spring学习（官网）——解决spring有多个匹配bean产生的冲突

来源：互联网发布：生日邀请函制作软件编辑：程序博客网时间：2024/04/19 16:52

1：使用@Primary注解微调：

通过类型自动匹配可能会导致多个候选对象，在选择过程中有更多限制是必须的，一种方式是使用spring 的@Primary注解实现，当一个单值的依赖有多个候选的bean时，@Primary注解指示给予一个优先的bean。如果在所有候选的bean中只有一个是primary的，这个bean将会被匹配。

@Configurationpublic class MovieConfiguration {    @Bean    @Primary    public MovieCatalog firstMovieCatalog() { ... }    @Bean    public MovieCatalog secondMovieCatalog() { ... }    // ...}

public class MovieRecommender {    @Autowired    private MovieCatalog movieCatalog;    // ...}

MovieRecommender将会被匹配为firstMovieCatalog。相应的bean定义：

<?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.xsd        http://www.springframework.org/schema/context        http://www.springframework.org/schema/context/spring-context.xsd">    <context:annotation-config/>    <bean class="example.SimpleMovieCatalog" primary="true">        <!-- inject any dependencies required by this bean -->    </bean>    <bean class="example.SimpleMovieCatalog">        <!-- inject any dependencies required by this bean -->    </bean>    <bean id="movieRecommender" class="example.MovieRecommender"/></beans>

基于注解的可以在类上使用@Component @Service等注解注册bean，然后在优先的类上添加@Primary注解；

当在选择处理上有更多限制，可以使用spring @Qualifier注解，你可以使用给定的参数关联qualifier值，

public class MovieRecommender {    @Autowired    @Qualifier("main")    private MovieCatalog movieCatalog;    // ...}

@Qualifier注解也可以在构造器参数和方法参数上指定：

public class MovieRecommender {    private MovieCatalog movieCatalog;    private CustomerPreferenceDao customerPreferenceDao;    @Autowired    public void prepare(@Qualifier("main")MovieCatalog movieCatalog,            CustomerPreferenceDao customerPreferenceDao) {        this.movieCatalog = movieCatalog;        this.customerPreferenceDao = customerPreferenceDao;    }    // ...}

相应的bean定义，构造器参数Qualifier值和bean的Qualifier值一致的话，对应bean将被匹配：

<?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.xsd        http://www.springframework.org/schema/context        http://www.springframework.org/schema/context/spring-context.xsd">    <context:annotation-config/>    <bean class="example.SimpleMovieCatalog">        <qualifier value="main"/>        <!-- inject any dependencies required by this bean -->    </bean>    <bean class="example.SimpleMovieCatalog">        <qualifier value="action"/>        <!-- inject any dependencies required by this bean -->    </bean>    <bean id="movieRecommender" class="example.MovieRecommender"/></beans>

CustomAutowireConfigurer是一个BeanFactoryPostProcessor允许你注册自定义的qualifier类型，即使他们没有被spring的@Qualifier注解标识。

<bean id="customAutowireConfigurer"        class="org.springframework.beans.factory.annotation.CustomAutowireConfigurer">    <property name="customQualifierTypes">        <set>            <value>example.CustomQualifier</value>        </set>    </property></bean>

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