Spring Boot中读取配置属性的几种方式

    @Value("str")
    private String str; // 注入普通字符串
  
    @Value("${hello}")
    private String hello; // 注入配置属性

    @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("#{userBean.name}")
    private String name; // 注入Bean属性

  @SpringBootApplication
  public class AttributeApplication {

    private static final String SPRING_BOOT_HELLO = "spring-boot.hello";

    @Value("${" + SPRING_BOOT_HELLO + "}")
    private String hello;

    /**
     * 1. 通过@Value注解获取值
     */
    public void getAttrByValueAnnotation() {
      System.out.println("1. 通过@Value注解获取值: " + hello);
    }

    public static void main(String[] args) {
      ConfigurableApplicationContext applicationContext = SpringApplication.run(AttributeApplication.class, args);
      AttributeApplication bean = applicationContext.getBean(AttributeApplication.class);
      bean.getAttrByValueAnnotation();
    }
    
  }

   @SpringBootApplication
   public class AttributeApplication {
   
     private static final String SPRING_BOOT_STR_ARRAY = "spring-boot.str-array";
     private static final String SPRING_BOOT_INT_ARRAY = "spring-boot.int-array";

     /**
     * Attention : it is error if use Integer[]
     */
    @Value("${" + SPRING_BOOT_INT_ARRAY + "}")
    private int[] array;

    /**
     * 通过@Value注解获取数组
     */
    public void getArrayAttr() {
      System.out.println("5. 通过@Value注解获取数组: " + Arrays.toString(array));
    }

    @Value("#{'${" + SPRING_BOOT_STR_ARRAY + "}'.split(',')}")
    private List<String> list;

    /**
     * 通过@Value注解获取List
     */
    public void getListAttr() {
      System.out.println("6. 通过@Value注解获取List: " + list.toString());
    }
    
    public static void main(String[] args) {
      ConfigurableApplicationContext applicationContext = SpringApplication.run(AttributeApplication.class, args);
      AttributeApplication bean = applicationContext.getBean(AttributeApplication.class);
      bean.getArrayAttr();
          bean.getListAttr();
    }
    
  }

  @SpringBootApplication
  public class AttributeApplication {

    private static final String SPRING_BOOT_HELLO = "spring-boot.hello";

    @Resource
    private Environment environment;

     /**
     * 2. 通过注入Environment获取值
     */
    public void getAttrByEnvironment() {
      String property = environment.getProperty(SPRING_BOOT_HELLO);
      System.out.println("2-1. 通过注入Environment获取值: " + property);
    }
    
    public static void main(String[] args) {
      ConfigurableApplicationContext applicationContext = SpringApplication.run(AttributeApplication.class, args);
      AttributeApplication bean = applicationContext.getBean(AttributeApplication.class);
      bean.getAttrByEnvironment();
    }

  }

  @SpringBootApplication
  public class AttributeApplication {
  
    private static final String UNDEFINED = "undefined";
    private static final String SPRING_BOOT_HELLO = "spring-boot.hello";
  
      public static void main(String[] args) {
      ConfigurableApplicationContext applicationContext = SpringApplication.run(AttributeApplication.class, args);
      System.out.println("2-2. 通过ApplicationContext获取Environment后再获取值: " + applicationContext
                      .getEnvironment().getProperty(SPRING_BOOT_HELLO, UNDEFINED));
    }
  
  }

  @SpringBootApplication
  public class AttributeApplication {

    private static final String APPLICATION_YML = "application.yml";
    private static final String SPRING_BOOT_PREFIX = "spring-boot";

    @Data
    @Component
    @PropertySource("classpath:" + APPLICATION_YML)
    @ConfigurationProperties(prefix = SPRING_BOOT_PREFIX)
    class Attribute {

      private String hello;
      private String world;

    }

    @Resource
    private Attribute attribute;

    /**
     * 3. 通过@ConfigurationProperties注入对象属性获取
     */
    public void getAttrByConfigurationPropertiesAnnotation() {
      System.out.println("3. 通过@ConfigurationProperties注入对象属性获取: " + attribute);
    }
    
    public static void main(String[] args) {
      ConfigurableApplicationContext applicationContext = SpringApplication.run(AttributeApplication.class, args);
      AttributeApplication bean = applicationContext.getBean(AttributeApplication.class);
      bean.getAttrByConfigurationPropertiesAnnotation();
    }
    
  }

  @SpringBootApplication
  public class AttributeApplication {
  
      private static final String UNDEFINED = "undefined";
      private static final String APPLICATION_PROPERTIES = "application.properties";
       private static final String SPRING_BOOT_HELLO = "spring-boot.hello";

    /**
     * 4. 通过PropertiesLoaderUtils获取(注意，此工具类仅可处理.properties或.xml配置文件)
     */
    public void getAttrByPropertiesLoaderUtils() {
      try {
        ClassPathResource resource = new ClassPathResource(APPLICATION_PROPERTIES);
        Properties properties = PropertiesLoaderUtils.loadProperties(resource);
        String property = properties.getProperty(SPRING_BOOT_HELLO, UNDEFINED);
        System.out.println("4. 通过PropertiesLoaderUtils获取: " + property);
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
    
    public static void main(String[] args) {
      ConfigurableApplicationContext applicationContext = SpringApplication.run(AttributeApplication.class, args);
      AttributeApplication bean = applicationContext.getBean(AttributeApplication.class);
      bean.getAttrByPropertiesLoaderUtils();
    }

  }