本文主要是介绍spring中少用的注解@primary解析，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
这次看下spring中少见的注解@primary注解，例子Java代码 
- @Component
- public class MetalSinger implements Singer{
- @Override
- public String sing(String lyrics) {
- return "I am singing with DIO voice: "+lyrics;
- }
- }
Java代码
- 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
Java代码
- public interface Singer {
- String sing(String lyrics);
- }
那么来个注入的：
Java代码
- @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:
Java代码
- @Primary
- @Component
- public class OperaSinger implements Singer{
- @Override
- public String sing(String lyrics) {
- return "I am singing in Bocelli voice: "+lyrics;
- }
- }
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