UNIT II EJB ARCHITECTURE CONTENTS. Preface. Introduction. Enterprise Java Bean:

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1 UNIT II EJB ARCHITECTURE CONTENTS EJB Intrductin EJB Architecture Overview f EJB sftware architecture View f EJB Cnversatin Building and Deplying EJBs Rles in EJB. Preface This unit intrduces the cre aspects f EJP cncepts. It deals with EJB Architecture and Views f EJB. This unit prtrays the cncepts f Building and Deplying EJBs. And als this unit cvers the rles in EJB. Intrductin Enterprise JavaBeans (EJB) are reusable Java cmpnents that implement business lgic and enable yu t develp cmpnent-based distributed business applicatins. EJBs reside in an EJB cntainer, which prvides a standard set f services such as persistence, security, transactins, and cncurrency. Enterprise JavaBeans are the standard fr defining server-side cmpnents. WebLgic Server's implementatin f the Enterprise JavaBeans cmpnent architecture is based n Sun Micrsystems EJB specificatin. Enterprise Java Bean: A server-side cmpnent technlgy Easy develpment and deplyment f Java technlgy-based applicatin that are: Transactinal, distributed, multi-tier, prtable, scalable, secure,

2 Leverages the benefits f cmpnent-mdel n the server side Separates business lgic frm system cde Cntainer prvides system services Prvides framewrk fr prtable cmpnents Over different J2EE-cmpliant servers Over different peratinal envirnments Enables deplyment-time cnfiguratin Deplyment descriptr (((Enterprise JavaBeans (EJB) are reusable Java cmpnents that implement business lgic and enable yu t develp cmpnent-based distributed business applicatins. EJBs reside in an EJB cntainer, which prvides a standard set f services such as persistence, security, transactins, and cncurrency. Enterprise JavaBeans are the standard fr defining server-side cmpnents. WebLgic Server's implementatin f the Enterprise JavaBeans cmpnent architecture is based n Sun Micrsystems EJB specificatin.)))

3 Why EJB? z EJB Architecture simplifies the develpment f distributed enterprise applicatins. z EJB Specificatin is a slutin that is perating-system independent. z Middleware Independence z EJB defines a slutin that eases the develpment and deplyment f distributed applicatins z EJB enables the develpment f reusable and prtable cmpnents. z EJB has Brad Industry Supprt: Server Vendrs and End Users. EJB Vs JavaBeans JavaBeans cmpnent mdel defines a standard mechanism t develp prtable, Java cmpnents, such as widgets r cntrls. JavaBeans technlgy can be used in any visual Java technlgy integrated develpment envirnment (IDE) Java Beans EJB cmpnent mdel lgically extends the JavaBeans cmpnent mdel t supprt server cmpnents. EJB cmpnents cannt be manipulated by a visual Java IDE in the same way that JavaBeans can, They are prepackaged pieces f applicatin functinality that are designed t run in an applicatin server. Characteristics f EJB: 1. Hides server-side system level issues frm develpers. 2. Defines a standard cmpnent architecture that enables yu t build distributed bject-riented business applicatins.

4 3. Facilitates creating enterprise-level applicatins by allwing easy integrating with ther EJB cmpnents as well as with ther cmpnents, such as servlets, Java Server Pages (JSP), and Java Beans. 4. Enables yu t create cmpnents and applicatins that are reusable acrss varius J2EE-cmpliant servers. The server-side cmpnents deplyed n the applicatin servers can be implemented using varius technlgies, such as EJB and Micrsft s COM/DCOM. Enterprise JavaBeans are different frm JavaBeans, anther similarly named Sun Micrsystems cmpnent based technlgy. Examples f real-life applicatins where yu can use the EJB cmpnent architecture are: Online share trading applicatin Online reservatin applicatin Online catalg applicatin Online library applicatin The EJB specificatin defines the fllwing fur types f Enterprise JavaBeans: Stateless sessin. These nn-persistent EJBs prvide a service withut string an interactin r cnversatin state between methds. Stateful sessin. These nn-persistent EJBs maintain state acrss methds and transactins. Each instance is assciated with a particular client. Entity. These persistent EJBs represent an bject view f the data, usually rws in a database. An entity bean has a primary key as a unique identifier. Message-driven. These EJBs are integrated with the Java Message Service (JMS) t enable message-driven beans t act as a standard JMS message cnsumer and perfrm asynchrnus prcessing between the server and the JMS message prducer. The WebLgic Server cntainer directly interacts with a message-driven bean by creating bean instances and passing JMS messages t thse instances as necessary.

5 Frm the EJB sub-nde, f the Deplyments nde f the Administratin Cnsle, yu can update r cnfigure EJBs deplyed n WebLgic Server r mnitr the their perfrmance. Cnfiguring EJBs T cnfigure an EJB fr deplyment t the WebLgic Server Administratin Cnsle: 1. Start the WebLgic Server Administratin Cnsle. 2. Select the Dmain in which yu will be wrking. 3. In the left pane f the Cnsle, click Deplyments. 4. In the left pane f the Cnsle, click EJB. A table is displayed in the right pane f the Cnsle shwing all the deplyed EJBs. 5. Select the Cnfigure a new EJB ptin. 6. Lcate the EAR, WAR r JAR file yu wuld like t cnfigure. Yu can als cnfigure an explded applicatin r cmpnent directry. Nte that WebLgic Server will deply all cmpnents it finds in and belw the specified directry. 7. Click [select] t the left f a directry r file t chse it and prceed t the next step. 8. Select a Target Server frm amng Available Servers. 9. Enter a name fr the EJB r applicatin in the prvided field. 10. Click Cnfigure and Deply. The Cnsle will display the Deply panel, which lists deplyment status and deplyment activities fr the EJB. 11. Using the available tabs, enter the fllwing infrmatin:

