1. Dependency Injection with Spring
in 10 minutes
Corneil du Plessis
corneil.duplessis@gmail.com
@corneil

2. Introduction
● Assumptions
– You have some appreciation of component-oriented
development
– You have seen Java code
– You have heard of the Spring Framework or Dependency
Injection
● Take away
– Some appreciation for benefits of dependency injection
– Some understanding of how Spring supports dependency
injection.

3. What is Dependency Injection?
● Robert C Martin and Martin Fowler has written some of the best
articles on the subject.
● Dependency Injection is also known as Inversion of Control or
Dependency Inversion.
● DI is a specific form of IoC.
● When an object is composed the responsibility for composing the
dependents of the object is not handled by the specific object.
● Modern applications uses one or more containers or frameworks to
take care of DI.
● Examples are EJB container and Spring Framework.
● We will look at mechanisms provider by Spring Framework

4. What is Spring Framework?
● The Spring Framework provides support for a large
number of useful programming patterns.
● Patterns in questions are:
– Singleton
– Factory
– Locator
– Visitor

5. DI – Best Practice
● Required unchanging dependencies via constructor.
● Assemble and fail early
● Be careful of the cost of DI frameworks.
– Don't use to create Data Transfer Objects.

6. DI – Sample Classes

7. DI – Sample Objects

8. DI – Code without DI
public ProfileDataAccessComponent() throws NamingException, FileNotFoundException, IOException {
super();
// In EJB or Web Container
try {
InitialContext ctx = new InitialContext();
dataSource = (DataSource) ctx.lookup("java:comp/env/jdbc/profile");
} catch(Throwable x) {
// Assume we are not in container.
}
if(dataSource == null) {
// Manual creation outside of container
Properties props = new Properties();
File propFile = new File("db.properties");
props.load(new FileInputStream(propFile));
BasicDataSource ds = new BasicDataSource();
ds.setDriverClassName(props.getProperty("db.driver"));
ds.setUsername(props.getProperty("db.username"));
ds.setPassword(props.getProperty("db.password"));
ds.setUrl(props.getProperty("db.url"));
ds.setMaxActive(Integer.parseInt(props.getProperty("db.maxActive", "10")));
ds.setMaxIdle(Integer.parseInt(props.getProperty("db.maxIdle", "5")));
ds.setInitialSize(Integer.parseInt(props.getProperty("db.initialSize", "5")));
ds.setValidationQuery(props.getProperty("db.validationQuery", "SELECT 1"));
dataSource = ds;
}
}

9. DI – More Code
public ProfileNotificationSender() throws NamingException {
super();
InitialContext ctx = new InitialContext();
factory = (ConnectionFactory)
ctx.lookup("java:comp/env/jms/queue/ConnectionFactory");
destination = (Destination) ctx.lookup("java:comp/env/jms/queue/Profile");
}

10. DI – Spring Beans from XML
<context:property-placeholder location="db.properties" />
<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
destroy-method="close">
<property name="driverClassName" value="${db.driver}" />
<property name="url" value="${db.url}" />
<property name="username" value="${db.username}" />
<property name="password" value="${db.password}" />
</bean>
<bean id="profileDAC"
class="org.springframework.di.demo.ProfileDataAccessComponent">
<constructor-arg ref="dataSource" />
</bean>

11. DI – Spring Beans from XML
<jee:jndi-lookup id="destination" jndi-name="jms/queue/Profile"
expected-type="javax.jms.Destination" />
<jee:jndi-lookup id="connectionFactory" jndi-name="jms/queue/ConnectionFactory"
expected-type="javax.jms.ConnectionFactory" />
<bean id="notificationSender"
class="org.springframework.di.demo.ProfileNotificationSender">
<constructor-arg ref="connectionFactory" />
<constructor-arg ref="destination" />
</bean>
<bean id="profileService" class="org.springframework.di.demo.ProfileService">
<constructor-arg ref="profileDAC" />
<constructor-arg ref="notificationSender" />
</bean>

12. DI – Spring Annotations Config
<context:property-placeholder location="db.properties" />
<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
destroy-method="close">
<property name="driverClassName" value="${db.driver}" />
<property name="url" value="${db.url}" />
<property name="username" value="${db.username}" />
<property name="password" value="${db.password}" />
</bean>
<jee:jndi-lookup id="destination" jndi-name="jms/queue/Profile"
expected-type="javax.jms.Destination" />
<jee:jndi-lookup id="connectionFactory" jndi-name="jms/queue/ConnectionFactory"
expected-type="javax.jms.ConnectionFactory" />
<context:component-scan base-package="org.springframework.di.autowire" />

13. DI – Spring Annotations Code
@Autowired
public ProfileNotificationSender(ConnectionFactory factory,
Destination destination) {
super();
this.factory = factory;
this.destination = destination;
}
@Service("profileService")
public class ProfileService implements ProfileInteface {
private ProfileDataAccessInterface dataAccess;
private ProfileNotificationInterface notification;
@Autowired
public ProfileService(ProfileDataAccessInterface dataAccess,
ProfileNotificationInterface notification) {
super();
this.dataAccess = dataAccess;
this.notification = notification;
}

14. DI – Spring Java Config
@Configuration
public class AppConfig {
@Autowired
Environment env;
@Bean
public Destination destination() {
JndiObjectFactoryBean bean = new JndiObjectFactoryBean();
bean.setJndiName("jms/queue/Profile");
bean.setExpectedType(Destination.class);
return (Destination) bean.getObject();
}
@Bean
public ConnectionFactory connectionFactory() {
JndiObjectFactoryBean bean = new JndiObjectFactoryBean();
bean.setJndiName("jms/queue/ConnectionFactory");
bean.setExpectedType(ConnectionFactory.class);
return (ConnectionFactory) bean.getObject();
}
}

15. DI – Spring Java Config
@Configuration
@PropertySource("db.properties")
public class AppConfig {
@Autowired
Environment env;
@Bean
public DataSource dataSource() {
BasicDataSource dataSource = new BasicDataSource();
dataSource.setDriverClassName(env.getProperty("db.driver"));
dataSource.setUrl(env.getProperty("db.url"));
dataSource.setUsername(env.getProperty("db.username"));
dataSource.setPassword(env.getProperty("db.password"));
return dataSource;
}
}

16. Questions
● Demo code at
https://github.com/corneil/demos/tree/master/spring-di-sample
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● Discuss on JUG Meetup