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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
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).
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。
classpath:/: resources 目录
classpath:/config/: resources 下 config 目录
file:./：工程根目录
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。
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)
2.2 属性值怎么取
优先级高的会覆盖优先级低的。
./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
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
