# 24.5. 属性占位符

当使用`application.properties`定义的属性时，Spring会先通过已经存在的`Environment`查找该属性，所以你可以引用事先定义的值（比如，系统属性）：

```java
app.name=MyApp
app.description=${app.name} is a Spring Boot application
```

**注** 你也可以使用该技巧为存在的Spring Boot属性创建'短'变量，具体参考[章节 74.4，使用'short'命令行参数](https://github.com/jack80342/spring-boot/tree/25350df33f8edd68b50ff6f6e1258c9df4f67d67/IX.%20‘How-to’%20guides/74.4%20Use%20‘Short’%20Command%20Line%20Arguments.md)。


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