManager.getConnection("jdbc:oracle:thin:@myserver.abc.com:1521:TEST", id, password);
if(con.isClosed())
returnText = "Cannot connect to Oracle server using TCP/IP...";
else
returnText = "Connection successful";
} catch (Exception e) { returnText = returnText + e; }
return returnText;
Thanks again!

Thanks for you help
I created the package and I get this error this time:
javax.servlet.ServletException: bean test not found within scope
     org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:822)
     org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:755)
     org.apache.jsp.login_jsp._jspService(login_jsp.java:68)
     org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
     javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
     org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:268)
     org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:277)
     org.apache.jasper.servlet.JspServlet.service(JspServlet.java:223)
     javax.servlet.http.HttpServlet.service(HttpServlet.java:856)

Create a web service from java bean and map exceptions to SOAP faults

Hi,
We have to expose our Session stateless EJB3 as web services. I've tried to use annotations and jdev wizard "java bean to web service" and it works fine.
Our problem now is that our methods can throw a business exception that contains a list of error message strings to be presented on the client.
I did not find any way to use annotations to make it build a wsdl with soap fault mapped to our exception class. Neither I could to make the wizard to create wsdl with faults.
As we are exposing already designed and implemented classes as web services, I think the bottom-top (java->wsdl) approach is better that top->botton (wsdl->java). Therefore, I'm looking for a possibility to generate the web services from the java beans and have the exception be mapped to a soap fault message.
We are using jdev 10.1.3.1 and OAS 10.1.3.1., is there a way to map exceptions to soap faults using bottom->top approach?
thank you

A couple of links that may be of help:
http://www.netbeans.org/servlets/ReadMsg?listName=nbj2ee&msgNo=1218
My last question concerning web services:
I have already written a session bean and I'd like to add some methods
as a web service to it, how do I do that?
Or I can only create another bean for a webservice and cannot modify the
original one?You might create web service with existing sources and select you bean. New web services with appropriate lookup method will be generated.
All web service method, that will be exposed in web service, you
should add itself (Pop-up menu Web Service -> Add operation)
http://usersguide.netbeans.org/files/documents/40/73/Chapter9-WebServices.pdf

Is there any difference between java Beans and general class library?

Hello,
I know a Java Bean is just a java object. But also a general class instance is also a java object. So can you tell me difference between a java bean and a general class instance? Or are the two just the same?
I assume a certain class is ("abc.class")
Second question is is it correct that we must only use the tag <jsp:useBean id="obj" class="abc.class" scope="page" /> when we are writng jsp program which engage in using a class?Any other way to use a class( create object)? such as use the java keyword "new" inside jsp program?
JohnWen604
19-July-2005

a bean is a Java class, but a Java class does not have to be a bean. In other words a bean in a specific Java class and has rules that have to be followed before you have a bean--like a no argument constructor. There are many other features of beans that you may implement if you so choose, but read over the bean tutorial and you'll see, there is a lot to a bean that is just not there for many of the Java classes.
Second question: I'll defer to someone else, I do way to little JSP's to be able to say "must only[\b]".

Problem with java beans and jsp on web logic 6.0 sp1

          HI ,
          I am using weblogic6.0 sp1.
          i have problem with jsp and java beans.
          i am using very simple java bean which stores name and email
          from a html form.
          but i am getting following errors:
          Full compiler error(s):
          D:\bea4\wlserver6.0sp1\config\mydomain\applications\DefaultWebApp_myserver\WEB-INF\_tmp_war_myserver_myserver_DefaultWebApp_myserver\jsp_servlet\_savename2.java:89:
          cannot resolve symbol
          symbol : class userbn
          location: class jsp_servlet._savename2
          userbn ud = (userbn) //[ /SaveName2.jsp; Line: 7]
          ^
          D:\bea4\wlserver6.0sp1\config\mydomain\applications\DefaultWebApp_myserver\WEB-INF\_tmp_war_myserver_myserver_DefaultWebApp_myserver\jsp_servlet\_savename2.java:89:
          cannot resolve symbol
          symbol : class userbn
          location: class jsp_servlet._savename2
          userbn ud = (userbn) //[ /SaveName2.jsp; Line: 7]
          ^
          D:\bea4\wlserver6.0sp1\config\mydomain\applications\DefaultWebApp_myserver\WEB-INF\_tmp_war_myserver_myserver_DefaultWebApp_myserver\jsp_servlet\_savename2.java:94:
          cannot resolve symbol
          symbol : class userbn
          location: class jsp_servlet._savename2
          ud = (userbn) java.beans.Beans.instantiate(getClass().getClassLoader(),
          "userbn"); //[ /SaveName2.jsp; Line: 7]
          ^
          3 errors
          in which directory should i place java bean source file(.java file)
          here is my jsp file:
          <%@ page language = "java" contentType = "text/html" %>
          <html>
          <head>
          <title>bean2</title>
          </head>
          <body>
          <jsp:usebean id = "ud" class = "userbn" >
          <jsp:setProperty name = "ud" property = "*" />
          </jsp:usebean>
          <ul>
          <li> name: <jsp:getProperty name = "ud" property = "name" />
          <li> email : <jsp:getProperty name = "ud" property = "email" />
          </ul>
          </body>
          <html>
          here is my bean :
          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          import java.io.*;
          public class userbn implements Serializable
               private String name ;
               private String email;
               public void setName(String n)
                    name = n;
               public void setEmail(String e)
                    email = e;
               public String getName()
                    return name;
               public String getEmail()
                    return email;
               public userbn(){}
          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          pls help me.
          Thanks
          sravana.


