DOS/V Power Report 2004 March/VPR0403.ISO/talks/208/paper.dkb

Extensible Markup Language | 2003-09-18 | 47KB | 821 lines

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<article id="paper-208">
  <articleinfo>
    <title>The JOnAS Open Source J2EE Platform</title>
    <author>
      <firstname>Fran輟is</firstname>
      <surname>Exertier</surname>
    </author>
    <copyright>
      <year>2003</year>
      <holder>Bull</holder>
    </copyright>
  </articleinfo>

    <para>This document presents the JOnAS J2EE platform. After a short
      introduction of the J2EE concepts, and of the ObjectWeb Consortium,
      the JOnAS server architecture and
      features are presented.
    </para>


<section>
  <title>Introduction</title>
  <section>
    <title>J2EE</title>
    <para>The <trademark>Sun</trademark>
      <ulink url="http://java.sun.com/j2ee/">J2EE specification</ulink>,
      together with its related specifications
      (<ulink url="http://java.sun.com/products/ejb/">
    <trademark>EJB</trademark></ulink>,
      <ulink url="http://java.sun.com/products/jms/">
    <trademark>JMS</trademark></ulink>,...),
      defines an architecture and interfaces for developing and deploying
      distributed internet <trademark>Java</trademark> server applications based on a
      multi-tier architecture. This
      specification intends to facilitate and normalize the development,
      deployment and assembling of applicative components; such components
      will be deployable on J2EE platforms. The resulting applications are
      typically web based, transactional, database-oriented, multi-user,
      secured, scalable and portable. More precisely, this specification
      describes two kinds of information:</para>
    <itemizedlist>
      <listitem><para>The first one is the runtime environment, called J2EE server, which
    provides the execution environment and the required system services
    such as the transaction service, the persistence service, the JMS
    service, the security service ...</para></listitem>
      <listitem><para>The second one is some kind of programmer's guide and user's guide
    explaining how an application component should be developed, deployed
    and used.</para></listitem>
    </itemizedlist>

    <para>Not only will an application component be independent of the platform
      and operating system (since written in Java), but also of the J2EE
      platform.
    </para>
    <para>A typical J2EE application is composed of presentation components,
      also called "web components" (<ulink url="http://java.sun.com/products/servlet">Servlets</ulink>
      and <ulink url="http://java.sun.com/products/jsp"><trademark>JSPs</trademark></ulink>),
      which define the application Web interface, and of enterprise components,
      the "Enterprise JavaBeans", which define the application business logic
      and application data. The J2EE server provides containers for hosting
      web and enterprise components. The container provides the component
      life cycle management and interfaces the components with the services
      provided by the J2EE server. There are two kinds of container, the web
      container handles Servlet and JSP components while the EJB container
      handles the Enterprise JavaBeans components.</para>

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  </section>
  <section>
    <title>ObjectWeb</title>
    <para>JOnAS is an open source implementation of J2EE, developed within
      the ObjectWeb consortium.
      <ulink url="http://www.objectweb.org">ObjectWeb</ulink> is an open source
      initiative which may be compared to Apache or Linux, but in the area of
      <emphasis>middleware</emphasis>. The aim of ObjectWeb is to develop
      and promote open source middleware softwares.</para>
    <para>ObjectWeb is an International Consortium hosted by INRIA, officially
      founded in February 2002 by Bull, France Telecom, and INRIA. All
      softwares are available with the LGPL licence.</para>
    <para>The technical objective of this consortium is to develop a distributed
      component-based middleware technology, in line with CORBA, Java and W3C
      standards. The idea is to apply the component model, as already used at
      the application level in J2EE or in the CORBA Component Model, at the
      middleware level by itself. The functional coverage of ObjectWeb
      projects addresses naming, trading, communication (events, messages),
      availability and safety (transactions, persistence, replication,
      fault tolerance), load balancing, and security. Some transversal
      topics are also addressed, like robustness, optimisation, code quality,
      as well as benchmarks, tests, evaluations, demonstrators and
      development tools.
    </para>
    <para>Thus, the global ObjectWeb architectural model goes top down, from
      applications (as benchmarks such as Rubis from the JMOB project)
      running on middleware platforms (such as JOnAS, OpenCCM or ProActive).
      The platforms are based on technical components such as a
      Message-Oriented Middleware (JORAM which implements JMS), a
      communication framework (CAROL), a persistence framework (JORM),
      a transactional monitor (JOTM), a Object Request Broker (Jonathan).
      A technical component such as C-JDBC allows any platform to benefit
      from database clusters. JOnAS makes use of all these ObjectWeb
      components (JORAM, CAROL, Jonathan, JORM, C-JDBC, and soon JOTM), but is
      also using open source components from other communities, this is the
      case for Tomcat or Jetty, used as Web container, or for AXIS, used for
      providing the "Web Services" environment.
