详解Java如何有效避免空指针

 public class ObjectUtil {
 ​
     /**
      * 把对象中的 String 类型的null字段，转换为空字符串
      *
      * @param <T>       待转化对象类型
      * @param object    待转化对象
      * @param fieldName 字段名字
      */
     public static <T> void noNullStringAttr(T object, String fieldName) {
         Field[] fields = object.getClass().getDeclaredFields();
         if (fields.length == 0) {
             return;
         }
         for (Field field : fields) {
             if ("String".equals(field.getType().getSimpleName())) {
                 field.setAccessible(true);
                 try {
                     Object value = field.get(object);
                     if (value == null && field.getName().equals(fieldName)) {
                         field.set(object, "");
                     }
                 } catch (IllegalArgumentException | IllegalAccessException e) {
                     e.printStackTrace();
                 }
             }
         }
     }
 }

     public static void main(String[] args) {
         // 构造参数：status, msg, data
         Result<Object> result = new Result<>(200, null, null);
         ObjectUtil.noNullStringAttr(result, "msg");
         System.out.println(result);
 ​
         User user = new User().setUsername("abc").setPassword(null);
         ObjectUtil.noNullStringAttr(user, "password");
         System.out.println(user);
 ​
         ObjectUtil.noNullStringAttr(user, "username");
         System.out.println(user);
     }