          You realy can do it like Xiang says, but the better way is to use packages. That's
          the way BEA is designed for. If you use packages you can but your bean classes
          in every subfolder beneath Classes. Here for example we have the subfolders test
          and beans:
          You have to declare the package on top of your Bean Source Code:
          package test.beans;
          In your JSP you don't need the import code of Xiang. You only have to refer the
          path of your bean class:
          <jsp:useBean id="testBean" scope="session" class="test.beans.TestBean" />
          There are some other AppServers that only can deploy Java Beans in packages. So
          if you use packages you are always on the right side.
          ciao bernd
          "sravana" <[email protected]> wrote:
          >
          >Thank you very much Xiang Rao, It worked fine.
          >Thanks again
          >sravana.
          >
          >"Xiang Rao" <[email protected]> wrote:
          >>
          >><%@ page import="userbn" language = "java" contentType = "text/html"
          >>%> should
          >>work for you.
          >>
          >>
          >>"sravana" <[email protected]> wrote:
          >>>
          >>>HI ,
          >>>
          >>>I am using weblogic6.0 sp1.
          >>>
          >>>i have problem with jsp and java beans.
          >>>
          >>>i am using very simple java bean which stores name and email
          >>>
          >>>from a html form.
          >>>
          >>>but i am getting following errors:
          >>>
          >>>________________________________________________________________
          >>>
          >>>Full compiler error(s):
          >>>D:\bea4\wlserver6.0sp1\config\mydomain\applications\DefaultWebApp_myserver\WEB-INF\_tmp_war_myserver_myserver_DefaultWebApp_myserver\jsp_servlet\_savename2.java:89:
          >>>cannot resolve symbol
          >>>symbol : class userbn
          >>>location: class jsp_servlet._savename2
          >>> userbn ud = (userbn) //[ /SaveName2.jsp; Line: 7]
          >>> ^
          >>>D:\bea4\wlserver6.0sp1\config\mydomain\applications\DefaultWebApp_myserver\WEB-INF\_tmp_war_myserver_myserver_DefaultWebApp_myserver\jsp_servlet\_savename2.java:89:
          >>>cannot resolve symbol
          >>>symbol : class userbn
          >>>location: class jsp_servlet._savename2
          >>> userbn ud = (userbn) //[ /SaveName2.jsp; Line: 7]
          >>> ^
          >>>D:\bea4\wlserver6.0sp1\config\mydomain\applications\DefaultWebApp_myserver\WEB-INF\_tmp_war_myserver_myserver_DefaultWebApp_myserver\jsp_servlet\_savename2.java:94:
          >>>cannot resolve symbol
          >>>symbol : class userbn
          >>>location: class jsp_servlet._savename2
          >>> ud = (userbn) java.beans.Beans.instantiate(getClass().getClassLoader(),
          >>>"userbn"); //[ /SaveName2.jsp; Line: 7]
          >>> ^
          >>>3 errors
          >>>
          >>>____________________________________________________________
          >>>
          >>>in which directory should i place java bean source file(.java file)
          >>>
          >>>here is my jsp file:
          >>>--------------------------------------------------------
          >>>
          >>><%@ page language = "java" contentType = "text/html" %>
          >>><html>
          >>><head>
          >>><title>bean2</title>
          >>></head>
          >>><body>
          >>><jsp:usebean id = "ud" class = "userbn" >
          >>><jsp:setProperty name = "ud" property = "*" />
          >>></jsp:usebean>
          >>><ul>
          >>><li> name: <jsp:getProperty name = "ud" property = "name" />
          >>><li> email : <jsp:getProperty name = "ud" property = "email" />
          >>></ul>
          >>></body>
          >>><html>
          >>>
          >>>-------------------------------------------------------------
          >>>
          >>>here is my bean :
          >>>
          >>>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          >>>
          >>>import java.io.*;
          >>>
          >>>public class userbn implements Serializable
          >>>{
          >>>
          >>>     private String name ;
          >>>
          >>>     private String email;
          >>>
          >>>     public void setName(String n)
          >>>     {
          >>>
          >>>          name = n;
          >>>     }
          >>>
          >>>     public void setEmail(String e)
          >>>     {
          >>>
          >>>          email = e;
          >>>     }
          >>>
          >>>     public String getName()
          >>>     {
          >>>
          >>>          return name;
          >>>     }
          >>>
          >>>     public String getEmail()
          >>>     {
          >>>
          >>>          return email;
          >>>     }
          >>>
          >>>     public userbn(){}
          >>>}
          >>>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          >>>
          >>>pls help me.
          >>>Thanks
          >>>sravana.
          >>>
          >>
          >