    </para>
    <para>ObjectWeb has already a significant number of corporate members,
      universities, and also individual members (individual membership is
      free). ObjectWeb members contribute to ObjectWeb orientations, and
      participate to all ObjectWeb working groups, meetings, workshops and
      conferences. The community of developers and users around
      ObjectWeb components and platforms is growing continuously.</para>
  </section>
</section>
<section>
    <title>JOnAS Features</title>
    <para>JOnAS is a pure Java open source application server conforming to the
      J2EE specification.
      However its high modularity allows to use it </para>
    <itemizedlist>
      <listitem><para>as a J2EE server, for deploying and running EAR applications (i.e.
    applications composed of both web and ejb components),</para></listitem>
      <listitem><para>as an EJB container, for deploying and running EJB components (e.g.
    for applications without web interfaces or when using JSP/Servlet
    engines that are not integrated as a JOnAS J2EE container),</para></listitem>
      <listitem><para>as a Web container, for deploying and running JSPs and Servlets
    (e.g. for applications without EJB components).</para></listitem>
    </itemizedlist>
  <section>
    <title>System Requirements</title>
    <para>JOnAS is available for JDK 1.3 or 1.4. It has been used on many
      operating systems (Linux, AIX, Windows, Solaris, HP-UX, etc.), and
      with different Databases (Oracle, PostgreSQL, MySQL, SQL server, Access,
      DB2, Versant, Informix, Interbase, etc.).</para>
  </section>
  <section>
    <title>Java Standard Conformance</title>
    <para>JOnAS is an implementation of J2EE 1.3. It
      currently conforms to EJB 2.0. Its
      current integration of Tomcat or Jetty as Web container insures
      conformity to Servlet 2.3 and JSP 1.2 specifications. The JOnAS
      server relies on or implements the following Java APIs: <trademark>JCA</trademark>
      1.0, <trademark>JDBC</trademark> 2.0, <trademark>JTA</trademark> 1.0.1,
      <trademark>JMS</trademark> 1.1,
      <trademark>JMX</trademark> 1.0, <trademark>JNDI</trademark> 1.2.1,
      <trademark>JAAS</trademark> 1.0,
      <trademark>JavaMail</trademark> 1.3.</para>
  </section>
  <section>
    <title>Key Features</title>
    <para>In addition to the implementation of all J2EE related standards, JOnAS
      provides the following advanced and important features:</para>
    <itemizedlist>
      <listitem><para><emphasis>Management:</emphasis> JOnAS server management uses JMX and
    provides a servlet based managment console.</para></listitem>
      <listitem><para><emphasis>Services:</emphasis> The service based architecture of JOnAS
    provides a high modularity and configurability of the server. It
    allows to apply a component model approach at the middleware level,
    and makes easy the integration of new modules (e.g. for open source
    contributors). It also allows to start only the services needed
    by a particular application, thus saving useless system resources.
    JOnAS services are manageable through JMX.</para></listitem>
      <listitem><para><emphasis>Scalability:</emphasis> JOnAS integrates several optimization
    mechanisms for increasing the server scalability. This includes
    pool of stateless session beans, pool of message-driven beans, pool
    of threads, cache of entity beans, activation/passivation of entity
    beans, pool of connections (for JDBC and JMS), storage access
    optimizations (shared flag, isModified).</para></listitem>
      <listitem><para><emphasis>Clustering:</emphasis> JOnAS clustering solutions, both at
    the WEB and EJB level provide load balancing, high availability and
    failover support.</para></listitem>
      <listitem><para><emphasis>Distribution: </emphasis> JOnAS is working with several
    distributed processing environments, thanks to the integration of
    the <ulink url="http://www.objectweb.org/carol/index.html">CAROL</ulink>
    (Common Architecture for RMI ObjectWeb Layer) ObjectWeb project,
    which allows simultaneous support of several communication protocols:
    <itemizedlist>
      <listitem><para><emphasis>RMI</emphasis> using the Sun proprietary protocol JRMP,</para></listitem>
      <listitem><para><emphasis>RMI</emphasis> on IIOP,</para></listitem>
      <listitem><para><emphasis>CMI</emphasis>, the "Cluster aware" distribution protocol of
        JOnAS,</para></listitem>
      <listitem><para>or <emphasis>Jeremie</emphasis>, the RMI personality of an Object Request
        Broker called
        <ulink url="http://www.objectweb.org/jonathan/index.html">Jonathan</ulink>,
        from Objectweb. Used with Jeremie, JOnAS benefits from transparent
        local RMI calls optimization.</para></listitem>
    </itemizedlist>
      </para></listitem>
      <listitem><para><emphasis>Support of "Web Services":</emphasis> by the integration of
    AXIS, JOnAS allows J2EE components to access "Web services" (i.e. to
    be "Web Services" clients), and
    allows J2EE components to be deployed as "Web Services" endpoints.</para></listitem>
    </itemizedlist>
    <para>Three critical J2EE aspects have been early implemented in the JOnAS
      server:</para>
    <itemizedlist>
      <listitem><para><emphasis>JCA:</emphasis> Enterprise Information Systems (EIS) may
    be easily accessed from JOnAS applications. By supporting the Java
    Connector Architecture, JOnAS allows to deploy any JCA compliant
    Resource Adapter (connector) that will make the corresponding EIS
    available from the J2EE application components. For example, Bull
    GCOS mainframes may be accessed from JOnAS using their associated
    <ulink url="http://www.bull.com/servers/gcos8/products/interop8/hoox_pr.htm">Hoox connectors</ulink>.</para></listitem>
      <listitem><para><emphasis>JMS:</emphasis> JMS implementations may be easily plugged into
    JOnAS. They run as a JOnAS service in the same JVM or in a separate JVM
    and JOnAS provides administration facilities that hide the JMS
    proprietary administration APIs. Currently two JMS implementations may
    be used: the <ulink url="http://www.objectweb.org/joram/">JORAM</ulink>
    open source JMS implementation from Objectweb and
    <ulink url="http://www.swiftmq.com/">SwiftMQ</ulink>.
