I have a json string which I need to validate and find any other keys other than in a list is there in the json string. The sample json string is
{
"required" : true,
"requiredMsg" : "Title needed",
"choices" : [ "a", "b", "c", "d" ],
"choiceSettings" : {
"a" : {
"exc" : true
},
"b" : { },
"c" : { },
"d" : {
"textbox" : {
"required" : true
}
}
},
"Settings" : {
"type" : "none"
}
}
To allow only predifined keys is exsist in the json string I want to get all the keys in the json string. How can I obtain all the keys in the json string. I am using jsonNode. My code till now is
JsonNode rootNode = mapper.readTree(option);
JsonNode reqiredMessage = rootNode.path("reqiredMessage");
System.out.println("msg : "+ reqiredMessage.asText());
JsonNode drNode = rootNode.path("choices");
Iterator<JsonNode> itr = drNode.iterator();
System.out.println("\nchoices:");
while (itr.hasNext()) {
JsonNode temp = itr.next();
System.out.println(temp.asText());
}
How to get all the keys from the json string using JsonNode
We can access a field, array or nested object using the get() method of JsonNode class. We can return a valid string representation using the asText() method and convert the value of the node to a Java int using the asInt() method of JsonNode class.
JsonNode is Jackson's tree model (object graph model) for JSON. Jackson can read JSON into a JsonNode instance, and write a JsonNode out to JSON. This Jackson JsonNode tutorial will explain how to deserialize JSON into a JsonNode and serialize a JsonNode to JSON.
JsonNode represents any valid Json structure whereas ObjectNode and ArrayNode are particular implementations for objects (aka maps) and arrays, respectively.
Read Object From JSON via URL ObjectMapper objectMapper = new ObjectMapper(); URL url = new URL("file:data/car. json"); Car car = objectMapper. readValue(url, Car. class);
forEach
will iterate over children of a JsonNode
(converted to String
when printed) and fieldNames()
gets an Iterator<String>
over keys. Here are some examples for printing elements of the example JSON:
JsonNode rootNode = mapper.readTree(option);
System.out.println("\nchoices:");
rootNode.path("choices").forEach(System.out::println);
System.out.println("\nAllKeys:");
rootNode.fieldNames().forEachRemaining(System.out::println);
System.out.println("\nChoiceSettings:");
rootNode.path("choiceSettings").fieldNames().forEachRemaining(System.out::println);
You'll probably need fields()
at some point that returns an Iterator<Entry<String, JsonNode>>
so you can iterate over key, value pairs.
This should do it.
Map<String, Object> treeMap = mapper.readValue(json, Map.class);
List<String> keys = Lists.newArrayList();
List<String> result = findKeys(treeMap, keys);
System.out.println(result);
private List<String> findKeys(Map<String, Object> treeMap , List<String> keys) {
treeMap.forEach((key, value) -> {
if (value instanceof LinkedHashMap) {
Map<String, Object> map = (LinkedHashMap) value;
findKeys(map, keys);
}
keys.add(key);
});
return keys;
}
This will print out result as
[required, requiredMsg, choices, exc, a, b, c, required, textbox, d, choiceSettings, type, Settings]
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