The Spring Framework J2EE without EJB

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					The Spring Framework
      J2EE without EJB

            Jürgen Höller

    J2EE Reviewed
    Introducing the Spring Framework
    Spring and J2EE
    Core Container
    AOP Framework
    Transactions & Data Access
    Remoting
    Further Services
J2EE Reviewed (1)
  Challenges of modern server-side software
   ▫   multi-threaded execution
   ▫   resource and transaction management
   ▫   remote service access
   ▫   HTTP server integration
  Java 2 Enterprise Edition (J2EE tm)
   ▫ set of specifications for standard application
     server infrastructure
   ▫ industry standard: backed by Sun, IBM, Oracle
   ▫ application server implements standard APIs
   ▫ application uses standard APIs
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?
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
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
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
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
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 container
          Spring service abstractions

             J2EE system services
       J2EE deployment and management
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
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
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
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
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 id="itemDao"
   <property name="dataSource" ref="dataSource"/>
   <property name="sqlMap" ref="sqlMap"/>

 <bean id="petStore"
   <property name="orderDao" ref="orderDao"/>
   <property name="itemDao" ref="itemDao"/>
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

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
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
   ▫ optional transaction semantics beyond EJB
      • nested, isolation level, timeout, read-only flag
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
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");
  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
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
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
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)