通过@Conditional注解可以根据代码中设置的条件装载不同的bean，在设置条件注解之前，先要把装载的bean类去实现Condition接口，然后对该实现接口的类设置是否装载的条件。

1 配合@Bean注解

1.1 创建Bean对象

@Data
public class Person {
    private String name;
    private Integer age;

    public Person(String name, Integer age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public String toString() {
        return "Person{" + "name='" + name + '\'' + ", age=" + age + '}';
    }
}

1.2 实现Condition接口

这里根据系统环境来决定是否注入Bean。

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.contains("Linux")){
            return true;
        }
        return false;
    }
}

public class WindowsCondition implements Condition {
    /**
     * @param conditionContext:判断条件能使用的上下文环境
     * @param annotatedTypeMetadata:注解所在位置的注释信息
     * */
    @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();
        //获取当前环境信息
        Environment environment = conditionContext.getEnvironment();
        //获取bean定义的注册类
        BeanDefinitionRegistry registry = conditionContext.getRegistry();

        //获得当前系统名
        String property = environment.getProperty("os.name");
        //包含Windows则说明是windows系统，返回true
        if (property.contains("Windows")){
            return true;
        }
        return false;
    }
}

1.3 使用@Conditional注解

@Configuration
@ComponentScan("com.test")
@Scope("prototype")
public class AppConfig {

    @Bean(name = "Windows")
    @Conditional({WindowsCondition.class})
    public Person person1(){
        return new Person("Windows",62);
    }

    @Bean("Linux")
    @Conditional({LinuxCondition.class})
    public Person person2(){
        return new Person("Linux",48);
    }
}

这样在Linux环境中调用person2就会提示错误。

2 配合@Component实现根据yml配置，加载不同的实现

2.1 定义接口

public interface ReceiveAnnouncementService {
    /** 
     * @description 接收信息
     * @param  
     * @return String 
     */
    String receiveAnnouncement();
}

2.2 定义多个实现和对应的Condition

在每个Condition中根据yml的配置来确定是否将该实例注册到Spring容器中。

• 通过MQ方式

public class ReceiveAnnouncementByMQCondition implements Condition {
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        Environment environment = context.getEnvironment();
        String property = environment.getProperty("receive-type");
        return Constants.RECEIVE_TYPE_MQ.equals(property);
    }
}

@Component
@Conditional({ReceiveAnnouncementByMQCondition.class})
@Slf4j
public class ReceiveAnnouncementServiceByMQImpl implements ReceiveAnnouncementService {
    @Override
    public String receiveAnnouncement() {
        log.info("使用MQ接收消息")
        return null;
    }
}

• 通过MYSQL方式

public class ReceiveAnnouncementByMySQLCondition implements Condition {
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        Environment environment = context.getEnvironment();
        String property = environment.getProperty("receive-type");
        return Constants.RECEIVE_TYPE_MYSQL.equals(property);
    }
}

@Component
@Conditional({ReceiveAnnouncementByMySQLCondition.class})
@Slf4j
public class ReceiveAnnouncementServiceByMySQLImpl implements ReceiveAnnouncementService {
    @Override
    public String receiveAnnouncement() {
        log.info("使用MySQL接收消息")
        return null;
    }
}

• yml文件

receive-type: MQ

• 调用类
  这里使用时，会直接根据yml中的配置获取到具体的receiveService

@Component
@EnableScheduling
@EnableAsync
@Slf4j
public class MultiThreadScheduleAnalyseTask {
    @Autowired
    private ReceiveAnnouncementService receiveService;

    @Scheduled(cron = "0/5 * * * * ?")
    @Async
    public void receiveAnnouncement() {
        String msg= receiveService.receiveAnnouncement();
    }