Spring --@Primary注解-蒲公英云

Spring --@Primary注解

我就是我 2022-03-09 13:58 378阅读 0赞

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

以下是一个例子：

package cn.myframe.test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Primary;
import org.springframework.stereotype.Component;
@Primary
@Component("metalSinger") // 加注解，让spring识别
 class MetalSinger implements Singer{ 
    @Override
    public String sing(String lyrics) { 
        return "I am singing with DIO voice: "+lyrics;
    }
}
@Component("operaSinger")
 class OperaSinger implements Singer { 
    @Override
    public String sing(String lyrics) { 
        return "I am singing in Bocelli voice: "+lyrics;
    }
}
 interface Singer { 
    String sing(String lyrics);
}
@Component
public class SingerService { 
    @Autowired
// @Qualifier("metalSinger")
    private Singer singer;
    public String sing(){ 
        return singer.sing("song lyrics");
    }
    public static void main(String[] args) { 
        ApplicationContext context = new AnnotationConfigApplicationContext("cn.myframe.test");
        SingerService singerService = context.getBean(SingerService.class);
        System.out.println(singerService.sing());
    }
}