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Matt Wheeler

Introduction to Spring. Matt Wheeler. Notes. This is a training NOT a presentation Please ask questions Prerequisites Introduction to Java Stack Basic Java and XML skills Installed LdsTech IDE (or other equivalent – good luck there ;). Overview.

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Matt Wheeler

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  1. Introduction to Spring Matt Wheeler

  2. Notes • This is a training NOT a presentation • Please ask questions • Prerequisites • Introduction to Java Stack • Basic Java and XML skills • Installed LdsTech IDE (or other equivalent – good luck there ;)

  3. Overview • Become familiar with Spring documentation • http://www.springsource.org/documentation • Learn basics of the Spring architecture • Learn about bean definition and creation • Learn about the application context • Inversion of Control (IoC) • Dependency Injection (DI) • Learn about bean scopes

  4. Goals of the Spring Framework • Simplify Java EE development • Solve problems not addressed by Java EE • Provide simple integration for best of breed technologies • Provide modular/pluggable architecture • Use what you want – don’t use what you don’t • http://www.springsource.org/about

  5. Explore the Spring Ecosystem • Main Page: http://www.springsource.org/ • Documentation: http://www.springsource.org/documentation • Forum: http://forum.springsource.org/ • Jira: https://jira.springsource.org/secure/Dashboard.jspa

  6. Spring Framework Modified from http://static.springsource.org/spring/docs/3.1.0.M1/spring-framework-reference/html/images/spring-overview.png

  7. Data Access Integration • Data Access Integration layer includes: • JDBC (abstraction layer over native JDBC) • ORM (integration support for JPA, Hibernate, …) • Transaction support (declarative and programmatic)

  8. Web • Basic web integration features • File upload • Initialization of IoC container using servlet listeners • Contains Spring’s model view controller (MVC) implementation

  9. Test • Test module provides integration with test frameworks • JUnit • TestNG • Provides ability to load test specific ApplicationContexts • Also provides helpful mock objects

  10. Core Container • Core and Beans modules provide framework fundamentals • Inversion of Control (IoC) and Dependency Injection (DI) • BeanFactory provides factory pattern implementation for creating Java objects • Allows decoupling of configuration and dependencies from actual code

  11. Spring Container / Application Context • Spring container / application context contains instances of objects • Spring managed object instances are called beans • Spring manages the creation, configuration, and destruction of these beans • Beans are defined for use in the application context • The definitions are a template for creating new bean instances • Bean definitions can be provided to Spring: • In xml • Using annotations • In Java code

  12. Defining Beans • Bean definition (beans.xml) <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"> <bean class="org.lds.training.SomeBean" /> <!-- more bean definitions go here --> </beans> • Application Context ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml"); SomeBeansomeBean = context.getBean(SomeBean.class); someBean.callMethod();

  13. Defining beans • Each bean has a unique id • If none is provided, Spring will create one • Class should contain fully qualified package and name of the object <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"> <bean id="someBean" class="org.lds.training.SomeBean" /> <!-- more bean definitions go here --> </beans>

  14. Defining Beans • Bean definition (beans.xml) <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"> <!– defines an id by which the bean can be uniquely referenced --> <bean id="someBean" class="org.lds.training.SomeBean" /> </beans> • Application Context ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml"); SomeBeansomeBean = context.getBean("someBean", SomeBean.class); someBean.callMethod();

  15. Lab 1: Bean Creation https://tech.lds.org/wiki/Introduction_to_Spring#Lab_1_Bean_Configuration

  16. Dependency Injection Dependency Injection (DI) & Inversion of Control (IoC)

  17. Object Dependencies • This is where your Spring investment starts to pay dividends • Most objects cannot do much by themselves • They depend on other objects to accomplish some tasks • For instance if an object wanted to insert something into a database it will need a connection to accomplish this • Most objects have properties that should be configurable • For example if you have an object that times out after a certain period, you might want to be able to configure the timeout period • Additionally, what if two objects need the same object dependency • For instance a data source might be used by many objects to persist data

  18. Inversion of Control (IoC) the Concept • Container injects dependencies when (or right after) the bean is created • Inverse of bean controlling instantiation and/or location of its dependencies • Objects instead obtain dependencies through • Constructor arguments • Setter arguments

  19. Inversion of Control (IoC) the Concept • Managing dependencies on other beans • Dependency lookup vs. Dependency Injection //dependency lookup public class Lookup { private SomeBeansomeBean; public SomeBeanfindBean(Container container) { //or new SomeBean("some param values"); return (SomeBean) container.getBean("someBean"); } } //dependency injection public class Injection { private SomeBeansomeBean; public void setSomeBean(SomeBeansomeBean) { this.someBean = someBean; } }

  20. Advantages of Inversion of Control (IoC) • Separates configuration from code • Simplifies component dependency and lifecycle management • Eliminates need for: • Calling new and managing dependencies • Looking up dependencies • Decouples code from IoC container • Injection is easier – less code – easier to maintain • Minimizes need for creational pattern implementation • Simplifies testing

