没有从字符串值反序列化的字符串参数构造函数/工厂方法

Question

我正在尝试使用外部 NYtimes API。这是一个示例数据输出示例：

{
    "status": "OK",
    "copyright": "Copyright (c) 2016 The New York Times Company. All Rights Reserved.",
    "section": "home",
    "last_updated": "2016-10-20T19:57:45-04:00",
    "num_results": 30,
    "results": [{
            "section": "Briefing",
            "subsection": "",
            "title": "Election, Dodgers, Duterte: Your Thursday Evening Briefing",
            "abstract": "Here’s what you need to know at the end of the day.",
            "url": "abc.co",
            "byline": "By KAREN ZRAICK and MERRILL D. OLIVER",
            "item_type": "Article",
            "updated_date": "2016-10-20T18:32:41-04:00",
            "created_date": "2016-10-20T17:58:30-04:00",
            "published_date": "2016-10-20T17:58:30-04:00",
            "material_type_facet": "",
            "kicker": "",
            "des_facet": [],
            "org_facet": [],
            "per_facet": [],
            "geo_facet": [],
            "multimedia": [{
                "url": "abc.co",
                "format": "Standard Thumbnail",
                "height": 75,
                "width": 75,
                "type": "image",
                "subtype": "photo",
                "caption": "",
                "copyright": "Damon Winter/The New York Times"
            }, {
                "url": "abc.co",
                "format": "thumbLarge",
                "height": 150,
                "width": 150,
                "type": "image",
                "subtype": "photo",
                "caption": "",
                "copyright": "Damon Winter/The New York Times"
            }, {
                "url": "abc.co",
                "format": "Normal",
                "height": 127,
                "width": 190,
                "type": "image",
                "subtype": "photo",
                "caption": "",
                "copyright": "Damon Winter/The New York Times"
            }, {
                "url": "abc.co",
                "format": "mediumThreeByTwo210",
                "height": 140,
                "width": 210,
                "type": "image",
                "subtype": "photo",
                "caption": "",
                "copyright": "Damon Winter/The New York Times"
            }, {
                "url": "abc.co",
                "format": "superJumbo",
                "height": 1365,
                "width": 2048,
                "type": "image",
                "subtype": "photo",
                "caption": "",
                "copyright": "Damon Winter/The New York Times"
            }],
            "short_url": "http://abc.co"
        }

    ]
}

这是bean定义

//Headline.class
public class Headline {

@JsonProperty("status")
String status;
@JsonProperty("copyright")
String copyright;
@JsonProperty("section")
String section;
@JsonProperty("last_updated")
String last_updated;
@JsonProperty("num_results")
int num_results;
@JsonProperty("results")
List<Story> results;

`

//Story.class
    @JsonProperty("section")
        String section;
        @JsonProperty("subsection")
        String subsection;
        @JsonProperty("title")
        String title;
        @JsonProperty("abstract")
        String storyAbstract;
        @JsonProperty("url")
        String url;
        @JsonProperty("byline")
        String byline;
        @JsonProperty("item_type")
        String item_type;
        @JsonProperty("updated_date")
        String updated_date;
        @JsonProperty("created_date")
        String created_date;
        @JsonProperty("published_date")
        String published_date;
        @JsonProperty("material_type_facet")
        String material_type_facet;
        @JsonProperty("kicker")
        String kicker;
        /*@JsonProperty("des_facet")
        List des_facet;
        @JsonProperty("org_facet")
        List org_facet;
        @JsonProperty("per_facet")
        List per_facet;
        @JsonProperty("geo_facet")
        List geo_facet;*/
        @JsonProperty("multimedia")
        List<Media> multimedia;
        @JsonProperty("short_url")
        String short_url;

//Media.class
        @JsonProperty("url")
        String url;
        @JsonProperty("format")
        String format;
        @JsonProperty("height")
        int height;
        @JsonProperty("width")
        int width;
        @JsonProperty("type")
        String type;
        @JsonProperty("subtype")
        String subtype;
        @JsonProperty("caption")
        String caption;
        @JsonProperty("copyright")
        String copyright;

这是我的来电者：

RestTemplate restTemplate = new RestTemplate();
        MappingJackson2HttpMessageConverter jsonConverter = new MappingJackson2HttpMessageConverter();
        jsonConverter.setSupportedMediaTypes(Arrays.asList(new MediaType("text","json",MappingJackson2HttpMessageConverter.DEFAULT_CHARSET)));
        restTemplate.getMessageConverters().add(jsonConverter);
        Headline headline =  restTemplate.getForObject("http://abc/svc/topstories/v1/home.json?api-key=key",Headline.class);
        logger.info("Headline"+headline.toString());

现在我打电话时得到的例外是：

Exception in thread "main" org.springframework.http.converter.HttpMessageNotReadableException: Could not read JSON: Can not construct instance of java.util.ArrayList: no String-argument constructor/factory method to deserialize from String value ('')
 at [Source: java.io.PushbackInputStream@22d9d; line: 1, column: 1185] (through reference chain: NYTimes.Payload.Headline["results"]->java.util.ArrayList[0]->NYTimes.Story.Story["multimedia"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: Can not construct instance of java.util.ArrayList: no String-argument constructor/factory method to deserialize from String value ('')
 at [Source: java.io.PushbackInputStream@22d9d; line: 1, column: 1185] (through reference chain: NYTimes.Payload.Headline["results"]->java.util.ArrayList[0]->NYTimes.Story.Story["multimedia"])

我一直在试图理解为什么它不会反序列化。如果字符串值为空 - 那么它应该导致一个空列表？

Answer 1

发生此异常是因为您收到的 json 响应 -

\n\n

{\n    "status": "OK",\n    "copyright": "Copyright (c) 2016 The New York Times Company. All Rights Reserved.",\n    "section": "home",\n    "last_updated": "2016-10-20T19:57:45-04:00",\n    "num_results": 30,\n    "results": [{\n            "section": "Briefing",\n            "subsection": "",\n            "title": "Election, Dodgers, Duterte: Your Thursday Evening Briefing",\n            "abstract": "Here\xe2\x80\x99s what you need to know at the end of the day.",\n            "url": "abc.co",\n            "byline": "By KAREN ZRAICK and MERRILL D. OLIVER",\n            "item_type": "Article",\n            "updated_date": "2016-10-20T18:32:41-04:00",\n            "created_date": "2016-10-20T17:58:30-04:00",\n            "published_date": "2016-10-20T17:58:30-04:00",\n            "material_type_facet": "",\n            "kicker": "",\n            "des_facet": [],\n            "org_facet": [],\n            "per_facet": [],\n            "geo_facet": [],\n            "multimedia": "",\n            "short_url": "http://abc.co"\n        }\n\n    ]\n} \n

\n\n

\n

“多媒体”字段是一个空字符串

\n

\n\n

所以你需要验证你的json并相应地映射你的pojo。

\n