Acquire an ObjectReader with ObjectMapper#readerFor(TypeReference) using a TypeReference describing the typed collection you want. Then use ObjectReader#readValue(JsonNode) to parse the JsonNode (presumably an ArrayNode).
For example, to get a List<String> out of a JSON array containing only JSON strings
CopyObjectMapper mapper = new ObjectMapper();
// example JsonNode
JsonNode arrayNode = mapper.createArrayNode().add("one").add("two");
// acquire reader for the right type
ObjectReader reader = mapper.readerFor(new TypeReference<List<String>>() {
});
// use it
List<String> list = reader.readValue(arrayNode);
Answer from Sotirios Delimanolis on Stack OverflowAcquire an ObjectReader with ObjectMapper#readerFor(TypeReference) using a TypeReference describing the typed collection you want. Then use ObjectReader#readValue(JsonNode) to parse the JsonNode (presumably an ArrayNode).
For example, to get a List<String> out of a JSON array containing only JSON strings
CopyObjectMapper mapper = new ObjectMapper();
// example JsonNode
JsonNode arrayNode = mapper.createArrayNode().add("one").add("two");
// acquire reader for the right type
ObjectReader reader = mapper.readerFor(new TypeReference<List<String>>() {
});
// use it
List<String> list = reader.readValue(arrayNode);
If an Iterator is more useful...
...you can also use the elements() method of ArrayNode. Example see below.
sample.json
Copy{
"first": [
"Some string ...",
"Some string ..."
],
"second": [
"Some string ..."
]
}
So, the List<String> is inside one of the JsonNodes.
Java
When you convert that inner node to an ArrayNode you can use the elements() method, which returns an Iterator of JsonNodes.
CopyFile file = new File("src/test/resources/sample.json");
ObjectMapper mapper = new ObjectMapper();
JsonNode jsonNode = mapper.readTree(file);
ArrayNode arrayNode = (ArrayNode) jsonNode.get("first");
Iterator<JsonNode> itr = arrayNode.elements();
// and to get the string from one of the elements, use for example...
itr.next().asText();
New to Jackson Object Mapper?
I like this tutorial: https://www.baeldung.com/jackson-object-mapper-tutorial
Update:
You can also use .iterator() method of ArrayNode. It is the same:
Same as calling
.elements(); implemented so that convenience "for-each" loop can be used for looping over elements of JSON Array constructs.
from the javadocs of com.fasterxml.jackson.core:jackson-databind:2.11.0
ObjectMapper mapper = new ObjectMapper();
List<Employee> e = new ArrayList<Employee>();
ArrayNode array = mapper.valueToTree(e);
ObjectNode companyNode = mapper.valueToTree(company);
companyNode.putArray("Employee").addAll(array);
JsonNode result = mapper.createObjectNode().set("company", companyNode);
List<String> yourList = new ArrayList<>();
((ObjectNode) someNode).set("listname", this.objectMapper.valueToTree(yourList));