Spring条件注解@Conditional

@Conditional 基于条件的Bean的创建，根据满足某一个特定条件创建特定的Bean，通过实现Condition接口，并重写matches接口来构造判断条件。

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下面的实例通过将以不同操作系统作为条件，我们将通过实现Condition接口，并重写其matchess方法来构造判断条件。若在Windows系统下运行程序，则输出列表命令为dir；若在Linux操作系统下运行程序，则输出列表命令为ls
1、判断条件定义
（1）判断Windows的条件

package com.lwh.highlight_spring4.ch3.conditional;

/**
 * Created by luwenhu on 2017/9/20.
 */

import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.type.AnnotatedTypeMetadata;

/**
 * @Conditional 基于条件的Bean的创建，根据满足某一个特定条件创建特定的Bean
 * 通过实现Condition接口，并重写matches接口来构造判断条件
 */
public class WindowsCondition implements Condition{

    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        //是否是在Windows系统下运行程序
        return context.getEnvironment().getProperty("os.name").contains("Windows");
    }
}

（2）判定Linux的条件

package com.lwh.highlight_spring4.ch3.conditional;

import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.type.AnnotatedTypeMetadata;

/**
 * Created by luwenhu on 2017/9/20.
 */
public class LinuxCondition implements Condition{
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        //判断是否在Linux环境下运行程序
        return context.getEnvironment().getProperty("os.name").contains("Linux");
    }
}

 2、不同系统下的Bean的类

（1）接口

package com.lwh.highlight_spring4.ch3.conditional;

/**
 * Created by luwenhu on 2017/9/20.
 */
//不同系统下Bean的类的接口
public interface ListService {
    public String showListCmd();
}

（2）Windows下所要创建的Bean的类

package com.lwh.highlight_spring4.ch3.conditional;

/**
 * Created by luwenhu on 2017/9/20.
 */
//Windows下面所要创建的Bean类
public class WindowsListService implements ListService{
    @Override
    public String showListCmd() {
        return "dir";
    }
}

（3）Linux下所要创建的Bean的类

package com.lwh.highlight_spring4.ch3.conditional;

/**
 * Created by luwenhu on 2017/9/20.
 */
//Linux下所要创建的Bean的类
public class LinuxListService implements ListService{
    @Override
    public String showListCmd() {
        return "ls";
    }
}

3、配置类

package com.lwh.highlight_spring4.ch3.conditional;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;

/**
 * Created by luwenhu on 2017/9/20.
 */
@Configuration
public class ConditionConfig {

    @Bean
    //使用@Conditional注解，符合Windows条件则实例化windowsListService
    @Conditional(WindowsCondition.class)
    public WindowsListService windowsListService(){
        return new WindowsListService();
    }

    @Bean
    //使用@Conditional注解，符合Linux条件则实例化linuxListService
    @Conditional(LinuxCondition.class)
    public LinuxListService linuxListService(){
        return new LinuxListService();
    }


}

4、运行

package com.lwh.highlight_spring4.ch3.conditional;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

/**
 * Created by luwenhu on 2017/9/20.
 */
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")+"系统下的列表命令为："+listService.showListCmd());
    }
}

运行结果：