Convert JSON String to Pretty Print JSON output using Jackson

To indent any old JSON, just bind it as Object, like:

Object json = mapper.readValue(input, Object.class);

and then write it out with indentation:

String indented = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(json);

this avoids your having to define actual POJO to map data to.

Or you can use JsonNode (JSON Tree) as well.

ObjectMapper.readTree() can do this in one line:

mapper.readTree(json).toPrettyString();

Since readTree produces a JsonNode, this should pretty much always produce equivalent pretty-formatted JSON, as it JsonNode is a direct tree representation of the underlying JSON string.

Prior to Jackson 2.10

The JsonNode.toPrettyString() method was added in Jackson 2.10. Prior to that, a second call to the ObjectMapper was needed to write the pretty formatted result:

mapper.writerWithDefaultPrettyPrinter()
        .writeValueAsString(mapper.readTree(json));

The new way using Jackson 1.9+ is the following:

Object json = OBJECT_MAPPER.readValue(diffResponseJson, Object.class);
String indented = OBJECT_MAPPER.writerWithDefaultPrettyPrinter()
                               .writeValueAsString(json);

The output will be correctly formatted!

The simplest and also the most compact solution (for v2.3.3):

ObjectMapper mapper = new ObjectMapper();
mapper.enable(SerializationFeature.INDENT_OUTPUT);
mapper.writeValueAsString(obj)