spring @conditional注解的使用

@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