@Conditional根据满足某一个特定的条件创建一个特定的Bean（基于条件的Bean的创建，即使用@Conditional注解）。

比方说，当一个jar包在一个类的路径下的时候，自动配置一个或多个Bean，或者只有某个Bean被创建才会去创建另外一个Bean。

通过实现Condition接口，并重写期matches方法来构造判断条件。若在windows系统洗运行程序，则输出列表命令dir,若在linux操作系统下运行程序，则输出命令为：ls.

1.判断条件定义

判断windows的条件

1 package ch2.conditional2; 2  3 //条件注解,并复写此类 4 import org.springframework.context.annotation.Condition; 5 //条件注解容器 6 import org.springframework.context.annotation.ConditionContext; 7 import org.springframework.core.type.AnnotatedTypeMetadata; 8  9 public class LinuxCondition implements Condition {10 11     @Override12     public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {13         // TODO Auto-generated method stub14         return context.getEnvironment().getProperty("os.name").contains("Linux");15     }16 17 }

判定linux的条件

1 package ch2.conditional2; 2  3 //条件注解接口类，复写metches 4 import org.springframework.context.annotation.Condition; 5 import org.springframework.context.annotation.ConditionContext; 6 import org.springframework.core.type.AnnotatedTypeMetadata; 7  8 public class WindowsCondition implements Condition { 9 10     @Override11     public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {12         // TODO Auto-generated method stub13         return context.getEnvironment().getProperty("os.name").contains("Windows");14     }15 16 }

 

2不同系统下的Bean类

1接口

1 package ch2.conditional2;2 3 public interface ListService {4 5     public String showListCmd();6 }

2windows下要创建的Bean类

1 package ch2.conditional2; 2  3 import ch2.conditional2.ListService; 4  5 public class WindowsListService implements ListService { 6  7     @Override 8     public String showListCmd() { 9         // TODO Auto-generated method stub10         return "dir";11     }12 13 }

3linux下要创建的Bean类

1 package ch2.conditional2; 2  3 import ch2.conditional2.ListService; 4  5 public class LinuxListService implements ListService { 6  7     @Override 8     public String showListCmd() { 9         // TODO Auto-generated method stub10         return "ls";11     }12 13 }

 

3配置类

package ch2.conditional2;//配置类声明import org.springframework.context.annotation.Configuration;//bean声明import org.springframework.context.annotation.Bean;//条件限制import org.springframework.context.annotation.Conditional;//声明为配置类@Configurationpublic class ConditionConfig {    //注解为Bean    @Bean    //注解条件判断    @Conditional(WindowsCondition.class)    public ListService windowsListService()    {        return new WindowsListService();    }        //注解为Bean    @Bean    //注解条件判断    @Conditional(LinuxCondition.class)    public ListService linuxListService()    {        return new LinuxListService();    }}

4运行

package ch2.conditional2;import org.springframework.context.annotation.AnnotationConfigApplicationContext;public class Main {    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") +                "系统的查看目录的命令是： " +                listService.showListCmd()                );        context.close();    }}

 

 

运行结果：Windows 10系统的查看目录的命令是： dir