无法读取JSON：无法反序列化START_OBJECT令牌中的hello.Country []实例 [英] Could not read JSON: Can not deserialize instance of hello.Country[] out of START_OBJECT token

问题描述

我有所有国家的网址 - http://api.geonames.org/countryInfoJSON?username=volodiaL 。

I have rest url that gives me all countries - http://api.geonames.org/countryInfoJSON?username=volodiaL.

我使用Spring 3中的RestTemplate将返回的json解析为java对象：

I use RestTemplate from spring 3 to parse returned json into java objects:

RestTemplate restTemplate = new RestTemplate();
Country[] countries = restTemplate.getForObject("http://api.geonames.org/countryInfoJSON?username=volodiaL",Country[].class);

当我运行此代码时，我得到一个例外：

When I run this code I get an exception:

Caused by: com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of hello.Country[] out of START_OBJECT token
 at [Source: sun.net.www.protocol.http.HttpURLConnection$HttpInputStream@1846149; line: 1, column: 1]
    at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:164)
    at com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:691)
    at com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:685)
    at com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.handleNonArray(ObjectArrayDeserializer.java:222)
    at com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:133)
    at com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:18)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2993)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2158)
    at org.springframework.http.converter.json.MappingJackson2HttpMessageConverter.readJavaType(MappingJackson2HttpMessageConverter.java:225)
    ... 7 more

最后我的国家课程：

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;

@JsonIgnoreProperties(ignoreUnknown = true)
public class Country {
    private String countryName;
    private long geonameId;

    public String getCountryName() {
        return countryName;
    }

    public long getGeonameId() {
        return geonameId;
    }

    @Override
    public String toString() {
        return countryName;
    }
}

问题是返回的json包含根元素geonames 其中包含国家元素数组，如下所示：

The problem is that returned json contains root element "geonames" which contains array of country elements like so:

{
"geonames": [
    {
        "continent": "EU",
        "capital": "Andorra la Vella",
        "languages": "ca",
        "geonameId": 3041565,
        "south": 42.42849259876837,
        "isoAlpha3": "AND",
        "north": 42.65604389629997,
        "fipsCode": "AN",
        "population": "84000",
        "east": 1.7865427778319827,
        "isoNumeric": "020",
        "areaInSqKm": "468.0",
        "countryCode": "AD",
        "west": 1.4071867141112762,
        "countryName": "Andorra",
        "continentName": "Europe",
        "currencyCode": "EUR"
    }
]
}

如何辨别 RestTemplate 将数组的每个元素转换为 Countr是对象？

How to tell RestTemplate to convert each element of array into Country object?

推荐答案

您需要执行以下操作：

public class CountryInfoResponse {

   @JsonProperty("geonames")
   private List<Country> countries; 

   //getter - setter
}

RestTemplate restTemplate = new RestTemplate();
List<Country> countries = restTemplate.getForObject("http://api.geonames.org/countryInfoJSON?username=volodiaL",CountryInfoResponse.class).getCountries();

如果您可以使用某种注释来跳过级别会很棒，但它是还不可能（参见这个和 this ）

It would be great if you could use some kind of annotation to allow you to skip levels, but it's not yet possible (see this and this)

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