      </para></listitem>
      <listitem><para><emphasis>JTA:</emphasis> The JOnAS platform supports distributed
    transactions that involve multiple components and transactional
    resources. The JTA transactions support is provided by a Transaction
    Monitor that has been developed on top of an implementation of
    the CORBA Transaction Service (OTS).
      </para></listitem>
    </itemizedlist>
  </section>
  <section>
    <title>JOnAS Packages</title>
    <para>JOnAS is available for download with three different packagings:</para>
    <itemizedlist>
      <listitem><para>a simple packaging only contains the JOnAS application server,
    without the associated Web Container implementation. In order to
    use it for J2EE Web applications, you need to have Tomcat or Jetty
    installed (with an adequate version) and to configure it and
    JOnAS so that they can work together.</para></listitem>
      <listitem><para>a JOnAS-Tomcat package contains both JOnAS and Tomcat,
    pre-configured, and with compiled examples. This is a ready to run
    J2EE application server. This package also contains AXIS, thus
    providing pre-configured "Web Services" support.</para></listitem>
      <listitem><para>a JOnAS-Jetty package contains both JOnAS and Jetty,
    pre-configured, and with compiled examples. This is a ready to run
    J2EE application server. This package also contains AXIS, thus
    providing pre-configured "Web Services" support.</para></listitem>
    </itemizedlist>
  </section>
</section>
<section>
    <title>JOnAS Architecture</title>
    <para>JOnAS is architectured in term of services. A service typically
      provides system resources to containers. Most of the components of the
      JOnAS application server are pre-defined JOnAS services. However it is
      possible and easy for an advanced JOnAS user to define its own service
      and to integrate it into JOnAS. J2EE applications do not necessarily
      need all services, it is thus possible to define, at JOnAS server
      configuration time, the set of services that are to be launched at
      server start.</para>
    <para>The JOnAS architecture is illustrated in the figure below, showing
      WEB and EJB containers relying on JOnAS services (all services are
      present on this figure). Two thin clients are also shown on this
      picture, one of them being the JOnAS administration console (called
      Jadmin).</para>

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  <section>
    <title>Communication and Naming Service</title>
    <para>This service (also called "Registry") is used for launching the
      RMI registry, the CosNaming, the CMI registry, and/or the Jeremie
      registry depending on the configuration of JOnAS (CAROL configuration
      which specifies which communication protocols are to be used). There are
      different registry launching modes, i.e. in the same JVM or not,
      automatically if not already running.</para>
    <para>This service provides the JNDI API to application components and
      to other services, in order to bind and lookup remote objects (e.g. EJB
      Homes) and resource references (JDBC DataSource, Mail and JMS connection
      factories, etc.). </para>
  </section>
  <section>
    <title>EJB Container Service</title>
    <para>This service is in charge of loading the EJB components and their
      containers. EJB containers are composed of a set of Java classes
      implementing the EJB specification and by a set of interposition classes
      interfacing the EJB components with the services provided by the
      JOnAS application server. Interposition classes are specific to
      each EJB component and are generated by the deployment tool called
      GenIC.</para>
    <para>JOnAS configuration allows to specify this service to be launched
      with a set of ejb-jar files to be loaded. Ejb-jar files may also
      be deployed at server runtime using the JOnAS administration tools.</para>
    <para>Enterprise JavaBeans (EJB) are software components implementing
      the business logic of an application (while the Servlets and JSPs
      implement the presentation). There are three kinds of Enterprise
      JavaBeans:</para>
    <itemizedlist>
      <listitem><para><emphasis>Session beans</emphasis> are objects associated to only one
    client, short-lived (one method call or a client session),
    that represent the current state of the client session. They can be
    transaction-aware, stateful or stateless.</para></listitem>
      <listitem><para><emphasis>Entity beans</emphasis> are objects that represent data in a
    database. They may be shared by several clients and are identified by
    means of a primary key. The EJB container is responsible for
    managing the persistence of such objects. The persistence management
    of such an object is entirely transparent to the client that will
    use it, and may be or may not be transparent to the bean provider that
    develops it depending if it is
    <itemizedlist>
      <listitem><para>An enterprise bean with <emphasis>Container-Managed Persistence</emphasis>.
