从头认识Spring-2.3 注解装配-@autowired-required
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这一章节我们来具体讨论一下@autowired里面的參数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)以下是会报错的厨师类
package com.raylee.my_new_spring.my_new_spring.ch02.topic_1_9; import org.springframework.beans.factory.annotation.Autowired; public class Chief { @Autowired 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; } }
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)以下是同意注入是空对象
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; } }
上面须要注意的是,@Autowired标签是默认强制注入非空对象,可是我们能够通过required=false属性,注入null对象
2.測试类:(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 { @Autowired private ApplicationContext applicationContext; @Test public 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.xsd http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-2.0.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.1.xsd http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.1.xsd http://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.0.xsd http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://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>
为了測试上面的样例,我们有益删除了cake的bean
总结:这一章节我们主要讨论了@autowired里面的參数required。
文件夹:http://blog.csdn.net/raylee2007/article/details/50611627
我的github:https://github.com/raylee2015/my_new_spring
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