这一章节我们来详细讨论一下@autowired里面的参数required。
1.domain（重点）
蛋糕类：
package com.raylee.my_new_spring.my_new_spring.ch02.topic_1_9;public class Cake {private String name = "";public String getName() {return name;}public void setName(String name) {this.name = name;}}
厨师类：
（1）下面是会报错的厨师类
package com.raylee.my_new_spring.my_new_spring.ch02.topic_1_9;import org.springframework.beans.factory.annotation.Autowired;public class Chief {@Autowiredprivate Cake cake = null;private String name = "";public String getName() {return name;}public Cake makeOneCake() {if (cake != null) {System.out.println(getName() + " make " + cake.getName());} else {System.out.println(cake);}return cake;}public void setName(String name) {this.name = name;}}
报错信息：
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [com.raylee.my_new_spring.my_new_spring.ch02.topic_1_9.Cake] 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)}
at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoSuchBeanDefinitionException(DefaultListableBeanFactory.java:920)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:789)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:703)
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:474)
... 40 more
（2）下面是允许注入是空对象
package com.raylee.my_new_spring.my_new_spring.ch02.topic_1_9;import org.springframework.beans.factory.annotation.Autowired;public class Chief {@Autowired(required = false)private Cake cake = null;private String name = "";public String getName() {return name;}public Cake makeOneCake() {if (cake != null) {System.out.println(getName() + " make " + cake.getName());} else {System.out.println(cake);}return cake;}public void setName(String name) {this.name = name;}}
上面需要注意的是，@Autowired标签是默认强制注入非空对象，但是我们可以通过required=false属性，注入null对象
2.测试类：（不变）
package com.raylee.my_new_spring.my_new_spring.ch02.topic_1_9;import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = {"/com/raylee/my_new_spring/my_new_spring/ch02/topic_1_9/ApplicationContext-test.xml" })
public class ChiefTest {@Autowiredprivate ApplicationContext applicationContext;@Testpublic void testChief() {Chief jack = applicationContext.getBean(Chief.class);jack.makeOneCake();}
}
3.配置文件（重点）
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"xmlns:context="http://www.springframework.org/schema/context" xmlns:p="http://www.springframework.org/schema/p"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:tx="http://www.springframework.org/schema/tx"xmlns:aop="http://www.springframework.org/schema/aop" xmlns:util="http://www.springframework.org/schema/util"xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsdhttp://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-2.0.xsdhttp://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsdhttp://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.1.xsdhttp://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.1.xsdhttp://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.0.xsdhttp://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsdhttp://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd"><bean id="jack"class="com.raylee.my_new_spring.my_new_spring.ch02.topic_1_9.Chief"p:name="jack" />
</beans>
为了测试上面的例子，我们故意删除了cake的bean
总结：这一章节我们主要讨论了@autowired里面的参数required。
目录：http://blog.csdn.net/raylee2007/article/details/50611627
我的github：https://github.com/raylee2015/my_new_spring