Spring(十三)：Spring条件注解@Conditional

Spring提供了一个通用的基于条件来创建Bean的注解@Conditional注解。

通过实现Condition接口，并重写其matches方法来构造判断条件。

示例

条件：根据操作系统返回对应的内容。

1. 定义判断条件

    //Windows系统的判断条件
    import org.springframework.context.annotation.Condition;
    import org.springframework.context.annotation.ConditionContext;
    import org.springframework.core.type.AnnotatedTypeMetadata;
   
    public class WindowsCondition implements Condition {
   
        @Override
        public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
            return context.getEnvironment().getProperty("os.name").contains("Windows");
        }
    }
   
    //Linux系统的判断条件
    import org.springframework.context.annotation.Condition;
    import org.springframework.context.annotation.ConditionContext;
    import org.springframework.core.type.AnnotatedTypeMetadata;
   
    public class LinuxCondition implements Condition {
   
        @Override
        public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
            return context.getEnvironment().getProperty("os.name").contains("Linux");
        }
    }
   

2. 不同系统下的Bean类

    //接口
    public interface ListService {
   
        public String showListCmd();
    }
   
    //Windows下的实现类
    public class WindowsListServiceImpl implements ListService {
   
        @Override
        public String showListCmd() {
            return "dir";
        }
    }
   
    //Linux下的实现类
    public class LinuxListServiceImpl implements ListService {
   
        @Override
        public String showListCmd() {
            return "ls";
        }
    }
   

3. 配置类
   @Conditional()注解调用条件判断的类并根据返回的结果来创建Bean

    import org.springframework.context.annotation.Bean;
    import org.springframework.context.annotation.Conditional;
    import org.springframework.context.annotation.Configuration;
   
    @Configuration
    public class ConditionConfig {
   
        @Bean
        @Conditional(WindowsCondition.class)
        public ListService windowsListService() {
            return new WindowsListServiceImpl();
        }
   
        @Bean
        @Conditional(LinuxCondition.class)
        public ListService linuxListService() {
            return new LinuxListServiceImpl();
        }
    }
   

4. 运行类

    import org.springframework.context.annotation.AnnotationConfigApplicationContext;
   
    public class ConditionMain {
   
        public static void main(String[] args) {
            AnnotationConfigApplicationContext context = 
                    new AnnotationConfigApplicationContext(ConditionConfig.class);
   
            ListService listService = context.getBean(ListService.class);
            System.out.println(context.getEnvironment().getProperty("os.name")
                    + "系统下的列表命令："
                    + listService.showListCmd());
   
            //context.close();
        }
    }