今天看了@Conditional,自己根据以下文章练了下，根据自己的理解操作的

转载出处:http://wiselyman.iteye.com/blog/2213054

17.1 @Conditional

@Conditional为按照条件配置spring的bean提供了支持,即满足某种条件下,怎么配置对应的bean;

应用场景

当某一个jar包在classpath中的时候,配置某几个bean;

当某一个bean配置好后,会自动配置一个特定的bean;

当某种环境变量被设置后,创建某个bean;

@Conditional为敏捷开发所提倡的原则"习惯优于配置"提供了支持;

@Conditional是Spring Boot快速开发框架实现"习惯优于配置"的核心技术;

17.2 示例

演示在windows和linux系统下,初始化不同的bean,windows和linux作为判断条件;

17.2.1 构造判断条件

条件的构造需要类实现Condition接口,并实现matches方法

WindowsCondition

packagecom.wisely.conditional;importorg.springframework.context.annotation.Condition;importorg.springframework.context.annotation.ConditionContext;importorg.springframework.core.type.AnnotatedTypeMetadata;publicclassWindowsConditionimplementsCondition{publicbooleanmatches(ConditionContextcontext,AnnotatedTypeMetadatametadata) {returncontext.getEnvironment().getProperty("os.name").contains("Windows");    }}

LinuxCondition

packagecom.wisely.conditional;importorg.springframework.context.annotation.Condition;importorg.springframework.context.annotation.ConditionContext;importorg.springframework.core.type.AnnotatedTypeMetadata;publicclassLinuxConditionimplementsCondition{publicbooleanmatches(ConditionContextcontext,AnnotatedTypeMetadatametadata) {returncontext.getEnvironment().getProperty("os.name").contains("Linux");    }}

17.2.2 编写不同条件下需要的bean

接口

packagecom.wisely.conditional;publicinterfaceCommandService{publicStringshowListCommand();}

WindowsCommnadService

packagecom.wisely.conditional;publicclassWindowsCommnadServiceimplementsCommandService{publicStringshowListCommand() {return"dir";    }}

LinuxCommandService

packagecom.wisely.conditional;publicclassLinuxCommandServiceimplementsCommandService{publicStringshowListCommand() {return"ls";    }}

17.2.3 编写配置类

packagecom.wisely.conditional;importorg.springframework.context.annotation.Bean;importorg.springframework.context.annotation.Conditional;importorg.springframework.context.annotation.Configuration;@ConfigurationpublicclassDemoConfig{@Bean@Conditional(WindowsCondition.class)publicCommandServicecommandService() {returnnewWindowsCommnadService();    }@Bean@Conditional(LinuxCondition.class)publicCommandServicelinuxEmailerService() {returnnewLinuxCommandService();    }}

17.2.4 测试

windows下

packagecom.wisely.conditional;importorg.springframework.context.annotation.AnnotationConfigApplicationContext;publicclassMain{publicstaticvoidmain(String[]args) {AnnotationConfigApplicationContextcontext=newAnnotationConfigApplicationContext("com.wisely.conditional");CommandServicecs=context.getBean(CommandService.class);System.out.println(cs.showListCommand());        context.close();    }}

输出结果

dir

Linux下(本例没有切换到linux,直接修改os.name为Linux)

packagecom.wisely.conditional;importorg.springframework.context.annotation.AnnotationConfigApplicationContext;publicclassMain{publicstaticvoidmain(String[]args) {System.setProperty("os.name","Linux");AnnotationConfigApplicationContextcontext=newAnnotationConfigApplicationContext("com.wisely.conditional");CommandServicecs=context.getBean(CommandService.class);System.out.println(cs.showListCommand());        context.close();    }}

输出结果

ls