本文實例講述了Spring條件注解用法。分享給大家供大家參考，具體如下：

一 點睛

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

@Conditional根據滿足僅一個特定條件創建一個特定的Bean。也就是根據特定的條件來控制Bean的創建行為，這樣就可以利用這個特性進行一些自動的配置。

二 項目說明

以不同的操作系統為條件，通過實現@Condition接口，并重寫matches方法來構造條件。若在windows系統下運行，則輸出列表命令為dir；若在Linux操作系統下運行程序，則輸出列表命令為ls。

三 實戰

1 判斷條件定義

1.1 windows的判定條件

package com.wisely.highlight_spring4.ch3.conditional;import org.springframework.context.annotation.Condition;import org.springframework.context.annotation.ConditionContext;import org.springframework.core.type.AnnotatedTypeMetadata;public class WindowsCondition implements Condition { public boolean matches(ConditionContext context,   AnnotatedTypeMetadata metadata) {  return context.getEnvironment().getProperty("os.name").contains("Windows"); }}

1.2 Linux的判定條件

package com.wisely.highlight_spring4.ch3.conditional;import org.springframework.context.annotation.Condition;import org.springframework.context.annotation.ConditionContext;import org.springframework.core.type.AnnotatedTypeMetadata;public class LinuxCondition implements Condition { public boolean matches(ConditionContext context,   AnnotatedTypeMetadata metadata) {  return context.getEnvironment().getProperty("os.name").contains("Linux"); }}

2 不同系統下的Bean類

2.1 接口

package com.wisely.highlight_spring4.ch3.conditional;public interface ListService {  public String showListCmd();}

2.2 Window下創建的Bean類

package com.wisely.highlight_spring4.ch3.conditional;public class WindowsListService implements ListService {  @Override  public String showListCmd() {   return "dir";  }}

2.3 Linux下所創建的Bean類

package com.wisely.highlight_spring4.ch3.conditional;public class LinuxListService implements ListService{  @Override  public String showListCmd() {   return "ls";  }}

3 配置類

package com.wisely.highlight_spring4.ch3.conditional;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Conditional;import org.springframework.context.annotation.Configuration;@Configurationpublic class ConditionConifg { @Bean @Conditional(WindowsCondition.class) //符合window條件，則實例化WindowsListService public ListService windowsListService() {  return new WindowsListService(); } @Bean @Conditional(LinuxCondition.class) //符合Linux條件，則實例化LinuxListService public ListService linuxListService() {  return new LinuxListService(); }}

4 主類

package com.wisely.highlight_spring4.ch3.conditional;import org.springframework.context.annotation.AnnotationConfigApplicationContext;public class Main {  public static void main(String[] args) {   AnnotationConfigApplicationContext context =    new AnnotationConfigApplicationContext(ConditionConifg.class);   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());   context.close();  }}