摘要：優先級如下使用文件使用文件，會根據以下目錄去尋找，添加到中，優先級依次遞增。目錄下目錄工程根目錄工程跟目錄下的目錄加載順序從優先級高的先加載。屬性值怎么取優先級高的會覆蓋優先級低的。但是在同等目錄下，優先級高于文件的配置信息。

在不同的環境，我們需要使用不同的配置，Spring boot 已經提供了相關功能，可以是 properties 文件， yaml 文件 或是命令行參數。優先級如下

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

@TestPropertySource annotations on your tests.

@SpringBootTest#properties annotation attribute on your tests.

Command line arguments.

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

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"}"

ServletConfig init parameters.

ServletContext init parameters.

JNDI attributes from java:comp/env.

Java System properties (System.getProperties()).

OS environment variables.

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]}

Profile-specific application properties outside of your packaged jar (application-{profile}.properties and YAML variants).

Profile-specific application properties packaged inside your jar (application-{profile}.properties and YAML variants).

Application properties outside of your packaged jar (application.properties and YAML variants).

Application properties packaged inside your jar (application.properties and YAML variants).

@PropertySource annotations on your @Configuration classes.

Default properties (specified by setting SpringApplication.setDefaultProperties).

使用 properties 文件，spring boot 會根據以下目錄去尋找，添加到 Spring Environment 中，優先級依次遞增。

classpath:/: resources 目錄

classpath:/config/: resources 下 config 目錄

file:./：工程根目錄

file:./config/: 工程跟目錄下的 config 目錄

從優先級高的先加載。

file:./config/

file:./

classpath:/config/

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)

優先級高的會覆蓋優先級低的。

./config/application.properties

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

./application.properties

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

classpath:/config/application.properties

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

classpath:/application.properties

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

輸出如下：

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)

加一個文件： classpath:/application-product.properties

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

通過 spring.profiles.active 來指定環境所對應的 properties 文件：
運行 java -jar build/libs/properties-0.0.1-SNAPSHOT.jar --spring.profiles.active=product, 輸出如下：

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/

也可以使用 yaml 格式的文件。但是在同等目錄下，properties 優先級高于 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 輸出為:

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

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