（七）SpringBoot2.0基础篇- application.properties属性文件的解析及获取

注：由于测试代码较多，影响查看效果，所以只放了核心代码，如需查看，请点示例代码

1. 默认访问的属性文件为application.properties文件，可在启动项目参数中指定spring.config.location的参数：

   java -jar myproject.jar --spring.config.location=classpath:/default.properties,classpath:/override.properties

   参考官方文档：https://docs.spring.io/spring-boot/docs/2.0.2.RELEASE/reference/htmlsingle/#boot-features-external-config-application-property-files

2. 使用@PropertySource来获取配置文件的中属性值（注意：在使用该注解时，属性文件必须为properties文件，yaml文件不可用）：

   @Configuration
   @PropertySource("classpath:/app.properties")
   public class AppConfig {
   
       @Autowired
       Environment env;
   
       @Bean
       public TestBean testBean() {
           TestBean testBean = new TestBean();
           testBean.setName(env.getProperty("testbean.name"));
           return testBean;
       }
   }  

   参考官方文档：https://docs.spring.io/spring/docs/5.0.6.RELEASE/javadoc-api/org/springframework/context/annotation/PropertySource.html

3. 使用@Value注解直接将属性值注入进修饰对对象中：

   import org.springframework.stereotype.*;
   import org.springframework.beans.factory.annotation.*;
   
   @Component
   public class MyBean {
   
       @Value("${name}")
       private String name;
   
       // ...
   
   }

   参考官方文档：https://docs.spring.io/spring-boot/docs/2.0.2.RELEASE/reference/htmlsingle/#boot-features-external-config

4. 使用@ConfigurationProperties(prefix="my")将属性值注入进对象，可以注入对象的属性key的对象，也可以注入进List或Set中，但是属性的书写需要有规范：

   my.servers0=dev.example.com
   my.servers1=another.example.com

   使用方式

   @ConfigurationProperties(prefix="my")
   public class Config {
       //set,list不需要Setter方法
       private List<String> servers = new ArrayList<String>();
   
       public List<String> getServers() {
           return this.servers;
       }
   }

   参考官方文档：https://docs.spring.io/spring-boot/docs/2.0.2.RELEASE/reference/htmlsingle/#boot-features-external-config-loading-yaml

5. 可以使用yaml文件格式来替换properties，属性获取方式不变（注：yaml文件后缀名为.yml）

6. 使用POJO方式直接将属性注入进实体对象中：

   application.yml

   acme:
       remote-address: 192.168.1.1
       security:
           username: admin
           password: admincss
           roles:
               - USER
               - ADMIN

   AcmeProperties.java

   package com.example;
   
   import java.net.InetAddress;
   import java.util.ArrayList;
   import java.util.Collections;
   import java.util.List;
   
   import org.springframework.boot.context.properties.ConfigurationProperties;
   
   @ConfigurationProperties("acme")
   public class AcmeProperties {
   
       private InetAddress remoteAddress;
   
       private final Security security = new Security();
   
       public InetAddress getRemoteAddress() { ... }
   
       public void setRemoteAddress(InetAddress remoteAddress) { ... }
   
       public Security getSecurity() { ... }
   
       public static class Security {
   
           private String username;
   
           private String password;
   
           private List<String> roles = new ArrayList<>(Collections.singleton("USER"));
   
           public String getUsername() { ... }
   
           public void setUsername(String username) { ... }
   
           public String getPassword() { ... }
   
           public void setPassword(String password) { ... }
   
           public List<String> getRoles() { ... }
   
           public void setRoles(List<String> roles) { ... }
   
       }
   }

参考文档：https://docs.spring.io/spring-boot/docs/2.0.2.RELEASE/reference/htmlsingle/#boot-features-external-config-typesafe-configuration-properties

代码示例：https://gitee.com/lfalex/spring-boot-example/tree/dev/spring-boot-properties