java - 使用 Jackson 获取数组的大小

Question

我的 json 文件中有以下数据。

{  
   "product":"Data",
   "data":{  
      "zip":[  
         {  
            "codeValue":"12345",
            "distance":[  
               {  
                  "5":"a c"
               },
               {  
                  "2":"z c"
               }
            ]
         },
         {  
            "codeValue":"60089",
            "distance":[  
               {  
                  "5":"a c"
               },
               {  
                  "2":"z c"
               }
            ]
         }
      ]
   }
}

我正在尝试使用以下代码打印 zip 大小。

public void getJsonResponse() throws Exception {
    String text = getTheData();
    System.out.println(text);
    ObjectMapper objMap = new ObjectMapper();
    Map<String, Object> map = objMap.readValue(text, new TypeReference<Map<String, Object>>() {
    });

    String mainMap = map.get("product").toString();
    String getData = map.get("data").toString();
    Map<String, Object> map1 = objMap.readValue(getData, new TypeReference<Map<String, Object>>() {
    });
    List zip = (List) map1.get("zip");
    System.out.println(zip.size());
}

此处而不是 zip.size() 上的 sysout，如果我使用 mainMap，我得到的输出为 Data，但是当我使用 zip.size() 时，我得到一些异常，如

Exception in thread "main" com.fasterxml.jackson.core.JsonParseException: Unexpected character ('z' (code 122)): was expecting double-quote to start field name at [Source: java.io.StringReader@60f82f98; line: 1, column: 3] at com.fasterxml.jackson.core.JsonParser._constructError(JsonParser.java:1524) at com.fasterxml.jackson.core.base.ParserMinimalBase._reportError(ParserMinimalBase.java:557) at com.fasterxml.jackson.core.base.ParserMinimalBase._reportUnexpectedChar(ParserMinimalBase.java:475) at com.fasterxml.jackson.core.json.ReaderBasedJsonParser._handleOddName(ReaderBasedJsonParser.java:1293) at com.fasterxml.jackson.core.json.ReaderBasedJsonParser._parseName(ReaderBasedJsonParser.java:1190) at com.fasterxml.jackson.core.json.ReaderBasedJsonParser.nextToken(ReaderBasedJsonParser.java:612) at com.fasterxml.jackson.databind.deser.std.MapDeserializer._readAndBindStringMap(MapDeserializer.java:412) at com.fasterxml.jackson.databind.deser.std.MapDeserializer.deserialize(MapDeserializer.java:312) at com.fasterxml.jackson.databind.deser.std.MapDeserializer.deserialize(MapDeserializer.java:26) at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2993) at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2105) at onlyJava.JsonDataCAll.getJsonResponse(JsonDataCAll.java:24) at onlyJava.Test.main(Test.java:13)

请让我知道我哪里出了问题以及如何解决这个问题。

Answer 1

String getData = map.get("data").toString();

这不会向您返回 JSON，因此会出现异常。你会得到类似 {zip=[{...

相反，请更改您的声明

Map<String, Object> map1 = objMap.readValue(getData, new TypeReference<Map<String, Object>>() {
        });

至

Map<String, Object> map1 = (Map<String, Object>) map.get("data");