Using JNDI from J2EE components

Transcription

1 Using JNDI from J2EE components Stand-alone Java program have to specify the location of the naming server when using JNDI private static InitialContext createinitialcontext() throws NamingException { Hashtable env = new Hashtable(); env.put(context.initial_context_factory, "com.sun.jndi.cosnaming.cnctxfactory"); env.put(context.provider_url, "iiop://localhost:1050"); return new InitialContext(env); } J2EE components don t need to specify the naming server location private static InitialContext createinitialcontext() throws NamingException { return new InitialContext(); }

2 Selecting JNDI names for J2EE components The people who write an application and its components are different from the people who buy, deploy, and administer the application Application developers need to look up various types of objects by name in the naming server Remote objects, DB connection factories, Messaging connection factories, etc. Application deployers like to control the JNDI names assigned to various components Corporate naming standards, Consistency between multiple applications, Personal preference Developers need to know JNDI names at development time, even though names aren t selected until deployment time Every deployer will probably use different names anyway, so which name should the application developer use?

3 Selecting JNDI names for J2EE components Solution: As usual, add another level of indirection Application developers can use whatever JNDI names they want to perform lookups in their code (these names are logical) Application deployers can pick whatever JNDI names they want when creating objects on the app server (these names are physical) When deploying the application, the deployer must map the logical names used by the application developer onto real, physical names

4 Selecting JNDI names for J2EE Example: JMS topic Developer chooses the name components java:comp/env/jms/bulletinboard Deployer choose the name jms/mybb When deploying application, the deployer maps the logical name java:comp/env/jms/bulletinboard to the physical name jms/mybb The JNDI InitialContext returned to the application at runtime performs the mapping between logical names and physical names dynamically Application looks up java:comp/env/jms/bulletinboard, which InitialContext maps to a lookup on jms/mybb

5 Selecting JNDI names for J2EE components Logical JNDI names always begin with the prefix java:comp/env/ Any JNDI lookup on a name that begins with this prefix is mapped by the InitialContext to a physical JNDI name Exception is thrown if no mapping was defined at deployment time If you are both the developer and deployer, you can hardcode the app to use physical JNDI names, but you lose flexibility by doing so

6 Enterprise Java Beans (EJB)

7 Review: What is an EJB? An EJB is a managed application logic component that runs inside an app server How is an EJB managed? Lazy bean instantiation Allocated from pool of reusable bean objects Swapped to and from disk Thread pooling Security Database connection pooling Transaction management

8 Common uses of EJBs Web Browser Presentation Logic Logic behind Web-based UI Thin Client Web Server Cell Phone Presentation Logic Application Logic Database Thin Client Web Server App Server Database Server GUI Client Application Logic Business-to-Business Integration (B2B) Fat Client App Server Logic behind GUI-based UI

9 Different kinds of classes At a high level, object-oriented designs typically include three kinds of classes: Boundary Classes Entity Classes Control Classes

10 Boundary Classes Different kinds of classes Classes that interact directly with the users of the system Store short-lived state to keep track of the current interactions (perhaps even persistently) Session ID, User name, Form data Examples: CashierUI LoanApplicationForm WireTransferProcessor

11 Entity Classes Different kinds of classes Classes that model people, places, things, concepts, or events inherently associated with the application domain Concepts that are long-lived and persistent, not short-lived or transient Examples: Account LoanApplication Loan Customer

12 Control Classes Different kinds of classes Classes that represent coordination, sequencing, processes, or work flows Implement significant algorithms that orchestrate the activities of other classes to accomplish larger goals It doesn t make sense to put such algorithms on one of the Entity classes because they invoke the services of multiple classes and belong to no class in particular Examples: LoanApplicationAnalyzer CreditHistoryVerifier InterestProcessor

13 Different kinds of classes U B C C C C E E E U B C E E

14 Different kinds of EJBs Session Beans Entity Beans Web Tier or Client Tier U U B B C C C C C E E E E E Application Logic Tier

15 Session Beans Boundary classes Different kinds of EJBs App Logic clients enter app logic tier through Session Beans Session Beans implement Façades that are highly customized to the needs of each client A façade provides precisely those operations needed by a particular client Session Bean may be thought of as an extension of the client that runs inside the app server Control classes Session Beans implement business logic (processes, algorithms) that doesn t belong on one of the Entity Beans App Logic clients invoke Session Beans Session Beans invoke other Session Beans, Entity Beans, and POJOs (Plain Old Java Objects) to perform their work May store state associated with the current client session (in memory or in a database)

16 Entity Beans Different kinds of EJBs Used to implement Entity classes Stored in some kind of persistent storage (usually a DBMS) Usually accessed by Session Beans to perform some task, not accessed directly by clients Message-Driven Beans Used to process JMS messages

17 Example: Job Agency EJBs Session Beans Entity Beans Message-Driven Beans Advertise Customer Customer UI AdvertiseJob Job Admin UI Applicant UI Agency Register Location Skill Applicant ApplicantMatch JobMatch Matched

18 Home & Business Interfaces In OO design, class features are associated with either 1) the class itself or 2) instances of the class Class variables vs. Instance variables Class methods vs. Instance methods Static vs. Non-Static Session and Entity Beans have two interfaces, one for class-level operations and one for instance-level operations The Home interface contains class-level operations The Business interface contains instance-level operations Typical Home Interface methods Factory methods (create a new EJB instance) Query methods (return all EJB instances that meet some criteria) Delete methods (delete all EJB instances that meet some criteria)

19 Home & Business Interfaces Location Transparency Security & Transactions Home RMI Stub Home RMI Tie Home Implementation (interceptor) Client Bean Business RMI Stub Business RMI Tie Business Implementation (interceptor) Generated by app server & associated tools Written by application developer

20 Home & Business Interfaces Making EJBs distributed objects allows an EJB and its clients to reside in different physical tiers But, The marshaling/unmarshaling performed by stubs/ties adds significant overhead If an EJB s client is running in the same process as the EJB, all of this overhead is unnecessary Some EJBs are never accessed by a client outside the EJB s process Entity Beans and the Session Beans which invoke them usually run within the same process For this reason, J2EE allows an EJBs to be implemented as nondistributed (i.e., local) objects that can be invoked only from within the same process, but can be invoked more efficiently

21 Local Home & Business Interfaces Security & Transactions Home Implementation (interceptor) Client Bean Business Implementation (interceptor) Generated by app server & associated tools Written by application developer

22 EJB Context EJB uses EJBContext reference to invoke the services of the EJB Container EJBContext J2EE App Server EJB Container EJB Interface EJBContext { getejbhome(); getcallerprincipal(); iscallerinrole(); setrollbackonly(); getusertransaction();... }

23 Job Agency EJBs Session Beans Entity Beans Message-Driven Beans Advertise Customer Customer UI AdvertiseJob Job Admin UI Applicant UI Agency Register Location Skill Applicant ApplicantMatch JobMatch Matched

24 EJB Example: Simplified Job Agency Session Beans Entity Beans Message-Driven Beans Agency Location Skill ApplicantMatch AgencyClient Register Applicant