spring 配置文件中 <bean> 节点的 autowire 参数可以控制 bean 自动装配的方式
- default – 默认的方式和 "no" 方式一样
- no – 不自动装配，需要使用 <ref />节点或参数
- byName – 根据名称进行装配
- byType – 根据类型进行装配
- constructor – 根据构造函数进行装配
文档解释
Attribute : autowireControls whether bean properties are "autowired". This is an automagical process in which bean references don't need to be coded explicitly in the XML bean definition file, but rather the Spring container works out dependencies. The effective default is "no". There are 4 modes: 1. "no" The traditional Spring default. No automagical wiring. Bean references must be defined in the XML file via the <ref/> element (or "ref" attribute). We recommend this in most cases as it makes documentation more explicit. Note that this default mode also allows for annotation-driven autowiring, if activated. "no" refers to externally driven autowiring only, not affecting any autowiring demands that the bean class itself expresses. 2. "byName" Autowiring by property name. If a bean of class Cat exposes a "dog" property, Spring will try to set this to the value of the bean "dog" in the current container. If there is no matching bean by name, nothing special happens. 3. "byType" Autowiring if there is exactly one bean of the property type in the container. If there is more than one, a fatal error is raised, and you cannot use byType autowiring for that bean. If there is none, nothing special happens. 4. "constructor" Analogous to "byType" for constructor arguments. If there is not exactly one bean of the constructor argument type in the bean factory, a fatal error is raised. Note that explicit dependencies, i.e. "property" and "constructor-arg" elements, always override autowiring. Note: This attribute will not be inherited by child bean definitions. Hence, it needs to be specified per concrete bean definition. It can be shared through the 'default-autowire' attribute at the 'beans' level and potentially inherited from outer 'beans' defaults in case of nested 'beans' sections (e.g. with different profiles). Data Type : stringDefault Value : defaultEnumerated Values : - default- no- byName- byType- constructor代码示例
1、no 方式
spring 配置文件，使用 ref 参数注入 bean，必须要有对象的 setter 方法，这里即Person 的 setFr 方法。
没有<property name="fr" ref="fr"></property> 因没有注入 fr 属性，会报空指针错误。
<?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.xsdhttp://www.springframework.org/schema/contexthttp://www.springframework.org/schema/context/spring-context.xsd"><bean id="person" class="constxiong.interview.assemble.Person" autowire="no"><property name="fr" ref="fr"></property></bean><bean id="fr" class="constxiong.interview.assemble.FishingRod"></bean></beans>鱼竿 bean
package constxiong.interview.assemble; /** * 鱼竿 * @author ConstXiong * @date 2019-07-17 09:53:15 */public class FishingRod { /** * 被使用 */public void used() {System.out.println("钓鱼...");}}人 bean
package constxiong.interview.assemble; /** * 人 * @author ConstXiong * @date 2019-07-17 09:54:56 */public class Person { private FishingRod fr;/** * 钓鱼 */public void fish() {fr.used();}public void setFr(FishingRod fr) {this.fr = fr;}}测试代码
package constxiong.interview.assemble; import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext; public class AssembleTest { public static void main(String[] args) {ApplicationContext context = new ClassPathXmlApplicationContext("spring_assemble.xml");Person person = (Person)context.getBean("person");person.fish();}}2、byName 也是需要相应的 setter 方法才能注入
修改 spring 配置文件autowire="byName"
<?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.xsdhttp://www.springframework.org/schema/contexthttp://www.springframework.org/schema/context/spring-context.xsd"><bean id="person" class="constxiong.interview.assemble.Person" autowire="byName"></bean><bean id="fr" class="constxiong.interview.assemble.FishingRod"></bean></beans>3、byType 也是需要相应的 setter 方法才能注入
修改 spring 配置文件autowire="byType"
<?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.xsdhttp://www.springframework.org/schema/contexthttp://www.springframework.org/schema/context/spring-context.xsd"><bean id="person" class="constxiong.interview.assemble.Person" autowire="byType"></bean><bean id="fr" class="constxiong.interview.assemble.FishingRod"></bean></beans>其他不变
4、constructor 无需 setter 方法，需要通过 构造方法注入 bean
修改 spring 配置文件autowire="byType"
Person 类去除 setFr 方法，添加构造方法设置 fr 属性
<?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.xsdhttp://www.springframework.org/schema/contexthttp://www.springframework.org/schema/context/spring-context.xsd"><bean id="person" class="constxiong.interview.assemble.Person" autowire="constructor"></bean><bean id="fr" class="constxiong.interview.assemble.FishingRod"></bean></beans>package constxiong.interview.assemble; /** * 人 * @author ConstXiong * @date 2019-07-17 09:54:56 */public class Person { private FishingRod fr;public Person(FishingRod fr) {this.fr = fr;}/** * 钓鱼 */public void fish() {fr.used();}}1、2、3、4 的测试结果一致，打印
钓鱼...
