Spring Framework

Ioc Container(DI)

reference:

https://docs.spring.io/spring-framework/docs/current/spring-framework-reference/core.html

def:objects define their dependencies only through constructor arguments

• org.springframework.beans
• org.springframework.context

A bean is an object that is instantiated, assembled, and otherwise managed by a Spring IoC container.

Container Overview

configuring metadata

• xml based

  this bean definition corresponds to the actual objects

  • service layer
  • data access objects

• annotation based

• java-based

instantiating a Container

ApplicationContext context = new ClassPathXmlApplicationContext("services.xml", "daos.xml");

service.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
        https://www.springframework.org/schema/beans/spring-beans.xsd">

    <!-- services -->

    <bean id="petStore" class="org.springframework.samples.jpetstore.services.PetStoreServiceImpl">
        <property name="accountDao" ref="accountDao"/>
        <property name="itemDao" ref="itemDao"/>
        <!-- additional collaborators and configuration for this bean go here -->
    </bean>

    <!-- more bean definitions for services go here -->

</beans>

Dependency

• constructor-based Dependency
• setter-based

Annotation-based

@Required for setter method | @Autowired for constructor

public class MovieRecommender {

    private final CustomerPreferenceDao customerPreferenceDao;

    @Autowired
    public MovieRecommender(CustomerPreferenceDao customerPreferenceDao) {
        this.customerPreferenceDao = customerPreferenceDao;
    }

    // ...
}

As of Spring Framework 4.3, an @Autowired annotation on such a constructor is no longer necessary if the target bean defines only one constructor to begin with. However, if several constructors are available, at least one must be annotated to teach the container which one to use.

1. traditional constructor

   public class MovieRecommender {
   
       private final CustomerPreferenceDao customerPreferenceDao;
   
       @Autowired
       public MovieRecommender(CustomerPreferenceDao customerPreferenceDao) {
           this.customerPreferenceDao = customerPreferenceDao;
       }
   
       // ...
   }

2. setter

   public class SimpleMovieLister {
   
       private MovieFinder movieFinder;
   
       @Autowired
       public void setMovieFinder(MovieFinder movieFinder) {
           this.movieFinder = movieFinder;
       }
   
       // ...
   }

3. arbitrary names and multiple arguments

   public class MovieRecommender {
   
       private MovieCatalog movieCatalog;
   
       private CustomerPreferenceDao customerPreferenceDao;
   
       @Autowired
       public void prepare(MovieCatalog movieCatalog,
               CustomerPreferenceDao customerPreferenceDao) {
           this.movieCatalog = movieCatalog;
           this.customerPreferenceDao = customerPreferenceDao;
       }
   
       // ...
   }

4. fileds

   public class MovieRecommender {
   
       private final CustomerPreferenceDao customerPreferenceDao;
   
       @Autowired
       private MovieCatalog movieCatalog;
   
       @Autowired
       public MovieRecommender(CustomerPreferenceDao customerPreferenceDao) {
           this.customerPreferenceDao = customerPreferenceDao;
       }
   
       // ...
   }

5. arrays and collections

   public class MovieRecommender {
   
       private Set<MovieCatalog> movieCatalogs;
   
       @Autowired
       public void setMovieCatalogs(Set<MovieCatalog> movieCatalogs) {
           this.movieCatalogs = movieCatalogs;
       }
   
       // ...
   }

6. map

   public class MovieRecommender {
   
       private Map<String, MovieCatalog> movieCatalogs;
   
       @Autowired
       public void setMovieCatalogs(Map<String, MovieCatalog> movieCatalogs) {
           this.movieCatalogs = movieCatalogs;
       }
   
       // ...
   }

autowiring fails when no matching candiate beans are available

AOP

Aspect Oriented Programming