第十一章 Spring条件注解@Conditional

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在第六章 Profile中有介绍，通过@Profile可以根据profile的不同，创建不同的Bean。Spring4提供了一个更通用的基于条件的Bean的创建，即@Conditional注解

下面的示例将以不同的操作系统为条件，实现在Windows系统下运行程序，输出dir，若在Linux系统下运行程序，则输出ls>

一、通过实现Condition接口，定义判断条件

package demo2.condition;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 arg1) {        return context.getEnvironment().getProperty("os.name").contains("Windows");    }}

package demo2.condition;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 arg1) {        return context.getEnvironment().getProperty("os.name").contains("Linux");    }}

二、定义Service接口

package demo2.service;public interface ListService {    public String showListCmd();}

三、定义Service的不同实现

package demo2.service;public class WindowsListService implements ListService {    @Override    public String showListCmd() {        return "dir";    }}

package demo2.service;public class LinuxListService implements ListService {    @Override    public String showListCmd() {        return "ls";    }}

四、配置类
通过@Conditional注解实现条件判断

package demo2.config;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.ComponentScan;import org.springframework.context.annotation.Conditional;import org.springframework.context.annotation.Configuration;import org.springframework.context.annotation.EnableAspectJAutoProxy;import org.springframework.scheduling.annotation.EnableAsync;import org.springframework.scheduling.annotation.EnableScheduling;import demo2.condition.LinuxCondition;import demo2.condition.WindowsCondition;import demo2.service.ListService;import demo2.service.WindowsListService;@Configuration@ComponentScan("demo2")@EnableAspectJAutoProxy@EnableAsync@EnableSchedulingpublic class DIConfig {    @Bean    @Conditional(WindowsCondition.class)    public ListService windowsListService() {        return new WindowsListService();    }    @Bean    @Conditional(LinuxCondition.class)    public ListService linuxListService() {        return new WindowsListService();    }}

五、运行

package demo2;import org.springframework.context.annotation.AnnotationConfigApplicationContext;import demo2.config.DIConfig;import demo2.service.ListService;public class Main {    public static void main(String[] args) {        AnnotationConfigApplicationContext cxt = new AnnotationConfigApplicationContext();        cxt.getEnvironment().setActiveProfiles("dev");        cxt.register(DIConfig.class);        cxt.refresh();        ListService ds = cxt.getBean(ListService.class);        System.out.println(ds.showListCmd());        cxt.close();    }}

结果

dir

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