6 Cnfiguratin Edit the staging mde and enter the deplyment rder. Targets Indicate the Targets-Server fr this cnfigured EJB r applicatin by mving the server frm the Available list t the Chsen list. Deply Deply the EJB r applicatin t all r selected targets r undeply it frm all r selected targets. Mnitring Enable sessin mnitring fr the EJB r applicatin. Ntes Enter ntes related t the EJB r applicatin. EJB Architecture EJB Server EJB Cntainer EJB Client Enterprise Java Beans Auxiliary Systems - JNDI, JTA, JavaMail

7 EJB is a server-side cmpnent architecture that simplifies the prcess f building enterprise-level, distributed applicatins in Java. EJB cmpnents are deplyed in EJB cntainers f J2EE-cmpliant applicatin servers, such as J2EE 1.4, Weblgic, and JBss. Varius cmpnents f EJB architecture are: EJB Cntainer: Prvides the runtime envirnment fr the EJB cmpnents and services, such as life cycle management, cnnectin pling, and security. EJB Cmpnent: Java classes that fllw the EJB specificatin t implement the business lgic f an applicatin. EJB cmpnents are deplyed in EJB cntainer and are accessed using the remte and hme interfaces f an enterprise bean. EJB Object: EJB cntainer generates an EJB bject, when a client needs t access an instance f the enterprise bean. The EJB bject acts as an interface between the client and bean instances. Hme Object: Hme bjects are generated by EJB cntainer. Clients access EJB bjects that are stred at different Java Virtual Machines (JVM), using the hme bject. An enterprise bean is a distributed server cmpnent that lives in an EJB cntainer and is accessed by remte clients ver netwrk via its remte interface r is accessed by ther lcal enterprise beans n the same server via its lcal interface. CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 7

8 The EJB cmpnent is a remtely executable cmpnent deplyed n its server and it is a self-descriptive cmpnent specified by its Deplyment Descriptr (DD) in a XML frmat. Each EJB cmpnent has a business lgic interface that clients can run the business lgic peratins via this interface withut knwing the detail implementatin behind the interface. We call such interface as a remte r lcal interface. An instance f an EJB cmpnent is created and managed by its factry named hme interface n the EJB cntainer. Every enterprise bean must have a hme interface and a remte (lcal) interface. The EJB cmpnent can be cnfigured at the deplyment time by specifying its deplyment descriptr. The EJB classes behind hme and remte (r lcal) interfaces are the implementatins f these tw interfaces. An EJB cmpnent is a black-bx cmpnent. A client f an EJB cmpnent nly knws what the cmpnent des but nt hw it des. A client makes a request t an EJB cmpnent with its deplyed name by lking up at JNDI t get an Object Reference (OR) f this EJB cmpnent. The client can then create an instance f this EJB cmpnent n the server accrding t the reference. Finally, the client invkes the business methds f this EJB instance. The EJB class may als lcate and access ther EJB beans at remte sites by using EJB cntext infrmatin. The message driven bean is an exceptin which des nt have any interface like the hme and remte interfaces that a classic EJB has. Enterprise beans prvide several benefits fr applicatin develpers: They allw yu t build distributed applicatins by cmbining cmpnents develped using tls frm different vendrs. They make it easy t write applicatins. Yu d nt have t deal with lw-level details f transactin and state management, multithreading, resurce pling, and ther cmplex lw-level APIs. Hwever, if necessary, expert prgrammers can still gain direct access t the lw-level APIs. They can be develped nce and then deplyed n multiple platfrms withut recmpilatin r surce cde mdificatin. CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 8

9 The EJB specificatin that gverns the use f enterprise beans is cmpatible with ther Java APIs and CORBA. It als prvides fr interperability between enterprise beans and nn-java applicatins. Enterprise beans An enterprise bean is a nn-visual cmpnent f a distributed, transactinriented enterprise applicatin. Enterprise beans are typically deplyed in EJB cntainers and run n EJB servers. Yu can custmize them by changing their deplyment descriptrs and yu can assemble them with ther beans t create new applicatins. There are three types f enterprise beans: sessin beans, entity beans, and message-driven beans. Sessin beans: Sessin beans are nn-persistent enterprise beans. They can be stateful r stateless. A stateful sessin bean acts n behalf f a single client and maintains client-specific sessin infrmatin (called cnversatinal state) acrss multiple methd calls and transactins. It exists fr the duratin f a single client/server sessin. A stateless sessin bean, by cmparisn, des nt maintain any cnversatinal state. Stateless sessin beans are pled by their cntainer t handle multiple requests frm multiple clients. Entity beans: Entity beans are enterprise beans that cntain persistent data and that can be saved in varius persistent data stres. Each entity bean carries its wn identity. Entity beans that manage their wn persistence are called bean-managed persistence (BMP) entity beans. Entity beans that delegate their persistence t their EJB cntainer are called cntainer-managed persistence (CMP) entity beans. Message-driven beans: Message-driven beans are enterprise beans that receive and prcess JMS messages. Unlike sessin r entity beans, message-driven beans have n interfaces. They can be accessed nly thrugh messaging and they d nt maintain any cnversatinal state. Message-driven beans allw asynchrnus CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 9

10 cmmunicatin between the queue and the listener, and prvide separatin between message prcessing and business lgic. Remte client view The remte client view specificatin became available beginning with EJB 1.1. The remte client view f an enterprise bean is lcatin independent. A client running in the same JVM as a bean instance uses the same API t access the bean as a client running in a different JVM n the same r different machine. Remte interface: The remte interface specifies the remte business methds that a client can call n an enterprise bean. Remte hme interface: The remte hme interface specifies the methds used by remte clients fr lcating, creating, and remving instances f enterprise bean classes. Lcal client view The lcal client view specificatin is available in EJB 2.0 r later. Unlike the remte client view, the lcal client view f a bean is lcatin dependent. Lcal client view access t an enterprise bean requires bth the lcal client and the enterprise bean that prvides the lcal client view t be in the same JVM. The lcal client view therefre des nt prvide the lcatin transparency prvided by the remte client view. Lcal interfaces and lcal hme interfaces prvide supprt fr lightweight access frm enterprise bean that are lcal clients. Sessin and entity beans can be tightly cuple with their clients, allwing access withut the verhead typically assciated with remte methd calls. Lcal interface: The lcal interface is a lightweight versin f the remte interface, but fr lcal clients. It includes business lgic methds that can be called by a lcal client. Lcal hme interface: The lcal hme interface specifies the methds used by lcal clients fr lcating, creating, and remving instances f enterprise bean classes. CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 10