        In such a case, the bean provider does not develop any data access
        code, persistence management is delegated to the container.
        The mapping between the bean and the persistent storage is provided
        in the deployment descriptor, in an application server specific
        way.
      </para></listitem>
      <listitem><para>An enterprise bean with <emphasis>Bean-Managed Persistence</emphasis>. In
        this case, the bean provider writes the database access operations
        in the methods of the enterprise bean that are specified for data
        creation, load, store, retrieval, and remove operations.</para></listitem>
    </itemizedlist>
      </para></listitem>
      <listitem><para><emphasis>Message-driven Beans</emphasis> are objects that may be
    considered as message listeners. They execute on receipt of a
    JMS (<ulink url="http://java.sun.com/products/jms">Java Message Service</ulink>) message,
    they are transaction aware and stateless. They implement some kind
    of asynchronous EJB method invocation.</para></listitem>
    </itemizedlist>
    <para>For implementing Container-Managed Persistence of EJB 2.0 (CMP2),
      JOnAS relies on the ObjectWeb
      <ulink url="http://www.objectweb.org/jorm">JORM</ulink> (Java Object Repository
      Mapping) framework. JORM supports complex mappings of EJBs to database
      tables, and several kinds of persistency support (relational databases,
      object databases, LDAP repositories, etc.).</para>
  </section>
  <section>
    <title>WEB Container Service</title>
    <para>This service is in charge of running a Servlet/JSP Engine in the
      JVM of the JOnAS server, and of loading web applications ("war" files)
      within this engine. Currently this service may be configured to use
      <ulink url="http://jakarta.apache.org/tomcat/">Tomcat</ulink> or
      <ulink url="http://www.jettyserver.org">Jetty</ulink>. Servlet/JSP engines
      are integrated within JOnAS as "web containers", i.e. such containers
      provide the web components with access to the system resources (of
      the application server) and to EJB components, in a J2EE compliant way.
    </para>
    <para>JOnAS configuration allows to specify this service to be launched
      with a set of war files to be loaded. War files may also
      be deployed at server runtime using the JOnAS administration tools.
      Tomcat and JOnAS users management has been unified. The class loading
      delegation policy (priority to the Webapp classloader or to the
      parent classloader) may be configured.</para>
    <para><ulink url="http://java.sun.com/products/servlet">Servlet</ulink>
      and <ulink url="http://java.sun.com/products/jsp"><trademark>JSP</trademark></ulink> are
      technologies for developing dynamic web pages. The Servlet approach
      allows the development of Java classes (HTTP Servlets) that may be
      invoked through HTTP requests and that generate HTML pages. Typically
      Servlets access the information system using Java APIs (as JDBC or the
      APIs of EJB components) in order to build the content of the HTML page
      they will generate in response to the HTTP request. The JSP technology
      is a complement of the Servlet technology. A JSP is an HTML page
      containing Java code within particular XML-like tags; this Java code is
      in charge of generating the dynamic content of the HTML page.</para>
    <para>Servlets and JSPs are considered as J2EE application components
      responsible of the application presentation logic. Such application
      components are able to access resources provided by the J2EE server
      (as JDBC datasources, JMS connection factories, EJBs, mail factories,
      ...). As for EJB components, the actual assignment of these resources
      is performed at component deployment time, and is specified in the
      deployment descriptor of each component (the component code use logical
      resources names).</para>
  </section>
  <section>
    <title>Ear Service</title>
    <para>This service is used for deploying complete J2EE applications, i.e.
      applications packaged in EAR files (themselves containing ejb-jar
      files and/or war files). This service will handle the EAR files, and
      will delegate the deployment of the war files, resp. ejb-jar files, to
      the WEB Container service, resp. to the EJB Container service. It will
      take care of creating the appropriate class loaders (as preconised in the
      J2EE specification) in order for the J2EE application to execute
      properly.</para>
    <para>For deploying J2EE applications, JOnAS must be configured to launch
      the EAR service, and the set of EAR files to be loaded may be
      specified. EAR files may also
      be deployed at server runtime using the JOnAS administration tools.</para>
  </section>
  <section>
    <title>Transaction Service</title>
    <para>This is a Java Transaction Monitor called JOnAS JTM. It is a mandatory
      service which handles distributed transactions. It provides transaction
      management for EJB components as defined in their deployment descriptors.
      It handles two-phase
      commit protocol against any number of Resource Managers (XA Resources).
      For J2EE, a transactional resource may be a JDBC connection,
      a JMS session
      or a JCA Resource Adapter connection. The transactional context is
      implicitly propagated with the distributed requests. The JTM may be
      distributed across one or more JOnAS servers; thus a transaction may
      involve several components located on different JOnAS servers. This
      service implements the JTA 1.0 specification, thus allowing to explicitly
      start and terminate transactions from application components or from
      application clients.
