Spring 4提供了一個更通用的基于條件的Bean的創建方式，即使用@Conditional注解。

下面的示例將以不同的操作系統作為條件，我們將通過實現Condition接口，并重寫其matches方法來構造判斷條件。如在Windows系統下運行程序輸出dir，Linux下輸出ls。

一、不同系統下的Bean

1、聲明接口

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下所要創建的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下所要創建的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、判斷條件定義

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、配置類

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條件就實例化LinuxListService

*

* @return the list service

*/

@Bean

@Conditional(LinuxCondition.class)

public ListService linuxListService() {

return new LinuxListServiceImpl();

}

/**

* 使用@Conditional注解，符合Windows條件就實例化WindowsListService

*

* @return the list service

*/

@Bean

@Conditional(WindowsCondition.class)

public ListService windowsListService() {

return new WindowsListServiceImpl();

}

}

四、測試類

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")

+ "系統下的列表命令為："

+ listService.showListCmd());

}

@After

public void closeContext() {

context.close();

}

}

轉載至鏈接:https://my.oschina.net/wuweixiang/blog/1932216

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