11 Web service client view In the EJB 2.1 specificatin, the EJB architecture intrduced the supprt fr Web services. A client fr a sessin bean can be a Web service client. A Web service client can make use f the Web service client view f a stateless sessin bean, which has a crrespnding service endpint interface.. Service endpint interface The service endpint interface fr a stateless sessin bean expses the functinality f the sessin bean as a Web service endpint. The Web Service Descriptin Language (WSDL) dcument fr a Web service describes the Web service as a set f endpints perating n messages. A WSDL dcument can include the service endpint interface f a stateless sessin bean as ne f its endpints. An existing stateless sessin bean can be mdified t include a Web service client view, r a service endpint interface can be mapped frm an existing WSDL t prvide the crrect interface. A Web service client view is independent f lcatin and can be accessed thrugh remte calls. EJB client JAR file An EJB client JAR file is an ptinal JAR file that can cntain the client interfaces that a client prgram needs t use the client views f the enterprise beans that are cntained in the EJB JAR file. If yu decide nt t create an EJB client JAR file fr an EJB mdule, all f the client interface classes will be in the EJB JAR file. By default, the wrkbench creates EJB client JAR prjects fr each crrespnding EJB prject. EJB cntainer An EJB cntainer is a runtime envirnment that manages ne r mre enterprise beans. The EJB cntainer manages the life cycles f enterprise bean bjects, crdinates distributed transactins, and implements bject security. Generally, CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 11

12 each EJB cntainer is prvided by an EJB server and cntains a set f enterprise beans that run n the server. Deplyment descriptr A deplyment descriptr is an XML file packaged with the enterprise beans in an EJB JAR file r an EAR file. It cntains metadata describing the cntents and structure f the enterprise beans, and runtime transactin and security infrmatin fr the EJB cntainer. EJB server An EJB server is a high-level prcess r applicatin that prvides a runtime envirnment t supprt the executin f server applicatins that use enterprise beans. An EJB server prvides a JNDI-accessible naming service, manages and crdinates the allcatin f resurces t client applicatins, prvides access t system resurces, and prvides a transactin service. An EJB server culd be prvided by, fr example, a database r applicatin server. Types f EJB Versin 1.1 f the EJB Specificatin [EJB ] defined tw types f EJB: the sessin EJB and the entity EJB. Versin 2.0 intrduces a third type, the message-driven EJB [EJB ]. It is pssible t envisage EJB applicatins where the EJBs dn t fit neatly int any f these categries, but in practice ne f these types can be adapted t suit mst jbs. (i)sessin EJBs A sessin EJB is a nnpersistent bject: Its lifetime is the duratin f a particular interactin between the client and the EJB. The client nrmally creates an EJB, calls methds n it, and then remves it. If the client fails t remve it, the EJB cntainer will remve it after a certain perid f inactivity. Sessin EJBs are subdivided int stateful and stateless types. A stateless sessin EJB is shared amngst a number f clients, while CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 12

13 a stateful sessin EJB is created fr a specific client and nt used by any thers. The use f stateless EJBs ffers efficiency advantages but, f curse, it is nt always pssible t use them. (ii) Entity EJBs Entity EJBs represent persistent bjects: Their lifetimes are nt related t the duratin f interactin with clients. In nearly all cases, entity EJBs are synchrnized with relatinal databases. This is hw persistence is achieved. Entity EJBs are always shared amngst clients: A client cannt get an entity EJB t itself. Thus, entity EJBs are nearly always used as a scheme fr mapping relatinal databases int bject-riented applicatins. Whereas a client nrmally creates a sessin EJB and remves it after use, clients nrmally lk up an existing entity EJB. Creatin f an entity EJB crrespnds t adding new data items t the applicatin (e.g., adding rws t database tables). An imprtant feature f entity EJBs is that they have identity that is, ne can be distinguished frm anther. This is implemented by assigning a primary key t each instance f the EJB, where primary key has the same meaning as it des fr database management. Primary keys that identify EJBs can be f any type, including prgrammerdefined classes. (iii)message-driven EJBs A message-driven bean acts as a cnsumer f asynchrnus messages: It cannt be called directly by clients, but is activated by the cntainer when a message arrives. Clients interact with these EJBs by sending messages t the queues r tpics t which they are listening. Althugh a message-driven EJB cannt be called directly by clients, it can call ther EJBs itself. Message-driven EJBs are the nly type that d nt fllw a strict request-respnse interactin with clients. CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 13

14 Why use EJBs? It is pssible t write applicatins that supprt distributin, transactin management, and security withut using EJBs. There are many such applicatins in use already. S what advantages d EJBs have t ffer ver ther techniques? The EJB develper wrks within the EJB framewrk t take advantage f its built-in supprt fr features like transactin management and security; nce understd, little develper effrt is required t make effective use f these features. With suitable servers, EJB applicatins can even make use f features as sphisticated as distributed transactin management with n cding whatsever. EJB 2.0 intrduces a very pwerful persistence management scheme, which supprts nt nly persistent data, but persistent relatinships between bjects. It takes a while t get used t, but nce mastered, this revlutinizes the develpment f persistent applicatin bjects. Again, very little cding is required t implement such bjects. The EJB framewrk presents the EJB with a managed perating envirnment. Fr example, the framewrk ensures that an EJB instance is never executing in mre than ne cncurrent thread, 3 s the develper des nt have t be cncerned abut the effects f cncurrency n data integrity. The cntainer is als respnsible fr memry and resurce management, s EJB develpers dn't have t be cncerned with these issues. EJBs can make use f the full range f Java APIs and class libraries. It is relatively straightfrward t cde an EJB that parses XML, sends , and cmmunicates with directry and database servers via standard APIs like JDBC and JNDI. EJBs islate database implementatin frm the applicatin's business lgic. If we use entity EJBs, fr example, as mdels f the underlying data, then theuse f that data is decupled frm its internal representatin. This leads t increased ease f maintenance and prtability f cde. We can als use EJBs as interfaces t legacy systems, with similar advantages. CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 14

