Autowiring in spring reduces lot of headache as a developer. The Autowiring in spring comes with 4 flavors.

1) No: No autowiring, in this case ref has to be used to do autowring(Manually)

2) byname: In this case Autowiring is done by bean name, if the defined bean name    and the name of bean property is same then autowire it.

3) byType: if the defined bean data type and the data type of bean property are same then Autowiring is done.

4) constructor: The autowiring is done using constructor argument using byType mode.

Prerequisites:

1) Spring MVC project
2) Spring 3.X

Let’s discuss one by one:
Consider two bean classes named as University and College.

Definition for University class

package com.springaddon.classes;

public class University {
	private College college;
	/**
	 * @return the college
	 */
	public College getCollege() {
		return college;
	}
	/**
	 * @param college the college to set
	 */
	public void setCollege(College college) {
		this.college = college;
	}
	/* (non-Javadoc)
	 * @see java.lang.Object#toString()
	 */
	@Override
	public String toString() {
		return "University [college=" + college + "]";
	}

}

Definition for College class:

package com.springaddon.classes;

public class College {

	private String name;

	/**
	 * @return the name
	 */
	public String getName() {
		return name;
	}

	/**
	 * @param name the name to set
	 */
	public void setName(String name) {
		this.name = name;
	}

	/* (non-Javadoc)
	 * @see java.lang.Object#toString()
	 */
	@Override
	public String toString() {
		return "College [name=" + name + "]";
	}

}

1) Autowiring ‘No’

The bean is autowired manually for any kind of assignment.

XML Entry:

The property college is assigned manually using ref tag.

2) Autowiring byname

In this type name of the property should go same as in the setter of the bean.

public void setCollege(College college) {
		this.college = college;
}

XML entry:

If the name does not matches with setter property the Autowiring won’t happen.

3) Autowiring byType

In this type type of the property should go same as in the setter of the bean.

public void setCollege(College college) {
		this.college = college;
}

XML Entry:

If there are more than one entry for same data type the autowiring won’t work and it will threw exception.

4) Autowiring by constructor

Auto-wire a bean by property data type in constructor argument. In this case, the University class contains the property and proper constructor for college.

private College college;

   public University(College college){
		this.college=college;
   }

XML Entry:

With autowire by constructor enabled, you can leave the constructor property unset. Spring will find the compatible data type and wire it automatcailly.

Hope the article helps you in Autowiring in spring, feedbacks and suggestions are welcome

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