spring boot学习(6)— 配置信息及其读取优先级

1. properties 信息从哪里取

在不同的环境，我们需要使用不同的配置，Spring boot 已经提供了相关功能，可以是 properties 文件， yaml 文件 或是命令行参数。优先级如下

1. Devtools global settings properties on your home directory (~/.spring-boot-devtools.properties when devtools is active).

2. @TestPropertySource annotations on your tests.

3. @SpringBootTest#properties annotation attribute on your tests.

4. Command line arguments.

   java -jar app.jar --name="Spring"
   

5. Properties from SPRING_APPLICATION_JSON (inline JSON embedded in an environment variable or system property).

   • environment vaiable：SPRING_APPLICATION_JSON='{"acme":{"name":"test"}}' java -jar myapp.jar
   • command line:
     • java -Dspring.application.json='{"name":"test"}' -jar myapp.jar
     • java -jar myapp.jar --spring.application.json='{"name":"test"}'

6. ServletConfig init parameters.

7. ServletContext init parameters.

8. JNDI attributes from java:comp/env.

9. Java System properties (System.getProperties()).

10. OS environment variables.

11. A RandomValuePropertySource that has properties only in random.*.

my.secret=${random.value}
my.number=${random.int}
my.bignumber=${random.long}
my.uuid=${random.uuid}
my.number.less.than.ten=${random.int(10)}
my.number.in.range=${random.int[1024,65536]}

12. Profile-specific application properties outside of your packaged jar (application-{profile}.properties and YAML variants).
13. Profile-specific application properties packaged inside your jar (application-{profile}.properties and YAML variants).
14. Application properties outside of your packaged jar (application.properties and YAML variants).
15. Application properties packaged inside your jar (application.properties and YAML variants).
16. @PropertySource annotations on your @Configuration classes.
17. Default properties (specified by setting SpringApplication.setDefaultProperties).

2. 使用 application.properties 文件

使用 properties 文件，spring boot 会根据以下目录去寻找，添加到 Spring Environment 中，优先级依次递增。

1. classpath:/: resources 目录
2. classpath:/config/: resources 下 config 目录
3. file:./：工程根目录
4. file:./config/: 工程跟目录下的 config 目录

2.1 加载顺序：

从优先级高的先加载。

1. file:./config/
2. file:./
3. classpath:/config/
4. classpath:/

2019-03-27 22:38:24.848 DEBUG 39802 --- [           main] o.s.boot.SpringApplication               : Loading source class com.example.exitcode.DemoApplication
2019-03-27 22:38:24.915 DEBUG 39802 --- [           main] o.s.b.c.c.ConfigFileApplicationListener  : Loaded config file 'file:./config/application.properties' (file:./config/application.properties)
2019-03-27 22:38:24.915 DEBUG 39802 --- [           main] o.s.b.c.c.ConfigFileApplicationListener  : Loaded config file 'file:./application.properties' (file:./application.properties)
2019-03-27 22:38:24.915 DEBUG 39802 --- [           main] o.s.b.c.c.ConfigFileApplicationListener  : Loaded config file 'jar:file:xxxxx-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/config/application.properties' (classpath:/config/application.properties)
2019-03-27 22:38:24.915 DEBUG 39802 --- [           main] o.s.b.c.c.ConfigFileApplicationListener  : Loaded config file 'jar:file:xxxxx-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/application.properties' (classpath:/application.properties)

2.2 属性值怎么取

优先级高的会覆盖优先级低的。

1. ./config/application.properties

   testconfig.first=./config/
   #testconfig.second=./config/
   #testconfig.third=./config/
   #testconfig.fourth=./config/
   

2. ./application.properties

   testconfig.first=./
   testconfig.second=./
   #testconfig.third=./
   #testconfig.fourth=./
   

3. classpath:/config/application.properties

   testconfig.first=classpath/config/
   testconfig.second=classpath/config/
   testconfig.third=classpath/config/
   #testconfig.fourth=classpath/config/
   

4. classpath:/application.properties

   testconfig.first=classpath
   testconfig.second=classpath
   testconfig.third=classpath
   testconfig.fourth=classpath
   

输出如下：

2019-03-27 23:29:12.434  INFO 1335 --- [           main] com.example.properties.DemoApplication   : No active profile set, falling back to default profiles: default
first: ./config/
second: ./
third: classpath/config/
fourth: classpath
2019-03-27 23:29:13.052  INFO 1335 --- [           main] com.example.properties.DemoApplication   : Started DemoApplication in 16.565 seconds (JVM running for 23.467)

2.3 多环境配置文件

加一个文件： classpath:/application-product.properties

testconfig.first=product-classpath
testconfig.second=product-classpath

通过 spring.profiles.active 来指定环境所对应的 properties 文件：
运行 java -jar build/libs/properties-0.0.1-SNAPSHOT.jar --spring.profiles.active=product, 输出如下：

2019-03-28 20:34:44.726  INFO 25859 --- [           main] com.example.properties.DemoApplication   : The following profiles are active: product
first: product-classpath
second: product-classpath
third: classpath/config/
fourth: classpath
fifth: ./config/
sixth: ./config/
seventh: ./config/
eightth: ./config/

2.3 使用 yaml 文件来代替 properties 文件。

也可以使用 yaml 格式的文件。但是在同等目录下，properties 优先级高于 yaml 文件的配置信息。

新增文件 ./config/application.yml

testconfig:
  frist: ./config/yml
  second: ./config/yml

命令 java -jar build/libs/properties-0.0.1-SNAPSHOT.jar 输出为:

first: ./config/
second: ./config/yml
third: classpath/config/
fourth: classpath
fifth: ./config/
sixth: ./config/
seventh: ./config/
eightth: ./config/

2.5 属性文件中可以使用变量已经声明过的变量值：

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