J2EE Java Beans and JSP

I need a little help. I would like to learn jsp programming. Ive been browsing lots of tutorials on net but i didnt find any way how to use your own classes in jsp. I suppose it could do something with Java Beans but im new them so i dont know. Lets say ive got a login form with a username and password. After i send it to another jsp lets say verify.jsp i would like to verify the user using a class ive got. It goes through a xml file with some accounts and looks for the desired user if the password is correct. Now how do i call a method: boolean verifyUser( String user, String password) in the verify.jsp file? Is it possible?
Thanks for help

you'll probably want to have a central servlet that all your JSPs will talk to and acts as a traffic cop to direct navigation between pages. it can be the one to add JavaBeans as attributes to page/request/session/application scope. Your JSP can then get the Bean as an atribute and call its isValid method.
Java Beans are NOT Enterprise Java Beans. Be sure you understand the difference. The former are Java objects that follow Bean conventions; the latter are Java objects that extend EJB types and run in a container. Very different.
%

Search in form by using java bean or PJC.

hi all
i am confused because i do not know java bean to much,is it possible to create a search button with one text item in java bean to display all records
example:
if i enter dept 10 then it display all records related to dept 10?
is it possible?
if yes please cany anyone send me a demo?
here is my email add.
[email protected]
sarah

hi
Francois thanks for the link and its very useful and i am studying the codes and also i downloaded demos and run them its working fine and its very very nice.
i like java and trying to learn and its very useful.
why i want to use java bean because one of my friend her name is sheela she wants me to do it but i am failed i did not do it in java bean
so i thought lets try on the forum may be someone help u.
so i posted a thread over here.
thanks Francois.
u r appreciated.once again thanks.
sarah

Java Beans and JBuilder

Hello,
I have written a small java program and the user can drag the push button on to his form. By calling the bean box i am able to do the same.Can anybody tell is there a possibililty for me to add the bean to the visual javabeans designers.
Thanks in advance.
Reg,
suri

In JBuilder you can add you own JavaBean through menu Tools|Configure palette. On appeared dialog choose Add components tab and there you are able to add your own library.
Hope this helps...
Tom

Java Beans and EJBs

Hi friends,
I am quite new to Java and am interested in understanding EJBs and their use in deploying distributed applications.
I am not sure if I am supposed to first understand Java Beans before jumping to EJBs. I did read some of the messages under the Java Beans forum page but am confused..please help!!!
Regards,
Ritu

if I am supposed to first understand Java Beans before jumping to EJBsYes! Even before understanding objects and inheritence and so on.

How to call the method from the java bean and pass it to JSP textbox

i'm quite new to java thats why i'm asking how to call a method in the java bean file and pass it to the JSP textbox. My projects are communicating JSP with C#. i had successfully created a C# client bean file for JSP. The whole process is to type something on the server(C# programming) and it would appear in the textbox.

your question doesn't provide much informartion. provide some other information and coding so that we could tell exactly what you are looking for?

What is the difference between Java Beans and EJBs ?

Hi,
Can someone tell me that ? Kind of confused... Thanks !
Philip

Hmm, I'm gonna have a go at this - hopefully someone will build on it with more differences or requirements:
A Java Bean is merely a Java class written to conform to some simply rules for construction and method naming eg:
public class MyBean
private String myField;
public MyBean()
public void setMyField(String myField)
this.myField = myField;
public String getMyField()
return myField;
}Applications can use Java Beans without having to know about the class in advance - a typical situation might be their use in visual GUI editors where the properties of the bean can be exposed and manipulated by the editor through examination of the method names or an accompanying descriptor.
An Enterprise Java Bean doesn't have all that much in common with a Java Bean. An EJB is a small set of classes meeting a single (usually) business requirement written to conform to the EJB specification. This enables them to be used by J2EE Application servers to perform enterprise business functions (data storage, manipulation, business logic etc.). The whole idea is that by writing to the specification the server can automatically provide support for transaction management, concurrent access, scaleability, etc that a mission-critical system might require without the programmer having to understand the workings of the application server.
Essentially an EJB can either
1) maintain the permanent state of a business object (eg, hold the data for a single product in a catalogue)
2) perform a small set of business operations (eg, place an order for a customer)
3) act in response to messages passed around the system (eg, send a mail to the user when the items have been shipped)
I would have a look at the following two pages to get a better overview:
http://java.sun.com/products/javabeans/
http://java.sun.com/products/ejb/
Hope this helps.

Java beans and PJC's

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