I am using Jackson (version 2.6+) to parse some ugly JSON that looks like this:
{
"root" : {
"dynamic123" : "Some value"
}
}
The name of the attribute dynamic123
is unfortunately not known until runtime and may differ from time to time. What I am trying to achieve is to use JsonPointer to get to the value "Some value"
. JsonPointer uses an XPath-like syntax that is described here.
// { "root" : { "dynamic123" : "Some value" } }
ObjectNode json = mapper.createObjectNode();
json.set("root", json.objectNode().put("dynamic123", "Some value"));
// Some basics
JsonNode document = json.at(""); // Ok, the entire document
JsonNode missing = json.at("/missing"); // MissingNode (as expected)
JsonNode root = json.at("/root"); // Ok -> { dynamic123 : "Some value" }
// Now, how do I get a hold of the value under "dynamic123" when I don't
// know the name of the node (since it is dynamic)
JsonNode obvious = json.at("/root/dynamic123"); // Duh, works. But the attribute name is unfortunately unknown so I can't use this
JsonNode rootWithSlash = json.at("/root/"); // MissingNode, does not work
JsonNode zeroIndex = json.at("/root[0]"); // MissingNode, not an array
JsonNode zeroIndexAfterSlash = json.at("/root/[0]"); // MissingNode, does not work
So, now to my question. Is there a way of retrieving the value "Some value"
using JsonPointer?
Obviously there are other ways of retrieving the value. One possible approach is to use the JsonNode
traversal functions – e.g. like this:
JsonNode root = json.at("/root");
JsonNode value = Optional.of(root)
.filter(d -> d.fieldNames().hasNext()) // verify that there are any entries
.map(d -> d.fieldNames().next()) // get hold of the dynamic name
.map(name -> root.get(name)) // lookup of the value
.orElse(MissingNode.getInstance()); // if it is missing
But, I am trying to avoid traversal and only use JsonPointer.
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.
Introduction This specification defines JSON Pointer, a string syntax for identifying a specific value within a JavaScript Object Notation (JSON) document [RFC4627]. JSON Pointer is intended to be easily expressed in JSON string values as well as Uniform Resource Identifier (URI) [RFC3986] fragment identifiers.
A ObjectNode provides a node for a linked list with Object data in each node.
I don't think the JsonPointer specification supports wildcards. It's pretty basic. Instead you can consider using JsonPath with the Jackson mapping provider. Here is an example:
public class JacksonJsonPath {
public static void main(String[] args) {
final ObjectMapper objectMapper = new ObjectMapper();
final Configuration config = Configuration.builder()
.jsonProvider(new JacksonJsonNodeJsonProvider())
.mappingProvider(new JacksonMappingProvider())
.build();
// { "root" : { "dynamic123" : "Some value" } }
ObjectNode json = objectMapper.createObjectNode();
json.set("root", json.objectNode().put("dynamic123", "Some value"));
final ArrayNode result = JsonPath
.using(config)
.parse(json).read("$.root.*", ArrayNode.class);
System.out.println(result.get(0).asText());
}
}
Output:
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
Some value
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