Transcript XML and JavaBeans

SEN 974 Client/Sever and
the Internet
Deploying Enterprise
JavaBeans
1
Topics



Deployment
XML
Enterprise Entity Beans Case Study

How to deploy the Advisor Bean
2
The Contents of an
Enterprise Bean

To develop an enterprise bean, you must provide the
following files:



Deployment descriptor: An XML file that specifies
information about the bean such as its persistence type and
transaction attributes. The deploy tool utility creates the
deployment descriptor when you step through the New
Enterprise Bean wizard.
Enterprise bean class: Implements the methods defined in
the following interfaces.
Interfaces: The remote and home interfaces are required for
remote access.



For local access, the local and local home interfaces are required.
For access by web service clients, the web service endpoint
interface is required.
Helper classes: Other classes needed by the enterprise bean
class, such as exception and utility classes.
3
Deployment Descriptors



Involves packaging the byte-code
(.class) files together with an EJB
Deployment Descriptor
Deployment Descriptor is represented
using XML
Let’s look at some basic XML concepts...
5
XML




The EXtensible Markup Language (XML) provides a
convenient modeling language for representing
declarative data within a computer application.
XML provides a domain independent way of representing
data that is easy for humans to read and software to
parse.
The particular representation of data used in any XML
document requires an a priori agreement among the
producers and consumers of the data and in the case of
EJB Deployment Descriptors is defined by the EJB
specification.
As a complete description of XML is beyond the scope of
this course and tutorials are readily available on the
Internet, we will use a simple example to introduce the
basics of XML.
6
XML

Consider the following data:
UML 2 and the Unified Process
Jim Arlow and Ila Neustadt
2nd 2005 0-321-321278
Pearson Education, Inc.
Upper Saddle River, NJ


Take a moment to look at the example data again, but this
time consider how is it that you already understand what
this data means and how easy it is for you to answer
questions such as who are the authors or what is the
copyright date?
Simplistically, you might suggest that the structural format
of this data, your understanding of the tokens/words and
their combinations, and your prior experience with similar
examples contribute to your ability to understand this data.
7
Simple XML Example


XML provides this alternative approach by marking up the data
with pre-defined tags that label the data.
Here’s an XML version of the previous data:
<Book title=”UML 2 and the Unified Process”
edition=”2”
copyright=”2005”
isbn=”0-321-321278”>
<Authors>
<Author name=”Jim Arlow”/>
<Author name=”Ila Neustadt”/>
</Authors>
<Publisher name=”Pearson Education, Inc.”>
<Address city=”Upper Saddle River”
state=”NJ”/>
</Publisher>
</Book>
8
Simple XML Example

Although this XML version of the data is more
cumbersome to read, it does have a number of
useful features:



It is reasonable easy for a human to read and
understand the data
It is very easy to write a computer program that
can parse this data (e.g., locating the authors or the
copyright date of the book, or for that fact, even
knowing that the data represents a book),
It uses a standardize format to structure the data.
9
XML Basics


XML represents data using elements and attributes of these
elements.
Consider the following XML fragment from the example in the
preceding slide:
<book title=”UML 2 and the Unified Process”
edition=”2”
copyright=”2005”
isbn=”0-321-321278”>
</book>



The XML element in this example is a book and this book element
contains four attributes.
The syntax of XML dictates that elements begin with a start tag
that consists of a less-than sign immediately followed by the
name of the element, an optional list of unique attributes, and a
greater than sign.
Each attribute in an element, if any, consists of an attribute name
followed by an equal sign and the value of the attribute, which is
10
typically enclosed in double quotes.
XML Basics



The semantics of XML require that the starting tag of
all elements be followed an end tag that consists of a
less than sign, followed by a slash, the name of the
element and a greater than sign, e.g., </book>.
The information, if any, between an element’s start
and end tag is referred to as the element’s content.
If an element has no content, referred to as being
empty, then for convenience XML allows an empty
element tag. That is, for all practical purposes, the
following two XML statements are equivalent:
<author name=”Jim Arlow”/>
and
<author name=”Jim Arlow”></author>
11
Deployment Descriptors




