JAVA,GSON :- add multiple data in json object using GSON

Question

I am trying to add multiple data in single JSON object but its getting overwritten.

I looked at some of the stackoverflow question but i couldn't find any answers .(maybe i dont know how to search in google)

Gson turn an array of data objects into json - Android

Java - Multiple GSON?

This is what i have done so far:-

This is my code using GSON library :-

JsonObject jsonObject = new JsonObject();

jsonObject.addProperty("metric", "name1");
jsonObject.addProperty("timestamp", 1443785014);
jsonObject.addProperty("value", 18);

JsonObject jObject = new JsonObject();

jObject.addProperty("host", "one");
jObject.addProperty("host1", "two");

jsonObject.add("tags",jObject);

jsonObject.addProperty("metric", "name2");
jsonObject.addProperty("timestamp", 1443785014);
jsonObject.addProperty("value", 9);

jObject.addProperty("host", "one");
jObject.addProperty("host1", "two");

jsonObject.add("tags",jObject);

System.out.println(jsonObject);

This is what i get as output :-

{
    "metric": "name2",
    "timestamp": 1346846400,
    "value": 9,
    "tags": {
       "host": "one",
       "host1": "two"
    }
}

here is what i want as output :-

[
    {
        "metric": "name1",
        "timestamp": 1346846400,
        "value": 18,
        "tags": {
           "host": "one",
           "host1": "two"
        }
    },
    {
        "metric": "name2",
        "timestamp": 1346846400,
        "value": 9,
        "tags": {
           "host": "one",
           "host1": "two"
        }
    }
]

Why i am not getting both name1 and name2 in JSON Object?

Answer 1

Creating JSONObjects and JSONArrays by hand can be really messy, here I show you how to create and show as json your data structure by using Gson library:

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
class Stats
{
    private String metric;
    private long timestamp;
    private int value;
    private Map<String,String> tags=new HashMap<>();
    /**
     * @return the metric
     */
    public String getMetric() {
        return metric;
    }
    /**
     * @param metric the metric to set
     */
    public void setMetric(String metric) {
        this.metric = metric;
    }
    /**
     * @return the timestamp
     */
    public long getTimestamp() {
        return timestamp;
    }
    /**
     * @param timestamp the timestamp to set
     */
    public void setTimestamp(long timestamp) {
        this.timestamp = timestamp;
    }
    /**
     * @return the value
     */
    public int getValue() {
        return value;
    }
    /**
     * @param value the value to set
     */
    public void setValue(int value) {
        this.value = value;
    }
    /**
     * @return the tags
     */
    public Map<String, String> getTags() {
        return tags;
    }
    /**
     * @param tags the tags to set
     */
    public void setTags(Map<String, String> tags) {
        this.tags = tags;
    }

}
public class JSON {

    public static final void main(String args[])
    {
        List<Stats> stats=new ArrayList<Stats>();
        // Fill data, you know, whatever
        Stats stat1=new Stats();
        stat1.setMetric("metric1");
        stat1.getTags().put("tag1","value1");
        stat1.getTags().put("tag2","value2");

        Stats stat2=new Stats();
        stat2.setMetric("metric2");  
        // ... Fill data...

        // ... Add stats to array
        stats.add(stat1);
        stats.add(stat2);        

        Gson gson=new GsonBuilder().setPrettyPrinting().create();
        System.out.println(gson.toJson(stats));
    }
}

Returning:

   [
  {
    "metric": "metric1",
    "timestamp": 0,
    "value": 0,
    "tags": {
      "tag2": "value2",
      "tag1": "value1"
    }
  },
  {
    "metric": "metric2",
    "timestamp": 0,
    "value": 0,
    "tags": {}
  }
]

Answer 2

You are writing into the same object and serializing it, that is why it is getting overwritten. JsonObject is just a map, writing to the same key will overwrite the existing value.

Create a JsonArray and two new JsonObject objects. Add each to the JsonArray.