Spring 开发过程中Value 注解的使用场景

@Value("normal")
private String normal; // 注入普通字符串

@Value("#{systemProperties['os.name']}")
private String systemPropertiesName; // 注入操作系统属性

@Value("#{ T(java.lang.Math).random() * 100.0 }")
private double randomNumber; //注入表达式结果

@Value("#{beanInject.another}")
private String fromAnotherBean; 
// 注入其他Bean属性：注入beanInject对象的属性another，类具体定义见下面

@Value("classpath:com/hry/spring/configinject/config.txt")
private Resource resourceFile; // 注入文件资源

@Value("http://www.baidu.com")
private Resource testUrl; // 注入URL资源

book.name=bookName
anotherfile.configinject=placeholder 
//作为第二个配置文件加载路径的变量值

book.name.placeholder=bookNamePlaceholder

@Component
// 引入外部配置文件组：${app.configinject}的值来自config.properties。
// 如果相同
@PropertySource({"classpath:com/hry/spring/configinject/config.properties",
  "classpath:com/hry/spring/configinject/config_${anotherfile.configinject}.properties"})
public class ConfigurationFileInject{
  @Value("${app.name}")
  private String appName; // 这里的值来自application.properties，spring boot启动时默认加载此文件

  @Value("${book.name}")
  private String bookName; // 注入第一个配置外部文件属性

  @Value("${book.name.placeholder}")
  private String bookNamePlaceholder; // 注入第二个配置外部文件属性

  @Autowired
  private Environment env; // 注入环境变量对象，存储注入的属性值

  public String toString(){
    StringBuilder sb = new StringBuilder();
    sb.append("bookName=").append(bookName).append("\r\n")
    .append("bookNamePlaceholder=").append(bookNamePlaceholder).append("\r\n")
    .append("appName=").append(appName).append("\r\n")
    .append("env=").append(env).append("\r\n")
    // 从eniroment中获取属性值
    .append("env=").append(env.getProperty("book.name.placeholder")).append("\r\n");
    return sb.toString();
  }
}

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-configuration-processor</artifactId>
  <optional>true</optional>
</dependency>

@Configuration
@Component
@ConfigurationProperties(prefix = "dingtalk")
@EnableConfigurationProperties(MapConfig.class)
public class MapConfig {
  /**
   * 从配置文件中读取的dingtalk.urls开头的数据
   * 注意：名称必须与配置文件中保持一致
   */
  private Map<String, String> urls;

  public Map<String, String> getUrls() {
    return urls;
  }

  public void setUrls(Map<String, String> urls) {
    this.urls = urls;
  }
}

dingtalk:
 urls:
  default: https://oapi.dingtalk.com/default
  test: https://oapi.dingtalk.com/test
  center: https://oapi.dingtalk.com/center

@Component
public class test {
  @Autowired
  private MapConfig mapConfig;
	private Map<String,String> urlsMap;

  public void test {
    urlsMap = mapConfig.getUrls();
		System.out.println(urlsMap.toString());
	}
}