@Primary注解

在看项目的时候看到了@Primary,因为之前没留意过，所以就去学习了一下，在此记录一下自己的理解，感叹一下还要学习的东西太多了，慢慢加油。

1.概述

 @Primary的作用就是当有多个相同类型的bean时，使用@Primary来赋予bean更高的优先级。
 比如Spring IOC容器中有多个相同类型的bean时，当要注入该类型的bean，就可以用@Primary来标注注入bean的优先，优先级高的bean先被注入。

2.具体案例

@Configuration
public class Config{
    
    
    @Bean
    public People people1() {
    
    
        return new People ("用户1");
    }

    @Bean
    public People people2() {
    
    
        return new People ("用户2");
    }
}
	//如果尝试运行应用程序，与@Autowired一起应用于注入。
public class Service{
    
    
	@Autowired
	private People p;
	//Spring会抛出NoUniqueBeanDefinitionException。
	public void use(){
    
    
		System.out.println(p.speak());
	}
}

3.解决办法

	1.使用@Qualifier(“beanName”)注解

@Component
@Qualifier("people1 ")
public class People1 implements People{
    
    
 
    @Override
    public String speaking(String content) {
    
    
        return "People1 Speaking: "+content;
    }
}
 
@Component
@Qualifier("people2")
public class People2 implements People{
    
    
    @Override
    public String speaking(String content) {
    
    
        return "People2 Speaking: "+content;
    }

//使用
@Component
public class Service{
    
    
    @Autowired
    @Qualifier("prople1")
    private People p;
 
    public String speaking(){
    
    
        return p.speak("how are you");
    }
 }

	2.使用@Primary注解

@Component
public class People1 implements People{
    
    
 
    @Override
    public String speaking(String content) {
    
    
        return "People1 Speaking: "+content;
    }
}
 
@Component
@Primary
public class People2 implements People{
    
    
    @Override
    public String speaking(String content) {
    
    
        return "People2 Speaking: "+content;
    }

//@Primary与@Component使用
@Component
public class Service{
    
    
    @Autowired
    private People p;
 
    public String speaking(){
    
    
        return p.speak("how are you");
    }

 }
 //@Primary与@Bean使用
@Configuration
public class Config{
    
    
    @Bean
    public People people1() {
    
    
        return new People ("hello,我是people1");
    }

    @Bean
    @Primary
    public People people2() {
    
    
        return new People ("hello,我是people2");
    }
}