Dependency Injection in Spring in 10min
1 like•1,516 views
Dependency injection with Spring allows managing object dependencies and compositions. It handles composing objects by externalizing the lookup and assembly of collaborating objects. This avoids tight coupling. Spring supports dependency injection through XML configuration, annotations, and Java configuration. It handles creating and assembling objects and their dependencies. Dependency injection improves testability and maintainability of applications.
Dependency Injection in Spring in 10min
- 1. Dependency Injection with Spring in 10 minutes Corneil du Plessis [email protected] @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 ● Discuss on JUG Facebook https://www.facebook.com/groups/jozijug ● Discuss on JUG Meetup