Application Servers

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					Application Servers
       Gökçe Banu Laleci




                           1
aim
    for building integrated, enterprise-class
     applications that share information, deliver
     services, and automate collaboration among
     networked companies at Internet volume and
     speed
            separate of presentation, business logic, and data
            provide the underlying core functionality
             necessary for the development and deployment of
             business-driven application
            connect legacy systems, and Web Services
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Why?
    applications with complex business logic
    potentially servicing tens of thousands of
     concurrent users in real-time
    require a scalability and reliability
    Distributed system
            Stock trading system
            Banking application


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What you need?
    RMI                                    Logging and auditing
    Load balancing                         System management
    Transparent fail over                  Threading
    Back-end integration                   Message-oriented
    Transaction                             middleware
    Clustering                             Object life cycle
    Dynamic                                Resource polling
     redeployement                          Security
    Clean shutdown                         Caching
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Adds..
    a new layer of
     functions and
     services
     between Web
     servers and
     underlying
     applications and
     databases



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What do they provide
    speeds application development and relieves developers of the
     effort and expense of creating these crucial services on their own
      Load balancing
      Fault tolerance
      Web Services
      Legacy integration
      Transaction management
      Security
      Messaging
      Multi-threading
      Persistence
      Database connectivity
      Resource pooling
      Development, testing, and packaging facilities


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Single server / clustered
servers




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J2EE based..
                 TM
             J2EE Patterns




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J2EE based…
    BEA WebLogic Java Application Server
    IBM WebSphere Java Application Server
    Oracle 9i Java Application Server
    Sun ONE Java Application Server (iPlanet)
    HP Application Server (HP-AS) (Bluestone)
    JBoss Application Server
    Enhydra Application Server

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J2EE Components used..
    Java Servlets & Java Server Pages (JSP)
    Enterprise Java Beans (EJB)
    Java Transaction API (JTA)
    Java Transaction Service (JTS)
    Java API for XML Parsing (JAXP)
    Java Messaging Service (JMS)
    Message Driven Beans (MDB)
    Remote Method Invocation (RMI)
    Java Database Connection 2 (JDBC2)
    Java Connector Architecture (JCA)
    Java Naming and Directory Interface (JNDI)
    JavaBeans Activation Framework (JAF)

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Three layered architecture
    The presentation layer
            managing the user interfaces of applications,
             including desktop applications, Web browsers,
             and pervasive devices
    The business layer
            contains the business logic
    The back-end layer
            provides connectivity with enterprise systems and
             databases
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Three layered architecture

             Hosting Organization




                                                           Subscriber 1


                        Presentation



                           Logic

                                                           Subscriber 2

                        Persistence




                                                           Subscriber 3



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Presentation Layer
    Thin clients
            such as Web browsers that send HTTP requests
             and receive HTTP responses for static HTML or
             dynamic Web pages built by Java Servlets and
             Java Server Pages (JSPs)
    Thick clients
            such as Java applets and applications, ActiveX
             controls, or Visual Basic clients that run on a
             desktop and communicate with BEA WebLogic
             Server through CORBA, Java RMI,IIOP, or COM+

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Presentation Layer
    Pervasive devices
            including wireless phones, PDAs, smart
             appliances, and other emerging remote clients
             that communicate with the server via specific and
             usually very compact
                can generate WML pages from Servlets and JSPs.
    Web Services
             that connect to the system using Web Services
             technologies, such as SOAP,UDDI, and WSDL

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Presentation Layer
    Provides a Web Server
            Servlet and JSP results caching and JSP tags
             caching
            provides high-reliability, scalability, monitoring,
             and other features required by enterprise
             applications
            plug-ins for Apache, iPlanet, and Microsoft IIS
             Web servers


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Additional Features
    Virtual hosting
            www.company1.com and www.company2.com
    Clustering
            scalability and high-availability
            insulates clients from hardware or power failures
             by eliminating single points of failure
    Load balancing
            Incoming requests can be distributed across
             multiple instances of AS
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Additional Features
    High availability with transparent fail-over
             The data contained in Web components can be
             replicated across multiple machines
             In the event of a failure, current client session
             information is maintained
                disk-based persistence
                in- memory replication of a client ’s session state




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Business Layer
    contains the application’s business logic
     independent of the user interface, including
     distributed components, running in the
     application server environment
    Enterprise Java Beans




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Enterprise Java Beans
    Reusable server components
            A manageable, discrete chunk of code
             implementing a set of well defined interfaces
    it has to be compliant to a well defined
     interfaces
            To be reusable
            To be able to use the AS functionalities



