# 74.5 使用YAML配置外部属性

YAML是JSON的一个超集，可以非常方便的将外部配置以层次结构形式存储起来，比如：

```javascript
spring:
    application:
        name: cruncher
    datasource:
        driverClassName: com.mysql.jdbc.Driver
        url: jdbc:mysql://localhost/test
server:
    port: 9000
```

创建一个`application.yml`文件，将它放到classpath的根目录下，并添加`snakeyaml`依赖（Maven坐标为`org.yaml:snakeyaml`，如果你使用`spring-boot-starter`那就已经包含了）。一个YAML文件会被解析为一个Java `Map<String,Object>`（和一个JSON对象类似），Spring Boot会平伸该map，这样它就只有1级深度，并且有period-separated的keys，跟人们在Java中经常使用的`Properties`文件非常类似。 上面的YAML示例对应于下面的`application.properties`文件：

```java
spring.application.name=cruncher
spring.datasource.driverClassName=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost/test
server.port=9000
```

查看'Spring Boot特性'章节的[24.6. 使用YAML代替Properties](https://docs.spring.io/spring-boot/docs/2.0.0.RELEASE/reference/htmlsingle/#boot-features-external-config-yaml)可以获取更多关于YAML的信息。


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