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Roman

Asked:2022-08-09 15:14:27 +0000 UTC2022-08-09 15:14:27 +0000 UTC 2022-08-09 15:14:27 +0000 UTC

Jackson 如何解析没有名称的数组

772

我正在尝试从天气 apishka 获得响应 apishka 向城市坐标请求发送这样的响应

[
    {
        "name": "Moscow",
        "local_names": {
            "it": "Mosca",
            "zh": "莫斯科",
            "lv": "Maskava",
            "id": "Moskwa",
            "ay": "Mosku",
            "lt": "Maskva",
            "ascii": "Moscow",
            "sh": "Moskva",
            "uz": "Moskva",
            "st": "Moscow",
            "co": "Moscù",
            "bo": "མོ་སི་ཁོ།",
            "fi": "Moskova",
            "wo": "Mosku",
            "dz": "མོསི་ཀོ",
            "sl": "Moskva",
            "ps": "مسکو",
            "sc": "Mosca",
            "hr": "Moskva",
            "kv": "Мӧскуа",
            "tk": "Moskwa",
            "sr": "Москва",
            "mg": "Moskva",
            "ko": "모스크바",
            "wa": "Moscou",
            "sg": "Moscow",
            "sv": "Moskva",
            "ch": "Moscow",
            "mn": "Москва",
            "ta": "மாஸ்கோ",
            "am": "ሞስኮ",
            "an": "Moscú",
            "io": "Moskva",
            "su": "Moskwa",
            "ro": "Moscova",
            "oc": "Moscòu",
            "feature_name": "Moscow",
            "bg": "Москва",
            "nn": "Moskva",
            "en": "Moscow",
            "li": "Moskou",
            "ga": "Moscó",
            "ak": "Moscow",
            "ba": "Мәскәү",
            "da": "Moskva",
            "so": "Moskow",
            "ru": "Москва",
            "be": "Масква",
            "is": "Moskva",
            "eo": "Moskvo",
            "cu": "Москъва",
            "uk": "Москва",
            "cs": "Moskva",
            "sk": "Moskva",
            "vo": "Moskva",
            "ab": "Москва",
            "qu": "Moskwa",
            "kg": "Moskva",
            "cy": "Moscfa",
            "az": "Moskva",
            "pl": "Moskwa",
            "jv": "Moskwa",
            "fo": "Moskva",
            "ia": "Moscova",
            "lg": "Moosko",
            "hu": "Moszkva",
            "vi": "Mát-xcơ-va",
            "eu": "Mosku",
            "mt": "Moska",
            "nb": "Moskva",
            "pt": "Moscou",
            "tl": "Moscow",
            "ar": "موسكو",
            "he": "מוסקווה",
            "gv": "Moscow",
            "sw": "Moscow",
            "de": "Moskau",
            "gd": "Moscobha",
            "ja": "モスクワ",
            "yo": "Mọsko",
            "dv": "މޮސްކޯ",
            "cv": "Мускав",
            "bi": "Moskow",
            "fa": "مسکو",
            "gn": "Mosku",
            "no": "Moskva",
            "iu": "ᒨᔅᑯ",
            "na": "Moscow",
            "bs": "Moskva",
            "kk": "Мәскеу",
            "ml": "മോസ്കോ",
            "zu": "IMoskwa",
            "za": "Moscow",
            "ca": "Moscou",
            "hi": "मास्को",
            "ln": "Moskú",
            "la": "Moscua",
            "mi": "Mohikau",
            "av": "Москва",
            "gl": "Moscova - Москва",
            "es": "Moscú",
            "os": "Мæскуы",
            "af": "Moskou",
            "se": "Moskva",
            "ht": "Moskou",
            "nl": "Moskou",
            "kn": "ಮಾಸ್ಕೋ",
            "yi": "מאסקווע",
            "ty": "Moscou",
            "br": "Moskov",
            "el": "Μόσχα",
            "ce": "Москох",
            "tt": "Мәскәү",
            "tr": "Moskova",
            "ku": "Moskow",
            "te": "మాస్కో",
            "ie": "Moskwa",
            "sq": "Moska",
            "et": "Moskva",
            "ss": "Moscow",
            "hy": "Մոսկվա",
            "tg": "Маскав",
            "kl": "Moskva",
            "kw": "Moskva",
            "mr": "मॉस्को",
            "ka": "მოსკოვი",
            "ky": "Москва",
            "fr": "Moscou",
            "my": "မော်စကိုမြို့",
            "sm": "Moscow",
            "fy": "Moskou",
            "mk": "Москва",
            "ms": "Moscow",
            "th": "มอสโก",
            "ug": "Moskwa",
            "ur": "ماسکو",
            "bn": "মস্কো"
        },
        "lat": 55.7504461,
        "lon": 37.6174943,
        "country": "RU",
        "state": "Moscow"
    }
]