15 EJBs are very accessible t Web cmpnents such as servlets and JSPs. There are a number f prducts available that supprt these cmpnents in the same applicatin framewrk (typically called applicatin servers). This makes it straightfrward t prvide EJB applicatins with a Web-based user interface and, perhaps, prvide Internet access t the applicatin. A High Level View f an EJB Cnversatin. In the EJB architecture, the client undertakes the fllwing tasks: Finding the bean Getting access t a bean Calling the bean s methds Getting rid f the bean Finding the bean EJB specificatin mentins tw ways in which a client can find a bean Using the Java Naming and Directry Interface Using the CORBA s Cmmn Object Service (COS) JNDI API prvides a unifrm interface t naming and directry services. A naming service is a service that assciates a Symblic Name with an bject Dmain Name Service is a cmmnly used naming service that is used t transfer symblic machine names int numeric IP addresses. Previus mdel f DNS, needed t maintain a file cntaining a list f symblic hst names alng with the numeric IP addresses that they shuld reslve t. Prblems in this apprach: If the /etc/hsts/file develped errrs, culdn t reslve symblic names. CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 15

16 Needed t maintain the change f addresses when new machines were added. If a machine did nt appear in the /etc/hsts file, need t knw its numeric IP address t cnnect t it. Using DNS apprach allws yu t avid many f these annyances. It wrks as fllws: A client makes a query t a DNS server If the DNS server knws hw t reslve the address, it returns the address. If the DNS server des nt knw hw t reslve the address, it prvides the query t anther DNS server Once the server is able t reslve the name, it returns the address t the client. Typically, it als caches the result s that, if the request is made again, it can be handled immediately. JNDI prvides a unifrm interface t naming services. JNDI client uses the Server s SPI (Server Prvider Interface) t access its services. A Java client can use JNDI t lkup an EJB cmpnent. The JNDI call returns a reference t an bject implementing the EJB cmpnent s hme interface, which can then be used t gain access t the EJB bject itself. The ther way t find an EJB cmpnent is t use CORBA s Cmmn Object Services (COS) naming service. COS refers t a grup f Services, including naming, that is prvided as part f the CORBA services specificatin. In additin t suing COS naming directly, can make use it via JNDI. Getting access t a bean The result f the naming lkup is a reference t an bject implementing the EJB cmpnents hme interface CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 16

17 A client uses the hme interface t lk up existing EJB instances, r t create new nes. This lkup result in a reference t an bject that implements the EJB bject s remte interface. The client uses the remte interface t interact with the EJB bjects n the server. Calling the bean s methds After the client has a reference t an bject implementing the bject s remte interface, it can then invke the methds that the EJB bject makes public in the remte interface. Getting rid f the bean When the client has finished with an EJB bject, it can call the remve() methd n the hme interface r n the bject s remte interface. Usually remve() is called n a stateful sessin bean when it is n lnger needed, s that the cntainer can discard it and use the space fr ther beans. remve() methd n the stateless bean can be invked, but generally has n effect; the server simply returns the instance t a pl. remve() n entity beans, wuld remve the underlying bject frm persistent strage. (Ex: when the custmer bean is remved, the data will be deleted frm the underlying database.) Clients can interact with EJB either thrugh CORBA r thrugh RMI. CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 17

18 Overview f the EJB Building and Deplying Prcess Building and deplying EJBs in the WebLgic Enterprise envirnment requires careful planning t define hw t lcate these EJBs in the WLE distributed envirnment. After the Bean Prvider has implemented an EJB's business lgic and has prduced an initial deplyment descriptr, the prcess fr building and deplying that EJB in the WLE envirnment includes the fllwing steps: Step 1: Obtain the EJB JAR file frm the bean prvider. Step 2: Mdify the deplyment descriptr. Step 3: Create the WebLgic EJB extensins t the deplyment descriptr DTD. Step 4: Prduce the deplyable EJB JAR file. Step 5: Cnfigure the EJB applicatin. Step 6: Specify the mdule initializer bject in the WebLgic EJB extensins t the deplyment descriptr DTD. When yu build the EJB that has been prduced by the Bean Prvider, the end result is an EJB JAR file. The WLE system allws yu t build tw kinds f EJB JAR files: Standard EJB JAR file An EJB that has been built, but lacks the specific deplyment infrmatin n any specific system. Yu typically build a standard EJB with the gal f being able t distribute that EJB t a variety f deplyment envirnments. If yu are nly creating a standard EJB JAR file, yu nly need t perfrm steps 1 and 2 in this tpic. Deplyable EJB JAR file An EJB that has been built with deplyment descriptr infrmatin specific t a particular deplyment envirnment. The steps described in this chapter fr building a deplyable EJB JAR file specifically create an EJB that can be deplyed n a WLE system, and require yu t perfrm CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 18

19 steps 1 thrugh 4 in this tpic. The remainder f this tpic discusses each f these steps in detail. Steps fr Building and Deplying EJBs This sectin describes the steps fr building and deplying EJBs in the WLE envirnment and als prvides the fllwing sectins: Scaling an EJB Applicatin Fr Mre Infrmatin Step 1: Obtain the EJB JAR file frm the bean prvider. The first step in deplying an EJB is t btain the EJB JAR file frm the Bean Prvider. In additin t the class files cntained in the EJB JAR file, the EJB JAR file als has a deplyment descriptr fr each bean in that file. The steps fr prducing the Bean Prvider's EJB JAR file are described in the sectin Develpment Steps. Because multiple EJBs can be jined tgether in a single, deplyable unit, part f the assembly prcess is jining the EJB JAR files fr each f the beans. Step 2: Mdify the deplyment descriptr. As stated in Designing and Develping Enterprise JavaBeans fr the WLE System, the deplyment descriptr ties tgether the different classes and interfaces, and is used t build the cde-generated class files. It als allws yu t specify sme aspects f the EJB's deplyment at run time. The Bean Prvider specifies sme initial deplyment infrmatin in the deplyment descriptr. The deplyer typically needs t add t r mdify that infrmatin, such as shwn in the fllwing table: The EJB's name Yu may change the enterprise bean's name defined in the ejb-name CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 19

