java - 即使检查空值，也会出现 JsonMappingException

Question

对传递给 ObjectMapper Json 解析器方法的字符串进行 null 和空检查时，出现异常。这是我的代码:

private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();

@RequestMapping(value = "/url", method = RequestMethod.GET)
    public ModelAndView displayStuff(
            @RequestParam(value = "item") int itemCode) throws JsonProcessingException, IOException {


           if (!text.equals("") || text != null) {
                JsonNode jsonThresholds = OBJECT_MAPPER.readTree(text);
                do stuff()..

          }else {
               do nothing();
          }
     }

我收到此异常:

com.fasterxml.jackson.databind.JsonMappingException: No content to map due to end-of-input
 at [Source: java.io.StringReader@182d2fd7; line: 1, column: 1]
    at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:164)
    at com.fasterxml.jackson.databind.ObjectMapper._initForReading(ObjectMapper.java:2840)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2782)
    at com.fasterxml.jackson.databind.ObjectMapper.readTree(ObjectMapper.java:1659)

有人可以向我解释一下发生了什么以及如何解决这个问题吗？

谢谢

Answer 1

改变

!text.equals("") || text != null

至

text != null && !text.equals("")

因为即使 text="" then text != null 也会变为 true 并进入 if..

你应该首先检查是否为空，因为如果值为空.equls将给出空指针异常

这也是错误的

 !text.equals("")  &&  text != null 
       ↑
     null pointer Exception can be occurred here