读取配置文件，利用反射给类属性赋值，

public class R{
     public static String TOKEN="default-value";
     public static String APPID;
     ...
}

      /**
      * 初始化变量，通过读取properties文件
      */
      public  static void init(){
           System. out.println( "开始初始化");

            try {
                 //1读取配置文件
                 Class c=R. class;
//              InputStream in = Class.forName("com.wupl.constant.R").getResourceAsStream("src/R.properties");
                InputStream in = new BufferedInputStream( new FileInputStream("src/R.properties" ));
                Properties properties = new Properties();
                properties.load(in);

                 //通过反射获取所有string类型成员变量信息，并以此读取配置文件中的值并赋值。
                Field [] fields = c.getDeclaredFields();

                 for( int i=0;i<fields. length;i++){
                     Field field = fields[i];
                     String fieldName=field.getName();
                      //判断是否是字符串类型,配置文件中有对应的key=value键值
                      if(field.getGenericType().toString().equals( "class java.lang.String")&&
                           properties.containsKey( fieldName)){
                           String value=properties.getProperty(fieldName); //取值
                           System. out.println( "取到" +fieldName+ "--的值--" +value);
                           field.set( fieldName, value);

                     }
                }
                System. out.println( "初始化完毕" );

           } catch (Exception e) {

                System. out.println( "初始化失败" );
                e.printStackTrace();
           }
     }