Jackson: A Guide to Extracting JSON Values

String url = "https://ko.wikipedia.org/w/api.php?action=query&format=json&list=search&srprop=sectiontitle&srlimit=1&srsearch=grand-theft-auto-v";

String result = restTemplate.getForObject(url, String.class);

Map<String, String> jsonResult = objectMapper.readValue(result, Map.class);

The value of jsonResult is:

{
    batchcomplete: "",
    continue: {
        sroffset: 1,
        continue: "-||",
    },
    query: {
        searchinfo: {
            totalhits: 12
        },
        search: [
            {
                ns: 0,
                title: "그랜드 테프트 오토 V",
                pageid: 797633,
            }
        ],
    },
}

I am trying to retrieve the value of title.

This is what I have tried:

jsonResult.get("title")

However, it returns null.

Is there a way to extract the value of title using jackson?

javajsonjackson

Answer №1

One approach to extracting a specific field from a JSON file is by deserializing it into a JsonNode object and utilizing the power of JSON Pointer:

JsonNode rootNode = mapper.readValue(jsonFile, JsonNode.class);
String requiredField = rootNode.at("/query/search/0/title").asText();

Answer №2

One way to handle the returned JSON result is by creating a custom class for it and parsing the data accordingly.

class SearchResult:
    def __init__(self, search_info, searches):
        self.search_info = search_info
        self.searches = searches

# Parsing the JSON result
result_json = json.loads(result)
search_result = SearchResult(result_json['searchinfo'], result_json['searches'])

# Accessing specific data from the parsed result
print(search_result.searches[0]['title'])

You can find more information about mapping dynamic objects using Jackson here.

Answer №3

Reading JSON into a generic class instance in this way is not possible due to the loss of generics information during runtime.

Jackson overcomes this limitation by using an sub-classed instance of TypeReference<T> to capture the generics data.

Map<String, String> jsonMap = objectMapper.readValue(test, new TypeReference<Map<String, String>>(){});

The issue with this approach is that Map<String, String> may not accurately represent complex data structures, as seen in the provided example. The example includes not only string values but also numbers and nested objects.

In cases where it's not feasible or desired to create a dedicated class to describe the JSON structure, a better alternative is to parse the JSON into a tree structure and navigate it accordingly. For example:

JsonNode rootNode = objectMapper.readTree(test);
String title = rootNode.get("query").get("search").get(0).get("title").asText();
Integer offset = rootNode.get("continue").get("strOffset").asInt()

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