spring @Primary @Autowired @Qualifier注解

一时失言乱红尘 2022-05-09 00:14 217阅读 0赞

当spring中管理两个类型一样的bean时，再进行注入时会报错：

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'com.xhx.spring.Spring5AutowiredQualifierApplicationTests': Unsatisfied dependency expressed through field 'user3'; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.xhx.spring.domain.User' available: expected single matching bean but found 2: user1,getUser2
    
    	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:586)
    	at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:90)

看下面代码，@Primary表示当遇到系统中有两个User类型时，优先使用@Primary注解的这个进行注入。

package com.xhx.spring.config;
    
    import com.xhx.spring.domain.User;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.context.annotation.Bean;
    import org.springframework.context.annotation.Configuration;
    import org.springframework.context.annotation.Primary;
    
    @Configuration
    public class UserConfig {
    
    
        @Bean(name = "user1")
        public User getUser1(){
            return new User("a23-fsa-ef","xu",25);
        }
    
        @Primary
        @Bean(name = "user2")
        public User user2(){
            return new User("brr-dfa-874","haixing",25);
        }
    
    
    
    }

看下面测试代码：

package com.xhx.spring;
    
    import com.xhx.spring.domain.User;
    import org.junit.Test;
    import org.junit.runner.RunWith;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.beans.factory.annotation.Qualifier;
    import org.springframework.boot.test.context.SpringBootTest;
    import org.springframework.test.context.junit4.SpringRunner;
    
    @RunWith(SpringRunner.class)
    @SpringBootTest
    public class Spring5AutowiredQualifierApplicationTests {
    
        @Autowired(required = false)  //一般在开发环境，不确定是否能注入时用
        private User user1;
    
        @Autowired
        @Qualifier(value = "user1")
        private User user2;
    
        @Autowired
        private User user3;
    
        @Test
        public void testAuto() {
            System.out.println(user2.getName());
            System.out.println(user1.getName());
            System.out.println(user3.getName());
        }
    
    }

@Autowired：spring中有两种注入方式，by type/by name，@Autowired使用byType注入，当出现两个类型一样的时候，可以显示的用@Qualifier指定名称，表明用by name方式进行注入。否则会注入@Primary那个类。如果没有指定则会报错。 当不确定系统中是否能注入时，可以使用required=false，不会强制注入。

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