20 element. Values envirnment entries f Yu may change existing values r define new values fr the envirnment prperties. Descriptin fields Yu may change existing r create new descriptin elements. Binding enterprise references f bean Yu may link an enterprise bean reference t anther enterprise bean in the EJB JAR file. Yu create the link by adding the ejb-link element t the referencing bean. Security rles Yu may define ne r mre security rles. The security rles define the recmmended security rles fr the clients f the enterprise beans. Yu define the security rles using the securityrle elements. Fr mre infrmatin abut EJB security, see Using Security in the WebLgic Enterprise nline dcumentatin. Methd permissins Yu may define methd permissins, which are binary relatinships between the security rles and the methds f the remte and hme interfaces f the EJBs. Yu define methd permissins using the methd-permissin elements. Linking security references f rle If yu define security rles in the deplyment descriptr, yu must link the security rle references declared by the Bean Prvider t the security rles. Yu define these links using the rle-link element. Fr mre infrmatin abut EJB security, see Using Security in the WebLgic Enterprise nline dcumentatin. Changing The deplyer can change the type f persistent strage used by a CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 20

21 persistent strage infrmatin, if necessary bean. If the persistentstretype is file, the serialized files are created in this directry. The default file is / pstre/ bean_name.dat, where the directry pstre represents the directry frm which the WLE applicatin was started, and bean_name is the fully qualified name f the EJB with underscres (_ ) replacing the perids (. ) in the name. If the persistentstretype is jdbc, the cntainer lks fr additinal values t determine the apprpriate values fr the JDBC cnnectin. Nte that if the bean's persistence is stred in a database via a JDBC cnnectin, the system administratr needs t add this infrmatin t the UBBCONFIG file as well. Fr mre infrmatin, see Using the JDBC Drivers in the WebLgic Enterprise nline dcumentatin. Nte that persistence infrmatin is specified in the WebLgic EJB extensins t the deplyment descriptr DTD file, as described in the sectin Specifying Persistence Infrmatin. T mdify a deplyment descriptr, yu can use either f the fllwing tw methds: The WebLgic EJB Deplyer The manual mdificatin f the deplyment descriptr in a text editr The type f deplyment descriptr yu prduce depends n whether yu are creating a standard EJB JAR file r a deplyable EJB JAR file. Creating a Standard EJB JAR File CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 21

22 If yu are creating a standard EJB JAR file, yu nly need t mdify the single deplyment descriptr cntained in the EJB JAR file prduced by the Bean Prvider. When mdifying this deplyment descriptr, use the syntax described in the EJB 1.1 Specificatin prduced by Sun Micrsystems, Inc. If yu are creating a standard EJB JAR file: 1. Make the apprpriate mdificatins t the bean's deplyment descriptr file. 2. Run the ejbc cmmand, specifying the -ndeply ptin. Fr mre infrmatin abut the ejbc cmmand, see the Cmmand Reference in the WebLgic Enterprise nline dcumentatin. Creating a Deplyable EJB JAR File If yu are creating a deplyable EJB JAR file, yu need t d the fllwing: Mdify the deplyment descriptr, as described in the sectin Creating a Standard EJB JAR File. Create a WebLgic Enterprise extended deplyment descriptr file, which is als created as an XML file, and which specifies the infrmatin described in the sectin Step 3: Create the WebLgic EJB extensins t the deplyment descriptr DTD.. Step 3: Create the WebLgic EJB extensins t the deplyment descriptr DTD. Fr an EJB applicatin t be deplyable in the WLE envirnment, yu need t create a file cntaining the WebLgic EJB extensins t the deplyment descriptr DTD. This file specifies the fllwing run time and cnfiguratin infrmatin fr the EJB applicatin: Custm applicatin startup and shutdwn prperties Registratin f the applicatin's hme interfaces Persistence infrmatin CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 22

23 Specifying the WebLgic EJB Extensins DTD The file that includes the WebLgic EJB extensins t the deplyment descriptr DTD must specify the fllwing DTD reference at the beginning: <!DOCTYPE weblgic-ejb-extensins SYSTEM "weblgic-ejb-extensins.dtd" > Specifying the Mdule Initializer Class Server applicatin startup and shutdwn can be handled autmatically by the EJB cntainer. Hwever, if yu have special server initializatin r shutdwn requirements, use the mdule-initializer-class-name element in the WebLgic EJB extensins t the deplyment descriptr DTD t specify the name f the mdule initializer bject. The syntax fr specifying a mdule initializer bject fr handling the initialize and release methds is similar t that fr CORBA and RMI. Hwever, with the CORBA and RMI mdels, the startup and shutdwn infrmatin is specified in an XML file and is serialized by the buildjavaserver cmmand. Fr EJB deplyment, XML elements fr startup and shutdwn prcedures are specified tgether with the ther elements in the WebLgic EJB extensins t the deplyment descriptr DTD, and yu prcess them using the ejbc cmmand. The WLE EJB cntainer parses the XML at run time and perfrms the startup and shutdwn prcessing. See the sectin Step 5: Cnfigure the EJB applicatin. fr a cmplete descriptin f startup and shutdwn handling in WLE. XML DTD Syntax <!ELEMENT mdule-initializer-class (mdule-initializer-class-name*))> <!ELEMENT mdule-initializer-class-name (#PCDATA)> Example <weblgic-ejb-extensins>... <mdule-initializer-class> <mduleinitializer-class-name>serverimpl CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 23

