Parsing nested JSON

Question

I have the following JSON:

{
 "registration": {
 "name": "Vik Kumar",
 "first_name": "Vik",
 "last_name": "Kumar",
 "bloodGroup": "B-",
 "gender": "male",
 "birthday": "10\/31\/1983",
 "email": "vik.ceo\u0040gmail.com",
 "cellPhone": "1234123456",
 "homePhone": "1234123457",
 "officePhone": "1234123458",
 "primaryAddress": "jdfjfgj",
 "area": "jfdjdfj",
 "location": {
 "name": "Redwood Shores, California",
 "id": 103107903062719
 },
 "subscribe": true,
 "eyePledge": false,
 "reference": "fgfgfgfg"
 }
}

I am using the following code to parse it:

JsonNode json = new ObjectMapper().readTree(jsonString);
JsonNode registration_fields = json.get("registration");
Iterator<String> fieldNames = registration_fields.getFieldNames();
while(fieldNames.hasNext()){
 String fieldName = fieldNames.next();
 String fieldValue = registration_fields.get(fieldName).asText();
 System.out.println(fieldName+" : "+fieldValue);
}

This works fine and it print all the values except for location which is kind of another level of nesting. I tried the same trick as above code to pass json.get("location") but that does not work. Please suggest how to make it work for location.

• Hunter McMillen: What do you mean by "does not work", do you get an error message? If so, what does it say?
• Vik: Just to be clear the above code works fine. but when i try to apply the same logic for location field then the line location_fields.getFieldNames() throws null pointer exception. I am sure i am passing the right name "location" on the first line

Answer 1

You need to detect when you are dealing with a (nested) Object using JsonNode#isObject:

public static void printAll(JsonNode node) {
 Iterator<String> fieldNames = node.getFieldNames();
 while(fieldNames.hasNext()){
 String fieldName = fieldNames.next();
 JsonNode fieldValue = node.get(fieldName);
 if (fieldValue.isObject()) {
 System.out.println(fieldName + " :");
 printAll(fieldValue);
 } else {
 String value = fieldValue.asText();
 System.out.println(fieldName + " : " + value);
 }
 }
}

Thus, when you reach an object, such as location, you'll call the printAll recursively to print all its inner values.

org.codehaus.jackson.JsonNode json = new ObjectMapper().readTree(jsonString);
org.codehaus.jackson.JsonNode registration_fields = json.get("registration");
printAll(registration_fields);

• Nagarajan Shanmuganathan: node.getFieldNames() is not available. Use node.fieldNames() instead?

Answer 2

Since location is nested within registration, you need to use:

registration_fields.get("location");

to get it. But isn't it already processed by the while-loop, why do you need to get it separately?

• João Silva: He wants to print the contents of location. Since it's an object, its text value will be empty.
• Vik: well true but in that case how do i get those values? the current code line String fieldValue = registration_fields.get(fieldName).asText() prints blank