  21. Dependency Injection (DI) • Two basic types of injection • Setter injection • Constructor injection

  22. DI (setter injection) • Say we have the following Rabbit class • Example public class Rabbit { private String favoriteFood; public void setFavoriteFood(String favoriteFood) { this.favoriteFood = favoriteFood; } public void printFavoriteFood() { System.out.println(favoriteFood); } } <bean id="rabbit" class="org.lds.training.Rabbit"> <property name="favoriteFood"value="lettuce" /> </bean>

  23. DI (constructor injection) • Say we have the following Rabbit class • Example public class Rabbit { private String favoriteFood; public Rabbit(String favoriteFood) { this.favoriteFood = favoriteFood; } public void printFavoriteFood() { System.out.println(favoriteFood); } } <bean id="rabbit" class="org.lds.farm.Rabbit"> <constructor-arg value="lettuce" /> </bean>

  24. DI (continued) • Ability to inject many data types • Lists, Sets, Properties, Maps (most collection types) • Other beans • Lets us look at a few examples: • http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/beans.html#beans-collection-elements

  25. Constructor Injection vs. Setter Injection • Which should you use? • Rule of thumb – write the bean as though Spring were not managing it • If the bean will not operate without a particular member variable use constructor injection • Otherwise use setter injection • This is a change from the past • Let’s look at some more examples

  26. DI Collections • Say our rabbit has many favorite foods public class Rabbit { private Set<String> favoriteFoods; public void setFavoriteFoods(Set<String> favoriteFoods) { this.favoriteFoods = favoriteFoods; } public void printFavoriteFood() { for (String favoriteFoods : favoriteFood) { System.out.println(favoriteFood); } } } <bean id="rabbit" class="org.lds.farm.Rabbit"> <property name="favoriteFoods"> <set> <value>lettuce</value> <value>carrot</value> </set> </property> </bean>

  27. DI Bean References • Lets expand our rabbit concept to an entire farm • And then modify our rabbit class as follows public class Farm { private List<Rabbit> rabbits; public void setRabbits(List<Rabbit> rabbits) { this.rabbits = rabbits; } } public class Rabbit { private String name; private float weight; public Rabbit(float weight) { this.weight = weight; } public void setName(String name) { this.name = name; } //… }

  28. Bean Reference Examples <bean id="rabbit" class="org.lds.training.Rabbit"> <constructor-arg name="weight" value=" 3.0" /> <property name="name" value="Bubba" /> </bean> <bean id="farm" class="org.lds.training.Farm"> <property name="rabbits"> <list> <ref bean="rabbit" /> <!– anonymous inner bean --> <bean class="org.lds.model.Rabbit"> <constructor-arg name="weight" value="2.5" /> </bean> </list> </property> </bean>

  29. More Examples public class Farm { private Rabbit prizeRabbit; public void setPrizeRabbit(Rabbit prizeRabbit) { this.prizeRabbit = prizeRabbit; } } • <bean id="prize" class="org.lds.model.Rabbit"> • <constructor-arg name="weight" value="12" /> • <property name="name" value="Queen Bee" /> • </bean> • <!– these are basically equivalent --> • <bean id="farm" class="org.lds.model.Farm"> • <property name="prizeRabbit" ref="prize" /> • </bean> • <bean id="farm" class="org.lds.model.Farm"> • <property name="prizeRabbit"> • <bean class="org.lds.model.Rabbit"> • <constructor-arg name="weight" value="12" /> • <property name="name" value="Queen Bee" /> • </bean> • </property> • </bean>

  30. Lab 2: Dependency Injection https://tech.lds.org/wiki/Introduction_to_Spring#Lab_2_Dependency_Injection

  31. Bean Scopes • Sometimes you want to be able to control the life of a bean • Bean scopes provide this ability • For instance, you may want a new instance of a bean every time it is requested, or you may want one instance for the entire application

  32. Available Bean Scopes

  33. Singleton Scope • Singleton - only one instance in a given context • Any time you request an instance of this bean you will get the single instance of this bean • For instance (if SomeBean is a singleton): • The new world context.getBean(SomeBean.class) == context.getBean(SomeBean.class) is true <!– singleton is the default so these two definitions are equivalent --> <bean id="whatever" class="org.lds.whatever.MyBean" /> <bean id="whatever" class="org.lds.whatever.MyBean" scope="singleton" />

  34. Prototype Scope • Equivalent to calling new every time an instance of a class is needed • Spring does not manage the lifecycle of prototype beans • For instance if SomeBean is prototype scope: • The configuration is as follows: context.getBean(SomeBean.class) == context.getBean(SomeBean.class) is false <bean id="whatever" class="org.lds.whatever.MyBean" scope="prototype" />

  35. Lab 3: Bean Scopes https://tech.lds.org/wiki/Introduction_to_Spring#Lab_3_Bean_Scopes

  36. Credit where credit is due • http://springsource.org • Spring Recipies 2nd Edition (Gary Mak, Josh Long and Daniel Rubio)

  37. Dedication • Mike Youngstrom and Bruce Campbell for their undying love and support through this process • And for reviewing and offering suggestions • And for Spencer Uresk and Mike Heath for the inspiration • And a special thanks to the rabbit farm who made this all possible

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