The Spring IoC container is at the core of the Spring Framework. The container will create the objects, wire them together, configure them, and manage their complete life cycle from creation till destruction. The Spring container uses dependency injection (DI) to manage the components that make up an application.
Spring provides following two types of containers.
- BeanFactory container
- ApplicationContext container
1. BeanFactory
A BeanFactory is essentially nothing more than the interface for an advanced factory capable of maintaining a registry of different beans and their dependencies.
The BeanFactory
enables us to read bean definitions and access them using the bean factory.
1.1. How to create BeanFactory
When using just the BeanFactory
we can create one and read in some bean definitions in the XML format as follows:
InputStream is = new FileInputStream("beans.xml"); BeanFactory factory = new XmlBeanFactory(is); //Get bean HelloWorld obj = (HelloWorld) factory.getBean("helloWorld");
Other ways to create bean factory are as below:
Resource resource = new FileSystemResource("beans.xml"); BeanFactory factory = new XmlBeanFactory(resource); ClassPathResource resource = new ClassPathResource("beans.xml"); BeanFactory factory = new XmlBeanFactory(resource);
Basically that’s all there is. Using getBean(String)
, you can retrieve instances of your beans; the client-side view of the BeanFactory
is surprisingly simple.
1.2. BeanFactory methods
The BeanFactory
interface has only six methods for client code to call:
boolean containsBean(String)
: returns true if theBeanFactory
contains a bean definition or bean instance that matches the given nameObject getBean(String)
: returns an instance of the bean registered under the given name. Depending on how the bean was configured by theBeanFactory
configuration, either a singleton and thus shared instance or a newly created bean will be returned. ABeansException
will be thrown when either the bean could not be found (in which case it’ll be aNoSuchBeanDefinitionException
), or an exception occurred while instantiating and preparing the beanObject getBean(String, Class)
: returns a bean, registered under the given name. The bean returned will be cast to the given Class. If the bean could not be cast, corresponding exceptions will be thrown (BeanNotOfRequiredTypeException
). Furthermore, all rules of thegetBean(String)
method apply (see above)Class getType(String name)
: returns theClass
of the bean with the given name. If no bean corresponding to the given name could be found, aNoSuchBeanDefinitionException
will be thrownboolean isSingleton(String)
: determines whether or not the bean definition or bean instance registered under the given name is a singleton. If no bean corresponding to the given name could be found, aNoSuchBeanDefinitionException
will be thrownString[] getAliases(String)
: Return the aliases for the given bean name, if any were defined in the bean definition
2. ApplicationContext
ApplicationContext container adds more enterprise-specific functionality such as the ability to resolve textual messages from a properties file and the ability to publish application events to interested event listeners. This container is defined by the org.springframework.context.ApplicationContext interface.
The ApplicationContext container includes all functionality of the BeanFactory container, so it is generally recommended over the BeanFactory. BeanFactory
can still be used for lightweight applications like mobile devices or applet based applications where data volume and speed is significant.
2.1. Types of ApplicationContext
The most commonly used ApplicationContext
implementations are:
- FileSystemXmlApplicationContext – This container loads the definitions of the beans from an XML file. Here you need to provide the full path of the XML bean configuration file to the constructor.
- ClassPathXmlApplicationContext – This container loads the definitions of the beans from an XML file. Here you do not need to provide the full path of the XML file but you need to set CLASSPATH properly because this container will look bean configuration XML file in CLASSPATH.
- WebXmlApplicationContext – This container loads the XML file with definitions of all beans from within a web application.
2.2. How to create ApplicationContext
A sample code for application context instantiation will look like this.
ApplicationContext context = new FileSystemXmlApplicationContext("beans.xml"); HelloWorld obj = (HelloWorld) context.getBean("helloWorld");
Drop me your questions in comments section.
Happy Leaning !!
References:
BeanFactory Java Doc
ApplicationContext Java Doc
Akshat Srivastava
Can you add beans.xml file screenshot ? It will make things more clear.
Suraj
Please add a next button at the end of the topic.
Daniel
+ AnnotationConfigApplicationContext and AnnotationConfigWebApplicationContext?
Nice article 😉
Sabrina
XmlBeanFactory is deprecated from Spring 3.1 in favor of DefaultListableBeanFactory and XmlBeanDefinitionReader
Ganga
FileSystemXmlApplicationContext: This container loads the definitions of the beans from an XML file. Here you need to provide the full path of the XML bean configuration file to the constructor.
but your example you mentioned simply xml file name FileSystemXmlApplicationContext constructor
Bhargav
one question is single spring web application have multiple container ? if yes can you please post configuration and how its work. I read below from spring website but make me confused “The scope of the Spring singleton is best described as per container and per bean”
Spring Website : Spring’s concept of a singleton bean differs from the Singleton pattern as defined in the Gang of Four (GoF) patterns book. The GoF Singleton hard-codes the scope of an object such that one and only one instance of a particular class is created per ClassLoader. The scope of the Spring singleton is best described as per container and per bean. This means that if you define one bean for a particular class in a single Spring container, then the Spring container creates one and only one instance of the class defined by that bean definition. The singleton scope is the default scope in Spring. To define a bean as a singleton in XML.
uday
Question: “The scope of the Spring singleton is best described as per container and per bean”
Answer: “bean per container” means only one bean in a container–it doesn’t mean many containers.
abhishyam
Nice explanation
tofek khan
Nice explanation. Thanks