spring @primary注解_springprimary-优快云博客

本文通过实例解析了Spring框架中@Primary注解的作用，当存在多个相同类型的Bean时，该注解用于指定默认注入的Bean，避免了NoUniqueBeanDefinitionException异常。通过对比OperaSinger和MetalSinger两个Singer接口实现类，阐述了如何使用@Primary注解解决依赖注入冲突。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

spring中少见的注解@primary注解，例子

文章引自：http://jackyrong.iteye.com/blog/2208000
@Component
public class MetalSinger implements Singer{

@Override  
public String sing(String lyrics) {  
    return "I am singing with DIO voice: "+lyrics;  
}

}

public class OperaSinger implements Singer {
@Override
public String sing(String lyrics) {
return "I am singing in Bocelli voice: "+lyrics;
}
}

这两个类都实现了singer接口

public interface Singer {
String sing(String lyrics);
}

那么来个注入的：

@Component
public class SingerService {
private static final Logger logger = LoggerFactory.getLogger(SingerService.class);

@Autowired  
private Singer singer;  

public String sing(){  
    return singer.sing("song lyrics");  
}

}

那么最后输出应该是：I am singing with DIO voice: song lyrics.

原因是只有MetalSinger使用了注解@component，那么autowird会只寻找这个标记的
进行注入:
如果也在OperaSinger 中使用了注解，则spring会报异常，不知道到底应该用
哪个：
org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type [main.service.Singer] is defined: expected single matching bean but found 2: metalSinger,operaSinger
而如果要让spring知道必须注入的是OperaSinger ，则可以用@primary注解告诉
spring:

@Primary
@Component
public class OperaSinger implements Singer{

@Override  
public String sing(String lyrics) {  
    return "I am singing in Bocelli voice: "+lyrics;  
}

}