springboot2.0 @Conditional派生注解@ConditionalOnMissingBean，@ConditionalOnProperty等详解

- 日理万妓 2021-09-28 23:14 295阅读 0赞

@Conditional派生注解（Spring注解版原生的@Conditional作用）

作用：必须是@Conditional指定的条件成立，才给容器中添加组件，配置配里面的所有内容才生效；

关于@Conditional的详细解释可以参看[《spring注解 @Conditional的使用》][spring_ _Conditional]

<table> 
 <thead> 
  <tr> 
   <th>@Conditional扩展注解</th> 
   <th>作用（判断是否满足当前指定条件）</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>@ConditionalOnJava</td> 
   <td>系统的java版本是否符合要求</td> 
  </tr> 
  <tr> 
   <td>@ConditionalOnBean</td> 
   <td>容器中存在指定Bean；</td> 
  </tr> 
  <tr> 
   <td>@ConditionalOnMissingBean</td> 
   <td>容器中不存在指定Bean；</td> 
  </tr> 
  <tr> 
   <td>@ConditionalOnExpression</td> 
   <td>满足SpEL表达式指定</td> 
  </tr> 
  <tr> 
   <td>@ConditionalOnClass</td> 
   <td>系统中有指定的类</td> 
  </tr> 
  <tr> 
   <td>@ConditionalOnMissingClass</td> 
   <td>系统中没有指定的类</td> 
  </tr> 
  <tr> 
   <td>@ConditionalOnSingleCandidate</td> 
   <td>容器中只有一个指定的Bean，或者这个Bean是首选Bean</td> 
  </tr> 
  <tr> 
   <td>@ConditionalOnProperty</td> 
   <td>系统中指定的属性是否有指定的值</td> 
  </tr> 
  <tr> 
   <td>@ConditionalOnResource</td> 
   <td>类路径下是否存在指定资源文件</td> 
  </tr> 
  <tr> 
   <td>@ConditionalOnWebApplication</td> 
   <td>当前是web环境</td> 
  </tr> 
  <tr> 
   <td>@ConditionalOnNotWebApplication</td> 
   <td>当前不是web环境</td> 
  </tr> 
  <tr> 
   <td>@ConditionalOnJndi</td> 
   <td>JNDI存在指定项</td> 
  </tr> 
 </tbody> 
</table>

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[spring_ _Conditional]: https://blog.csdn.net/qq_28410283/article/details/91356551
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