JAVA TECHNOLOGY

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JAVA TECHNOLOGY

• PRESENTED BY
• KOTESWARA RAO KOMMINENI

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TOPICS

• SERVLETS
• JDBC
• RMI
• JavaIDL
• JMS

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SERVLETS
4
Servlets

• Introduction
• Why do we need Servlets?
• Working of a Servlet
• Servlet API
• Example
• Job of a HTTP Servlet

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Introduction

• What is a servlet?
• Server side extension of a web server.
• Dynamically loaded Java class.
• Provide a component-based, platform independent
  method for building web-based applications
  without performance limitations of CGI.

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Why do we need Servlets?

• Efficient
• Uses light weight java thread to handle a
  request.
• Single copy of servlet processes N requests from
  the client.
• They remain active even after response.
• Convenient
• Provides infrastructure for automatic parsing and
  decoding HTML form data, reading and setting HTTP
  headers, tracking sessions etc.
• Powerful
• Can talk directly to the web server.
• Makes it easier to translate relative URLs into
  concrete path names.
• Multiple servlets can also share data by making
  it easy to implement database connection pooling.
• Portable
• Secure
• Inexpensive

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Working of a Servlet
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Servlet API

• Java Provides two packages for developing
  Servlets.
• Package javax.servlet
• Package javax.servlet.http
• Two types of Servlets
• Temporary
• Permanent
• Web server communicates with a servlet through a
  simple interface, javax.servlet.Servlet. This
  interface consists of three main methods
• init()
• service()
• destroy()

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Example Servlet

• import java.io.
• import javax.servlet.
• public class SampleServlet extends Servlet
• private ServletConfig config
• public void init(ServletConfig config)
• throws ServletException
• this.configconfig
• public void destroy()
• public ServletConfig getServletConfig()
• return config
• public String getServletInfo()
• return A Simple Servlet

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Example Servlet(cont)

• public void service(ServletRequest
  req,ServletResponse res)
• throws ServletException, IOException
• res.setContentType(text/html)
• PrintWriter outres.getWriter()
• out.println(lthtmlgt)
• out.println(ltheadgt)
• out.println(lttitlegt A Sample Servletlt/titlegt)
• out.println(lt/headgt)
• out.println(lth1gtA Sample Server lt/h1gt)
• out.println(lt/bodygt)
• out.println(lt/htmlgt)
• out.close()

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Job of a HTTP Servlet

• Read any data sent by the user.
• Look up any other information about the request
  that is embedded in the HTTP request.
• Generate the results.
• Format the results inside a document.
• Set the appropriate HTTP response parameters.
• Send the document back to the client.

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JAVA DATABASE CONNECTIVITY
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JDBC API

• JDBC is a Java API that provides universal data
  access for the java programming language.
• It supports standard way to access
  object-relational features supported by todays
  relational database management systems.
• It provides connection pooling mechanism with
  server.

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JDBC API VERSUS ODBC

• Why do we need JDBC?
• ODBC uses a C interface.
• Translation of ODBC C API into a Java API is not
  desirable.
• ODBC is hard to learn.
• To develop a pure java solution.

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Basic Steps in Using JDBC

• There are seven standard steps in querying
  databases
• Load the JDBC Driver.
• Define the connection URL.
• Establish the connection.
• Create a Statement object.
• Execute a query.
• Process the results.
• Close the connection.

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Load the JDBC Driver

• try
• Class.forName(connect.microsoft.MicrosoftDriver)
  
• Class.forName(oracle.jdbc.driver.OracleDriver)
• Class.forName(com.sybase.jdbc.SybDriver)
• catch(ClassNotFoundException cnfe)
• System.out.println(Error Loading Driver
  cnfe)

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Define the connection URL

• String host dbhost.yourcompany.com
• String dbnamesomeName
• int port1234
• String oracleURLjdbcoraclethin_at_hostpor
  tdbname
• String
• sybaseURLjdbcsybaseTdshostport?S
  ERVICENAMEdbname

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Establish the connection

• String usernamejay_debesee
• String passwordsecret
• Connection connectionDriverManager.getConnection(
  oracleURL,username,password)

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Create a Statement

• Statement statementconnection.CreateStatement()

Execute a Query
String querySELECT col1,col2,col3 FROM
sometable ResultSet resultsetstatement.executeQ
uery(query)
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Process the Results

• while(resultset.next())
• int xresultset.getInt(col1)
• String sresultset.getString(col2)
• float fresultset.getFloat(col3)

Close the Connection
connection.close()
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Prepared Statements (Precompiled Queries)

• Connection connectionDriverManager.getConnection(
  url,username,password)
• String templateUPDATE employees SET SALSAL ?
  WHERE EID?

