Spring中@Conditional註解的說明

@Conditional

它的作用是按照一定的條件進行判斷，滿足註解中的條件就給容器註冊bean。其他則不注入。這個註解既可以寫在方法上也可以寫在類上。這個註解被大量的使用在spring Boot中。

實現condition

1. 首先定義一個配置類

@Configuration
//定義在類上
@Conditional(WindowCondition.class)
public class MyConfig2 {
    @Bean("window")
    //定義在方法上
    @Conditional(WindowCondition.class)
    public Person person01(){
        return new Person("王五",50);
    }
    @Bean("linux")
     //定義在方法上
    @Conditional(LinuxCondition.class)
    public Person person02(){
        return new Person("linux",48);
    }
}

2. 寫兩個條件也就是condition類，這個類要實現condition接口，並且要重寫matches方法

public class LinuxCondition implements Condition {
    @Override
    public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) {
        Environment environment = conditionContext.getEnvironment();
        String property = environment.getProperty("os.name");
        if (property.toLowerCase().contains("linux")){
            return true;
        }
        return false;
    }
}

public class WindowCondition implements Condition {
    @Override
    public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) {
        Environment environment = conditionContext.getEnvironment();
        String property = environment.getProperty("os.name");
        if (property.toLowerCase().contains("window")){
            return true;
        }
        return false;
    }
}

3. 測試類

public class App {
    public static void main(String[] args) {

        //讀取註解
        ApplicationContext applicationContext1 = new AnnotationConfigApplicationContext(MyConfig.class);
        //打印出IOC容器中已經加載的組件
        String[] names=  applicationContext1.getBeanNamesForType(Person.class);
        for (String name:names){
           System.out.println(name);
        }
    }
}