The Spring Framework J2EE without EJB

1. The Spring FrameworkJ2EE without EJB Jürgen Höller http://www.springframework.com juergen@interface21.com

2. Agenda • J2EE Reviewed • Introducing the Spring Framework • Spring and J2EE • Core Container • AOP Framework • Transactions & Data Access • Remoting • Further Services

3. J2EE Reviewed (1) • Challenges of modern server-side software development • multi-threaded execution • resource and transaction management • remote service access • HTTP server integration • Java 2 Enterprise Edition (J2EE tm) • set of specifications for standard applicationserver infrastructure • industry standard: backed by Sun, IBM, Oracle • application server implements standard APIs • application uses standard APIs

4. J2EE Reviewed (2) • J2EE specifies system services • Servlets, JSP, JTA, JDBC, JMS, JavaMail • builds on underlying standard Java runtime • J2EE also specifies component models • Servlets for HTTP endpoints • EJBs for middle tier components • Focus on traditional 3-tier server layout • focus on physical separation between tiers • middle tier always requires application server • Low-level APIs • direct usage in applications often cumbersome • comfortable high-level APIs?

5. J2EE Reviewed (3) • Scope of J2EE is limited • EJBs are coarse-grained components • mainly for (remote) service façades • special deployment effort for every component • How to deal with fine-grained,co-located application objects? • forced to use custom solutions • common: open source libraries / frameworks • How to run outside of an application server? • not covered by traditional J2EE • important for unit tests and integration tests • also important for productive development

6. Spring Framework (1) • Java / J2EE Application Framework • based on Rod Johnson’s book“J2EE Design & Development” (Wiley, 2002) • current book: "J2EE Development without EJB"(Rod Johnson, Jürgen Höller; Wiley, 2004) • Focus on "Plain Old Java Objects" (POJOs) • natural, generic component model for applications • flexible alternative to EJB, not tied to J2EE • Open Source Project on SourceForge • Apache license • since February 2003 • 25 developers

7. Spring Framework (2) • Business objects as decoupled POJOs • configuration and wiring through framework • or usage as normal Java objects • independent from the actual environment • no unnecessary ties to a framework • reusable in any kind of environment • in particular: testability in unit / integration tests • Generic middleware services • e.g. declarative transactions for POJOs • flexible alternative to EJB CMT • for all applications, including standalone • leverage J2EE container services when available

8. Spring Framework (3) • Integration with existing solutions • Object/Relational Mapping tools • web frameworks • remoting protocols • "It‘s all about choice" • JDBC, Hibernate, JDO, Oracle TopLink,Apache OJB, iBATIS SQL Maps • Spring Web MVC, Spring Web Flow,Struts, WebWork, Tapestry, JSF • HTTP invoker, RMI invoker, conventional RMI,JAX-RPC (WSDL/SOAP), Hessian, Burlap

9. Spring and J2EE (1) • J2EE provides standard system services • to be leveraged by higher-level components • Spring abstractions can run on top of J2EE Application components Spring application containerSpring service abstractions J2EE system servicesJ2EE deployment and management

10. Spring and J2EE (2) • Spring is a de-facto standard Java / J2EE application framework • typically running on top of J2EE server • but: application components are not tied to J2EE • Most popular "lightweight container" • widespread adoption over the past 2.5 years • endorsed / supported by BEA, IBM, Oracle • e.g.: support partnership for Spring on WebLogic • EJB3 specification will follow Spring model • adopts some important ideas from Spring

11. Spring and J2EE (3) • Constantly increasing download numbers • ~30.000 downloads of every point release • >400.000 downloads overall • Growing Spring ecosystem • Spring sister projects • Acegi Security, Spring Web Flow • used or supported by many other products • open source and commercial • e.g. Atlassian Confluence, Liferay Portal • 5 dedicated books on Spring already available • by various authors • more books in the works

12. Core Container (1) • "Inversion of Control" • configuration and lifecycle of application objects • objects do not configure themselves, but get configured from the outside • objects don't know the origin of their configuration • "Dependency Injection" • "setter-based" (JavaBean properties) • "constructor-based" (constructor arguments) • alternative: "Service Lookup" • for example: JNDI

13. Core Container (2) • Fine-grained externalized configuration • representing the internal structure of the application • references to other components • configuration parameters • enables flexible configuration management • at fine-grained component level • switching between different deployment scenarios • XML bean definitions • most common configuration format • often: separate admin properties file • linked into XML bean definitions through placeholders

