@Primary注解

梦里梦外; 2024-03-23 16:32 60阅读 0赞

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");
        }
    }