Dependency injection (DI) with Spring allows defining beans and their dependencies in code rather than XML configuration files. Spring supports DI through its bean factory and container. Beans can be defined through XML configuration or Java configuration using annotations. The Spring container handles injecting dependencies and calling lifecycle methods like @PostConstruct. This allows loose coupling between classes and testability through dependency injection.

1. Dependency Injection
with Spring
Presenter: Danil Kornishev 1

2. Introduction
• DI is a defined methodology
• DI is needed
• DI is not magical
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3. Conceptual Model
Interface Programming to an Interface
Deployment
creates need for a wiring
Impl1 Impl2 Impl3 component in the deployment layer
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4. Bean Definition
<bean id="sslContextFactory" class="com.db.fw.entl.remoteClient.rest.impl.ssl.EtlSSLConfig“ scope="prototype" >
<property name="keyStoreFile" value="certs/keystore_rds" />
<property name="keyStorePass" ref="password" />
<property name="trustStoreFile" value="certs/truststore_rds" />
<property name="trustStorePass" ref="password" />
</bean>
<bean id="serviceLocator" class="com.db.fw.entl.locator.LoadAwareHTTPServiceLocator" init-method="startPolling">
<constructor-arg>
<map>
<entry key="READ_SERVICE">
<bean class="java.lang.String">
<constructor-arg value="https://localhost:1998" />
</bean>
</entry>
</map>
</constructor-arg>
<constructor-arg value="300000" />
<constructor-arg name="sslCtx">
<bean factory-bean="sslContextFactory" factory-method="createSSLContext" />
</constructor-arg>
</bean>
<bean id="staticFactoryCreated" class="com.static.factory" factory-method="newSSLContext" destroy-method="close" />
Beans Constructor Factory bean Init
Scope
Inline Property Static Factory Destroy
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5. Additional Initialization
• @PostConstruct
Annotations
• Invoked when DI is finished
• @PreDestroy
• Invoked before context is destroyed
@PostConstruct
public void warmup()
Init/Cleanup
{
// initialize using injected properties
}
@PreDestroy
public void teardown()
{
// close connections, send notifications...etc
}
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6. Collections
<list> <util:list id="emails">
<value>pechorin@hero.org</value> <value>pechorin@hero.org</value>
Lists
<value>raskolnikov@slums.org</value> <value>raskolnikov@slums.org</value>
<value>stavrogin@gov.org</value> <value>stavrogin@gov.org</value>
<value>porfiry@gov.org</value> <value>porfiry@gov.org</value>
</list> </util:list>
<set> <util:set id="emails">
<value>pechorin@hero.org</value> <value>pechorin@hero.org</value>
Sets
<value>raskolnikov@slums.org</value> <value>raskolnikov@slums.org</value>
<value>stavrogin@gov.org</value> <value>stavrogin@gov.org</value>
<value>porfiry@gov.org</value> <value>porfiry@gov.org</value>
</set> </util:set>
<map> <util:map id="emails">
<entry key="pec" value=“chorin@hero.org"/> <entry key="pech" value=“chorin@hero.org"/>
Maps
<entry key="rask" value="rask@slums.org"/> <entry key="rask" value="rask@slums.org"/>
<entry key="starogin" value=“sn@gov.org"/> <entry key="stavrogin" value=“sn@gov.org"/>
<entry key="porfiry" value=“iry@gov.org"/> <entry key="porfiry" value=“iry@gov.org"/>
</map> </util:map>
Inline Stand-Alone
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7. Spring Context Usage
Create the Context
ApplicationContext ctx = new ClassPathXmlApplicationContext("/path/to/config1.xml","/path/to/config2.xml");
Obtain the Bean
ServiceLocator locator = (ServiceLocator)ctx.getBean("serviceLocator");
Use
URL sererHost = locator.locate("myservice");
Close when done
ctx.close();
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8. Raising Context Awareness
Create a class that implements Context Awareness
class SpringContext implements ApplicationContextAware
{
@Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException
{
// Do something like caching the context
}
}
Reference it in a configuration file
<bean id="contextAware" class="com.db.fw.entl.context.SpringContext" />
Now, when Spring is done loading the context, it
will invoke SpringContext.setApplicationContext
passing in the context created.
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9. Life after XML
Spring 3 allows Java-only configuration
Define beans using familiar language
No XML files -- live XML-free
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10. Spring 3 Annotations
• @Configuration
• Marks a class as a bean provider
• @Bean
• Marks a method as a bean provider
• @Lazy, @Scope, @Primary
• Same goodies you know and love
• @ImportResource
• Interoperability with Spring XML
@Configuration @Lazy @Primary
@Bean @Scope @ImportResource
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11. Java-only Bean Factory
@Configuration
public class AnnotationConfiguredBeans
{
@Bean
public String greeting()
{
return "Hello World ";
}
@Primary
@Bean
@Lazy
public ComplexValue complex()
{
return new ComplexValue(simpleValue1(), simpleValue2());
}
@Bean
@Scope(BeanDefinition.SCOPE_PROTOTYPE)
public SimpleValue simpleValue1()
{
return new SimpleValue("Good Bye“, Math.random()*1000);
}
}
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12. Annotation Driven Context
Create the Context
ApplicationContext ac = new AnnotationConfigApplicationContext(AnnotationConfiguredBeans.class);
Use it in the same way as you
would an XML generated context.
Programming to an interface
works!
Freedom from the XML tyranny!
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13. Alternative DI Frameworks
EJB 3.0 Google Guice
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14. Q&A
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