      Starting transactions from application components is only allowed
      from Web components or from session beans or message-driven beans
      (and only these two kinds of beans, this is called
      <emphasis>"Bean-managed    transaction demarcation"</emphasis>).</para>
    <para>One of the main advantages of the EJB
      support for transactions is its declarative aspect, which means that
      transaction control is no longer hard coded in the server application,
      but is
      configured at deployment time. This is known as "<emphasis>Container-managed
    transaction demarcation</emphasis>".With "<emphasis>Container-managed transaction
    demarcation</emphasis>" the transactional behaviour of an enterprise bean
      is defined at configuration time, and is part of the deployment
      descriptor of the bean.
      The EJB container is responsible for providing the transaction
      demarcation for the enterprise beans, according to the value of
      transactional attributes associated to EJB methods which can be one of
      the following:</para>
    <itemizedlist>
      <listitem><para><emphasis>NotSupported:</emphasis> if the method is called
    within a transaction, this transaction is suspended during the time
    of the method execution.</para></listitem>
      <listitem><para><emphasis>Required</emphasis>: if the method is called
    within a transaction, the method is executed in the scope of this
    transaction, else, a new transaction is started for the execution of
    the method, and    committed before the method result is sent to the
    caller.</para></listitem>
      <listitem><para><emphasis>RequiresNew:</emphasis> the method will always be
    executed within the scope of a new transaction. The new transaction is
    started for the execution of the method, and committed before the
    method result is sent to the caller. If the method is called within a
    transaction, this transaction is suspended before the new one is
    started, and resumed when the new transaction has completed.</para></listitem>
      <listitem><para><emphasis>Mandatory</emphasis>: the method should always be
    called within the scope of a transaction, else the container will throw
    the <emphasis>TransactionRequired</emphasis> exception.</para></listitem>
      <listitem><para><emphasis>Supports:</emphasis> the method is invoked within
    the caller transaction scope, if the caller does not have an associated
    transaction, the method is invoked without a transaction scope.</para></listitem>
      <listitem><para><emphasis>Never</emphasis>: with this attribute the client
    is required to call the method without a transaction context else the
    Container throws the java.rmi.RemoteException exception.
      </para></listitem>
    </itemizedlist>
    <para>The <ulink url="http://www.objectweb.org/jotm">JOTM</ulink> (Java Open
      Transaction Manager) project from ObjectWeb has been created based
      on the JOnAS transaction service. It has been enhanced to provide
      advanced transaction features, such as nested transactions, "Web
      Services" transactions (an implementation of DBTP is available). JOTM
      will be integrated in JOnAS in a near future.</para>
  </section>
  <section>
    <title>Database Service</title>
    <para>This service is responsible for handling Datasource objects. A
      Datasource is a standard JDBC administrative object for handling
      connections to a database. The Database service
      creates and loads such datasources on the JOnAS server. Datasources
      to be created and deployed may be specified at JOnAS configuration time,
      or they may be created and deployed at server runtime using the JOnAS
      administration tools. The Database service is also responsible for
      connection pooling, i.e. it manages a pool of database connections to
      be used by the application components, thus avoiding many physical
      connection creations which are time consuming operations.</para>
  </section>
  <section>
    <title>Security Service</title>
    <para>This service implements the authorization mechanisms for accessing EJB
      components, as specified in the EJB specification. EJB security is based
      on the notion of <emphasis>roles</emphasis>.
      The methods can be accessed by a given set of roles. In order to
      access the methods, the user <emphasis>must</emphasis> be at least in one of this
      set of roles.
      The mapping between roles and methods (permissions) is done in the
      deployment descriptor using the security-role and
      method-permission elements. Programmatic security management
      is also possible using two methods  of the EJBContext interface, in
      order to enforce or complement security check in the bean code:
      getCallerPrincipal() and
      isCallerInRole (String roleName).
      The role names used in the EJB code (in the isCallerInRole method)
      are in fact references to actual security roles, which makes the EJB
      code independent of the security configuration described
      in the deployment descriptor. The programmer makes these role
      references available to the bean deployer or application assembler by the
      way of  the security-role-ref
      elements included in the session or entity
      elements of the deployment descriptor.
    </para>
    <para>
      In JOnAS, the mapping between roles and user identification is done
      in the user identification repository. When using Tomcat for user
      authentification, this user identification repository may either be
      stored in files, in a JNDI repository (such as LDAP), or in a relational
      database. This is achieved through a JOnAS implementation of the
      Tomcat Realms, i.e. UserDatabaseRealm, MemoryRealm , JDBCRealm,
      JNDIRealm. These realms are in charge to propagate the security context
      to the EJB container during EJB calls. For Java clients authentification,
      JAAS login modules are provided.
    </para>
  </section>
  <section>
    <title>Messaging Service</title>
    <para>Asynchronous EJB method invocation is possible on Message-driven
      Beans components, as specified in the EJB 2.0 specification.
      A Message-driven Bean is an EJB component which may be considered as
      a JMS (<ulink url="http://java.sun.com/products/jms">Java Message Service</ulink>)
      MessageListener, i.e. which processes
      JMS messages asynchronously, it is associated with a JMS
      destination, its <emphasis>onMessage</emphasis> method will be activated on the
      reception of messages sent by a client application to this destination.
