Spring由类型(Type)自动装配

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我是靠谱客的博主失眠御姐，最近开发中收集的这篇文章主要介绍Spring由类型(Type)自动装配，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

在Spring中，“类型自动装配”的意思是如果一个bean的数据类型与其它bean属性的数据类型相同，将自动兼容装配它。

例如，一个“persion” bean 公开以“ability”类数据类型作为属性，Spring会找到ability类相同的数据类型，并自动装配它的Bean。如果没有匹配找到，它什么也不做。

1. Beans

两个Bean，person 和 ability.

public class Person {

	private Ability ability;

	public Ability getAbility() {
		return ability;
	}

	public void setAbility(Ability ability) {
		this.ability = ability;
	}

	@Override
	public String toString() {
		return "Person [ability=" + ability + "]";
	}
	
}

public class Ability {

	private String skill;

	public String getSkill() {
		return skill;
	}

	public void setSkill(String skill) {
		this.skill = skill;
	}

	@Override
	public String toString() {
		return "Ability [skill=" + skill + "]";
	}
	
}

2. Spring Wiring

通常情况下，明确地装配 bean：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

	<bean id="person" class="com.ray.common.Person">
		<property name="ability" ref="invisible"/>
	</bean>
	
	<bean id="invisible" class="com.ray.common.Ability">
		<property name="skill" value="Invisible"/>
	</bean>
</beans>

输出

Person [ability=Ability [skill=Invisible]]

随着自动装配按类型启用后，可以保留ability属性未设置。Spring会发现相同的数据类型并自动装配它。

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

	<bean id="person" class="com.ray.common.Person" autowire="byType"/>

	
	<bean id="invisible" class="com.ray.common.Ability">
		<property name="skill" value="Invisible"/>
	</bean>
</beans>

输出

Person [ability=Ability [skill=Invisible]]

如果你有两个Bean，都是类“ability”相同的数据类型？

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

	<bean id="person" class="com.ray.common.Person" autowire="byType"/>

	
	<bean id="invisible" class="com.ray.common.Ability">
		<property name="skill" value="Invisible"/>
	</bean>
	
	<bean id="steal" class="com.ray.common.Ability">
		<property name="skill" value="Invisible"/>
	</bean>
</beans>

输出

Exception in thread "main" org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'person' defined in class path resource [beans.xml]: Unsatisfied dependency expressed through bean property 'ability'; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.ray.common.Ability' available: expected single matching bean but found 2: invisible,steal
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1439)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1326)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:582)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:502)
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:312)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:310)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:200)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:761)
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:868)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:549)
	at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:144)
	at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:85)
	at com.ray.test.Test.main(Test.java:12)
Caused by: org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.ray.common.Ability' available: expected single matching bean but found 2: invisible,steal
	at org.springframework.beans.factory.config.DependencyDescriptor.resolveNotUnique(DependencyDescriptor.java:215)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1116)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1065)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1424)
	... 13 more

在这种情况下，它会打出 UnsatisfiedDependencyException 的错误消息。

注意:

在类型的自动装配模式，就必须确保只有Bean 只有一个唯一的数据类型声明。