java – 使用GSON解析具有多种类型的数组

[
    [
        "hello",1,[2]
    ],[
        "world",3,[2]
    ]
]

// String json just contains the aforementioned json string.

ArrayList<ArrayList<XXX>> data = new ArrayList<ArrayList<XXX>>();

Type arrayListType = new Typetoken<ArrayList<ArrayList<XXX>>>(){}.getType();

data = gson.fromJson(json,arrayListType);

Gson具有特殊的处理方法,可以将一些单组件阵列反序列化为非阵列类型.例如,int data = gson.fromJson(“[3]”,int.class);将int值3分配给数据.

当然,不需要将单组件阵列反序列化为非数组类型.例如,前面的例子可以反序列化为int [] data = gson.fromJson(“[3]”,int [].

当询问时,Gson还会将非String值反序列化为String.将这个应用到第一个例子,String data = gson.fromJson(“[3]”,String.class);工作也是如此.

请注意,告诉Gson将第一个示例反序列化为Object类型不起作用. Object data = gson.fromJson(“[3]”,Object.class);导致一个解析异常抱怨[3]不是一个原始的.

适用于上述原始问题的示例,如果将所有值视为字符串是可以接受的,则反序列化变得简单.

// output:
// hello 1 2 
// world 3 2 

public class Foo
{
  static String jsonInput = 
    "[" +
      "[\"hello\",[2]]," +
      "[\"world\",[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();
    }
  }
}

不幸的是,使用Gson,我无法找出一种简单的反序列化方法,可以在数组中更好地绑定到更具体和混合的类型,因为Java不提供定义混合类型数组的语法.例如,原始问题中的集合的首选类型可能是List< List< String,List< int>>,但是不可能在Java中定义.所以,你必须满足List< List< String>> (或String [] []),或者转到使用更多“手动”解析的方法.

(是的,Java允许List< Object>>的类型声明,但是Object并不是有意义地反序列化的特定的类型.而且,如所讨论的,尝试反序列化[3]到Object导致解析异常. )

小更新：我最近不得不反驳一些粗糙的JSON,包括一个与原来的问题不太相似的结构.我最终只是使用自定义解串器从混乱的JSON数组创建一个对象.类似于以下示例.

// 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\"," +
          "[\"world\",[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,third);
  }
}

Gson用户指南涵盖了混合类型集合的反序列化,与the “Serializing and Deserializing Collection with Objects of Arbitrary Types” section类似.