As you may recall, one of the goals of middleware EJB
environments is to allow software engineers to focus primarily on
business solutions by freeing them from the tedious details
required to deploy large-scale enterprise applications.
One way to help simplify the deployment of enterprise beans is to
make certain aspects of the deployment process data driven and,
consequently, declarative in nature.
For example, as opposed to writing the code required to support
transaction process within, and among beans, it is simpler to
simply declare that a bean has a certain transactional processing
capability and let the EJB container automatically generate the
code required to support this capability.
Within an EJB environment, these declarations are made in an
XML file containing a Deployment Descriptor.
12
Deployment Descriptors



Java 2 platform, Enterprise Edition (J2EE)
enterprise applications are made up of one or
more individual J2EE modules.
J2EE modules have deployment descriptors
specific to the module type, and J2EE
enterprise applications also have their own
deployment descriptor format.
J2EE EJB application module deployment
descriptors are defined in XML files named
ejb-jar.xml.
13
Deployment Descriptors –
EJB JAR Files

The top-level elements of an EJB
deployment descriptor are elements used
to define




EJB application metadata
EJB structure
assembly information
and the archive filename for any EJB client
files
14
EJB JAR Files



An EJB JAR file represents the deployable JAR
library that contains the server-side code and
configuration of the EJB module.
During deployment, the ejb-jar.xml file is
placed in the META-INF directory of the EJB
JAR file.
Any entity and session beans defined within
the ejb-jar.xml file must have the .class files for
their implementations, home interfaces, and
remote interfaces, as well as any dependent
classes, archived inside the EJB JAR file.
15
EJB JAR Files




Any client stub and interface classes needed to access
the EJBs in a particular EJB JAR file can be placed in a
separate EJB client JAR file.
The URL of this EJB client JAR file can then be
specified in the ejb-jar.xml file's <ejb-clientjar> element.
Any EJB clients of the EJBs in the associated serverside EJB JAR file can then automatically receive
downloaded interface and stub classes as they are
needed if the EJB client's class loader can reach the
URL defined within the <ejb-client-jar> element.
If no automatic class-downloading mechanism is
supported or used by the client, the EJB client JAR
libraries should be installed on the EJB client's
machine.
16
Application
Deployment Descriptor:
ejb-jar.xml
17
Other Method – use *
<container-transaction>
<method>
<ejb-name>AdvisorEB</ejb-name>
<method-name>*</method-name>
</method>
<trans-attribute>Required<transattribute>
</container-transaction>
Instead of defining one for each method –
use the “*” – much easier!
18
sun-ebj-jar.xml (Vendor-Specific Jar file)
EJB Deployment Procedures
(Vendor Independent)

The process for deploying J2EE
applications involves establishing:





environment variables,
configuring server properties,
compiling Java code,
creating XML-based deployment descriptors,
packaging archive files,
and deploying archives to a J2EE server
environment.
20
EJB Deployment Procedures
(Vendor Independent)
1. Set J2EE server environment variables—Environment
variables must be set for running a J2EE server environment and
vary per vendor implementation and operating-system platform.
2. Configure J2EE server properties—Configuration properties
for most J2EE server implementations can be set to suit your
particular network and operating environment.
3. Compile J2EE EJB application code—All J2EE EJB
implementation, home, remote, and dependent utility code must
be compiled using a standard Java compiler.
4. Create a J2EE EJB application deployment descriptor—An
XML-based deployment descriptor is created according to the EJB
application DTD. Some vendor products can create this file for
you from a GUI-based configuration tool.
21
EJB Deployment Procedures
(Vendor Independent)
5. Create vendor-specific deployment descriptors—Because no
standard means exists to bind J2EE standard EJB reference names to a
J2EE server's JNDI-based naming service, a vendor-specific deployment
descriptor mechanism is required to perform this mapping.


