How to parse a JSON string into JsonNode in Jackson?

Question

It should be so simple, but I just cannot find it after being trying for an hour #embarrasing.

I need to get a JSON string, for example, {"k1":v1,"k2":v2}, parsed as a JsonNode.

JsonFactory factory = new JsonFactory();
JsonParser jp = factory.createJsonParser("{\"k1\":\"v1\"}");
JsonNode actualObj = jp.readValueAsTree();

gives

java.lang.IllegalStateException: No ObjectCodec defined for the parser, can not deserialize JSON into JsonNode tree

Answer 1

A slight variation on Richards answer but readTree can take a string so you can simplify it to:

ObjectMapper mapper = new ObjectMapper();
JsonNode actualObj = mapper.readTree("{\"k1\":\"v1\"}");

Answer 2

You need to use an ObjectMapper:

ObjectMapper mapper = new ObjectMapper();
JsonFactory factory = mapper.getJsonFactory(); // since 2.1 use mapper.getFactory() instead
JsonParser jp = factory.createJsonParser("{\"k1\":\"v1\"}");
JsonNode actualObj = mapper.readTree(jp);

Further documentation about creating parsers can be found here.

Answer 3

A third variant:

ObjectMapper mapper = new ObjectMapper();
JsonNode actualObj = mapper.readValue("{\"k1\":\"v1\"}", JsonNode.class);

Answer 4

Richard's answer is correct. Alternatively you can also create a MappingJsonFactory (in org.codehaus.jackson.map) which knows where to find ObjectMapper. The error you got was because the regular JsonFactory (from core package) has no dependency to ObjectMapper (which is in the mapper package).

But usually you just use ObjectMapper and do not worry about JsonParser or other low level components -- they will just be needed if you want to data-bind parts of stream, or do low-level handling.

Answer 5

import com.github.fge.jackson.JsonLoader;
JsonLoader.fromString("{\"k1\":\"v1\"}")
== JsonNode = {"k1":"v1"}