Gson parsing string that has no key-value pairs

Question

I'm trying to parse a string with Gson library but without success. Here is my string:

[["-1.816513","52.5487566"],["-1.8164913","52.548824"]]

the problem in this example is that there are no key-value pairs. I looked at other examples but all of them had key-value pairs and didn't look like my problem.

Possible duplicate of http://stackoverflow.com/questions/2034643/parsing-json-feeds-with-google-gson?rq=1 — , Aug 30 '13 at 05:04
I think [this may be relevant](http://stackoverflow.com/questions/10800508/). But I agree with OP, this is not a candidate for closing as duplicate, at least not for the original link. This is a separate problem with a very different solution. — Brian, Aug 30 '13 at 05:31

giampaolo · Accepted Answer · 2013-08-30T07:39:11.677

My solution to parse a list of list of strings.

package stackoverflow.answers;

import java.lang.reflect.Type;
import java.util.List;

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

public class GsonTest {

  public static void main(String[] arg) {

    Gson gson = new Gson();
    String jsonOutput = "[[\"-1.816513\",\"52.5487566\"],[\"-1.8164913\",\"52.548824\"]]";
    Type listType = new TypeToken<List<List<String>>>() {}.getType();
    List<List<String>> strings = (List<List<String>>) gson.fromJson(jsonOutput, listType);
    for(List<String> inner: strings){
      for(String s: inner){
        System.out.println(s);
      }
    }

  }
}

But since values can be "thinked" also a doubles, you can parse them directly changing type into solution:

package stackoverflow.answers;

import java.lang.reflect.Type;
import java.util.List;

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

public class GsonTest {

  public static void main(String[] arg) {

    Gson gson = new Gson();
    String jsonOutput = "[[\"-1.816513\",\"52.5487566\"],[\"-1.8164913\",\"52.548824\"]]";
    Type listType = new TypeToken<List<List<Double>>>() {}.getType();
    List<List<Double>> numbers = (List<List<Double>>) gson.fromJson(jsonOutput, listType);
    for(List<Double> inner: numbers){
      for(Double d: inner){
        System.out.println(d);
      }
    }

  }
}

Not important in the context, but for future references: Java 7, Gson 2.2.4

Thanks trapo. after using String instead of Double type it worked. — Ismail Sahin, Aug 30 '13 at 05:59
:) ofcourse they should have, but in this form it gives this error : Expected BEGIN_ARRAY but was STRING at line 1 column 3 — Ismail Sahin, Aug 30 '13 at 06:06
Just since I'm curious. Are you using same Gson version as me? Moreover, are you sure that you do not have extra " ? — giampaolo, Aug 30 '13 at 06:09
Version is the same but there is much more :) sory have made a mistake now your code is working perfectly — Ismail Sahin, Aug 30 '13 at 06:13

score 1 · Answer 2 · answered Aug 30 '13 at 05:51

One solution, with raw types:

package com.stackoverflow.so18525283;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

import java.util.List;

public class App {

    private static final String INPUT = "[[\"-1.816513\",\"52.5487566\"],[\"-1.8164913\",\"52.548824\"]]";

    public static void main(final String[] args) {
        final Gson gson = new GsonBuilder().create();
        final List<?> fromJson = gson.fromJson(INPUT, List.class);
        if (fromJson != null && fromJson.size() > 0 && fromJson.get(0) instanceof List) {
            System.out.println(((List<?>) fromJson.get(0)).get(0)); // this is a String
        }
    }
}

Another solution is to recreate a valid JSON object, same App as below but with:

public static void main(String[] args) {
    final Gson gson = new GsonBuilder().create();
    final Foo fromJson = gson.fromJson("{ data: " + INPUT + "}", Foo.class);
    // TODO: check for null
    System.out.println(fromJson.data.get(0).get(0)); // this is a Double
}

private static class Foo {
    List<List<Double>> data;
}

"package com.stackoverflow.so18525283;" nice! I take the liberty of copying your package naming style :) — giampaolo, Aug 30 '13 at 05:52

Gson parsing string that has no key-value pairs

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