My problem is, PHP encodes arrays differently, based on if they are consecutive & begin with a zero index, or not. Example:
$arr = array(array(12), array(13));
===> [[12], [13]]
$arr = array("0" => array(12), "1" => array(13));
===> [[12], [13]]
$arr = array("0" => array(12), "2" => array(13));
===> {"0": [12], "2": [13]}
Why is the third one so radically different?
The first example produces a list of lists, the third example produces an object with lists. I need to convert all of these to Java 's Map<Integer, List<Double>>
. That is the most generic datatype I could find in Java for these PHP objects. I am using Gson from Google. However, since the examples produces different types of objects, I cannot just read this into a map. I have to first check if it has indices and then adding one by one to a custom map. Please look at the line that says "THERE HAS TO BE A BETTER WAY TO DO THIS PART". This is my code:
import java.lang.StringBuilder;
import com.google.gson.*;
import com.google.gson.reflect.*;
import java.util.Map;
import java.util.HashMap;
import java.util.List;
public class Saving {
public static void main(String[] args) {
String json = "[[12], [13]]";
json = json.trim();
Map<Integer, List<Double>> fuelSavings = null;
// such a cluster****
if(json.startsWith("[[")) { // THERE HAS TO BE A BETTER WAY TO DO THIS PART
// ANY WAY I CAN AVOID THIS ENTIRE IF CONDITION
//implicit keys
fuelSavings = new HashMap<Integer, List<Double>>();
List<List<Double>> temporaryList = new Gson().fromJson(json, new TypeToken<List<List<Double>>>(){}.getType());
int index = 0;
for(List<Double> temporaryListMember: temporaryList) {
fuelSavings.put(index, temporaryListMember);
index++;
}
} else {
// explicit keys
// THIS PART IS PERFECT
fuelSavings = new Gson().fromJson(json, new TypeToken<Map<Integer, List<Double>>>(){}.getType());
}
System.out.println(fuelSavings);
}
}
Any help is appreciated, thanks!
What you do in PHP are two different things. Array in PHP serves as Arrays, Maps, Lists.
array(array(12), array(13));
and array("0" => array(12), "2" => array(13));
are not the same even in PHP.
What you need to do in Java using Gson is to parse the json as String and check whether the main object is a Map
or a List
and then advise. If you have loaded a List then you know it was a array(array(12), array(13));
otherwise it was the other one.
Can't you do something from the PHP side to generate it always the same?
Edit:
If you cannot do anything from the PHP side then your check will be identical to instantiate a JsonParser
parse then checking if JsonObject.isJsonArray()
returns true, except that it will be eventually quicker but you won't rely on the gson library.
Map<Integer, List<Double>> fuelSavings = null;
JsonElement jElement = new JsonParser().parse("[[12], [13]]");
JsonObject jObject = jelement.getAsJsonObject();
if (jObject.isJsonArray()) {
fuelSavings = new HashMap<Integer, List<Double>>();
List<List<Double>> temporaryList = new Gson().fromJson(jElement, new TypeToken<List<List<Double>>>(){}.getType());
int index = 0;
for(List<Double> temporaryListMember: temporaryList) {
fuelSavings.put(index++, temporaryListMember);
}
} else /* this is a map */ {
fuelSavings = new Gson().fromJson(jElement, new TypeToken<Map<Integer, List<Double>>>(){}.getType());
}
Very interesting!
As I understood, PHP server serves its data as an ordered map encoded as JSON, but some times in a bad luck its keys are consecutive integers, which makes json_encode()
understand it as a simple array and use a different format for the outputted JSON.
As I understand, all PHP arrays are ordered maps. But when one array has consecutive integer keys, json_encode()
generates an array with no keys intead a "JSON Object" (map). And that breaks client's code that's not expecting an array instead of an "object".
Incredibly, I found no existing Java function to convert a JsonArray
to a JsonObject
, and we may even face some Exception sometimes if we try to get an array as an Object! Gosh, a JsonArray
is just a JsonObject
with implicit consecutive integer keys, it should be casted automatically!! :p
I didn't try it, but maybe JsonObject::entrySet()
can solve it. It returns a Set<Map.Entry<String,JsonElement>>
, which maybe may be converted to a Map<Integer, AnyObject>
, if Integer parses String automatically and JsonElement
can be converted with a proper TypeToken
.
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