但作为回应，我得到了这样的例外

Exception in thread "main" org.springframework.web.client.RestClientException: Error while extracting response for type [class com.romanperkov.spring.rest.entity.cord] and content type [application/json;charset=utf-8]; nested exception is org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Cannot deserialize instance of `com.romanperkov.spring.rest.entity.cord` out of START_ARRAY token; nested exception is com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `com.romanperkov.spring.rest.entity.cord` out of START_ARRAY token
 at [Source: (PushbackInputStream); line: 1, column: 1]
    at org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:120)
    at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:741)
    at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:674)
    at org.springframework.web.client.RestTemplate.getForObject(RestTemplate.java:315)
    at com.romanperkov.spring.rest.Communication.test(Communication.java:81)
    at com.romanperkov.spring.rest.App.main(App.java:35)
Caused by: org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Cannot deserialize instance of `com.romanperkov.spring.rest.entity.cord` out of START_ARRAY token; nested exception is com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `com.romanperkov.spring.rest.entity.cord` out of START_ARRAY token
 at [Source: (PushbackInputStream); line: 1, column: 1]
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:284)
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.read(AbstractJackson2HttpMessageConverter.java:242)
    at org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:105)
    ... 5 more
Caused by: com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `com.romanperkov.spring.rest.entity.cord` out of START_ARRAY token
 at [Source: (PushbackInputStream); line: 1, column: 1]
    at com.fasterxml.jackson.databind.exc.MismatchedInputException.from(MismatchedInputException.java:59)
    at com.fasterxml.jackson.databind.DeserializationContext.reportInputMismatch(DeserializationContext.java:1468)
    at com.fasterxml.jackson.databind.DeserializationContext.handleUnexpectedToken(DeserializationContext.java:1242)
    at com.fasterxml.jackson.databind.DeserializationContext.handleUnexpectedToken(DeserializationContext.java:1190)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeFromArray(BeanDeserializer.java:604)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeOther(BeanDeserializer.java:190)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:166)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4526)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3521)
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:273)
    ... 7 more

Process finished with exit code 1

我了解问题是apishka的响应以方括号开头，即它返回一个数组，但它没有名称，这种情况下如何进行？

描述要从响应 API 获取的实体的类

@Getter
@Setter
@NoArgsConstructor
public class cord {

    private List<String> name;
}

问题的解决方法是将类指定为数组

String url="http://api.openweathermap.org/geo/1.0/direct?q=QWERTY&limit=5&appid=fe7e6bcec3fedc63d4a158abd1c3c3eb";
        cord[] responseEntity=restTemplate.getForObject
                (url.replace("QWERTY","москва"), cord[].class);
        System.out.println(responseEntity[0]);

2 个回答

Voted

Михаил Ребров · Answer 1 · 2022-08-09T16:10:08Z

模型

描述我们要提取的对象

本地化的城市名称更容易融入Map<String, String>

private Map<String, String> localNames;

为了不违反约定并按应有的方式调用变量 CamelCase，而不是 JSON 中的 snake_case，我们将使用 JSON 中的字段名称在字段上添加注释

@JsonProperty("local_names")
private Map<String, String> localNames;

为了更方便地使用 Map 中的本地化名称，您可以添加一个辅助方法，通过区域设置代码提取所需的名称

public String getLocalName(String locale){
    return localNames.get(locale);
}

因此，要获得法语名称，您需要调用：

city.getLocalName("fr")

