使用Jackson將json轉換為Java對象的正確類型參考是什么

Question

我有以下從api獲得的json輸出，

{"HYR":"[{\"LastUpdatedBy\":\"Bug 101510: VMukkanagoudar\",\"IATACountryCode\":\"US\",\"MetroCodeBool\":false,\"AirportName\":\"Sawyer County\",\"Latitude\":46,\"CityName\":\"Hayward\",\"MajorAirportBool\":false,\"Longitude\":-91,\"StatusCode\":\"A\",\"DisplayNameLocal\":\"Hayward, WI (HYR-Sawyer County)\",\"DisplayNameInternational\":\"Hayward, WI, United States (HYR-Sawyer County)\",\"UpdateDate\":\"2009-03-06 20:44:00.0\",\"AirportCode\":\"HYR\",\"AirportID\":5396808,\"RegionName\":\"Wisconsin\",\"IdenticalMetroCodeBool\":false,\"ExternalName\":\"HYR\",\"CountryCode\":\"USA\"}]",
 "VAA":"[{\"LastUpdatedBy\":\"fmoneo\",\"IATACountryCode\":\"FI\",\"MetroCodeBool\":false,\"AirportName\":\" \",\"Latitude\":63,\"CityName\":\"Vaasa\",\"MajorAirportBool\":true,\"Longitude\":22,\"StatusCode\":\"A\",\"DisplayNameLocal\":\"Vaasa (VAA)\",\"DisplayNameInternational\":\"Vaasa, Finland (VAA)\",\"UpdateDate\":\"2008-08-12 17:26:00.0\",\"AirportCode\":\"VAA\",\"AirportID\":4276566,\"RegionName\":\" \",\"IdenticalMetroCodeBool\":false,\"ExternalName\":\"VAA\",\"CountryCode\":\"FIN\"}]"
....(and so on)}

java對象如下

@JsonIgnoreProperties(ignoreUnknown = true)
public class Config {

  @JsonProperty("AirportCode")
  String airportCode;

  @JsonProperty("AirportID")
  Integer airportId;

  @JsonProperty("MetroCodeBool")
  Boolean metroCodeBool;

  @JsonProperty("MajorAirportBool")
  Boolean majorAirportBool;

  @JsonProperty("IdenticalMetroCodeBool")
  Boolean identicalMetroCodeBool;

  @JsonProperty("StatusCode")
  Character statusCode;

  //Getters and setters
}

轉換的代碼是

String jsonStr = apiCall();

if(jsonStr != null)
{
   ObjectMapper mapper = new ObjectMapper();

   TypeReference<HashMap<String, ArrayList<Config>>> typeRef = new TypeReference<HashMap<String, ArrayList<Config>>>() {};

   HashMap<String, ArrayList<AirConfig>> configMap = mapper.readValue(jsonStr, typeRef);
 }

但是，我得到的錯誤是

com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of java.util.ArrayList out of VALUE_STRING token
at [Source: java.io.StringReader@2b82d59e; line: 1, column: 2] (through reference chain: java.util.HashMap["HYR"])

我相信我創建的TypeReference不正確。 任何有關如何更改它的解決方案。

Answer 1

在您的情況下，此JSON無效。 看部分

{"HYR":"[{\\"LastUpdatedBy\\":\\"Bug 101510:

有一種"不應該在那里，所以有效的部分是這樣的：

{"HYR":[{\\"LastUpdatedBy\\":\\"Bug 101510:

在您的情況下，您需要將HYR的值設置為數組，但該值必須為String值（由於引用）。 刪除引號確實會產生有效的JSON數組。

Answer 2

數組"[ ]"開頭和結尾處的json中有額外的" 。您需要刪除它們。

    try {
        String jsonStr = "{\"HYR\":[{\"LastUpdatedBy\":\"Bug 101510: VMukkanagoudar\",\"IATACountryCode\":\"US\",\"MetroCodeBool\":false,\"AirportName\":\"Sawyer County\",\"Latitude\":46,\"CityName\":\"Hayward\",\"MajorAirportBool\":false,\"Longitude\":-91,\"StatusCode\":\"A\",\"DisplayNameLocal\":\"Hayward, WI (HYR-Sawyer County)\",\"DisplayNameInternational\":\"Hayward, WI, United States (HYR-Sawyer County)\",\"UpdateDate\":\"2009-03-06 20:44:00.0\",\"AirportCode\":\"HYR\",\"AirportID\":5396808,\"RegionName\":\"Wisconsin\",\"IdenticalMetroCodeBool\":false,\"ExternalName\":\"HYR\",\"CountryCode\":\"USA\"}]}";
        if (jsonStr != null) {
            ObjectMapper mapper = new ObjectMapper();
            TypeReference<HashMap<String, ArrayList<Config>>> typeRef = new TypeReference<HashMap<String, ArrayList<Config>>>() {};
            HashMap<String, ArrayList<Config>> configMap = mapper.readValue(jsonStr, typeRef);
            ArrayList<Config> configList = configMap.get("HYR");
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
}

Answer 3

使用（與您的Config一起使用適當的toString ）：

public static void main(String[] args) throws IOException {
    String jsonStr = "{\"HYR\":\"[{\\\"LastUpdatedBy\\\":\\\"Bug 101510: VMukkanagoudar\\\",\\\"IATACountryCode\\\":\\\"US\\\",\\\"MetroCodeBool\\\":false,\\\"AirportName\\\":\\\"Sawyer County\\\",\\\"Latitude\\\":46,\\\"CityName\\\":\\\"Hayward\\\",\\\"MajorAirportBool\\\":false,\\\"Longitude\\\":-91,\\\"StatusCode\\\":\\\"A\\\",\\\"DisplayNameLocal\\\":\\\"Hayward, WI (HYR-Sawyer County)\\\",\\\"DisplayNameInternational\\\":\\\"Hayward, WI, United States (HYR-Sawyer County)\\\",\\\"UpdateDate\\\":\\\"2009-03-06 20:44:00.0\\\",\\\"AirportCode\\\":\\\"HYR\\\",\\\"AirportID\\\":5396808,\\\"RegionName\\\":\\\"Wisconsin\\\",\\\"IdenticalMetroCodeBool\\\":false,\\\"ExternalName\\\":\\\"HYR\\\",\\\"CountryCode\\\":\\\"USA\\\"}]\"}";
    ObjectMapper mapper = new ObjectMapper();

    // step one: deserialize the map
    HashMap<String, String> configMap = mapper.readValue(jsonStr, new TypeReference<HashMap<String, String>>() {});

    // step two, deserialize the value for HYR
    final String hyr = configMap.get("HYR");
    List<Config> configs = mapper.readValue(hyr, new TypeReference<List<Config>>() {});

    System.out.println(configs);
}

在這里工作（傑克遜2.3.2）並輸出：

[Foo.Config(airportCode=HYR, airportId=5396808, metroCodeBool=false, majorAirportBool=false, identicalMetroCodeBool=false, statusCode=A)]