spring常用注解-@Conditional条件注册bean

@Conditional可以根据代码中设置的条件装载不同的bean，比如说当一个接口有两个实现类时，我们要把这个接口交给Spring管理时通常会只选择实现其中一个实现类，这个时候我们总不能使用if-else吧，所以这个@Conditional的注解就出现了。

cat

public class Cat {
    public Cat(){
        System.out.println("this is cat");
    }
}

Dog

public class Dog {
    public  Dog(){
        System.out.println("容器加载Dog完成");
    }
}

windowsCondition控制类

public class WindowsCondition implements Condition {
    /**
     *
     * @param conditionContext: 判断条件能是用的上下文环境
     * @param annotatedTypeMetadata ：注解所在位置的注释信息
     * @return
     */
    @Override
    public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) {
        //获取IOC使用的BeanFactory
        ConfigurableListableBeanFactory beanFactory = conditionContext.getBeanFactory();
        //获取类加载器
        ClassLoader classLoader = conditionContext.getClassLoader();
        //获取系统环境
        Environment environment = conditionContext.getEnvironment();

        String osName = environment.getProperty("os.name");
        if(osName.contains("Windows")){
            return true;
        }
        return false;
    }

}

LinuxCondition控制类

public class LinuxCondition implements Condition {

    /**
     *
     * @param conditionContext: 判断条件能是用的上下文环境
     * @param annotatedTypeMetadata ：注解所在位置的注释信息
     * @return
     */
    @Override
    public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) {
        //获取IOC使用的BeanFactory
        ConfigurableListableBeanFactory beanFactory = conditionContext.getBeanFactory();
        //获取类加载器
        ClassLoader classLoader = conditionContext.getClassLoader();
        //获取系统环境
        Environment environment = conditionContext.getEnvironment();

        String osName = environment.getProperty("os.name");
        if(osName.contains("Linux")){
            return true;
        }
        return false;
    }
}

配置类

@Configuration
public class MainConfig {

    @Conditional(value = {WindowsCondition.class})
    @Bean
    public Dog dog(){
        return new Dog();
    }

    @Conditional(value = {LinuxCondition.class})
    @Bean
    public Cat cat(){
        return new Cat();
    }
}

测试类

public class ConfigurationTest {

    public static void main(String[] args) {
        ApplicationContext anno = new AnnotationConfigApplicationContext(MainConfig.class);
        System.out.println("容器加载完成");
        String os = anno.getEnvironment().getProperty("os.name");
        System.out.println("当前系统环境为："+os);
        String[] beans = anno.getBeanDefinitionNames();
        for ( String bean : beans) {
            System.out.println(os+">>>>>beanName:"+bean);
        }

    }

}

运行结果

windows运行结果

17:05:18.022 [main] DEBUG org.springframework.core.env.PropertySourcesPropertyResolver - Could not find key 'spring.liveBeansView.mbeanDomain' in any property source
容器加载完成
17:05:18.027 [main] DEBUG org.springframework.core.env.PropertySourcesPropertyResolver - Found key 'os.name' in PropertySource 'systemProperties' with value of type String
当前系统环境为：Windows 10
Windows 10>>>>>beanName:org.springframework.context.annotation.internalConfigurationAnnotationProcessor
Windows 10>>>>>beanName:org.springframework.context.annotation.internalAutowiredAnnotationProcessor
Windows 10>>>>>beanName:org.springframework.context.annotation.internalRequiredAnnotationProcessor
Windows 10>>>>>beanName:org.springframework.context.annotation.internalCommonAnnotationProcessor
Windows 10>>>>>beanName:org.springframework.context.event.internalEventListenerProcessor
Windows 10>>>>>beanName:org.springframework.context.event.internalEventListenerFactory
Windows 10>>>>>beanName:mainConfig
Windows 10>>>>>beanName:dog

Linux运行结果

17:05:18.022 [main] DEBUG org.springframework.core.env.PropertySourcesPropertyResolver - Could not find key 'spring.liveBeansView.mbeanDomain' in any property source
容器加载完成
17:05:18.027 [main] DEBUG org.springframework.core.env.PropertySourcesPropertyResolver - Found key 'os.name' in PropertySource 'systemProperties' with value of type String
当前系统环境为：Linux
Linux>>>>>beanName:org.springframework.context.annotation.internalConfigurationAnnotationProcessor
Linux>>>>>beanName:org.springframework.context.annotation.internalAutowiredAnnotationProcessor
Linux>>>>beanName:org.springframework.context.annotation.internalRequiredAnnotationProcessor
Linux>>>>>beanName:org.springframework.context.annotation.internalCommonAnnotationProcessor
Linux>>>>>beanName:org.springframework.context.event.internalEventListenerProcessor
Linux>>>>>beanName:org.springframework.context.event.internalEventListenerFactory
Linux>>>>>beanName:mainConfig
Linux>>>>>beanName:cat

从上面的运行结果来看我们通过@Condition注解中value的LinuxCondition和WindowsCondition两个类来控制cat和dao实例的加载，