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Java Beans vs. EJB
    Generic java                         Standard for building
     component model                       distributed systems
    Can be either visible or             Non-visible remote
     not                                   objects
    Local to a single                    Remotely executable
     process on the client                 comp. deployed in the
     side                                  server
    Uses BeanInfo classes                Uses Deployment
     to define themselves                  descriptor to describe
                                           itself
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Why EJB
    Architectural independence from middleware
    WORA for sever side components
    Establishes roles for application development
    Take care of transaction management
    Provides distributed transaction support
    Portable
    Integrates seamlessly with CORBA

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The EJB architecture




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What do containers provide
    Remote invocation
    Pool and cache services
    Security
    Transaction
    Integration with external data sources




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Containers
    Interface btw EJBeans
     & outside world
    EJB Clients never
     access an EJB directly-
     any access is done
     through container-
     generated methods in
     turn invoke bean
     methods


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Home interface
    Contains factory methods for locating,
     creating and instances of EJBs
    The EJB developer defines the Home
     Interface for his bean
    Object generated by the Container vendor




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An example




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Remote Interface & EJBObject
    Lists the business methods present in EJB
    Interface defined by the developer
    Object created by the container vendor
    Clients use this object to invoke business
     methods




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An example




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EJB Client
    Finds EJB containers using JNDI
    Uses EJB container to invoke EJB methods
    Uses Home Object to locate, create or
     destroy and EJB class
    Uses the EJBObject instance to invoke
     methods



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JNDI
                            Client API provides
                             naming & directory
                             services for Java Apps
                            Does not replace DNS,
                             CORBA, RMI etc
                            Allows multiple
                             directory services co-
                             exist
                            Provides a federated
                             name server
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An example
     // get the JNDI naming context
     Context initialCtx = new InitialContext ();
     // use the context to lookup the EJB Home interface
     AccountHome home
     =(AccountHome)initialCtx.lookup
     ("com/~gopalan/Account");
     // use the Home Interface to create a Session bean
     object
     Account account = home.create (1234, "Athul",
     1000671.54d);

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EJB Types
    Entity Beans
    Session Beans
    Message-Driven Beans




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Entity Beans
    Used to represent business data in an application
    Correspond with information stored in databases or other
     persistent storage
    Have primary key
    Participate in transactions
    Long-lived
    Can survive EJB server clashes
    Multiple clients can access and work with the same entity bean
    When not used
      Preserved in persistent location and returned to the pool
    When used
      Can be cached


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Entity Bean Interface
    ejbActivate ()
    ejbLoad ()
    ejbPassivate ()
    ejbRemove ()
    ejbStore ()




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Persistence
        Container Managed                          Bean Managed
    Container is responsible for            Bean is itself responsible for
     saving state of bean                     saving its own state
    Container needs to                      Bean needs to code its own
     generate DB calls                        DB calls
    Bean persistence is                     Bean persistence is hard-
     independent of data source               coded and is hence less
    specify container-managed                adaptable
     fields in Deployment
     Descriptor


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Session Beans
    Execute on behalf of a single client
    They may or may-not be transaction-aware
    They may or may-not update data in the underlying
     database
    Their lifetime is limited to that of the client and hence
     they are relatively short-lived
    They do not survive server crashes
    They do not represent data in the database
    Since they only represent conversational state with
     a single client, their identity is hidden

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Stateless/Stateful
Stateless Session Bean            Stateful Session Bean
 Have no internal state          Have internal state

 need not be passivated          need to handle
  or activated                     Activation/Passivation
 Objects can be pooled           One Session Bean
  to service multiple              object per client
  clients




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Message-Driven Beans
    Do not have home or remote interface
    Used to integrate with JMS
    Called JMS message consumers
            Listen from a message from JMS server
            Performs a set of actions defined when message
             is received




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Deployment Descriptors
    While deploying your EJB to container
            Provide a deployment descriptor file (xml)
                JNDI name
                Transactional rules
                Security roles and permissions of a component




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Additional Features
    Instance pooling
            pre-load a given number of instances and prepare
             them for use, thereby saving time by not having to
             create a new instance for each request
    Clustering
            EJBs can be deployed in a cluster of BEA
             WebLogic Servers
            by means of distributed naming and directory
             facilities

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Additional Features
    High availability with transparent fail-over
            replicate state that EJB hold across a cluster of
             separate physical AS processes
            creating redundancy in case of
            transparently fail-over to a backup machine in the
             cluster in the event of a failure
    Load balancing
            route requests from remote clients to EJB
             components using a predetermined algorithm or
             custom-algorithm
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Additional Features
    EJB Caching
            store a configurable number of EJBs in memory to
             save on database access
            In case another instance of the server in the
             cluster updates the same bean, all the cached
             instances of the bean cached in the cluster will be
             invalidated, and reloaded with the next access
            increases performance and reduces the load on
             the database