This deployment descriptor must map EJB reference names used by J2EE
components to the actual JNDI names associated with EJB home interfaces.
Other vendor-specific properties may also be set for customizing both session
and entity beans. Vendors may provide a GUI-based means to configure these
files.
6. Package J2EE EJB application code—The EJB deployment
descriptors, all compiled J2EE EJB implementation classes, all compiled
J2EE EJB implementation interfaces, and all other compiled classes
dependent on your EJBs need to be packaged into an EJB JAR file with a
.jar extension. J2EE-based products might supply command-line or GUIbased utilities for this purpose.
7. Start the J2EE server—The J2EE-compliant server must generally be
started at this stage. The exact mechanism for starting a server is often
vendor-dependent but can be as simple as invoking a single startup
command from the command line.
22
EJB Deployment Procedures
(Vendor Independent)
8. Create a J2EE application deployment descriptor—A J2EE
application deployment descriptor must be created to collect one
or more Web, EJB, and application client modules into a cohesive
J2EE application. Many products will create this file for you
automatically or via a GUI-based configuration tool.
9. Package J2EE application code—The application and JNDI
mapping deployment descriptor, Web applications, EJB
applications, and application clients need to be packaged into an
enterprise archive (EAR) file with an extension of .ear. Many
products also create this archive for you automatically or via GUIbased development tools.
10.Deploy the J2EE enterprise application code—Finally, the
integrated J2EE application is deployed to the J2EE server
environment for access by enterprise application clients. This step
is also often automated via GUI tools.
23
SEN 974 Client/Sever and
the Internet
Session Beans
JSP Tutorial
24
Session Beans (SB)



Session Beans are a set of objects that
implement the business logic of an
application
SBs tend to be responsible for a group of
related functionality
Not using persistent storage
25
Types of Session Beans

Stateless Beans




Do not care declare any instance (class-level)
variables so that the methods contained within can
only act upon any local parameters
There is no way to maintain state across method
calls
Provide excellent scalability because EJB container
does not have to keep track of their state across
method calls
Ex: Provide some generic service to clients like
signing in or a

Catalog bean – browsing different products and categories
– generic to any client
26
Types of Session Beans

Stateful Beans





Can hold client state across method invocations –
contains conversational state on behalf of the client
Possible with the use of instance variables declared
in the class definition of session bean
Client will then set the values for these variables
and then use these values in other method calls
Storing the state of an EJB is very resource
intensive – therefore does not scale as well as
stateless beans
Ex: Shopping Cart for an online store
27
Decisions, Decisions...

How do you decide whether a given
enterprise bean should be a session or
entity bean?

Session beans are great at implementing
business logic, processes, and workflow


Ex: StockTrader bean with buy() and sell()
methods
Entity bean are the persistence data objects
of the EJB application


Ex: getPrice() and setPrice()
StockTrader SB could call the above methods in
28
the EB
Decisions, Decisions...

It is good practice to have the client only
interface with session beans and the session
beans interface with the entity beans for these
reasons:




Single point of entry for the client
Calling entity beans directly tends to push the
business logic into the UI logic
UI doesn’t have to be as dependent upon changes
to the entity beans – session beans shield the UI
from these changes
There are usually many more entity beans so
restricting client access to session beans conserves
server and network resources considerably
29
Anatomy of a Session Bean
UI calls the methods of the session bean as it requires the functionality
they provide. Session beans can call other session beans and entity beans
30
31
Java Server Pages Overview
32
JSP Resources

Sun’s website




Free Online Books




http://java.sun.com/products/jsp/docs.html
J2EE 1.4 Tutorial
Search the site for JSP – there are whitepapers, articles,
blueprints (best practices), etc.
http://www.coreservlets.com
Free Online books – they are the previous rev but most of the
information is relevant and the author indicates where it is
not.
Register with email address
Others:


http://www.jsptut.com
http://www.theserverside.com/articles/index.tss
33
J2EE and EJB Resources

Sun’s Resources:

EJB Specification


J2EE 1.4 Tutorial (Update 7)


http://java.sun.com/j2ee/1.4/docs/api/index.html
Bean Training


http://java.sun.com/j2ee/1.4/docs/index.html
API


http://java.sun.com/j2ee/1.4/docs/tutorial/doc/index.html
J2EE Documentation


http://java.sun.com/products/ejb/ - Want the EJB 2.1 Spec
http://java.sun.com/developer/onlineTraining/Beans/bean01/index.ht
ml
Other:


http://my.execpc.com/~gopalan/java/ejb.html
www.javaworld.com
34