Spring Tutorial - Spring Auto Wire Bean

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Spring can wire beans automatically. To enable it, define the "autowire" attribute in <bean>.

<bean id="customer" class="com.java2s.common.Customer" autowire="byName" />

Spring has five Auto-wiring modes.

• no - Default, no auto wiring
• byName - Auto wiring by property name.
• byType - Auto wiring by property data type.
• constructor - byType mode in constructor argument.
• autodetect - If a default constructor is found, use "autowired by constructor"; Otherwise, use "autowire by type".

Java Beans

Customer Java bean.

package com.java2s.common;
public class Customer 
{
  private Person person;
  public Customer(Person person) {
    this.person = person;
  }
  public void setPerson(Person person) {
    this.person = person;
  }
}

Person Java bean

package com.java2s.common;
public class Person 
{
}

Auto-Wiring 'no'

This is the default mode, we need to wire the Java bean via 'ref' attribute.

<bean id="customer" class="com.java2s.common.Customer">
         <property name="person" ref="person" />
</bean>
<bean id="person" class="com.java2s.common.Person" />

Auto-Wiring 'byName'

The following code add autowire byName to the bean declaration.

<bean id="customer" class="com.java2s.common.Customer" autowire="byName" />

Since the name of "person" bean is same with the name of the "customer" bean's "person" property, Spring will auto wire it via method setPerson(Person person).

<bean id="customer" class="com.java2s.common.Customer" autowire="byName" />
<bean id="person" class="com.java2s.common.Person" />

Auto-Wiring 'byType'

The following xml configuration declares the autowire type as byType.

<bean id="customer" class="com.java2s.common.Customer" autowire="byType" />

Since the data type of "person" bean is same as the data type of the "customer" bean's property person object, Spring will auto wire it via method setPerson(Person person).

<bean id="customer" class="com.java2s.common.Customer" autowire="byType" />
<bean id="person" class="com.java2s.common.Person" />

Auto-Wiring 'constructor'

The following code declares a bean's autowire type as constructor.

<bean id="customer" class="com.java2s.common.Customer" autowire="constructor" />

The data type of "person" bean is same as the constructor argument data type in "customer" bean's property (Person object), Spring will auto wire it via constructor method - "public Customer(Person person)".

<bean id="customer" class="com.java2s.common.Customer" autowire="constructor" />
<bean id="person" class="com.java2s.common.Person" />

Auto-Wiring 'autodetect'

The following code shows how to use autodetect autowire. If a constructor is found, uses "constructor"; Otherwise, uses "byType".

<bean id="customer" class="com.java2s.common.Customer" 
      autowire="autodetect" dependency-check="objects />

Since there is a constructor in "Customer" class, Spring will auto wire it via constructor method - "public Customer(Person person)".

<bean id="customer" class="com.java2s.common.Customer" autowire="autodetect" />
<bean id="person" class="com.java2s.common.Person" />

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