24 </mduleinitializer-class-name> </mdule-initializer-class> </weblgic-ejb-extensins> Registering Names fr the EJB Hme Classes A name fr the EJB hme class must be registered in the glbal WLE JNDI namespace. This allws Java clients t perfrm a lkup n the JNDI name fr the EJB hme and gain access t the bject. The name fr the EJB hme class can be different than the <ejbname> element specified in the standard EJB XML. The <ejb-name> in the standard deplyment descriptr must be unique nly amng the names f the EJBs in the same EJB JAR file. Hwever, the JNDI name must be unique amng all glbal hme r factry names in a WLE dmain; this includes EJB hmes, CORBA factries, and RMI named bjects. XML DTD Syntax <!ELEMENT jndi-name (#PCDATA)> Example <weblgic-ejb-extensins> <weblgic-versin> WebLgic Enterprise Server 5.0 </weblgic-versin> <weblgic-enterprise-bean> <ejb-name> racle </ejb-name> <weblgic-deplyment-params> <max-beans-in-free-pl> 20 </max-beans-in-free-pl> CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 24

25 <max-beans-in-cache> 1000 </max-beans-in-cache> <idle-timeut-secnds> 5 </idle-timeut-secnds> <!-- JNDI name that is assciated with this EJB; used fr lkup --> <jndi-name> racle.oraclehme </jndi-name>... </weblgic-ejb-extensins> Specifying Persistence Infrmatin The WLE EJB cntainer prvides cntainer-managed persistence. The cde fr implementing the persistence is generated by the ejbc cmmand based n the deplyment descriptrs. The persistence stre can be a flat file r it can be a database managed with a JDBC cnnectin pl. Fr the EJB state t fully cperate in a WLE glbal transactin, cnfigure the EJB t use the JDBC-managed database stre prvided in WLE. Use filebased persistence nly during develpment and prttyping. The standard deplyment descriptr created by the Bean Prvider nrmally specifies: The fields in the EJB that are t be persistent, via the cmp-field element Infrmatin abut the primary key Hwever, yu, as the deplyer, need t specify additinal infrmatin fr mapping an EJB t its persistent stre via the WebLgic EJB extensins t the deplyment descriptr DTD. CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 25

26 File-based Persistence The fllwing cde shws the WebLgic EJB extensins t the deplyment descriptr DTD fr specifying file-based persistence: <!-- Persistence stre descriptr. Specifies what type f persistence stre EJB cntainer shuld use t stre state f bean. --> <!ELEMENT persistence-stre-descriptr (descriptin?, (persistence-stre-file persistence-stre-jdbc)?)> <!-- Persistence stre using file. Bean is serialized t a file. Mainly used t stre state f Stateful Sessin Beans. --> <!ELEMENT persistence-stre-file (descriptin?, persistence-stre-directry-rt?)> <!-- Rt directry n File system fr string files per bean. --> <!ELEMENT persistence-stre-directry-rt (#PCDATA)> The infrmatin supplied fr the persistence-stre-directry-rt element is used by the EJB cntainer t stre all instances f the EJB, with the ejb-name element cnverted t a directry name. Database-stred Persistence The fllwing cde shws the WebLgic EJB extensins t the deplyment descriptr DTD fr specifying a JDBC cnnectin fr database-stred persistence: <!-- Persistence stre is any RDBMS. JDBC driver is used t talk t database. CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 26

27 Required fr CMP. --> <!ELEMENT persistence-stre-jdbc (descriptin?, pl-name, user?, passwrd?, driver-url?, driver-class-name?, table-name, attribute-map, finder-descriptr*)> <!-- Required fr CMP --> <!ELEMENT pl-name (#PCDATA)> <!-- Ignred in WebLgic Enterprise Server as this is part f cnnectin pl setup at startup --> <!ELEMENT user (#PCDATA)> <!-- Ignred in WebLgic Enterprise Server as this is part f cnnectin pl setup at startup --> <!ELEMENT passwrd (#PCDATA)> <!-- Ignred in WebLgic Enterprise Server as this is part f cnnectin pl setup at startup --> <!ELEMENT driver-url (#PCDATA)> <!-- Ignred in WebLgic Enterprise Server as this is part f cnnectin pl setup at startup --> <!ELEMENT driver-class-name (#PCDATA)> <!-- Required fr CMP --> <!ELEMENT table-name (#PCDATA)> CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 27

28 <!-- Required fr CMP --> <!ELEMENT attribute-map (descriptin?, attribute-map-entry+)> <!-- Required fr CMP --> <!ELEMENT attribute-map-entry (bean-field-name, table-clumn-name)> <!-- Required fr CMP --> <!ELEMENT bean-field-name (#PCDATA)> <!-- Required fr CMP --> <!ELEMENT table-clumn-name (#PCDATA)> <!-- Required fr CMP --> <!ELEMENT finder-descriptr (descriptin?, methd?, query-grammar?)> <!-- Required fr CMP --> <!ELEMENT query-grammar (#PCDATA)> The EJB instances are stred in a database that has been previusly set up with a JDBC cnnectin pl, which is identified by the pl-name element. The table-name and attribute-map elements map the EJB fields t the apprpriate table clumns in the database. Finder descriptrs are the WLE implementatin f the EJB find methds. The finderdescriptr elements are pairs f methd signatures and expressins. Yu specify a methd signature in the EJBHme interface, and yu specify the methd's expressin in the deplyment descriptr via the query-grammar element. The finder methds return an enumeratin f EJBs. Fr mre infrmatin abut specifying finder descriptrs, see the EJB XML Reference in the WebLgic Enterprise nline dcumentatin. Example CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 28