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Back-End Layer
    provides access to other enterprise systems
            databases, ERP, CRM, mainframe or other
             existing applications
    Integration layer
            messaging, e-mail, Web Services, and other
             technologies to connect and communicate with
             enterprise systems



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Databases
    JDBC
            Thin clients – servlet, JSP
            Thick clients – RMI to remote databases
            most recommended way is to use entity beans
             and benefit from the underlying services
            Connection pooling




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Integration
    integrating new applications with any legacy
     Enterprise Information System (EIS)
    J2EE Connector Architecture (J2CA)
    CORBA
            integration with legacy systems that implement the CORBA
             specifications
    COM/DCOM (COM+)
            bi-directional interoperability with Microsoft ’s COM+
              can access data in Microsoft applications, communicate
                with Visual Basic clients

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JCA
    a standard architecture for connecting the
     J2EE platform to heterogeneous EIS systems
            ERP, mainframe transaction processing,
             database systems, and legacy applications not
             written in the Java programming language
            enables the integration of EISs with application
             servers and enterprise applications
                By defining a a set of scalable, secure, and
                 transactional mechanisms


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JCA
    enables an EIS vendor to provide a standard
     resource adapter for its EIS
    The resource adapter plugs into an application
     server, providing connectivity between the EIS, the
     application server, and the enterprise application
    An EIS vendor needs to provide just one standard
     resource adapter which has the capability to plug in
     to any application server that supports the J2EE
     Connector architecture


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JCA
    Multiple resource adapters are pluggable into
     an application server
    enables application components deployed on
     the application server to access the
     underlying EIS systems




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JCA




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Resource Adapter
    To achieve a standard system-level
     pluggability between application servers and
     EISs, the J2EE Connector architecture
     defines a standard set of system-level
     contracts between an application server and
     EIS
    The resource adapter implements the EIS-
     side of these system-level contracts

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Resource Adapter
    system-level software driver used by an
     application server or an application client to
     connect to an EIS
    By plugging into an application server, the
     resource adapter collaborates with the server
     to provide the underlying mechanisms, the
     transactions, security, and connection pooling
     mechanisms
    A resource adapter is used within the
     address space of the application server
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Application Contract
    An application server and an EIS collaborate to
     keep all system-level mechanisms, such as
     transactions, security, and connection management,
     transparent from the application components
    A Connection Management contract
    A Transaction Management contract
    Security contract
    A Message Inflow contract
    A Lifecycle Management contract
    A Work Management contract

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Web Service Support
    Automatically wraps the business components in to Web
     services
    Support for WSDL and UDDI
      Publish, search, host
    Support for Web Services Security standard
    Reliable SOAP implementation
      based on a sequence of asynchronous SOAP communications,
        receipts, and notifications
      guaranteed delivery, “exactly-once ” delivery, ordered
        conversation
    A set of convenient graphical tools for development, search, and
     composing of the Web Services
      BEA WebLogic Workshop


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Messaging
    Asynchronous method invocations
    Why?
            Performance
            Reliability
            Support for multiple senders and receivers

                              Message
    Application                                     Application
                              Oriented
                             Middleware



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MOM
    Provides
            Guaranteed message delivery
            Fault tolerance
            Load balancing of destinations
            Subscription mech.
    Proprietary solutions
            Tibco Rendezvous
            IBM MQSeries
            BEA Tuxedo/Q
            Microsoft MSMQ

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Java Message Service
    API
            Write code to send and receive msg
    Service Provider Interface (SPI)
            Plug in JMS drivers
                to allow existing companies to JMS-enable their
                 applications without impacting client-side development
    Supports
            Publish/subscribe
            Point-to-point
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JMS System
    ConnectionFactory
    Connection
    Session
    Destination
    MessageProducer
    MessageConsumer
    Message

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                   2:Create            JMS Connection
                   Connection             Factory

                      3:Create
                      Session
                                       JMS Connection
                                                                      Serialized
                                                                      Message
                    5:Create            JMS Session
     Client         Producer or
                                                                      Connection

                    Consumer
                                        JMS Producer
                   6:Send or
1:RetrieveJ
MS Driver          Receive                   Or
                   Message
Connection                              JMS Consumer
Factory
         4:Lookuo JMS
         Destination              JMS Driver Client Runtime