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CONNECTION POOLING

• What is connection pooling?
• A Connection Pool class should be able to do the
  following tasks
• Preallocate the connections.
• Manage available connections.
• Allocate New Connections.
• Wait for a connection to become available.
• Close connections when required.

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Preallocate the Connections

• availableConnections new Vector(initialConnection
  s)
• busyConnectionsnew Vector()
• for(int i0iltinitialConnectionsi)
• availableConnections.addElement(makeNewConnection(
  ))

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Application Development Using JDBC

• Two types of Application models
• Two-tier Application Model
• Three-tier Application Mode.

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Two-tier Application Design
Client
JDBC Driver
TCP/IP socket
Database

• Simple Design
• Used for developing small applications

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Three-tier Application Design
Middle Tier
JDBC Driver
Client
TCP/IP socket
RMI/CORBA
Database

• Preferred Design.
• Additional benefits from middle tier
• Isolation of business/application logic
• Provision of simple API
• Integration of several database systems.

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Three-Tier Design Advantages

• Data Validation moves to the middle tier.
• Client can access multiple databases through a
  single socket connection.
• Protocol between client and middle-tier is
  DBMS-independent.
• Has Control over access and the kinds of updates
  that can be made to the database.

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REMOTE METHOD INVOCATION(RMI)
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RMI Architecture Overview
Java RMI Client
Java RMI Server
RMI System
Stubs
Skeletons
Remote Reference Layer
Remote Reference Layer
Transport
Transport
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RMI Architecture

• RMI Architecture consists of four layers
• Application
• Stub/Skeleton
• Remote reference
• Transport

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RMI
Registry
RMI
Client
RMI
RMI
Server
URL protocol
URL protocol
Web Server
URL protocol
Web Server
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Application Layer

• Consists of actual implementation of the client
  and the server applications.
• Remote methods are described in an interface.
• Remote object implements the remote methods.
• Server creates servant instances and informs
  registry.
• Client looks up in the server registry and call
  the remote methods.

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Stub and Skeleton Layer

• Is an interface between an application layer and
  the remaining RMI system.
• Transmits data to the remote reference layer.
• Client invoking a method use a stub.
• A skeleton is a server side entity.

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Remote Reference Layer

• Carries out semantics of method invocation.
• Manages communications between stub/skeleton and
  lower-level transport interface.
• Manages references to objects.
• Manages reconnection strategies.
• Includes client and server side components.

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Transport Layer

• Is responsible for
• Setting up connection and management
• Tracking and dispatching remote objects
• Performs the following tasks
• Receives request from RRL on client
• Locates RMI server
• Establishes socket connection
• Passes connection to RRL on client
• Adds object to table of remote objects
• Monitors connection

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RMI Naming Service

• Enables remote objects to be retrieved and
  registered.
• Has simple names for remote objects.
• Has URL-based lookup mechanism.
• rmi//hostport/name

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Creating Distributed Applications Using RMI

• General Steps involved are
• Design and Implement the application components.
• Defining the remote interfaces.
• Implementing the remote objects.
• Implementing the clients.
• Compile sources and generate stubs.
• Make classes network accessible.
• Start the application.

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JavaIDL
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JavaIDL

• It is a technology for distributed objects.
• Enables objects to interact regardless of the
  language in which they are developed.
• Uses CORBA technology.
• It provides ORB( a class library that supports
  interaction between objects in separate
  programs).

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Java IDL Development Process

• Define the Remote Interface.
• Compile the remote interface.
• Implement the Server.
• Implement the Client.
• Start the applications.

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RMI vs. JavaIDL

• From the development points of views
• There are three types of developers
• CORBA veterans.
• Java purists.
• Novice developers.

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RMI vs. CORBA

• Advantages of CORBA
• No Special language requirements.
• Interfaces between clients and servers are
  defined in IDL.
• Standardized services like Naming and Event
  Service.
• Dynamic method discovery and invocation.