29 The fllwing WebLgic EJB extensins t the deplyment descriptr DTD fragment specify autmatic saving using JDBC persistence f tw fields f an entity bean (accuntid and salary ) t a database table (emp ) using a cnnectin pl (pl1 ), shwn in bldface type: <weblgic-ejb-extensins> <weblgic-versin> WebLgic Enterprise Server 5.0 </weblgic-versin> <weblgic-enterprise-bean> <ejb-name> racle </ejb-name> <weblgic-deplyment-params> <max-beans-in-free-pl> 20 </max-beans-in-free-pl> <max-beans-in-cache> 1000 </max-beans-in-cache> <idle-timeut-secnds> 5 </idle-timeut-secnds> <!-- JNDI name that is assciated with this EJB;used fr lkup --> <jndi-name> racle.oraclehme </jndi-name> <!-- This is CMP EJB. Specify persistence infrmatin --> <persistence-stre-descriptr> CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 29

30 <persistence-stre-jdbc> <!-- Pl name is lked up by the EJB surce --> <pl-name> jdbc/pl1 </pl-name> <!-- *** DATABASE INFORMATION SPECIFIC TO INSTALLATION SITE *** --> <!-- Default user URL is fr Oracle 8i--> <user> sctt </user> <!-- Default passwrd URL is fr Oracle 8i--> <passwrd> tiger </passwrd> <!-- Default driver URL is fr Oracle 8i, and default instance Beq-Lcal is used --> <driver-url> jdbc:weblgic:racle:beq-lcal </driver-url> <table-name> emp </table-name> <!-- CMP Fields and database table clumn mapping--> <attribute-map> <attribute-map-entry> <bean-field-name> accuntid CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 30

31 </bean-field-name> <table-clumn-name> empn </table-clumn-name> </attribute-map-entry> <attribute-map-entry> <bean-field-name> salary </bean-field-name> <table-clumn-name> sal </table-clumn-name> </attribute-map-entry> </attribute-map> <!-- Finder Specificatins --> <finder-descriptr> <methd> <ejb-name> racle </ejb-name> <methd-name> findaccunt(duble salaryequal) </methd-name> </methd> <query-grammar> (= salary $salaryequal) </query-grammar> </finder-descriptr> </persistence-stre-jdbc> </persistence-stre-descriptr> CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 31

32 </weblgic-deplyment-params> </weblgic-enterprise-bean> </weblgic-ejb-extensins> Fr mre infrmatin abut JDBC cnnectins, see Using the JDBC Drivers in the WebLgic Enterprise nline dcumentatin. Step 4: Prduce the deplyable EJB JAR file. In this step, yu package the deplyment descriptr, the cmpiled files fr the EJB classes, the WLE extensins t the deplyment descriptr DTD, and any additinal required classes int a deplyable EJB JAR file. Yu can d this using the ejbc cmmand, as in the fllwing example: java cm.beasys.ejb.utils.ejbc -validate -i DDfile -x WLEXfile archive-file The ejbc cmmand perfrms the fllwing steps: 1. Parses the standard EJB deplyment descriptr and WebLgic Enterprise extended deplyment descriptr XML files, which are represented, respectively, as DDfile and WLEXfile in the preceding cmmand. 2. Checks the deplyment descriptrs fr semantic cnsistency, and writes any incnsistencies t standard utput. 3. Generates the wrapper Java classes and cmpiles them. This is perfrmed fr each EJB in the deplyment descriptr. 4. Packages the XML deplyment descriptrs and the generated class files int a deplyable EJB JAR file. The cmmand-line argument archive-files specifies the files that are archived int the EJB JAR file. If yu have multiple bean packages meant t be assembled as a deplyable unit, the bean packages must be specified in a single deplyment descriptr. Fr mre infrmatin abut the ejbc cmmand, see the Cmmand Reference in the WebLgic Enterprise nline dcumentatin. CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 32

33 Step 5: Cnfigure the EJB applicatin. In the SERVERS sectin f the UBBCONFIG file, the administratr uses the MODULES keywrd t identify the deplyed EJB JAR files. Optinally, a related set f startup arguments can be specified fr each EJB JAR file. Fr infrmatin abut cnfiguring the EJB cntainer, cnfiguring the WLE EJB server prcess, and specifying values in the UBBCONFIG file, see Creating a Cnfiguratin File in the WebLgic Enterprise nline dcumentatin. Step 6: Specify the mdule initializer bject in the WebLgic EJB extensins t the deplyment descriptr DTD. Server applicatin startup and shutdwn can be handled autmatically by the EJB cntainer. Hwever, if yu have special server initializatin r shutdwn requirements, yu need t implement an applicatin entity called the mdule initializer bject. The mdule initializer bject implements peratins that execute the fllwing tasks: Perfrming basic mdule initializatin (r EJB JAR file deplyment) peratins, which may include allcating resurces needed by the EJB JAR file. Perfrming basic server applicatin initializatin peratins, which may include registering hmes r factries managed by the server applicatin and allcating resurces needed by the server applicatin. Perfrming server prcess shutdwn and cleanup prcedures when the server applicatin has finished servicing requests. Nte: Fr EJBs, the scpe f the mdule initializer bject is at the EJB JAR file level and nt f the entire server applicatin, as with the Server bject and WLE CORBA applicatins. EJB Rles An interesting feature f the EJB Specificatin is that its requirements are largely divided int different 'rles.' When reading the Specificatin, it is therefre quite clear t whm the varius requirements crrespnd. CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 33

34 Cmpnent prvider The cmpnent prvider [EJB ] is a sftware develper wh authrs EJBs. These EJBs may be destined fr a particular applicatin, r they may be generalpurpse r part f a sftware library. The EJB authr may nt knw the names f the EJBs with which it is t interact althugh, f curse, their methd specificatins must be knwn. Similarly, the EJB authr may nt knw the names f external resurces like databases. The Specificatin indicates hw the cmpnent prvider uses the XML deplyment descriptr t indicate that these EJBs and resurces are required, and the names by which it has referenced them. Applicatin assembler The applicatin assembler [EJB ] is smene wh builds an applicatin ut f cmpnent EJBs. The same persn r peple may be perating in this rle as are fulfilling the cmpnent prvider rle, but the Specificatin is quite clear that the tw are distinct jbs. The applicatin assembler reslves references between EJBs, unifies the CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 34