      It is also possible for any EJB component to use the JMS API, and this
      within the scope of transactions managed by the application server.
    </para>
    <para>For supporting Message-driven Beans, and
      JMS operations coded within application components, the JOnAS
      application server relies on a JMS implementation.
      JOnAS makes use of a third party JMS implementation: currently
      the <ulink url="http://www.objectweb.org/joram">Joram</ulink>
      opensource software is integrated and delivered with JOnAS, the
      <ulink url="http://www.swiftmq.com/">SwiftMQ</ulink> product may also be used,
      other JMS provider implementations may easily be integrated. JORAM
      provides several points of interest, in particular reliability (with
      a persistent mode), distribution (it may run as several servers,
      transparently to the JMS client, thus allowing load balancing), the
      choice of TCP or SOAP as communication protocol for transmitting
      messages.</para>
    <para>
      The JMS service is in charge of launching (or establishing connection to)
      the integrated JMS server, that may run in the same JVM as JOnAS or not.
      It also provides connection pooling, and thread pooling (for
      Message-driven Beans).
      Through this service, JOnAS provides facilities to create
      JMS administered objects such as the connection factories and the
      destinations either at server launching time, or at runtime using the
      JOnAS administration tools.</para>
  </section>
  <section>
    <title>J2EE CA Resource Service</title>
    <para>The J2EE Connector Architecture (J2EE CA) allows the connection of
      different Enterprise Information Systems (EIS) to a J2EE application
      server. It is based on the Resource Adapter (RA), an architecture
      component comparable to a software driver, connecting the EIS, the
      application server, and the enterprise application (J2EE components).
      The RA is generally provided by an EIS vendor, and
      provides a Java interface (the Common Client Interface or CCI) to the
      J2EE components  for accessing the EIS (this may also be a specific
      Java interface). The RA also provides standard
      interfaces for being plugged to the application server, so that they can
      collaborate to keep all system-level mechanisms (transactions, security,
      and connection management) transparent from the application components.
    </para>

      <para>
        <inlinemediaobject>
          <imageobject>
            <imagedata fileref="picture-208-03.gif" format="GIF"/>
          </imageobject>
        </inlinemediaobject>
      </para>

    <para> The application performs "business logic" operations on the EIS data
      using the RA client API (CCI), while transactions, connections
      (including pooling) and security on the EIS is managed by the
      application server through the RA (system contract).
    </para>
    <para>The JOnAS Resource service is in charge of deploying J2EE CA compliant
      Resource Adapters (connectors), packaged as RAR files, on the JOnAS
      server. RAR files may also be included in EAR files, in this case the
      connector will be loaded by the application classloader. Once Resource
      Adapters are deployed, a connection factory instance is available in
      the JNDI namespace to be looked up by application components.
    </para>
  </section>
  <section>
    <title>Management Service</title>
    <para>The Management service is needed in order to administrate a JOnAS
      server from
      the JOnAS Jadmin administration console. Each server running this
      service is visible from the administration console. This service is
      based on JMX. Standard MBeans are defined within the JOnAS application
      server, they expose the management methods of the instrumented JOnAS
      server objects such as services, containers, the server by itself. The
      Management service runs a JMX server (currently the
      MX4J one, the Sun RI one is also available). The MBeans of the JOnAS
      server are registered within this JMX server. The JOnAS administration
      console is a Web application (servlet/JSP based), which accesses the JMX
      server in order to present the managed features within
      the administration console. It is thus possible, through a simple Web
      browser, to manage one or several JOnAS application servers. The
      administration console allows to configure all JOnAS services (and to
      make the configuration persistent), to deploy any kind of applications
      (EJB-JAR, WAR, EAR) and any kind of resources (DataSources, JMS and Mail
      connection factories, J2EE CA connectors), all that without the need to
      stop/restart the server. The administration console shows many
      information allowing to monitor your servers and applications: used
      memory, used threads, number of EJB instances, which component currently
      uses which resources, etc..</para>
  </section>
  <section>
    <title>Mail Service</title>
    <para>A J2EE application component may send e-mails using
      <ulink url="http://java.sun.com/products/javamail/"><trademark>JavaMail</trademark></ulink>.
      The Mail service of the JOnAS application server provides the necessary
      resources to such application components. The same way the database
      service or the JMS service create Datasources or ConnectionFactories
      and register these objects in the JNDI namespace, the Mail service
      creates mail factories and register these resources in the JNDI
      namespace.
      There are two kinds of mail factories: <emphasis>javax.mail.Session</emphasis> and
      <emphasis>javax.mail.internet.MimePartDataSource</emphasis>.</para>
  </section>
</section>
<section>
    <title>JOnAS Development and Deployment Environment</title>
  <section>
    <title>JOnAS Configuration and Deployment Facilities</title>
    <para>Once JOnAS has been installed, in a directory referred by the
      JONAS_ROOT environment variable, it is possible to configure servers
      and to deploy applications into several execution environments. This
      is achieved using the JONAS_BASE environment variable. JONAS_ROOT and
      JONAS_BASE may be compared to CATALINA_HOME and CATALINA_BASE variables
      of Tomcat. While JONAS_ROOT is dedicated to JOnAS installation,
      JONAS_BASE is used to specify a particular JOnAS instance configuration.
