spring中少用的注解@primary解析

这次看下spring中少见的注解@primary注解，例子

@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

以上报错因为根据bean的值找到对应两个类导致冲突；如果某个@component("singer") ,spring就能默认找到bean名称，而确定注入哪一个实现类

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;
}
}

巴特西

spring中少用的注解@primary解析

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