HashMap to Json Array Object - Java

Question

I have a HashMap which I need to parse into JSON:

HashMap<String, Integer> worders = new HashMap<>();

I need to parse it into a JSON array of objects. Current values:

{"and": 100},
{"the": 50}

Needed JSON format:

[
{"word": "and",
"count": 100},
{"word": "the",
"count": 50}
]

I have realised that I need to use a loop to put it into the correct format, but not sure where or how to start.

I have also used the ObjectMapper() to write it as JSON, however, that does not correct the format, thank for help.

So you want to create a WordWithCount class, and populate a List<WordWithCount> with what your HashMap contains, right? HashMap has an entrySet() method, which is a set of all its entries. So you can loop over if and transform each entry into a WordWithCount. Read the javadoc. try something. — JB Nizet
– JB Nizet, Commented Dec 2, 2018 at 13:21
It's not entirely clear what you want to do here. Are you attempting to print out the JSON formatted values to the console, or store them in a data structure, or perhaps a file? Please clarify. — Matt Morgan
– Matt Morgan, Commented Dec 2, 2018 at 13:24

Tim Biegeleisen · Accepted Answer · 2018-12-02 13:23:57Z

3

You don't actually need to create a formal Java class to do this. We can try creating an ArrayNode, and then adding child JsonNode objects which represent each entry in your original hash map.

HashMap<String, Integer> worders = new HashMap<>();
worders.put("and", 100);
worders.put("the", 50);

ObjectMapper mapper = new ObjectMapper();
ArrayNode rootNode = mapper.createArrayNode();

for (Map.Entry<String, Integer> entry : worders.entrySet()) {
    JsonNode childNode = mapper.createObjectNode();
    ((ObjectNode) childNode).put("word", entry.getKey());
    ((ObjectNode) childNode).put("count", entry.getValue());
    ((ArrayNode) rootNode).add(childNode);
}

String jsonString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(rootNode);
System.out.println(jsonString);

edited Dec 2, 2018 at 13:23

answered Dec 2, 2018 at 13:17

Tim Biegeleisen

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1 Comment

dali Sarib Over a year ago

Thanks so much, exactly what I was looking for!

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