      JONAS_BASE designates a directory containing a specific JOnAS
      configuration, and subdirectories containing the EJB-JAR, WAR, EAR, and
      RAR files that may be loaded in this application environment. There is
      an ANT target in the JOnAS build.xml file to create a new JONAS_BASE
      directory structure. So from one JOnAS installation, but just changing
      the value of the JONAS_BASE variable, it is possible to switch from
      one application environment to another. For configuring a JOnAS
      application server and for loading applications, you should use the
      administration console, or edit the configuration files. There are
      also "autoload" directories for each kind of application (EJB-JAR, WAR
      or EAR) that allow the JOnAS server to automatically load the
      applications located in these directories when starting.</para>
    <para>About deployment, JOnAS provides several facilities.</para>
    <itemizedlist>
      <listitem><para>First to write
    the deployment descriptors, plugins for Integrated Development
    Environments (IDE) provide some generation and editing features
    (Eclipse and JBuilder plugins are available). The
    NewBean JOnAS built-in tool generates template deployment descriptors.
    The Xdoclet tool also generates deployment descriptors for JOnAS.
    The <ulink url="http://debian-sf.objectweb.org/projects/apollon">Apollon</ulink>
    ObjectWeb project generates Graphical User Interfaces for editing any
    XML file, it has been
    used to generate deployment descriptor editor GUI. A tool developed
    by the ObjectWeb JOnAS community will also be available to work with
    the JSR88 compliant (J2EE 1.4) deployment APIs provided by the
    ObjectWeb
    <ulink url="http://debian-sf.objectweb.org/projects/ishmael">Ishmael</ulink>
    project.
      </para></listitem>
      <listitem><para>For the deployment by itself, the basic tools are the JOnAS GenIC
    command line tool and the corresponding ANT ejbjar task. The IDE
    plugins integrate the use of these tools for deployment operations.
    The Ishmael project main feature will be the deployment of applications
    on the JOnAS platform.
      </para></listitem>
    </itemizedlist>
  </section>
  <section>
    <title>JOnAS Development Environments</title>
    <para>There are many plugins and tools for making easier the development of
      J2EE applications to be deployed on JOnAS. IDE plugins for JBuilder and
      Eclipse allows to develop, deploy and debug J2EE components on JOnAS. The
      <ulink url="http://xdoclet.sourceforge.net/">Xdoclet</ulink> code generation
      engine is able to generate EJB interfaces, deployment descriptors
      (standard and JOnAS specific ones), taking as input the EJB
      implementation class containing specific JavaDoc tags. The JOnAS NewBean
      tool generates templates of interfaces, implementation class, and
      deployment descriptors for any kind of EJB. Many development tools may
      work with JOnAS, see the
      <ulink url="http://www.objectweb.org/jonas/tools.html">JOnAS tools page</ulink>
      for more details.
    </para>
    <para>Moreover, JOnAS is delivered with complete J2EE examples, providing
      build.xml ANT file with all necessary targets for compiling, deploying
      and installing J2EE applications.
    </para>
  </section>
</section>
<section>
    <title>Clustering and Performance</title>
    <para>Clustering for an application server generally brings three features:
      Load Balancing (LB), High Availability (HA) and Failover.
      Such mechanisms may be provided at the Web container level (by
      dispatching requests to several Servlet/JSP engine instances, at
      the EJB container level (by dispatching EJB requests to several
      EJB container instances), and at the database level by using several
      databases. A replicated JNDI naming is also necessary.</para>
    <para>JOnAS provides Load Balancing, HA and Failover at the WEB container
      level, using the Apache Tomcat mod_jk plugin and an HTTP in memory
      session replication mechanism based on JavaGroup. The plugin dispatches
      HTTP requests from the Apache web server towards Tomcat instances running
      as JOnAS web container. Servers going down and up are automatically taken
      into account. This plugin supports
      round-robin and weighted round-robin load balancing algorithms, with a
      sticky session option.
    </para>
    <para>
      Load balancing and HA is provided at the EJB container level in JOnAS.
      Operations invoked one EJB Home interfaces (EJB creation and retrieving)
      are dispatched on the nodes of the cluster. The mechanism is based on
      a "clustered aware" replicated JNDI registry
      using a Clustered remote Method Invocation protocol (CMI). The stubs
      contain the knowledge of the cluster, and implement the load balancing
      policy, which may be round-robin, and weighted round-robin. In a near
      future, a load balancing mechanism based on the nodes load will be
      available. Failover at the EJB level will be provided by implementing
      a stateful session bean state replication mechanism.