14. Core Container (3) <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"> <property name="driverClassName" value="${jdbc.driver}"/> <property name="url" value="${jdbc.url}"/> <property name="username" value="${jdbc.username}"/> <property name="password" value="${jdbc.password}"/> </bean> <bean id="itemDao" class="org.springframework.samples.jpetstore.dao.ibatis.SqlMapItemDao"> <property name="dataSource" ref="dataSource"/> <property name="sqlMap" ref="sqlMap"/> </bean> <bean id="petStore"class="org.springframework.samples.jpetstore.domain.logic.PetStoreImpl"> <property name="orderDao" ref="orderDao"/> <property name="itemDao" ref="itemDao"/> </bean>

15. AOP Framework (1) • "Aspect-Oriented Programming" • proxies for arbitrary POJOs • flexible combination of interceptors • no fixed component model ("EJB a la carte") • "Cross-Cutting Concerns" • actions at the beginning/end of a method call Caller Target method intercept

16. AOP Framework (2) • Do not repeat code: factor out interceptor • e.g. logging: configurable trace log • e.g. security: authorization checks • e.g. common exception handling • e.g. transaction demarcation • Method interceptor • interceptor can be applied to any methods • interceptor can be enabled/disabled • AOP Alliance: MethodInterceptor interface • reuse of pre-built interceptors

17. Transactions & DAOs (1) • Transaction Strategy Abstraction • PlatformTransactionManager SPI • switching between JTA and native transactions • Transaction Demarcation Options • programmatic demarcation a la JTA • declarative demarcation for arbitrary POJOs • Transaction Definitions • all EJB CMT propagation codes supported • REQUIRED, REQUIRES_NEW, etc • optional transaction semantics beyond EJB • nested, isolation level, timeout, read-only flag

18. Transactions & DAOs (2) • DataAccessException hierarchy • independent of JDBC, Hibernate, JDO, etc • unchecked, as most failures are not recoverable • subclasses like OptimisticLockingFailureException • Support for DAO implementations • implicit access to resources • many operations become one-liners • no try/catch blocks anymore • Pre-built integration classes for many solutions • JDBC: JdbcTemplate • Hibernate: HibernateTemplate

19. Transactions & DAOs (3) • Example for a JDBC-based DAO public class ExampleJdbcDao extends JdbcDaoSupport { public void clearDatabase() throws DataAccessException {getJdbcTemplate().update("DELETE FROM imagedb");  }  public void deleteImage(int imageId) throws DataAccessException {getJdbcTemplate().update("DELETE FROM imagedb WHERE id=?", new Object[] {new Integer(imageId)});  }  public int getNrOfImages() throws DataAccessException {    return getJdbcTemplate().queryForInt( "SELECT COUNT(*) FROM imagedb");  }}

20. Remoting • Export POJOs as remote services • in server-side Spring applications • through Spring remote service exporter • Make remote services accessible • in client-side Spring applications • through Spring remote proxy factory • Protocol choice is configuration matter • Hessian, Burlap, SOAP, RMI, HTTP invoker • protocol to be chosen according to requirements • Support for integration of EJBs • through Spring EJB proxy factory • declarative proxies for Stateless Session Beans

21. Further Services • JMS Support • lightweight messaging • JCA Support • access to J2EE Connectors • Mail Support • JavaMailSender • Scheduling Support • Quartz, Timer • Web Application Support • Struts, JSF, WebWork, Tapestry • Spring Web MVC, Spring Web Flow

22. Summary (1) • Spring is a popular Java application framework • core container, AOP framework • transactions, data access, remoting • dedicated support for J2EE environments • integrating with many existing solutions • Solves ubiquitous architectural issues • wiring and configuration of components • flexible configuration of interceptors • declarative transaction demarcation • implicit management of resources

23. Summary (2) • Works in any environment • no special compilation or deployment steps • no special class loader • can run on J2EE, but not tied to J2EE • seamless switching between deployment scenarios • For any kind of application • J2EE web applications running on e.g. Tomcat • full J2EE applications running on e.g. WebLogic • rich clients (usually with J2EE server as backend) • standalone applications (with GUI or headless)

24. http://www.springframework.orghttp://www.springframework.com