一、手動裝配

假設有個Person類

package com.at.beans.autowire;

public class Person {

	private String name;
	
	private Address address;
	
	private Car car;

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public Address getAddress() {
		return address;
	}

	public void setAddress(Address address) {
		this.address = address;
	}

	public Car getCar() {
		return car;
	}

	public void setCar(Car car) {
		this.car = car;
	}

	@Override
	public String toString() {
		return "Person [name=" + name + ", address=" + address + ", car=" + car
				+ "]";
	}


	
	
}

Address類

package com.at.beans.autowire;

public class Address {

	private String city;
	private String street;
	public String getCity() {
		return city;
	}
	public void setCity(String city) {
		this.city = city;
	}
	public String getStreet() {
		return street;
	}
	public void setStreet(String street) {
		this.street = street;
	}
	@Override
	public String toString() {
		return "Address [city=" + city + ", street=" + street + "]";
	}
	
	
}

Car類

package com.at.beans.autowire;

public class Car {

	private String brand;
	private double price;
	public String getBrand() {
		return brand;
	}
	public void setBrand(String brand) {
		this.brand = brand;
	}
	public double getPrice() {
		return price;
	}
	public void setPrice(double price) {
		this.price = price;
	}
	@Override
	public String toString() {
		return "Car [brand=" + brand + ", price=" + price + "]";
	}
	
	
}

配置文件如下

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:p="http://www.springframework.org/schema/p"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
	
	<bean id="address" class="com.at.beans.autowire.Address"
		p:city="BeiJing" p:street="xierqi"></bean>

	<bean id="car" class="com.at.beans.autowire.Car"
		p:brand="Audi" p:price="300000"></bean>
	
	<!-- 通過ref 手工裝配 -->	
	<bean id="person" class="com.at.beans.autowire.Person"
		p:name="luoyepiaoxue2014" p:address-ref="address" p:car-ref="car"></bean>
		
</beans>

測試函數

package com.at.beans.autowire;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class TestPerson {

	public static void main(String[] args) {
		ApplicationContext ctx = new ClassPathXmlApplicationContext("beans-autowire.xml");
		Person person = (Person) ctx.getBean("person");
		System.out.println(person);
	}
}

輸出結果如下

五月 20, 2017 9:47:10 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@539269cb: startup date [Sat May 20 21:47:10 CST 2017]; root of context hierarchy
五月 20, 2017 9:47:10 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [beans-autowire.xml]
Person [name=luoyepiaoxue2014, address=Address [city=BeiJing, street=xierqi], car=Car [brand=Audi, price=300000.0]]

二、自動裝配

1、通過byName自動裝配，配置文件如下

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:p="http://www.springframework.org/schema/p"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
	
	<bean id="address" class="com.at.beans.autowire.Address"
		p:city="BeiJing" p:street="xierqi"></bean>

	<bean id="car" class="com.at.beans.autowire.Car"
		p:brand="Audi" p:price="300000"></bean>
	
	<!-- 通過byName自動裝配 -->	
	<bean id="person" class="com.at.beans.autowire.Person"
		p:name="luoyepiaoxue2014" autowire="byName"></bean>

</beans>

2、通過byType自動裝配，配置文件如下

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:p="http://www.springframework.org/schema/p"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
	
	<bean id="address22" class="com.at.beans.autowire.Address"
		p:city="BeiJing" p:street="xierqi"></bean>

	<bean id="car" class="com.at.beans.autowire.Car"
		p:brand="Audi" p:price="300000"></bean>
	
	<!-- 通過byName自動裝配 -->	
	<bean id="person" class="com.at.beans.autowire.Person"
		p:name="luoyepiaoxue2014" autowire="byType"></bean>

</beans>

但是通過byType自動裝配的時候，如果多個bean的類型一樣，就會出現錯誤

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:p="http://www.springframework.org/schema/p"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
	
	<bean id="address22" class="com.at.beans.autowire.Address"
		p:city="BeiJing" p:street="xierqi"></bean>
		
	<bean id="address33" class="com.at.beans.autowire.Address"
		p:city="BeiJing" p:street="xierqi"></bean>

	<bean id="car" class="com.at.beans.autowire.Car"
		p:brand="Audi" p:price="300000"></bean>
	
	<!-- 通過byName自動裝配 -->	
	<bean id="person" class="com.at.beans.autowire.Person"
		p:name="luoyepiaoxue2014" autowire="byType"></bean>

</beans>

運行結果就會出現如下的錯誤

五月 20, 2017 10:05:52 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@539269cb: startup date [Sat May 20 22:05:52 CST 2017]; root of context hierarchy
五月 20, 2017 10:05:52 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [beans-autowire.xml]
Exception in thread "main" org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'person' defined in class path resource [beans-autowire.xml]: Unsatisfied dependency expressed through bean property 'address': : No qualifying bean of type [com.at.beans.autowire.Address] is defined: expected single matching bean but found 2: address22,address33; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type [com.at.beans.autowire.Address] is defined: expected single matching bean but found 2: address22,address33
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1278)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1170)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:537)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:475)
	at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:304)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:300)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:195)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:700)
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:760)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:482)
	at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)
	at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)
	at com.at.beans.autowire.TestPerson.main(TestPerson.java:9)
Caused by: org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type [com.at.beans.autowire.Address] is defined: expected single matching bean but found 2: address22,address33
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:967)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:855)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1263)
	... 13 more

從以上我們可以看出在根據類型（byType）自動裝配時候，若 IOC 容器中有多個與目標 Bean 類型一致的 Bean. 在這種情況下, Spring 將無法判定哪個 Bean 最合適該屬性, 所以不能執行自動裝配。

總結：在 Bean 配置文件裏設置 autowire 屬性進行自動裝配將會裝配 Bean 的所有屬性。然而，若只希望裝配個別屬性時，autowire 屬性就不夠靈活了.。
autowire 屬性要麼根據類型自動裝配,，要麼根據名稱自動裝配，不能兩者兼而有之。
一般情況下，在實際的項目中很少使用自動裝配功能，因爲和自動裝配功能所帶來的好處比起來，明確清晰的配置文檔更清晰一些。

By luoyepiaoxue2014

微博地址： http://weibo.com/luoyepiaoxue2014 點擊打開鏈接

Spring 手動裝配和自動裝配

一、手動裝配

二、自動裝配

Spring快速入門示例

Spring 使用外部屬性文件

Spring中bean的生命週期

Spring中通過註解配置bean（1）

Spring Bean之間的關係

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