      JNDI




   Naming
   Service


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Example
try {
     queueConnectionFactory =(QueueConnectionFactory)
     jndiContext.lookup("QueueConnectionFactory");
     queue =(Queue)jndiContext.lookup(queueName);
}…
try {
     queueConnection =
     queueConnectionFactory.createQueueConnection();
     queueSession =            queueConnection.createQueueSession(false,
     Session.AUTO_ACKNOWLEDGE);
     queueSender =queueSession.createSender(queue);
     message =queueSession.createTextMessage();
     for (int i =0;i <NUM_MSGS;i++){
            message.setText("This is message "+(i +1));
            System.out.println("Sending message:"+ message.getText());
            queueSender.send(message);
     }
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EJB JMS Integration
    Message Driven Beans
    Do not have home/remote interface
            Just to consume messages
            Not a component interface
            onMessage method
    Why not use existing beans
            Threading
            Life cycle management

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Security
    Java Authentication and Authorization Server (JAAS)
    Encryption
    Auditing
    HTTPS,
    basic HTTP authentication with Base64 encoding for services
     protected by firewalls
    Role based security
      User and group definition
      Built-in security data store retains the role,profile,and entitlement
        data,and is built on a highly optimized LDAP directory
    Single Sign-On
    WS-Security

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Adding security to EJB
    JAAS
            Portable interface
            Java applications to remain independent from
             underlying authentication technologies
    Authentication
            Basic
            Digest
            Certificate

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Authorization
    Programmatic
            Hard code security checks in to your bean code
    Declarative
            Through deployment descriptor
            Container handles the rest




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Role based
    Each user must be uniquely identified
    User should be assigned one or more
     security roles
    Each security role is assigned a set of
     method permissions




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Example role definition




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Example method permission




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Transaction
   A series of operations that appear to execute
    as one large atomic operation
        All-or-nothing
        Allow multiple users to share the same data
   ACID
        Atomicity
            Many operations are bundled together and appear as
             one atomic unit


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ACID
    Consistency
            A transaction leaves the system in a consistent
             state
    Isolation
            Protects concurrently executing transactions from
             seeing each other’s incomplete results
    Durability
            Guarantees that updates to managed resources,
             such as database records, survive failures
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Transaction
    Type
            Flat
            Nested
    Rollback is not an undo logic
            Resource managers are transaction aware
            They do no not make the changes persistent until
             a commit statement issued



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EJB and transactions
    EJB never interact with a transaction
     manager or a resource manager
    The container handles all the low-level things
    Demarcating transactional boundries
            Programmatically
            Declaratively
            Client-initiated


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  Programmatic Transactions
      Put the transaction logic in to your application
       code
      The programmer is responsible for issuing
              begin, commit and abort

Client Code                                                          EJB Container

               1:call                      2:delegate
               method   EJB object
                                                      3:call begin
                                                                       Transaction
                                            EJB                          Service
                             4:perform                 5:call commit
                             business                  or abort
                             operations
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Declarative Transactions
    EJB container handles
    Declare in deployment descriptor




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Declarative Transactions

Client Code                                                   EJB Container

                                             3:call begin
             1:call                                           Transaction
             method   EJB object              5:call commit     Service
                                              or abort

                            2:delegate


                                         EJB

                          4:perform
                          business
                          operations




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Client Initiated Transactions

                                                                EJB Container

                          3:call begin
Client Code                                                     Transaction
                           5:call commit                          Service
                           or abort
             1:call
             method   EJB object

                                                  2:delegate

                                                               EJB

                                                  4:perform
                                                  business
                                                  operations



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Container-Managed
Transactions
    Bean deployer has to provide instructions to
     the container
            Deployment descriptor
            Transaction Attributes
                Entire bean
                Individual methods




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Transaction Attribute Values




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Transaction Attribute Values
Transaction Attribute   Client’s transaction       Bean’s transaction

                        none                       T2
Required
                        T1                         T1
                        none                       T2
RequiresNew
                        T1                         T2
                        none                       None
Supports
                        T1                         T1
                        none                       Error
Mandatory
                        T1                         T1
                        none                       None
NotSupported
                        T1                         None
                        none                       None
Never
                        T1                         error
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Programmatic Transactions
    CORBA’s Object Transaction Service (OTS)
            Multiple parties participating in a transaction
            Basic interfaces that transactional object,
             resources, resource managers, and transaction
             managers use to interoperate




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Java Transaction Service
    Corba OTS
            Java Transaction Service
            Java Transaction API
    JTAJTS OTS
            To have various vendors to interoperate
            Used by AS
    JTA
            Application developers
            Programmaticaly control transaction boundaries

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Java Transaction API
    begin()
    Commit()
    getStatus()
    rollBack()
    setRollbackOnly()
    setTransactionTimeout()




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Example




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