EJB in the real world

Transcription

1 Computas AS kunnskap system EJB in the real world INF Geir Arne Waagbø Slide

2 Master s degree Computer Science, NTH 1990 PhD Mathematics, UiO 1997 Employed by Computas since 1997 Worked with Java technology since 1998 Worked with EJB since 2000 Slide

3 Agenda Enterprise applications what is it? Why use an EJB-server? Java, EJB, and JEE JEE Java Enterprise Editon EJB in some detail EJB 2.1 vs EJB 3.0 Some examples Slide 3

4 Enterprise applications Business applications both in the private and the public sector Online shopping Order entry and billing Personnel and payroll Case handling and workflow... What is not: Embedded software Games Operating systems etc Engineering software Word processors, spreadsheets, Slide

5 Enterprise applications Lots of persistent data Large relational database (>100GB) Lots of simultaneous users (>1000) Web clients Desktop clients OLTP Online Transaction Processing The opposite OLAP Online Analytical Processing (or BI Business Intelligence) Integration with other systems Slide

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7 Problems Security: All clients have database connections Web clients: sql-injection No such thing as client side security Performance Connection pooling Network Transactions Client code and business logic Integration: Let other systems use the database? Slide

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9 Java, EJB and JEE Java programming language In the same way as C#, C++,... Java technology platform In the same way as.net Can use other programming languages! JEE Java Enterprise Edition Slide

10 JEE - Java Enterprise Edition Before it was called J2EE EJB Enterprise Java Beans API-specifications: JDBC, JMS, RMI,... Web container Servlets, JSP - Java Server Pages and JSF Java Server Faces Portlets Slide

11 JEE Products JBoss (open source) IBM WebSphere BEA WebLogic Oracle Application Server (OC4J) Sun Glassfish In theory applications should be portable between products Slide

12 EJB Enterprise Java Beans EJB is an API + specification EJB runtime Java VM EJB Container Current version: EJB 3.0 Slide

13 Services provided by the EJB Container Remoting RMI (Remote method invocation) Transactions Persistence JNDI Java naming and directory services Security JAAS Java authentication and authorization services LDAP-integration Resource pooling Deployment Slide

14 Types of EJBs Session Beans (Stateless) Remoting Transaction demarcation Can be exposed as web services Entity Beans O/R-Mapping Persistence Message Driven Beans Typically used for asynchronous interfaces Slide

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16 Transactions As for databases ACID Atomicity (all or nothing) Consistency (the state is consistent) Isolation (isolated from other users) Durability (the data is stored) Distributed transactions Slide

17 Persistence Entity Beans - databases EJB-servers always used in conjunction with a relational database MySQL (open source) Hypersonic (bundled with JBoss) IBM DB2, Oracle, MS SQLServer Entity Beans O/R-Mapping Slide

18 Connection pooling A database connection is expensive Literally! Requires lots of system resources Takes time to establish Therefore: Use a pool Closing a connection returns it to the pool The same pattern can be used for other kinds of resources as well Slide

19 EJB 2.1 EJB-classes had to implement specific interfaces Deployment descriptors, xml-files that describe: Transactional properties O/R-mapping Example: EJBOrgUnitBean Slide

20 EJB 3.0 Instead of deployment descriptors: Annotations No interfaces needs to be implemented Annotated POJOs can be container managed! Java Persistence API JBoss uses Hibernate to implement EJB 3.0 Example: Person Slide

21 Benefits of EJB 3.0 Defaults Ease of development Can use POJOs Possible to write unit tests Can do without xml deployment descriptors Fewer artifacts Slide

22 Some advice Use some caching A client needs just one JNDI-context Don t duplicate code! Getting the JNDI-context Getting a database connection Handling exceptions Use try... finally... when accessing resources Slide