Manav Goyal

Spring Core - Java

Coupling

Tight => The two classes often change together
- Composition

Loose => Means the two classes are mostly independent

Example => Code is still tightly coupled to the object creation logic

    public class Employee {
        private String name;
        private Address address;
        public Employee (Address address) {
            this.address=address;
        }
    }

Association
- Association in Java defines the connection between two classes that are set up through their objects
- Relationships
  - one-to-one
  - one-to-many
  - many-to-one
  - many-to-many
- Types
  - is-a => Inheritance
  - has-a
    - Aggregation
      - If two entities are in the aggregation composition, and one entity fails due to some error, it will not affect the other entity
    - Composition
      - A restricted form of the Aggregation where the entities are strongly dependent on each other
      - If an object contains the other object and the contained object cannot exist without the existence of that object, then it is called composition
      - The composition is achieved by using an instance variable that refers to other objects
      - Java doesn’t support multiple inheritances but by using composition we can achieve it
IoC (Inversion of Control)
- Normal flow of control is achieved by JVM
- Java follows container component modal, all objects acts as component
- Runtime capable of creating object and priving it back to the code
- Frameworks
  - Spring
    - Dependency Injection
      - Spring Container => File xml/java
        
        BeanFactory
        
        ApplicationContext
      - Setter Injection
        
        If happened through Setter methods
        
        XML shortcut with p-namespace
        
        Enables you to use the bean element attributes, instead of nested <property/> elements
      - Container Injection
        
        Its dependencies are Mandatory dependencies
        
        Order should be same, Can use type or index or name attribute instead to order
        
        XML shortcut with c-namespace
        
        Usage of inline attributes for configuring the constructor arguments
      - Mixed dependency injection
        
        Constructor based used for immutable dependencies, and Setter based for optional dependencies
      - Inner Bean
        
        Bean inside a bean, can't be used outside the bean it is defined
      - Bean Scopes
        
        Singleton
        
        Prototype
        
        Create a new bean instance each time a bean is requested
      - Injection using Factory Bean
    - Auto-wiring
      - Automatic Dependency injection
      - Eliminates the need to specify bean references via property & contructor-org element
      - Modes
        
        byName, byType, Constructor
  - Guice
  - Pico
Annotations
- Will not work with static fields and methods, done before XML injection
- Types
  - Spring Standard Annotations
    - @Value("#{nameObj}") => Injects value from the properties file
    - @Autowired => AUtomatically wires Spring beans into other beans
  - JSR 250
    - @Resource
  - JSR 330
    - @Inject
    - @Named
    - @Singleton
  - Stero type
    - @Component => Used to mark any class as Spring managed component or bean
    - @Repository => Indicates class is a DAO that interacts with the database
    - @Service => Indicates class is service in service layer of the application
    - @Controller => Indicates that class is responsible for hadling web req & res
- Java Configurations
  - @Configuration => Used to declare a XML file as Spring configuration
  - @Bean
  - @ComponentScan => Used to scan stereotype annotations
Spring Expression Language (SpEL)
- Quering & Manipulating an object at runtime
- Expression => #{expression}
- Operators
Spring Test
- Frameworks
  - junit
  - testng
- Annotations
  - @ContextConfigurations => Defines how to load and configure ApplicationContext for JUnit test, can point to both XML and java files
    - @RunWith(SprintJunit4ClassRunner.class)
  - @DirtiesContext => Indicates the ApplicationContext is dirty
    - Provies methodMode & classMode
  - @ActiveProfiles => Activate one or more profiles for the test cases