Spring conditional相关注解的学习

前言

最近在看SpringCloud loadbalancer的源码，发现里面用到了很多@contional的注解，还有其很多衍生注解例如@ConditionalOnBean、@ConditionalOnMissingBean等注解，发现我不太熟悉，那么就来学习一下把。

@Conditional注解

@Conditional是Spring 4新提供的注解，它的作用是按照一定的条件进行判断，满足条件的容器进行bean注册。它作用于类和方法上，需要传入一个实现了condition接口的class数组

代码示例

创建一个Condition接口的实现类，判断是否为Windows系统

public class OSCondition implements Condition{

    private static final Logger log = LoggerFactory.getLogger(OSCondition.class);


    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        return context.getEnvironment().getProperty("os.name").contains("Windows");
    }
}


public class OsServiceImpl {

    private static final Logger log = LoggerFactory.getLogger(OsServiceImpl.class);


    public OsServiceImpl() {
        log.info("{}被创建",System.getProperty("os.name"));
    }
}



@SpringBootApplication
public class Example01Application {

	public static void main(String[] args) {
		SpringApplication.run(Example01Application.class, args);
	}

	@Conditional(OSCondition.class)
	@Bean
	public OsServiceImpl osService(){
		return new OsServiceImpl();
	}



}