@Conditional根据满足某一个条件创建一个特定的Bean。比如说当一个jar包在一个类路径下时，自动配置一个或多个Bean，或者只有某个Bean被创建时才会创建另一个Bean。Spring Boot中将大量使用到进行一些自动配置。

以下示例根据不同操作系统作为条件，实现condition接口重写matches方法判断条件，若在windows下运行则输出列表命令dir，若在linux下则输出ls。

windows判断条件类

import org.springframework.context.annotation.Condition;import org.springframework.context.annotation.ConditionContext;import org.springframework.core.type.AnnotatedTypeMetadata;/** * @author Kevin * @description * @date 2016/7/1 */public class WindowsCondition implements Condition {    @Override    public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) {        return conditionContext.getEnvironment().getProperty("os.name").contains("Windows");    }}

linux判断条件

import org.springframework.context.annotation.Condition;import org.springframework.context.annotation.ConditionContext;import org.springframework.core.type.AnnotatedTypeMetadata;/** * @author Kevin * @description * @date 2016/7/1 */public class LinuxCondition implements Condition {    @Override    public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) {        return conditionContext.getEnvironment().getProperty("os.name").contains("Linux");    }}

命令接口

/** * @author Kevin * @description * @date 2016/7/1 */public interface ListService {    public String showListCmd();}

windows条件下创建的Bean类

/** * @author Kevin * @description * @date 2016/7/1 */public class WindowsListService implements ListService {    @Override    public String showListCmd() {        return "dir";    }}

linux条件下创建的Bean类

/** * @author Kevin * @description * @date 2016/7/1 */public class LinuxListService implements ListService {    @Override    public String showListCmd() {        return "ls";    }}

配置类

import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.ComponentScan;import org.springframework.context.annotation.Conditional;import org.springframework.context.annotation.Configuration;/** * @author Kevin * @description * @date 2016/7/1 */@Configuration@ComponentScan("ch03.condition")public class ConditionConfig {    @Bean    // 通过该注解，符合WindowsCondition条件则实例化    @Conditional(WindowsCondition.class)    public ListService windowsListService() {        return new WindowsListService();    }    @Bean    @Conditional(LinuxCondition.class)    public ListService linuxListService() {        return new LinuxListService();    }}

运行

import org.springframework.context.annotation.AnnotationConfigApplicationContext;/** * @author Kevin * @description * @date 2016/7/1 */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") + "系统下列表命令为：" + listService.showListCmd());        context.close();    }}

结果