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.

Answer 1

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

Answer 2

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;
}