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。
可以通过自动装配 autowire="byType"象下面这样：
<!-- person has a property type of class "ability" -->
<bean id="person" class="com.gp6.autoAssemblyBean.Person" autowire="byType" />
<bean id="invisible" class="com.gp6.autoAssemblyBean.Ability" >
<property name="skill" value="Invisible" />
</bean>
看下面由Spring按类型自动装配的完整例子。
1. Beans
两个Bean，person 和 ability.
package com.gp6.autoAssemblyBean.type;
public class Ability {
private String skill;
public String getSkill() {
return skill;
}
public void setSkill(String skill) {
this.skill = skill;
}
}
package com.gp6.autoAssemblyBean.type;
public class Person {
private Ability ability;
public Ability getAbility() {
return ability;
}
public void setAbility(Ability ability) {
this.ability = ability;
}
}
2. Spring Wiring
通常情况下，明确地装配 bean：
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-2.5.xsd">
<bean id="person" class="com.gp6.autoAssemblyBean.type.Person">
<property name="ability" ref="invisible" />
</bean>
<bean id="invisible" class="com.gp6.autoAssemblyBean.type.Ability" >
<property name="skill" value="Invisible" />
</bean>
</beans>
package com.gp6.autoAssemblyBean.type;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Test {
public static void main( String[] args ) {
ApplicationContext context = new ClassPathXmlApplicationContext("com/gp6/autoAssemblyBean/type/applicationContext.xml");
Person person = (Person)context.getBean("person");
System.out.println(person.getAbility().getSkill());
}
}
输出
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。
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-2.5.xsd">
<bean id="person" class="com.gp6.autoAssemblyBean.type.Person" autowire="byType">
</bean>
<bean id="invisible" class="com.gp6.autoAssemblyBean.type.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？
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-2.5.xsd">
<bean id="person" class="com.gp6.autoAssemblyBean.type.Person" autowire="byType">
</bean>
<bean id="invisible" class="com.gp6.autoAssemblyBean.type.Ability" >
<property name="skill" value="Invisible" />
</bean>
<bean id="steal" class="com.gp6.autoAssemblyBean.type.Ability" >
<property name="skill" value="Steal" />
</bean>
</beans>
输出
log4j:WARN No appenders could be found for logger (org.springframework.core.env.StandardEnvironment).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
Exception in thread "main" org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'person' defined in class path resource [com/gp6/autoAssemblyBean/type/applicationContext.xml]: Unsatisfied dependency expressed through bean property 'ability': : No unique bean of type [com.gp6.autoAssemblyBean.type.Ability] is defined: expected single matching bean but found 2: [invisible, steal]; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [com.gp6.autoAssemblyBean.type.Ability] is defined: expected single matching bean but found 2: [invisible, steal]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1199)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1091)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:517)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:294)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:225)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:291)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:193)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:585)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:913)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:464)
at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)
at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)
at com.gp6.autoAssemblyBean.type.Test.main(Test.java:8)
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [com.gp6.autoAssemblyBean.type.Ability] is defined: expected single matching bean but found 2: [invisible, steal]
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:800)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:707)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1184)
... 13 more
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