Main Tutorials

Spring Auto-Wiring Beans

In Spring framework, you can wire beans automatically with auto-wiring feature. To enable it, just define the “autowire” attribute in <bean>.


	<bean id="customer" class="com.mkyong.common.Customer" autowire="byName" />

In Spring, 5 Auto-wiring modes are supported.

  • no – Default, no auto wiring, set it manually via “ref” attribute
  • byName – Auto wiring by property name. If the name of a bean is same as the name of other bean property, auto wire it.
  • byType – Auto wiring by property data type. If data type of a bean is compatible with the data type of other bean property, auto wire it.
  • constructor – byType mode in constructor argument.
  • autodetect – If a default constructor is found, use “autowired by constructor”; Otherwise, use “autowire by type”.

Examples

A Customer and Person object for auto wiring demonstration.


package com.mkyong.common;

public class Customer 
{
	private Person person;
	
	public Customer(Person person) {
		this.person = person;
	}
	
	public void setPerson(Person person) {
		this.person = person;
	}
	//...
}

package com.mkyong.common;

public class Person 
{
	//...
}

1. Auto-Wiring ‘no’

This is the default mode, you need to wire your bean via ‘ref’ attribute.


	<bean id="customer" class="com.mkyong.common.Customer">
                  <property name="person" ref="person" />
	</bean>

	<bean id="person" class="com.mkyong.common.Person" />

2. Auto-Wiring ‘byName’

Auto-wire a bean by property name. In this case, since the name of “person” bean is same with the name of the “customer” bean’s property (“person”), so, Spring will auto wired it via setter method – “setPerson(Person person)“.


	<bean id="customer" class="com.mkyong.common.Customer" autowire="byName" />
	
	<bean id="person" class="com.mkyong.common.Person" />

See full example – Spring Autowiring by Name.

3. Auto-Wiring ‘byType’

Auto-wire a bean by property data type. In this case, since the data type of “person” bean is same as the data type of the “customer” bean’s property (Person object), so, Spring will auto wired it via setter method – “setPerson(Person person)“.


	<bean id="customer" class="com.mkyong.common.Customer" autowire="byType" />
	
	<bean id="person" class="com.mkyong.common.Person" />

See full example – Spring Autowiring by Type.

4. Auto-Wiring ‘constructor’

Auto-wire a bean by property data type in constructor argument. In this case, since the data type of “person” bean is same as the constructor argument data type in “customer” bean’s property (Person object), so, Spring auto wired it via constructor method – “public Customer(Person person)“.


	<bean id="customer" class="com.mkyong.common.Customer" autowire="constructor" />
	
	<bean id="person" class="com.mkyong.common.Person" />

See full example – Spring Autowiring by Constructor.

5. Auto-Wiring ‘autodetect’

If a default constructor is found, uses “constructor”; Otherwise, uses “byType”. In this case, since there is a default constructor in “Customer” class, so, Spring auto wired it via constructor method – “public Customer(Person person)“.


	<bean id="customer" class="com.mkyong.common.Customer" autowire="autodetect" />
	
	<bean id="person" class="com.mkyong.common.Person" />

See full example – Spring Autowiring by AutoDetect.

Note
It’s always good to combine both ‘auto-wire’ and ‘dependency-check’ together, to make sure the property is always auto-wire successfully.


	<bean id="customer" class="com.mkyong.common.Customer" 
			autowire="autodetect" dependency-check="objects />
	
	<bean id="person" class="com.mkyong.common.Person" />

Conclusion

In my view, Spring ‘auto-wiring’ make development faster with great costs – it added complexity for the entire bean configuration file, and you don’t even know which bean will auto wired in which bean.

In practice, i rather wire it manually, it is always clean and work perfectly, or better uses @Autowired annotation, which is more flexible and recommended.

About Author

author image
Founder of Mkyong.com, love Java and open source stuff. Follow him on Twitter. If you like my tutorials, consider make a donation to these charities.

Comments

Subscribe
Notify of
25 Comments
Most Voted
Newest Oldest
Inline Feedbacks
View all comments
sathyajith
9 years ago

Thanks a lot Mkyong, Your way of writing is very simple to grab. usually ability to explain this much clear shows how clearly and comprehensively You know the subject …End to End. ..You are doing noble work….

rocky
9 years ago

thanks

Bashi Bazouk
9 years ago

What do you mean by ‘wire’? I am trying to find what is meant by auto-wiring and diving in straight in does not help.

Ranjith
10 years ago

great and simple explanation for spring newbies.earlier i had referred some books to understand this auto wiring concept,but your explanation solved my problem.

Prem Tiwari
10 years ago

I think you dont need to go anywhere such a crystal clear explanation.

Thanks alot for your efforts Sir ..please keep posting. God bless you. 🙂

sites
10 years ago

I in addition to my friends happened to be reading through the best tips from your site and instantly I had a terrible feeling I never expressed respect to the web site owner for them. All of the men were definitely as a consequence excited to read through all of them and have clearly been loving those things. Appreciate your really being simply helpful and then for deciding upon these kinds of superb things millions of individuals are really eager to be informed on. Our own sincere regret for not saying thanks to you sooner.

rm
11 years ago

“there is a default constructor in “Customer” class”
There isn’t.

I thought, default constructor means:

public Customer() {
  // something
}

Without any arguments.

Why do you call it default?

Arun
11 years ago

simple and sweet!

Raju
11 years ago

Easy to learn basic concepts.

suresh
11 years ago

very nice..

Nagesh
11 years ago

It is very nice tutorials;
Excellent effort for bring all most all JAVA/JAVA frame works on single thread.
It is very useful for me to revise quickly.
Thanks a lot for your efforts.
Please keep posting such type of atricles.

Vivek
11 years ago

This is not what I was looking for. You stink!!

Roshan
11 years ago
Reply to  Vivek

Please do not discourage.
He is doing a very good work.
I have been greatly entertained by his articles as part of my interview preparations.

Prashant Pratap Singh
11 years ago

Very simple to understand.
Thanks a lot.

Siddhraj Atodaria
11 years ago

Great…..
Thanks ……….

Natraj
12 years ago
 Very nice tutorial. 
Manish
12 years ago

Wonderfully simple & good tutorial,
Thanks

reddy
4 years ago

good mterial

Engin
6 years ago

“no – Default, no auto wiring, set it manually via “ref” attribute” –> this is FALSE !
The default is ‘by Type’ !!!

rr
8 years ago

This confused me initially. Please put in the header that this applies only to XML based a/w.

hariii
9 years ago

what is meant by dependency check here???

PosTi85
9 years ago
Reply to  hariii

If there isn’t any matching to autowire in a bean which has an object property that should be set, it would throw an exception

benson
10 years ago

I think there is a typo in your note.
Missing a mark ‘”‘ in the attribute dependency-check.
BTW,I’m your big fan.

Dhandapani S
11 years ago

Wonder full explanation…. thanks

nagraj palwencha
11 years ago
Reply to  Dhandapani S

good explanation with example
Thanks a lot