How to iterate JSON Array and extract each JSON Object from it using GSON?

Question

Below is my JSON String which I am getting back by calling from a service API. I have shorten it down by having only three reportRecords for the understanding purpose. In general, it might have ~500 reportRecords

{
   "aggRecords": {
      "reportRecords": [
         {
            "min": 0,
            "max": 12,
            "avg": 0.3699187,
            "count": 246,
            "sumSq": 571,
            "stddev": 1.4779372,
            "median": 0,
            "percentileMap": {
               "95": 4
            },
            "metricName": "TransactionDuration",
            "dimensions": {
               "env": "dev",
               "pool": "titan",
               "Name": "PostProcessing",
               "Type": "PostProcessing"
            },
            "value": 91
         },
         {
            "min": 0,
            "max": 23,
            "avg": 2.3991289E-4,
            "count": 1463031,
            "sumSq": 3071,
            "stddev": 0.045814946,
            "median": 0,
            "percentileMap": {
               "95": 0
            },
            "metricName": "TransactionDuration",
            "dimensions": {
               "env": "dev",
               "pool": "titan",
               "Name": "ResourceContext",
               "Type": "ResourceContext"
            },
            "value": 351
         },
         {
            "min": 0,
            "max": 1209,
            "avg": 1.9203402,
            "count": 7344636,
            "sumSq": 71832774,
            "stddev": 2.4683187,
            "median": 2,
            "percentileMap": {
               "95": 4
            },
            "metricName": "TransactionDuration",
            "dimensions": {
               "env": "dev",
               "pool": "titan",
               "Name": "Client::Sync",
               "Type": "Client::Sync"
            },
            "value": 14104200
         }
      ]
   },
   "minRecordsMap": {}
}

Now From the above JSON response, I need to extract reportRecords whose Name is Client::Sync. Meaning, I need to extract below reportRecords from the above JSON response only.

         {
            "min": 0,
            "max": 1209,
            "avg": 1.9203402,
            "count": 7344636,
            "sumSq": 71832774,
            "stddev": 2.4683187,
            "median": 2,
            "percentileMap": {
               "95": 4
            },
            "metricName": "TransactionDuration",
            "dimensions": {
               "env": "dev",
               "pool": "titan",
               "Name": "Client::Sync",
               "Type": "Client::Sync"
            },
            "value": 14104200
         }

And now I need to parse the above reportRecords for Client::Sync to below object -

public class DataMetrics {

    private String pool;
    private String name;
    private String type;
    private String env;
    private String metricName;
    private String percentile;
    private String median;
    private String stdDev;
    private String sumSq;
    private String count;
    private String avg;
    private String max;
    private String min;

    // getters and setters here
}

Above variable, maps like this -

pool is titan
name is Client::Sync 
type is Client::Sync
env is dev
metricNname is TransactionDuration
95th  percentile is 4
median is 2
stdDev is 2.4683187 
sumSq is 71832774 
count is 7344636 
avg is 1.9203402
max is 1209
min is 0

I am using GSON library here and below is what I have tried so far -

private static RestTemplate restTemplate = new RestTemplate();

public static void main(String[] args) {

    String jsonLine = restTemplate.getForObject("some_url", String.class);
    System.out.println(jsonLine); // here jsonLine will give me above big JSON String

    JsonElement jelement = new JsonParser().parse(jsonLine);
    JsonObject  jobject = jelement.getAsJsonObject();
    jobject = jobject.getAsJsonObject("aggRecords");
    JsonArray jarray = jobject.getAsJsonArray("reportRecords");

    // now how do I iterate JsonArray and get each JSON object
    // and then check "name" property of each object, if "Client::Sync" found, read that object for all properties
    // and set it using setters.

}

Now I am not able to understand how do I iterate JsonArray and extract each JSON object from it?

Answer 1

So you have the JsonArray object with your records, here's what you do to get your functional objects:

Type type = new TypeToken<List<DataMetrics>>() {}.getType();
List<DataMetrics> records = gson.fromJson(jsonArrayThatYouHave, type);

Then you iterate through you objects and filter the ones you need. In java 8 you can do this:

List<DataMetrics> result = records.stream().filter(record -> record.name.equals("Client::Sync")).collect(toList());

This approach is converting all objects and iterating after, if exactly this part of code is performance critical, you can still iterate through json and convert only necessary objects (but i doubt that this will be actually faster than described above).

Anyway this is more maintainable and understandable code.

UPDATE:

the same for java 7 will be:

List<DataMetrics> result = new LinkedList<>();

for(DataMetrics record : records){
   if(record.name.equals("Client::Sync")){
      result.add(record);
   }
}