【Spring Boot架构】条件注解@Conditional的使用

  Spring Boot 是根据配置文件中的内容，决定是否创建 bean，以及如何创建 bean 到 Spring 容器中，而 Spring boot 自动化配置的核心控制，就是 @Conditional 注解。

1、新建EncodingConverter接口，以及两个实现类。

public interface EncodingConverter {
}

public class GBKEncodingConverter implements EncodingConverter {
}

public class UTF8EncodingConverter implements EncodingConverter {
}

2、GBKCondition类

public class GBKCondition implements Condition {
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        String encoding = System.getProperty("file.encoding");
        if ("gbk".equals(encoding.toLowerCase())) {
            return true;
        }
        return false;
    }
}

3、UTF8Condition类

public class UTF8Condition implements Condition {
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        String encoding = System.getProperty("file.encoding");
        if ("utf-8".equals(encoding.toLowerCase())) {
            return true;
        }
        return false;
    }
}

4、EncodingConverterConfig配置类

@SpringBootConfiguration
public class EncodingConverterConfig {

    @Bean
    @Conditional(UTF8Condition.class)
    public EncodingConverter createUTF8Converter() {
        return new UTF8EncodingConverter();
    }

    @Bean
    @Conditional(GBKCondition.class)
    public EncodingConverter createGBKConverter() {
        return new GBKEncodingConverter();
    }
}

5、BootConditionConfigApplication类

@SpringBootApplication
public class BootConditionConfigApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(BootConditionConfigApplication.class, args);
                
		//获取该接口所有实现类的Bean
        Map<String, EncodingConverter> beansOfType = context.getBeansOfType(EncodingConverter.class);
        System.out.println(beansOfType);
        System.out.println(System.getProperty("file.encoding"));

        context.close();
    }
}

6、控制台输出

{createUTF8Converter=com.boot.condition.bootconditionconfig.converter.UTF8EncodingConverter@263f04ca}
UTF-8