Beans Autowiring in spring

This is 10 of 16 parts of tutorial series

Tutorial Content: Spring tutorial for beginners

You have learnt how to declare beans using the element and inject with using and elements in XML configuration file.

In Spring framework, you can wire beans automatically with auto-wiring feature. To enable it, just define the “autowire” attribute in .The Spring container can autowire relationships between collaborating beans without using and elements which helps cut down on the amount of XML configuration

Autowiring modes:

There are following autowiring modes which can be used to instruct Spring container to use autowiring for dependency injection.

no:

Default, no auto wiring, set it manually via “ref” attribute as we have done in dependency injection via settor method post.

byName:

Autowiring by property name. Spring container looks at the properties of the beans on which autowire attribute is set to byName in the XML configuration file and it tries to match it with name of bean in xml configuration file.

byType:

Autowiring by property datatype. Spring container looks at the properties of the beans on which autowire attribute is set to byType in the XML configuration file. It then tries to match and wire a property if its type matches with exactly one of the beans name in configuration file. If more than one such beans exists, a fatal exception is thrown.

contructor:

byType mode in constructor argument.

autodetect:

Spring first tries to wire using autowire by constructor, if it does not work, Spring tries to autowire by byType.

Example:

I am taking example of autowire “byName” here.It will be almost same as Dependency injection via setter method with some changes in XML configuration file.

1.Country.java:

This is simple pojo class having some attributes so here country has name and object of Capital class.
Create Country.java under package org.arpit.javapostsforlearning.Copy following content into Country.java.

2.Capital.java

This is also simple pojo class having one attribute called “capitalName”.

Create Capital.java under package org.arpit.javapostsforlearning.java.Above Country class contains object of this class.Copy following content into Capital.java

3.BeanAutowirngByNameMain.java

This class contains main function.Create BeanAutowiringByNameMain.java under package org.arpit.javapostsforlearning.Copy following content into BeanAutowiringByNameMain.java
You can note here that we have used ClassPathXmlApplicationContext for getting bean here.There are various ways for getting beans.In hello world example we have used XmlBeanFactory for getting beans.

4.ApplicationContext.xml

Here in ,we have used autowire attribute and set it to “byName”.So now spring container will match “capital” reference in Country class with id or name of other beans in XML configuration file. So here you can see we have bean with id as “capital”

5.Run it

When you will run above application,you will get following as output.

Limitations of Autowiring :

  • OverRiding possibilities:You can still define dependencies using or tag which will always override autowiring.
  • Primitive data type:you have to define primitive data type like String or Interger using or tag.You can not autowire them.
  • Confusing Nature:If you have lot of dependency in program,then its very hard to find out using autowire attribute of bean.

Source code:

In next post,we will see inheritance in spring.

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