"Welcome To Ashok IT"				
			                     "Spring Boot and MicroServices"
                                              Topic : Dependency Injection Using Objects
                                              Date  : 27/08/2024
                                                (Session - 11)                               
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Today Session : Bean Autowiring
===============================
* Bean wiring is nothing but configuring the dependencies of abean along with bean in xml file.

* If you manually configure bean dependencies into an xml file then the size of xml file will be increased.

* Inorder to cut down the xml configuration the framework has introduced the autowiring facility.

* Incase of autowiring we no need to configure the dependencies explictly in xml file based on autowire strategy the
  container will inject the dependencies of abean automatically.

* Bean autowiring facility is only applicable for "Dependency in the form of Objects".

* To add autowiring facility we need to configure "autowire" attribute with <bean> tag.

* The values of autowire attribute are 
    1) no
    2) byName
    3) byType
    4) constructor
    
* Bean Autowiring facility can be achieved using two approaches
    1) XML Approach
    2) Annotation Approach

1) no
======
* The default value of autowire attribute is "no" it means the dependencies of abean must configured explictly,
  the container doesn't apply autowiring facility.

2) byName
==========
* In this type of autowiring the container checks for property name of bean is matched with id of abean in xml file or not.

* If bean id is matched with the property name to be injected then container calls setter injection and injects the             dependency object.

* If bean id is not matched with the property name then the dependency will not injected.

 Example:
 ========
       public class ExampleBean1{
	  private ExampleBean2 exampleBean2;

          public void setExampleBean2(ExampleBean2 exampleBean2){
             this.exampleBean2 = exampleBean2;
          }                             
       }      

       spring.xml
       ==========
        <beans>
            <bean id ="exampleBean1" class="ExampleBean1" autowire="byName"/>
              
            <bean id="exampleBean2" class="ExampleBean2"/>
        </beans>


3) byType:
==========
* In this type of autowire strategy the container checks for the property type is matched with Bean class configured in xml     file or not.

* If a bean class of xml file is matched with property type to be injected then the container calls setter injection and     injects the dependency object.

* If a bean class of xml file is not matched with the property type then the property will not be injected.

* If a bean class of xml file is matched with more than onces with the property type then the exception will be thrown.

    Example:
   	public class ExampleBean1{
	  private "ExampleBean2" exampleBean2;

          public void setExampleBean2(ExampleBean2 exampleBean2){
             this.exampleBean2 = exampleBean2;
          }                             
       }      

       spring.xml
       ==========
        <beans>
            <bean id ="exampleBean1" class="ExampleBean1" autowire="byType"/>
              
            <bean id="exampleBean2" class="ExampleBean2"/>
        </beans>

4) constructor:
===============
 * In this type of autowiring the container checks for a property type of a bean class configured in xml file are                matched or not.
  
 * If abean class is matched with the property Type to be injected then the container injects the dependency object
   through constructor injection.

 * If abean class is not matched with the property Type then container throws an exception.

 * If more than one bean class is matched with property Type then again container throws an exception.

 * constructor strategy and byType strategy are common in verfication but there is differences injections.
   byType means setter injection and constructor means constructor injection is applied.


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