I have mixed feelings about Spring. I definitely prefer its primary focus on the Dependency Injection pattern (DI) instead of the more typical JavaEE model of using the Service Locator pattern (think JNDI lookups). If used the right way, both patterns can help promote loosely coupled and easily unit-testable solutions. However, Spring's prescriptive DI approach makes the process of developing loosely-coupled solutions feel more intuitive and natural. Also, Spring offers an easy way to leverage Aspect Oriented Programming (AOP) when needed (and yes I emphasise the word when - excessive sprinkling of aspects can make applications hard to understand, debug and troubleshoot).
On the downside, it sometimes feels like Spring has evolved from a light-weight framework for making J2EE easier, into a vast and competing component model for building enterprise applications. It's not clear to me how much the balance in Spring has shifted from Innovating to Re-inventing, and whether this shift is a good thing or not.
Fortunately, WebLogic makes it pretty easy to deploy Spring based apps, whether your application uses Spring in a just-enough-dependency-injection way or in a use-nearly-every-Spring-feature-under-the-sun way. On most levels it doesn't really matter what version of Spring you use with a particular version of WebLogic. If you have an issue, you use the Oracle Support organisation for help with WebLogic specific problems and any Spring parts to your application are treated just like your own custom code is, from an Oracle Support perspective.
In addition, Oracle actually provides explicit certification for specific versions of Spring running on specific versions of WebLogic. For example, on WLS 10.3.x, Oracle explicitly certifies the use of Spring version 2.5.3 (and any later `double-dot' Spring releases). For the official certification matrix, see the spreadsheet titled System Requirements and Supported Platforms for Oracle WebLogic Server 10.3 on the supported configurations page. As a matter of interest, it's also worth noting that internally* WebLogic uses elements of Spring and its AOP capabilities to implement some of WebLogic's newer JavaEE features like EJB 3.0, by using the Spring Pitchfork codebase under the covers.
* WebLogic prefixes the package names of its internally bundled Spring classes to avoid potential class-loading clash issues with Spring classes bundled in any deployed applications. Application developers can also separately choose to bundle the classes from the Spring Pitchfork project to enable Spring beans to be injected into Servlets and EJBs in their own developed application.
When using an Oracle certified version of Spring with WebLogic, extra integration features are also available to help Spring based applications become first-class WebLogic citizens, in the same way that normal JavaEE applications are. This is described in WebLogic's help documentation on Spring. By including some boilerplate text in your web-app's Manifest.mf file to refer to an optional package and by ensuring WL_HOME/server/lib/weblogic-spring.jar is first deployed to WebLogic as a shared library, the following 3 WebLogic features are automatically enabled:
1. Spring MBeans. WebLogic automatically generates a set of Spring related MBeans, hanging off the normal WebLogic ApplicationRuntimeMBeans, into each server's Runtime Service JMX tree. Examples of these MBeans are SpringRuntimeMBean, SpringApplicationContextRuntimeMBean and SpringTransactionManagerRuntimeMBean. See the WebLogic MBean Reference for more info on these Spring MBeans. The Spring MBeans are read-only and enable administrators to have better visibility into what's going on inside the Spring parts of deployed applications. The screenshot below shows the use of WLST to inspect some of these MBeans. If the Manifest.mf file is not correctly defined, WebLogic does not detect the presence of Spring elements in the application and thus will not generate the Spring MBeans; SpringRuntimeMBean would not appear in the list of child MBeans shown in the screenshot.
2. Spring Console Extension. WebLogic provides an Admin Console extension for Spring to provide administrators with visual tools for monitoring the Spring parts of deployed applications (first navigate to WebLogic Admin Console's Preferences | Extension menu option and and enable spring-console). This Spring console extension is basically a set of pages which are added amongst the normal pages of the standard WebLogic admin console, rather than being a separate console per se. The extension provides a view onto the values of the WebLogic generated Spring MBeans (see point 1). If you navigate to the deployed web-app in the Admin Console, select the Configuration tab, and then select the Spring Framework sub-tab, you will see a read-only view of the contents of the application's Spring application context(s), as shown in the example screenshot below.
In the Deployment's Monitoring tab, if you select the Spring Framework sub-tab, as shown in the example below, you can drill into read-only views of the types and amounts of Spring beans that have currently been created in the deployed application's Spring application context(s). It also lets you view the WebLogic managed transactions that have been initiated via the Spring library code in the deployed application.
By selecting one of the Spring application contexts listed in this table, you will see statistics showing how many beans have been created in the context, what scope they have and their performance metrics, as shown in the screenshot below.
3. WebLogic Injected Spring Beans. During the start-up process for the Spring-enabled web-application (see point 1), WebLogic intercepts the creation of the web-app's normal Spring Application Context (using AOP under the covers), and transparently adds a parent context to the normal context. This parent context is pre-populated with the following 3 WebLogic specific beans, ready to be used by the application:
- A WebLoigc Transaction Manager bean (ref="transactionManager") which extends org.springframework.transaction.jta.JtaTransactionManager
- A WebLogic Edit Server MBean Connection bean (ref="editMBeanServerConnection") which implements javax.management.MBeanServerConnection
- A WebLogic Runtime Server MBean Connection bean (ref="runtimeMBeanServerConnection") which implements javax.management.MBeanServerConnection
<bean id="myTestBean" class="com.acme.MyTestBean">The exact set of WebLogic beans injected into the parent application context can be deduced by unzipping the file WL_HOME/wlserver_10.3/server/lib/weblogic-spring.jar and viewing the contents of the file weblogic/spring/beans/SpringServerApplicationContext.xml.
<property name="mbeanSvrConn" ref="runtimeMBeanServerConnection"/>
Using the Spring console extension discussed in point 2, we can actually navigate to and view the contents of the parent application context, at runtime, in addition to the normal app context, as shown in the first two screenshots in point 2.
During the application initialisation process, WebLogic also sets the application's default Spring Transaction Manager to be org.springframework.transaction.jta.WebLogicJtaTransactionManager to enable WebLogic's Transaction Manager to always be used for managing JTA transactions initiated in Spring code.
Note: A 4th bean (a WebLogic System Work Manager bean) is also populated in the parent context. However, this bean is meant for internal WebLogic system usage and is not for application developers to use, as it does not implement commonj.work.WorkManager. Developers who do want to utilise WebLogic Work Managers, should just declare the work managers they require in the WebLogic domain's configuration, in the normal way, and then use org.springframework.scheduling.commonj.WorkManagerTaskExecutor in their Spring Bean context XML files, to enable the work managers to be injected into application code.
In summary, in this blog topic I have described some of the ways that WebLogic handles applications that use Spring. Not all the integration points between WebLogic and Spring have been discussed. For example, I have not described how WebLogic can integrate with Spring Security (a.k.a. Acegi), how WebLogic's fast RMI/T3 binary wire protocol can be used for Spring Remoting and I have only mentioned in passing the ability to use Spring Dependency Injection into Servlets and EJBs.
Footnote: Brand new in WebLogic 10.3.2 is un-documented and un-supported tech-preview support for the Service Component Architecture (SCA) using Spring. This tech-preview uses Spring to wire up the POJOs inside components and composites, and to declaratively specify the invocation protocol bindings for these composites. The WebLogic-Spring capabilities discussed here in my blog entry are unrelated to the SCA tech-preview support.
Song for today: Rid of Me by PJ Harvey