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copied!<p>Gson has special handling for deserializing some single-component arrays into a non-array type. For example, <code>int data = gson.fromJson("[3]", int.class);</code> would assign the int value 3 to data.</p> <p>Of course, deserializing a single-component array into a non-array type is not required. For example, the previous example could be deserialized as <code>int[] data = gson.fromJson("[3]", int[].class);</code>.</p> <p>Gson will also often deserialize a non-String value into a String, when asked. Applying this to the first example, <code>String data = gson.fromJson("[3]", String.class);</code> works just as well.</p> <p>Note that it does not work to tell Gson to deserialize the first example as type Object. <code>Object data = gson.fromJson("[3]", Object.class);</code> results in a parse exception complaining that [3] is not a primitive.</p> <p>Applied to the example in the original question above, if it's acceptable to treat all of the values as Strings, then deserialization becomes simple.</p> <pre><code>// output: // hello 1 2 // world 3 2 public class Foo { static String jsonInput = "[" + "[\"hello\",1,[2]]," + "[\"world\",3,[2]]" + "]"; public static void main(String[] args) { Gson gson = new Gson(); String[][] data = gson.fromJson(jsonInput, String[][].class); for (String[] data2 : data) { for (String data3 : data2) { System.out.print(data3); System.out.print(" "); } System.out.println(); } } } </code></pre> <p>Unfortunately, with Gson I've not been able to figure out a simple deserialization approach that would allow for "better" binding to more specific and mixed types in an array, since Java doesn't provide a syntax for defining a mixed type array. For example, the preferred type of the collection in the original question might be <code>List<List<String, int, List<int>>></code>, but that's not possible to define in Java. So, you gotta be content with <code>List<List<String>> (or String[][])</code>, or turn to an approach with more "manual" parsing.</p> <p>(Yes, Java allows a type declaration of <code>List<List<Object>></code>, but <code>Object</code> is not a specific enough type to meaningfully deserialize to. Also, as discussed, attempting to deserialize [3] to Object results in a parse exception.)</p> <hr> <p>Small Update: I recently had to deserialize some sloppy JSON that included a structure not too dissimilar from that in the original question. I ended up just using a custom deserializer to create a object from the messy JSON array. Similar to the following example.</p> <pre><code>// output: // [{MyThreeThings: first=hello, second=1, third=[2]}, // {MyThreeThings: first=world, second=3, third=[4, 5]}] import java.lang.reflect.Type; import java.util.Arrays; import com.google.gson.Gson; import com.google.gson.GsonBuilder; import com.google.gson.JsonArray; import com.google.gson.JsonDeserializationContext; import com.google.gson.JsonDeserializer; import com.google.gson.JsonElement; import com.google.gson.JsonParseException; public class FooToo { static String jsonInput = "[" + "[\"hello\",1,[2]]," + "[\"world\",3,[4,5]]" + "]"; public static void main(String[] args) { GsonBuilder gsonBuilder = new GsonBuilder(); gsonBuilder.registerTypeAdapter(MyThreeThings.class, new MyThreeThingsDeserializer()); Gson gson = gsonBuilder.create(); MyThreeThings[] things = gson.fromJson(jsonInput, MyThreeThings[].class); System.out.println(Arrays.toString(things)); } } class MyThreeThings { String first; int second; int[] third; MyThreeThings(String first, int second, int[] third) { this.first = first; this.second = second; this.third = third; } @Override public String toString() { return String.format( "{MyThreeThings: first=%s, second=%d, third=%s}", first, second, Arrays.toString(third)); } } class MyThreeThingsDeserializer implements JsonDeserializer<MyThreeThings> { @Override public MyThreeThings deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException { JsonArray jsonArray = json.getAsJsonArray(); String first = jsonArray.get(0).getAsString(); int second = jsonArray.get(1).getAsInt(); JsonArray jsonArray2 = jsonArray.get(2).getAsJsonArray(); int length = jsonArray2.size(); int[] third = new int[length]; for (int i = 0; i < length; i++) { int n = jsonArray2.get(i).getAsInt(); third[i] = n; } return new MyThreeThings(first, second, third); } } </code></pre> <p>The Gson user guide does cover handling deserialization of collections of mixed types with a similar example as this in <a href="https://sites.google.com/site/gson/gson-user-guide#TOC-Serializing-and-Deserializing-Collection-with-Objects-of-Arbitrary-Types" rel="noreferrer">the "Serializing and Deserializing Collection with Objects of Arbitrary Types" section</a>.</p>

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