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Spring Framework.md

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Spring Framework

Inversion of Control

  • Container maintains your class dependencies
  • Objects are injected at runtime or startup time

If your class cannot operate without the dependency, it should be injected via constructors. If your class can treat the dependency as optional or can accept multiple but variable concrete instances of the dependency, then it can be injected via setter injection

Benefits of DI

  • Reduces noise in your code
  • Reduces object coupling
  • Reduces defects from incorrect construction
  • Focus on the API contract

Application Context

  • Acts as heart of Spring Applications
  • Encapsulate the BeanFactory
  • Provides metadata for bean creation
  • Provides mechanism for creation of beans in the correct order

Environment

  • Populated by default by environment variables
  • Supplement with property files

Profiles

-Dspring.profiles.active=dev

@Bean @Profile("dev")

TODO: Learn more about SPEL

Spring Expression Language

@Value("#{new Boolean(environment['spring.profiles.active']!='dev')}") private boolean isActive;

Bean Scopes

Singletons

  • The default scope of every bean is singleton
  • One instance per contect definition

Prototype

  • New instance every time it is referenced
  • Difinition is stored in IoC, instances are not
  • Very useful for transcient data or types that flex based on application state

Session

  • Applies to web environment only
  • One instance of bean per user session
  • Difinition is stored in IoC, instances are not

Request

  • Applies to web environments only
  • One instance per requests
  • Difinition is stored in IoC, instances are not

Proxies

Everything is a proxy

Component Scanning

@Component

  • Indicates that a class should be loaded into the BeanFactory
  • Component scanning scans a base package and loads configuration automatically for each bean it finds
  • Dependency Injection is achieved through the @Autowired annotation
  • @Qualifier is used when multiple implementations of an interface are needed
  • Properties injected with @Value

@ComponentScan(basePackages = "com.myapp.mypackage")

Lifecycle Methods

Post Construction

Called after property setting

@PostConstruct public void init(){ // do some init work }

Pre Destroy

Executed when ApplicationContext closes

@PreDestroy public void destroy(){ // destroy work }

The Bean Lifecycle

Initialization

Use

Destruction

Aspect-Oriented Programming

Aspects are reusable blocks of code that are injected into your application at runtime.

Common Applications of Aspects

  • Logging
  • Transaction management
  • Caching
  • Security

Parts of a Spring Aspect

  • Join Point
  • Pintcut
  • Advice
  • Aspect

Annotations

@PropertySource("classpath:application.properties")

@Value("Jorge") private String name;

@Configuration @Autowired