35 references t external resurces, and packages the cmpnents int a single file ready fr deplyment. It is slightly cnfusing fr the newcmer t EJB develpment that mst f the graphical tls used fr building EJB applicatins dn't distinguish between what they are ding in the prvider rle versus in the assembler rle. It ften appears that the develper is supplying redundant infrmatin r infrmatin that is duplicated; this is because the deplyment descriptr being built des supprt the ntin f a separate prvider and assembler, even if they are in practice the same persn. Deplyer The deplyer [EJB ] takes a file frm the applicatin assembler that cntains the EJBs and ther cmpnents required fr the applicatin and installs it n the server, making apprpriate custmizatins fr the site. These custmizatins include replacing database references with real database infrmatin, mapping the security rles in the applicatin nt real users and grups in the rganizatin, and supplying values fr ther cnfiguratin parameters. Server vendr The server vendr supplies EJB server prducts. An EJB develper shuld nt assume that the sectins in the EJB Specificatin that deal with the respnsibilities f the server vendr are nt f interest. On the cntrary: The server sets the perating envirnment f the EJB, and this sectin f the EJB Specificatin gives the develper an insight int what envirnment the EJB can expect. Administratr CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 35

36 An administratr [EJB ] is a persn respnsible fr the maintenance and perfrmance tuning f an applicatin. Tl prvider A tl prvider authrs EJB packaging and deplyment tls. 2 Marks Questins & Answers 1. What is an Enterprise JavaBean? An enterprise bean r Enterprise JavaBean (EJB) is a self-cntained, reusable cmpnent that has data members, prperties, and methds. 2. What is the lgical architecture f an EJB? An EJB system is lgically a three-tier system. The three tiers are: a) The client b) The EJB server c) The database(r ther persistent stre) This structure is a lgical architecture because the three tiers dn t necessarily have t reside n three different machines. 3. Mentin the rle f EJB in each tier. EJB s rle in each f these tiers is: a) A prgram n the client side makes calls t remte EJBs # The client needs t knw hw t find the EJB server and hw t interact with the bjects that reside n the EJB server. b) The EJB cmpnents live in the middle tier # The EJB bjects reside inside an EJB cntainer, which in turn resides in an EJB server. c) The underlying database resides in the third tier # EJB beans can access the database themselves, via Java Database Cnnectivity (JDBC). 4. What are the key features f the EJB architecture? CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 36

37 It illustrates several key features f the EJB Architecture: The EJB bean exists within the cntainer The client never cmmunicates directly with the EJB bean The EJB server des nt take part in the lgical cnversatin between client and EJB bean 5. Define EJB server. The EJB server is a cntainer it cntains the EJB cntainer. This server is respnsible fr prviding the cntainer with lwer-level services such as netwrk cnnectivity. 6. What is the rle f an EJB cntainer? An EJB cntainer is an envirnment in which Enterprise JavaBeans Execute. Its primary rle is t server as a buffer between an EJB and the utside wrld. 7. What are the services prvided by an EJB cntainer? The cntainer is als respnsible fr prviding the beans with services, s that the bean can remain blissfully unaware f the underlying mechanisms used in implementing these services. These services are: Supprt fr transactins Supprt fr persistence Supprt fr management f multiple instances Supprt fr security 8. List ut the mdes f transactin management. EJB prvides six mdes f transactin management TX_NOT_SUPPRTED TX_BEAN_MANAGED TX_REQUIRED TX_SUPPORTS TX_REQUIRES_NEW CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 37

38 TX_MANDATORY 9. What are the varius tasks perfrmed by server? a) Instance passivatin b) Instance pling c) Database cnnectin pling d) Pre-cached instances e) Optimized methd invcatins 10. Define Instance passivatin. It is the temprary swapping f an EJB bean ut t strage. If a cntainer needs resurces, it may chse t temprarily swap ut a bean. Bth sessin bean and entity bean can be passivated. 11. Define instance pling. It means that the cntainer shares instances f EJB beans amng multiple clients. It allws the EJB cntainer t initiate fewer cpies f a given bean t service requests. 12. What is database cnnectin pling? When a cmpnent wishes t access a database, it des nt create a new database cnnectin; in stead, it simply grabs a cnnectin frm a pl f available cnnectins. 13. List ut the benefits f database cnnectin pling. It avids the verhead f stabling a new database cnnectin. Maintaining an pen database cnnect in cnsumes resurces n the database. Cnnectin pling allws a system manager t prvide an applicatin with the resurces it needs, withut crating unnecessary verhead n the database. 14. Define pre-cached instances. It may be used when an EJB needs t lad sme state infrmatin frm a database when it is created. 15. What is an ptimized methd invcatin? CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 38

39 They are emplyed t prevent verhead csts assciated with remte invcatin. Whether the client f an EJB is a remte client r anther EJB in the same cntainer, the APIs used t gain access t it are always the same. 16. Define persistence. Persistence means that the state f an bject is saved t sme srt f permanent strage (a file r a database), allwing the bject t be read in and used at later time instead f being recreated each time. 17. What is an ACL? The main mechanism used in EJB security is the Access Cntrl List (ACL). An ACL is a list f persns r grups that are allwed t access particular pieces f functinality. A deplyer can specify ACLs fr a bean as a whle as well as fr any f the bean s methds. 18. What are the difference between Enterprise JavaBeans and JavaBeans? Enterprise JavaBeans: EJBs need a cntainer EJBs are deplyable cmpnents EJBs are assembled t frm a cmplete Applicatin EJBs are base dn RMI IIOP and JNDI technlgies JavaBeans: JBs dn nt need a cntainer JBs are develpment cmpnents JBs are classes with n argument cnstructr JBs have a get and a set methd n them 19. When t use EJB? If any f these requirements hld fr yur applicatin The applicatin must be scalable and distributable Transactins will be required t ensure data integrity The applicatin will have a variety f clients. 20. What are the benefits f EJB? CHETTINAD COLLEGE OF ENGG AND TECHNOLOGY 39