spring笔记-@Primary注解

1.问题

当一个接口有2个不同实现时,使用@Autowired注解时会报org.springframework.beans.factory.NoUniqueBeanDefinitionException异常信息

2.方案1-@Qualifier

使用Qualifier注解，选择一个对象的名称,通常比较常用

3. 方案2-@Primary

Primary可以理解为默认优先选择,同时不可以同时设置多个,
内部实质是设置BeanDefinition的primary属性

示例

@Component("metalSinger") // 加注解，让spring识别
public class MetalSinger implements Singer{

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

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

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

@Component
public class SingerService {
    private static final Logger logger = LoggerFactory.getLogger(SingerService.class);
    @Autowired
    @Qualifier
    private Singer singer;
    public String sing(){
        return singer.sing("song lyrics");
    }

    public static void main(String[] args) {

        ApplicationContext context = new AnnotationConfigApplicationContext("context.annotation.primary");
        SingerService singerService = context.getBean(SingerService.class);
        System.out.println(singerService.sing());
    }

}