Spring 条件注解 @Conditional-优快云博客

本文介绍如何使用Spring的@Conditional注解，在不同操作系统环境下选择性地创建相应的Bean。通过实现Condition接口并重写matches方法，可以实现在Windows下创建显示'dir'命令的Bean，在Linux下创建显示'll'命令的Bean。

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Spring 4提供了一个更通用的基于条件的Bean的创建方式，即使用@Conditional注解。

下面的示例将以不同的操作系统作为条件，我们将通过实现Condition接口，并重写其matches方法来构造判断条件。如在Windows系统下运行程序输出dir，Linux下输出ls。

一、不同系统下的Bean

1、声明接口

package cn.wuweixiang.springbootdemo.service;

/**
 * ListService
 *
 * @author weixiang.wu
 * @date 2018 -08-22 15:39
 */
public interface ListService {
	/**
	 * Show list cmd string.
	 *
	 * @return the string
	 */
	String showListCmd();
}

2、Windows下所要创建的Bean

package cn.wuweixiang.springbootdemo.service.impl;

import cn.wuweixiang.springbootdemo.service.ListService;

/**
 * WindowsListServiceImpl
 *
 * @author weixiang.wu
 * @date 2018-08-22 15:40
 **/
public class WindowsListServiceImpl implements ListService {
	@Override
	public String showListCmd() {
		return "dir";
	}
}

3、Linux下所要创建的Bean

package cn.wuweixiang.springbootdemo.service.impl;

import cn.wuweixiang.springbootdemo.service.ListService;

/**
 * LinuxListServiceImpl
 *
 * @author weixiang.wu
 * @date 2018-08-22 15:42
 **/
public class LinuxListServiceImpl implements ListService {
	@Override
	public String showListCmd() {
		return "ll";
	}
}

二、判断条件定义

package cn.wuweixiang.springbootdemo.condition;

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

import java.util.Objects;

/**
 * ConditionalConfig
 *
 * @author weixiang.wu
 * @date 2018-08-22 15:55
 **/
public class LinuxCondition implements Condition {


	@Override
	public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
		return Objects.requireNonNull(context.getEnvironment().getProperty("os.name")).contains("Linux");
	}
}

package cn.wuweixiang.springbootdemo.condition;

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

import java.util.Objects;

/**
 * ConditionalConfig
 *
 * @author weixiang.wu
 * @date 2018-08-22 15:55
 **/
public class WindowsCondition implements Condition {


	@Override
	public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
		return Objects.requireNonNull(context.getEnvironment().getProperty("os.name")).contains("Windows");
	}
}

三、配置类

package cn.wuweixiang.springbootdemo.config;

import cn.wuweixiang.springbootdemo.condition.LinuxCondition;
import cn.wuweixiang.springbootdemo.condition.WindowsCondition;
import cn.wuweixiang.springbootdemo.service.ListService;
import cn.wuweixiang.springbootdemo.service.impl.LinuxListServiceImpl;
import cn.wuweixiang.springbootdemo.service.impl.WindowsListServiceImpl;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Conditional;

/**
 * ConditionalConfig
 *
 * @author weixiang.wu
 * @date 2018 -08-22 15:55
 */
public class ConditionalConfig {

	/**
	 * 使用@Conditional注解，符合Linux条件就实例化LinuxListService
	 *
	 * @return the list service
	 */
	@Bean
	@Conditional(LinuxCondition.class)
	public ListService linuxListService() {
		return new LinuxListServiceImpl();
	}

	/**
	 * 使用@Conditional注解，符合Windows条件就实例化WindowsListService
	 *
	 * @return the list service
	 */
	@Bean
	@Conditional(WindowsCondition.class)
	public ListService windowsListService() {
		return new WindowsListServiceImpl();
	}

}

四、测试类

package cn.wuweixiang.springbootdemo;

import cn.wuweixiang.springbootdemo.config.ConditionalConfig;
import cn.wuweixiang.springbootdemo.service.ListService;
import org.junit.After;
import org.junit.Test;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

/**
 * SpringConditionalTest
 *
 * @author weixiang.wu
 * @date 2018-08-22 16:00
 **/
public class SpringConditionalTest {

	AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(ConditionalConfig.class);

	@Test
	public void contextTest() {
		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());
	}

	@After
	public void closeContext() {
		context.close();
	}

}

转载于:https://my.oschina.net/wuweixiang/blog/1932216