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RMI vs. CORBA

• Disadvantages of CORBA
• Do not support pass by value.
• Cannot allow a type-safe object passing.
• It is mandatory that both sides know in advance
  exactly what object will be passed.
• Support for heterogeneous systems.

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RMI vs. CORBA

• Advantages of RMI
• Invoke methods as if they were local.
• Uses optimized protocol. Data marshalling is
  handled transparently for the developer.
• Java Objects in different VMs can transparently
  invoke each others methods.
• Enables garbage collection of inactive objects.
• parameters cab be passed both by reference as
  well as by value.

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RMI vs. CORBA

• Disadvantages of RMI
• Pure Java Solution.
• No event support is provided in RMI.
• RMI naming service is primitive.
• Uses TCP/IP instead of IIOP.

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JMS API
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JAVA MESSAGE SERVICE

• What is Messaging?
• What is JMS API?
• When to Use JMS API?
• How JMS API works with J2EE?
• JMS API Architecture
• Messaging Domains
• Message Consumption

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• Messaging
• Messaging is the method of communication between
  the software components.
• What is JMS API ?
• JMS is a Java API that allows applications to
  create, send, receive and read messages. It
  enables not only loosely coupled messaging but
  also supports Asynchronous and Reliable
  communication.

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When to Use JMS API?

• Provider wants the components not to depend on
  information about other interfaces, so that
  components can be easily replaced.
• Provider wants the application to run whether or
  not all components are up and running
  simultaneously.
• The application business model allows a component
  to send information to another and continue to
  operate without receiving an immediate response.

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How JMS works with J2EE?

• JMS API of J2EE platform has the following
  features
• Application Clients, EJB components and web
  components can send or synchronously receive a
  JMS message.
• A new kind of EJB, the Message-Driven Bean,
  enables asynchronous consumption of messages.
• Message sends and receives can participate in
  distributed transactions.

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JMS API Architecture

• JMS Provider
• JMS Clients
• Messages
• Administered Objects

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JMS API ARCHITECTURE
JNDI Namespace
CF
Bind
Administrative Tool
D
Lookup
JMS Client
JMS Provider
Logical Connection
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Messaging Domains

• Before JMS Existed
• Point to Point(PTP)
• Publish/Subscribe(pub/sub)
• JMS API Provides separate domain for each
  approach
• JMS Provides both the domains.
• Some clients use both the domains in same
  application.

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Point to Point Messaging Domains
Msg
Client 2
Msg
Client 1
Queue
Consumes
Sends
Acknowledges
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Point-to-Point Messaging Domain

• Characteristics of Point-to-Point Messaging
  Domain
• Only one consumer for each Message.
• No time Dependencies.
• Receiver Acknowledges.
• When to use this Domain?
• When every message that is sent must be
  successfully processed by one consumer.

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Publish/Subscribe Messaging Domain
Topic
Client 2
Subscribes
Msg
Delivers
Client 1
Msg
Client 3
Publishes
Subscribes
Delivers
Msg
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Publish/Subscribe Messaging Domain

• Characteristics of Publish/Subscribe Messaging
  Domain
• Multiple Consumers.
• Time Dependency.
• No Receiver Acknowledgements.
• When to use this Domain?
• When each message that is sent must be processed
  by zero, one or more consumers.

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Building Blocks of JMS client Application

• Administered Objects Connection factories and
  Destinations
• Connections
• Sessions
• Message Producers
• Message Consumers
• Messages

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JMS API Programming Model
Connection Factory
Creates
Connection
Creates
Message Consumer
Session
Message Producer
Creates
Creates
Receives From
Sends To
Creates
Destination
Destination
Msg
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References

• http//java.sun.com/docs/books/tutorial/rmi/index.
  html
• http//java.sun.com/j2se/1.4.1/docs/guide/jdbc/get
  start/intro.html1018464
• http//csajsp-chapters.corewebprogramming.com/CSAJ
  SP-Chapter18.pdf
• http//java.sun.com/docs/books/tutorial/idl/summar
  y/index.html
• http//www.javaworld.com/javaworld/jw-01-2000/jw-0
  1-howto.html
• http//www.weblogic.com/docs45/classdocs/API_jndi.
  htmldistributed
• http//developer.java.sun.com/developer/onlineTrai
  ning/Servlets/Fundamentals/servlets.html
• http//java.sun.com/products/servlet/articles/tuto
  rial/
• www.acm.org