全班：

import com.fasterxml.jackson.annotation.JsonProperty;
import java.util.HashMap;
import java.util.Map;

public class City {
    private String name;
    @JsonProperty("local_names")
    private Map<String, String> localNames;
    private Double lat;
    private Double lon;
    private String country;
    private String state;

    public City() {
        this.localNames = new HashMap<>();
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Map<String, String> getLocalNames() {
        return localNames;
    }

    public void setLocalNames(Map<String, String> localNames) {
        this.localNames = localNames;
    }

    public Double getLat() {
        return lat;
    }

    public void setLat(Double lat) {
        this.lat = lat;
    }

    public Double getLon() {
        return lon;
    }

    public void setLon(Double lon) {
        this.lon = lon;
    }

    public String getCountry() {
        return country;
    }

    public void setCountry(String country) {
        this.country = country;
    }

    public String getState() {
        return state;
    }

    public void setState(String state) {
        this.state = state;
    }

    public String getLocalName(String locale){
        return localNames.get(locale);
    }
}

萃取

从 JSON 中提取对象最不愉快的时刻是参数化类型（它们是泛型）

在我们的例子中，对象列表直接返回给我们，我们必须以某种方式确定类型。

我们List.class无法指定。

对于此类任务，Jackson 有一个类型工厂，可以帮助您创建基于集合类和嵌套对象类的泛型类型描述

JavaType type = mapper.getTypeFactory().constructCollectionType(List.class, City.class);

从 json 中提取对象的实际代码

String json = getSOJsonString(); // получаем JSON
ObjectMapper mapper = new ObjectMapper();
// Так как дженерики нельзя просто указать через `getClass` 
// Создаем тип для извлечения коллекции объектов 
// с помощью встроенных в Jackson конструкторов типов
JavaType type = mapper.getTypeFactory().constructCollectionType(List.class, City.class);
// маппим одно на другое
List<City> cities = mapper.readValue(json, type);
for (City city: cities) {
    // System.out.println(city.getName());
    // тут выводим все что нам надо
}

一切都正确检索。
这是从调试器中提取的示例：

更新

На момент начала написания ответа кода с RestTemplate в вопросе не было, поэтому дополняю вариант с онным.

Конкретно в случае с RestTemplate тип лучше указывать с помощью вспомогательного класса Spring'а, предназначенного ровно для того же что и вышеописанная фабрика.

В Spring есть класс ParameterizedTypeReference с помощью которого можно описать тип параметризируемого объекта (или дженерика)

Делается это так:

ParameterizedTypeReference<List<City>> type = new ParameterizedTypeReference<List<City>>() {};

при этом данный тип можно пристроить далеко не в каждый метод RestTemplate.

Лучше всего воспользоваться следующим способом:

restTemplate.exchange(myUrl, HttpMethod.GET, null, type);

В итоге код получения и извлечения объектов из REST'сервиса будет выглядеть так:

String url="http://api.openweathermap.org/geo/1.0/direct?q=QWERTY&limit=5&appid=fe7e6bcec3fedc63d4a158abd1c3c3eb";
ParameterizedTypeReference<List<City>> type = new ParameterizedTypeReference<List<City>>() {};
List<City> cities = restTemplate.exchange(url.replace("QWERTY","москва"), HttpMethod.GET, null, type).getBody();

for (City city: cities) {
    System.out.println(city);
}

注意：
在你的情况下，只会有一个类City，而不是一个类coord
。我没有举手那样称呼类，所以我从我提到的类似答案中取了名字。
类必须以大写字母命名。
这是一个约定。

不知怎的，我猜...

String url="http://api.openweathermap.org/geo/1.0/direct?q=QWERTY&limit=5&appid=fe7e6bcec3fedc63d4a158abd1c3c3eb";
ParameterizedTypeReference<List<coord>> type = new ParameterizedTypeReference<List<coord>>() {};
List<coord> coords = restTemplate.exchange(url.replace("QWERTY","москва"), HttpMethod.GET, null, type).getBody();

for (coord c: coords) {
    System.out.println(c);
}

Vadik · Answer 2 · 2022-08-09T16:27:56Z

Vadik

2022-08-09T16:27:56Z2022-08-09T16:27:56Z

你想解析一个对象，你会得到一个列表。传递TypeReferencecList<City>来解析列表：

ObjectMapper objectMapper = new ObjectMapper();
String content = "[{\"name\": \"Moscow\"}]";
TypeReference<List<City>> type = new TypeReference<>() {};
List<City> cities = objectMapper.readValue(content, type);
System.out.println(cities);

0

Jackson 如何解析没有名称的数组

模型

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Jackson 如何解析没有名称的数组

2 个回答

模型

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