spring boot: 條件注解@Condition

@Conditional根據滿足某一個特定的條件創建一個特定的Bean（基於條件的Bean的創建，即使用@Conditional注解）。

比方說，當一個jar包在一個類的路徑下的時候，自動配置一個或多個Bean，或者只有某個Bean被創建才會去創建另外一個Bean。

通過實現Condition接口，並重寫期matches方法來構造判斷條件。若在windows系統洗運行程序，則輸出列表命令dir,若在linux操作系統下運行程序，則輸出命令為：ls.

1.判斷條件定義

判斷windows的條件

package ch2.conditional2;

//條件注解,並復寫此類
import org.springframework.context.annotation.Condition;
//條件注解容器
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) {
        // TODO Auto-generated method stub
        return context.getEnvironment().getProperty("os.name").contains("Linux");
    }

}

判定linux的條件

package ch2.conditional2;

//條件注解接口類，復寫metches
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) {
        // TODO Auto-generated method stub
        return context.getEnvironment().getProperty("os.name").contains("Windows");
    }

}

 

2不同系統下的Bean類

1接口

package ch2.conditional2;

public interface ListService {

    public String showListCmd();
}

2windows下要創建的Bean類

package ch2.conditional2;

import ch2.conditional2.ListService;

public class WindowsListService implements ListService {

    @Override
    public String showListCmd() {
        // TODO Auto-generated method stub
        return "dir";
    }

}

3linux下要創建的Bean類

package ch2.conditional2;

import ch2.conditional2.ListService;

public class LinuxListService implements ListService {

    @Override
    public String showListCmd() {
        // TODO Auto-generated method stub
        return "ls";
    }

}

 

3配置類

package ch2.conditional2;

//配置類聲明
import org.springframework.context.annotation.Configuration;
//bean聲明
import org.springframework.context.annotation.Bean;
//條件限制
import org.springframework.context.annotation.Conditional;

//聲明為配置類
@Configuration
public class ConditionConfig {

    //注解為Bean
    @Bean
    //注解條件判斷
    @Conditional(WindowsCondition.class)
    public ListService windowsListService()
    {
        return new WindowsListService();
    }
    
    //注解為Bean
    @Bean
    //注解條件判斷
    @Conditional(LinuxCondition.class)
    public ListService linuxListService()
    {
        return new LinuxListService();
    }
}

4運行

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") +
                "系統的查看目錄的命令是： " +
                listService.showListCmd()
                );
        context.close();
    }
}

 

 

運行結果：Windows 10系統的查看目錄的命令是： dir