Spring(十三)： Spring 条件注解 @Conditional

Spring 提供了一个通用的基于条件来创建Bean的注解@Conditional注解。

通过实现Condition接口，并重写其matches方法来构造判断条件。

例如，根据操作系统返回对应的内容。

1. 定义判断条件

例如，根据操作系统返回对应的内容。

//Windows系统的判断条件
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) {
		return context.getEnvironment().getProperty("os.name").contains("Windows");
	}
}


//Linux系统的判断条件
import org.springframework.context.annotation.Condition;
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) {
		return context.getEnvironment().getProperty("os.name").contains("Linux");
	}
}

2. 不同系统下的Bean类

//接口
public interface ListService {
	
	public String showListCmd();
}

//Windows下的实现类
public class WindowsListServiceImpl implements ListService {

	@Override
	public String showListCmd() {
		return "dir";
	}
}

//Linux下的实现类
public class LinuxListServiceImpl implements ListService {

	@Override
	public String showListCmd() {
		return "ls";
	}
}

3. 定义配置类 Bean

**@Conditional()**注解调用条件判断的类并根据返回的结果来创建Bean

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

@Configuration
public class ConditionConfig {
	
	@Bean
	@Conditional(WindowsCondition.class)
	public ListService windowsListService() {
		return new WindowsListServiceImpl();
	}
	
	@Bean
	@Conditional(LinuxCondition.class)
	public ListService linuxListService() {
		return new LinuxListServiceImpl();
	}
}

4. 注解生效使用

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class ConditionMain {
	
	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："
				+ listService.showListCmd());
		
		//context.close();
	}
}