Spring入门（6）-使用注解装配
本文介绍如何使用注解装配。
0. 目录
- 使用Autowired
- 可选的自动装配
- 使用Qualifier选择
1. 使用Autowired
package com.chzhao.springtest;
import org.springframework.beans.factory.annotation.Autowired;
public class PersonBll implements IPersonBll {
public Person getPerson() {
return person;
}
public void setPerson(Person person) {
this.person = person;
}
@Autowired
private Person person;
public void show() {
System.out.println(this.person.getName());
}
}
注：@Autowired也可以放在setPerson上面。
<?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:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd
"
>
<context:annotation-config/>
<bean name="laoli" class="com.chzhao.springtest.Person">
<property name="name" value="老李" />
</bean>
<bean name="PersonBll" class="com.chzhao.springtest.PersonBll"/>
</beans>
2. 可选的自动装配
如果没有定义可装配的Bean，会如何呢？
<?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:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd"
>
<context:annotation-config/>
<bean id="bll" class="com.chzhao.springtest.PersonBll"></bean>
</beans>
如上配置文件中没有定义Bean，程序运行后，会抛出以下异常。
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'bll': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.chzhao.springtest.Person com.chzhao.springtest.PersonBll.person; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [com.chzhao.springtest.Person] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
只需要增加required=false即可，当然程序会抛出空指针异常。
package com.chzhao.springtest;
import org.springframework.beans.factory.annotation.Autowired;
public class PersonBll implements IPersonBll {
public Person getPerson() {
return person;
}
public void setPerson(Person person) {
this.person = person;
}
@Autowired(required=false)
private Person person;
public void show() {
System.out.println(this.person.getName());
}
}
3. 使用Qualifier选择
如果定义了两个Bean，会出现什么情况呢？
<?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:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd"
>
<context:annotation-config/>
<bean id="laowang" class="com.chzhao.springtest.Person">
<property name="name" value="老王"></property>
</bean>
<bean id="laoli" class="com.chzhao.springtest.Person">
<property name="name" value="老李"></property>
</bean>
<bean id="bll" class="com.chzhao.springtest.PersonBll"></bean>
</beans>
如上，定义了两个person，laowang和laoli，自动注入的时候会选择哪个呢？
实际上，会抛出如下异常：
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'bll': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.chzhao.springtest.Person com.chzhao.springtest.PersonBll.person; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type [com.chzhao.springtest.Person] is defined: expected single matching bean but found 2: laowang,laoli
通过Qualifier指定装配哪个Bean就可以了。
package com.chzhao.springtest;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
public class PersonBll implements IPersonBll {
public Person getPerson() {
return person;
}
public void setPerson(Person person) {
this.person = person;
}
@Autowired
@Qualifier("laoli")
private Person person;
public void show() {
System.out.println(this.person.getName());
}
}