當spring中管理兩個型別一樣的bean時，再進行注入時會報錯：

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)
 

看下面程式碼，@Primary表示當遇到系統中有兩個User型別時，優先使用@Primary註解的這個進行注入。

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);
    }



}
 

看下面測試程式碼：

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)  //一般在開發環境，不確定是否能注入時用
    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中有兩種注入方式，by type/by name，@Autowired使用byType注入，當出現兩個型別一樣的時候，可以顯示的用@Qualifier指定名稱，表明用by name方式進行注入。否則會注入@Primary那個類。如果沒有指定則會報錯。 當不確定系統中是否能注入時，可以使用required=false，不會強制注入。