Question

我是一名来自Python背景的新Java程序员。我有收集/返回的天气数据作为带有嵌套键的JSON，我不明白在这种情况下如何拉出值。我确定之前已经问过这个问题，但我发誓我已经搜索了很多内容而我似乎无法找到答案。现在我使用json-simple，但我尝试切换到Jackson，但仍然无法弄清楚如何做到这一点。由于Jackson / Gson似乎是最常用的库，我很乐意看到使用其中一个库的示例。下面是数据样本，后面是我目前编写的代码。

{
    "response": {
        "features": {
            "history": 1
        }
     },
    "history": {
        "date": {
            "pretty": "April 13, 2010",
            "year": "2010",
            "mon": "04",
            "mday": "13",
            "hour": "12",
            "min": "00",
            "tzname": "America/Los_Angeles"
        },
        ...
    }
}

主要功能

public class Tester {

    public static void main(String args[]) throws MalformedURLException, IOException, ParseException {
        WundergroundAPI wu =  new WundergroundAPI("*******60fedd095");

        JSONObject json = wu.historical("San_Francisco", "CA", "20100413");

        System.out.println(json.toString());
        System.out.println();
        //This only returns 1 level. Further .get() calls throw an exception
        System.out.println(json.get("history"));
    }
}

功能＆＃39;历史＆＃39;调用另一个返回JSONObject的函数

public static JSONObject readJsonFromUrl(URL url) throws MalformedURLException, IOException, ParseException {

    InputStream inputStream = url.openStream();

    try {
        JSONParser parser = new JSONParser();
        BufferedReader buffReader = new BufferedReader(new InputStreamReader(inputStream, Charset.forName("UTF-8")));

        String jsonText = readAll(buffReader);
        JSONObject json = (JSONObject) parser.parse(jsonText);
        return json;
    } finally {
        inputStream.close();
    }
}

Answer 1

使用杰克逊的树模型（Route::any('/', function() { // your redirect code goes here });），你有两个＆＃34;字面意思＆＃34;存取方法（＆＃39; get＆＃39;），返回JsonNode表示缺失值，＆＃34;安全＆＃34;访问者（＆＃39;路径＆＃39;），允许您遍历＆＃34;缺失＆＃34;节点。所以，例如：

null

将返回给定路径的值，或者，如果缺少路径，则返回0（默认值）

但更方便的是，您只需使用JSON指针表达式：

JsonNode root = mapper.readTree(inputSource);
int h = root.path("response").path("history").getValueAsInt();

还有其他方法，通常将结构实际建模为普通旧Java对象（POJO）更方便。您的内容可能类似于：

int h = root.at("/response/history").getValueAsInt();

如果是这样，您将像任何Java对象一样遍历结果对象。

Answer 2

使用Jsonpath

整数h = JsonPath.parse（json）.read（“$。response.repository.history”，Integer.class）;

Answer 3

查看杰克逊的ObjectMapper。您可以创建一个类来为JSON建模，然后使用ObjectMapper的readValue方法来反序列化＆＃39;您的JSON String到您的模型类的实例中。反之亦然。

Answer 4

尝试使用jpath API。它是JSON Data的xpath等价物。您可以通过提供将遍历JSON数据并返回请求值的jpath来读取数据。

这个Java类是实现，它有关于如何调用API的示例代码。

https://github.com/satyapaul/jpath/blob/master/JSONDataReader.java

自述 -

https://github.com/satyapaul/jpath/blob/master/README.md

示例：

JSON数据：

{
    "data": [{
        "id": "13652355666_10154605514815667",
        "uid": "442637379090660",
        "userName": "fanffair",
        "userFullName": "fanffair",
        "userAction": "recommends",
        "pageid": "usatoday",
        "fanPageName": "USA TODAY",
        "description": "A missing Indonesian man was found inside a massive python on the island of Sulawesi, according to local authorities and news reports. ",
        "catid": "NewsAndMedia",
        "type": "link",
        "name": "Indonesian man swallowed whole by python",
        "picture": "https:\/\/external.xx.fbcdn.net\/safe_image.php?d=AQBQf3loH5-XP6hH&w=130&h=130&url=https%3A%2F%2Fwww.gannett-cdn.com%2F-mm-%2F1bb682d12cfc4d1c1423ac6202f4a4e2205298e7%2Fc%3D0-5-1821-1034%26r%3Dx633%26c%3D1200x630%2Flocal%2F-%2Fmedia%2F2017%2F03%2F29%2FUSATODAY%2FUSATODAY%2F636263764866290525-Screen-Shot-2017-03-29-at-9.27.47-AM.jpg&cfs=1&_nc_hash=AQDssV84Gt83dH2A",
        "full_picture": "https:\/\/external.xx.fbcdn.net\/safe_image.php?d=AQBQf3loH5-XP6hH&w=130&h=130&url=https%3A%2F%2Fwww.gannett-cdn.com%2F-mm-%2F1bb682d12cfc4d1c1423ac6202f4a4e2205298e7%2Fc%3D0-5-1821-1034%26r%3Dx633%26c%3D1200x630%2Flocal%2F-%2Fmedia%2F2017%2F03%2F29%2FUSATODAY%2FUSATODAY%2F636263764866290525-Screen-Shot-2017-03-29-at-9.27.47-AM.jpg&cfs=1&_nc_hash=AQDssV84Gt83dH2A",
        "message": "Akbar Salubiro was reported missing after he failed to return from harvesting palm oil.",
        "link": "http:\/\/www.usatoday.com\/story\/news\/nation-now\/2017\/03\/29\/missing-indonesian-man-swallowed-whole-reticulated-python\/99771300\/",
        "source": "",
        "likes": {
            "summary": {
                "total_count": "500"
            }
        },
        "comments": {
            "summary": {
                "total_count": "61"
            }
        },
        "shares": {
            "count": "4"
        }
    }]

}

代码段：

String jPath = "/data[Array][1]/likes[Object]/summary[Object]/total_count[String]";

String value = JSONDataReader.getStringValue(jPath, jsonData);

使用Java（Jackson）读取JSON中嵌套键的值

4 个答案: