gson parsing nested json objects from google matrix api

Question

I want to do something like this posted here, but using this JSON response:

{
  "status": "OK",
  "origin_addresses": [ "Vancouver, BC, Canada", "Seattle, État de Washington, États-Unis" ],
  "destination_addresses": [ "San Francisco, Californie, États-Unis", "Victoria, BC, Canada" ],
  "rows": [ {
    "elements": [ {
      "status": "OK",
      "duration": {
        "value": 340110,
        "text": "3 jours 22 heures"
      },
      "distance": {
        "value": 1734542,
        "text": "1 735 km"
      }
    }, {
      "status": "OK",
      "duration": {
        "value": 24487,
        "text": "6 heures 48 minutes"
      },
      "distance": {
        "value": 129324,
        "text": "129 km"
      }
    } ]
  }, {
    "elements": [ {
      "status": "OK",
      "duration": {
        "value": 288834,
        "text": "3 jours 8 heures"
      },
      "distance": {
        "value": 1489604,
        "text": "1 490 km"
      }
    }, {
      "status": "OK",
      "duration": {
        "value": 14388,
        "text": "4 heures 0 minutes"
      },
      "distance": {
        "value": 135822,
        "text": "136 km"
      }
    } ]
  } ]
}

my classes are:

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

import com.google.gson.Gson;
import com.google.gson.stream.JsonReader;

class Response {
    private String status;
    private String[] destination_addresses;
    private String[] origin_addresses;
    private Elements[] rows;

    public String getStatus() {
        return status;
    }

    public void setStatus(String status) {
        this.status = status;
    }

    public String[] getDestination_addresses() {
        return destination_addresses;
    }

    public void setDestination_addresses(String[] destination_addresses) {
        this.destination_addresses = destination_addresses;
    }

    public String[] getOrigin_addresses() {
        return origin_addresses;
    }

    public void setOrigin_addresses(String[] origin_addresses) {
        this.origin_addresses = origin_addresses;
    }

    public Elements[] getRows() {
        return rows;
    }

    public void setRows(Elements[] rows) {
        this.rows = rows;
    }
}

class Distance {
    private String text;
    private String value;

    public String getText() {
        return text;
    }

    public void setText(String text) {
        this.text = text;
    }

    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }
}

class Duration {
    private String text;
    private String value;

    public String getText() {
        return text;
    }

    public void setText(String text) {
        this.text = text;
    }

    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }
}

class Elements {
    Duration duration[];
    Distance distance[];
    String status;
}

public class JSON {
    public static void main(String[] args) throws IOException {
        JsonReader reader = new JsonReader(new BufferedReader(new FileReader(
                "json.json")));
        reader.setLenient(true);
        Response r = (new Gson().fromJson(reader, Response.class));
        StringBuilder sb = new StringBuilder();
        for (String s : r.getDestination_addresses()) {
            sb.append(s);
        }
        System.out.println("getDestination_addresses: " + sb.toString());
        StringBuilder sb1 = new StringBuilder();
        for (String s : r.getOrigin_addresses()) {
            sb1.append(s);
        }
        System.out.println("getOrigin_addresses: " + sb1.toString());
        System.out.println("getStatus(): " + r.getStatus());
        System.out.println("Rows length " + r.getRows().length);
        System.out.println(r.getRows()[0].status);   // here i get null
    }
}

But it does not work fully, I can get only this fields correctly:

private String status;
private String[] destination_addresses;
private String[] origin_addresses;

the are information is null.

Did you try my solution?

giampaolo
– giampaolo

2013-12-14 06:42:12 +00:00
Commented Dec 14, 2013 at 6:42 — giampaolo
– giampaolo, Commented Dec 14, 2013 at 6:42

giampaolo · Accepted Answer · 2013-12-06 22:55:37Z

Your declarations are wrong. Change Response into

class Response {
    private String status;
    private String[] destination_addresses;
    private String[] origin_addresses;
    private Item[] rows;
    ...
}

where Item is:

 class Item {
    private Element[] elements;
    ...
 }

and Element is:

 class Element{
    Duration duration;
    Distance distance;
    String status;
    ...
 }

This should solve. Three more tips for you:

We are in full generics era, so avoid Element[] and use List instead (and so on, anycase I kept you "style" in answer)
Use something like this to visualize your JSON, it will help you to understand its structure
Duration and Distance have the same structure, maybe you can save a declaration, Gson does not care about name of classes, it looks at structure of it. From Gson point of view, Duration and Distance are the same: a string plus an integer.

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