    </para>
    <para>
      The JOnAS clustering architecture is illustrated in the figure
      below.</para>

      <para>
        <inlinemediaobject>
          <imageobject>
            <imagedata fileref="picture-208-04.gif" format="GIF"/>
          </imageobject>
        </inlinemediaobject>
      </para>

    <para>Apache is used as the font-end HTTP server, Tomcat as the JOnAS web
      container. The JOnAS servers share the same database. The mod_jk
      plug-in provides Load Balancing / High Availability at the
      Servlet/JSP level. Failover is provided through the in-memory
      session replication mechanism. Load Balancing / High Availability is
      provided at the EJB level through the CMI protocol associated with
      the replicated clustered aware JNDI registry.
      Tomcat may run in the same JVM as the EJB container or not. JOnAS
      provides some documentation for configuring such an architecture.
    </para>
    <para>The use of the
      <ulink url="http://www.objectweb.org/c-jdbc/index.html">C-JDBC</ulink>
      ObjectWeb project allows to provide load balancing and high availability
      at the database level. The use of C-JDBC is transparent to the
      application (in our case to JOnAS), as it is viewed as a usual JDBC
      driver. However this "driver" implements the cluster mechanisms
      (reads are load balanced and writes are broadcasted). The
      database is distributed and replicated among several nodes and C-JDBC
      load balances the queries between these nodes. An evaluation of C-JDBC
      using the TPC-W benchmark on a 6 nodes cluster has shown performance
      scaling linearly up to 6 nodes.</para>
    <para>In addition to clustering solutions, JOnAS provides many mechanisms,
      intrinsic to the JOnAS server, for being highly scalable and efficient.
      This includes</para>
    <itemizedlist>
      <listitem><para>Pool of stateless session bean instances</para></listitem>
      <listitem><para>Pool of entity bean instances, configurable for each entity bean,
    within its deployment descriptor</para></listitem>
      <listitem><para>Activation/passivation of entity beans, passivation may be controlled
    through the management console</para></listitem>
      <listitem><para>Pools of connections, for JDBC, JMS, J2EE CA connectors</para></listitem>
      <listitem><para>Pool of threads for message-driven beans</para></listitem>
      <listitem><para>Session bean timeout may be specified at deployment</para></listitem>
      <listitem><para>A "shared" flag in the specific deployment descriptor of an entity
    bean indicates if the persistent representation of this entity bean
    is shared by several servers/applications, or if it is dedicated
    to the JOnAS server where it is loaded. In the last case, the
    optimization done by JOnAS consists in not reloading the
    corresponding data between transactions.</para></listitem>
      <listitem><para>The usual EJB 1.1 "isModified" (or "Dirty") mechanism is available,
    avoiding to store non modified data.</para></listitem>
    </itemizedlist>
    <para>Some benchmarks and JOnAS usecases have already shown that JOnAS
      was highly scalable, see for example the
      <ulink url="http://www.cs.rice.edu/CS/Systems/DynaServer/perf_scalability_ejb.pdf">Rubis</ulink> results, or the
      <ulink url="http://openuss.sourceforge.net/openuss/">OpenUSS</ulink> usecase.
      Rubis is a benchmark for e-commerce J2EE applications, which now belongs
      to the ObjectWeb
      <ulink url="http://www.objectweb.org/jmob/index.html">JMOB</ulink> (Java
      Middleware Open Benchmarking) project. OpenUSS is an operational
      University portal with about 5000 users.
    </para>
</section>
<section>
    <title>Perspectives</title>
    <para>As an open source implementation of a J2EE server, JOnAS is
      continuously evolving to satisfy the user requirements and to follow
      the related standards. The main JOnAS evolutions currently planned
      are the following:
    </para>
    <itemizedlist>
      <listitem><para>A J2EE CA 1.0 Resource Adapter for JDBC is planned for the middle of
    the year. It will replace the current JOnAS database service for
    plugging JDBC drivers and managing connection pools. In addition, it
    will provide JDBC PreparedStatement pooling. At the end of the
    year, a new version of this resource adapter, compliant to J2EE CA 1.5
    (J2EE 1.4), will be available, and will provide JDBC resultsets re-use
    by the EJB container (this optimization reduces the number of SQL
    statements executed by the EJB container).</para></listitem>
      <listitem><para>The support of EJB 2.1 (J2EE 1.4) specification will be provided by
    the end of the year. This will include a "Timer" service.</para></listitem>
      <listitem><para>The support of "Web Services" will be completed, in order
    to support standard deployment, as specified in J2EE 1.4. Tools
    for developing "Web Services" and an open source UDDI implementation
    will be integrated.</para></listitem>
      <listitem><para>Deployment APIs as specified in JSR88 (J2EE 1.4) will be supported
    by the end of the year, thanks to the Ishmael project.</para></listitem>
      <listitem><para>JOnAS administration will be enhanced by introducing the concept of
    management domain.</para></listitem>
      <listitem><para>The ObjectWeb JOTM project  will be integrated within the JOnAS
    Transaction service. This will allow to support nested transactions,
    CORBA transactions and "Web Services" transactions.</para></listitem>
    </itemizedlist>
</section>
<section><title/>
    <para><emphasis>Sun, Java, and all
    Java-based trademarks are trademarks or registered trademarks of Sun
    Microsystems, Inc. in the U.S. and other countries.</emphasis></para>
</section>
</article>