I have some json:
{"continue":{"continue":"||","rvcontinue":"20021126020855|1194424"},"query":{"pages":{"468997":{"ns":0,"revisions":[{"revid":445765,"comment":"","user":"Nate Silva","parentid":0,"timestamp":"2002-11-26T02:01:24Z"}],"pageid":468997,"title":"Vodafone"}}}}
I want to parse the timestamp from the json recursively:
private static LocalDate getTimeStamp(JSONObject json) throws IOException {
Iterator<?> keys = json.keys();
LocalDate ld = null;
// iterate recursively over all keys from the JSON until current key is
// timestamp
while (keys.hasNext()) {
String key = (String) keys.next();
if (key.equals("timestamp")) {
// timezone does not matter, as we just want to extract the date
DateTimeFormatter formatter = DateTimeFormatter.ofPattern(
"yyyy-MM-dd'T'HH:mm:ss'Z'", Locale.ENGLISH);
ld = LocalDate.parse(json.get(key).toString(), formatter);
System.out.println(ld);
break;
}
// if the current value is another JSON object, call setTimeStamp
// with value as param
else if (json.get(key) instanceof JSONObject) {
getTimeStamp((JSONObject) json.get(key));
}
// handle current value being JSON array
else if (json.get(key) instanceof JSONArray) {
JSONArray jarray = (JSONArray) json.get(key);
for (int i = 0; i < jarray.length(); i++) {
if (jarray.get(i) instanceof JSONObject) {
getTimeStamp((JSONObject) jarray.get(i));
}
}
}
}
System.out.println(ld);
return ld;
}
I tried debugging it and I don't get why the method is called after I invoke break
. It returns null instead of the timestamp although it reaches that part of the code.
The "timestamp"
key is nested inside your JSON, so it takes a few recursive calls of your method to get to it.
When you make a recursive call, you should use the value returned by those calls.
change
getTimeStamp((JSONObject) json.get(key));
to
ld = getTimeStamp((JSONObject) json.get(key));
if (ld != null) return ld;
and change
getTimeStamp((JSONObject) jarray.get(i));
to
ld = getTimeStamp((JSONObject) jarray.get(i));
if (ld != null) return ld;
Your code returns null
because you ignore the results of your recursive invocations. You should store them in a variable, and return it if it's not null
:
while (keys.hasNext() && ld == null) {
...
else if (json.get(key) instanceof JSONObject) {
ld = getTimeStamp((JSONObject) json.get(key));
}
// handle current value being JSON array
else if (json.get(key) instanceof JSONArray) {
JSONArray jarray = (JSONArray) json.get(key);
for (int i = 0; i < jarray.length(); i++) {
if (jarray.get(i) instanceof JSONObject) {
ld = getTimeStamp((JSONObject) jarray.get(i));
if (ld != null)
break;
}
}
}
}
Note that since you are looking for the first timestamp, the while
loop should stop when ld
becomes non- null
.
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