@Conditional

条件装配：满足Conditional指定的条件，则进行组件注入
有很多派生出来的注解

我们举例使用ConditionalOnBean说明

import com.daijunyi.springboot1.bean.Person;
import com.daijunyi.springboot1.bean.User;
import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class MyConfig {
//    @Bean("user")
    public User user(){
        return new User();
    }
    @ConditionalOnBean(name = {"user"})//如果容器中有user 我们才生成bean
    @Bean
    public Person person(){
        return new Person();
    }
}

然后测试代码

package com.daijunyi.springboot1;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
@SpringBootApplication
public class SpringBoot1Application {
    public static void main(String[] args) {
        ConfigurableApplicationContext run = SpringApplication.run(SpringBoot1Application.class, args);
        boolean user = run.containsBean("user");
        System.out.println("是否存在user:"+user);
        boolean person = run.containsBean("person");
        System.out.println("是否存在 person:"+person);
    }
}

运行结果

是否存在user:false
是否存在 person:false
Process finished with exit code 0

发现person也不存在了

这个注解也可以加在类上面，这样会要条件成立整个类才会条件成立