用gson反序列化泛型 [英] deserializing generics with gson

问题描述

我正在使用GSON 1.4并使用两个通用的 arraylist< myObject> 序列化一个对象，如下所示：
String data = Gson.toJson （object，object.class）。当我desirialize它我做 gson.fromJson（json，类型）;

可悲的是我得到

java.lang.IllegalArgumentException：无法将java.util.ArrayList
字段...设置为java.util.LinkedList

这是为什么？ GSON doc指出，如果我使用object.class参数序列化，它支持泛型。任何想法？

我的课程是： b
$ b公共列表< IndexParams> indicesParams;
public List< WeightParams> weightsParams;

public IndicesAndWeightsParams（）{
indicesParams = new ArrayList< IndexParams>（）;
weightsParams = new ArrayList< WeightParams>（）;
}
public IndicesAndWeightsParams（ArrayList< IndexParams> indicesParams，ArrayList< WeightParams> weightsParams）{
this.indicesParams = indicesParams;
this.weightsParams = weightsParams;

$ b $ public class IndexParams {

public IndexParams（）{
}
public IndexParams（String key，float value，String名称）{
this.key = key;
this.value = value;
this.name = name;
}
public String key;
公共浮动值;
公共字符串名称;

解决方案

由于Java的类型擦除。您可以阅读更多有关此处的信息。

从你的问题中我看到你正在使用 ArrayList 和 LinkedList 。你确定你不是只想使用 List ，接口？

这段代码有效： p>

 列表< String> listOfStrings = new ArrayList< String>（）; 
 
 listOfStrings.add（one）; 
 listOfStrings.add（two）; 
 
 Gson gson = new Gson（）; 
 String json = gson.toJson（listOfStrings）; 
 
 System.out.println（json）; 
 
 Type type = new TypeToken< Collection< String>>（）{}。getType（）; 
 
列表< String> fromJson = gson.fromJson（json，type）; 
 
 System.out.println（fromJson）; 
  

更新：我将您的课程更改为此，所以我不不得不乱用其他类：

  class IndicesAndWeightsParams {
 
 public List< Integer> indicesParams; 
 public List< String> weightsParams; 
 
 public IndicesAndWeightsParams（）{
 indicesParams = new ArrayList< Integer>（）; 
 weightsParams = new ArrayList< String>（）; 
} 
 public IndicesAndWeightsParams（ArrayList< Integer> indicesParams，ArrayList< String> weightsParams）{
 this.indicesParams = indicesParams; 
 this.weightsParams = weightsParams; 
 
 
 $ / code> 

使用这段代码，一切都适用于我： / p>



  ArrayList< Integer> indices = new ArrayList< Integer>（）; 
 ArrayList< String> weights = new ArrayList< String>（）; 
 
 indices.add（2）; 
 indices.add（5）; 
 
 weights.add（five）; 
 weights.add（twenty）; 
 
 IndicesAndWeightsParams iaw =新的IndicesAndWeightsParams（指数，权重）; 
 
 Gson gson = new Gson（）; 
 String string = gson.toJson（iaw）; 
 
 System.out.println（string）; 
 
 IndicesAndWeightsParams fromJson = gson.fromJson（string，IndicesAndWeightsParams.class）; 
 
 System.out.println（fromJson.indicesParams）; 
 System.out.println（fromJson.weightsParams）; 
  




I am using GSON 1.4 and serializing an object with two generic arraylist<myObject> as follows String data = Gson.toJson(object, object.class). When I desirialize it I do gson.fromJson(json, type);

sadly I get

java.lang.IllegalArgumentException: Can not set java.util.ArrayList field ... to java.util.LinkedList

Why is that ? GSON doc notes that if I serialize with object.class parameter it supports generics. any idea? thanks.

my class is :

public class IndicesAndWeightsParams {

    public List<IndexParams> indicesParams;
    public List<WeightParams> weightsParams;

    public IndicesAndWeightsParams() {
        indicesParams = new ArrayList<IndexParams>();
        weightsParams = new ArrayList<WeightParams>();
    }
    public IndicesAndWeightsParams(ArrayList<IndexParams> indicesParams, ArrayList<WeightParams> weightsParams) {
        this.indicesParams = indicesParams;
        this.weightsParams = weightsParams;
    }
}    
public class IndexParams {

    public IndexParams() {
    }
    public IndexParams(String key, float value, String name) {
      this.key = key;
      this.value = value;
      this.name = name;
    }
    public String key;
    public float value;
    public String name;
}

解决方案

Gson has some limitations regarding collections because of Java's type erasure. You can read more about it here.

From your question I see you're using both ArrayList and LinkedList. Are you sure you didn't mean to use just List, the interface?

This code works:

List<String> listOfStrings = new ArrayList<String>();

listOfStrings.add("one");
listOfStrings.add("two");

Gson gson = new Gson();
String json = gson.toJson(listOfStrings);

System.out.println(json);

Type type = new TypeToken<Collection<String>>(){}.getType();

List<String> fromJson = gson.fromJson(json, type);

System.out.println(fromJson);

Update: I changed your class to this, so I don't have to mess around with other classes:

class IndicesAndWeightsParams {

    public List<Integer> indicesParams;
    public List<String> weightsParams;

    public IndicesAndWeightsParams() {
        indicesParams = new ArrayList<Integer>();
        weightsParams = new ArrayList<String>();
    }
    public IndicesAndWeightsParams(ArrayList<Integer> indicesParams, ArrayList<String> weightsParams) {
        this.indicesParams = indicesParams;
        this.weightsParams = weightsParams;
    }
}

And using this code, everything works for me:

ArrayList<Integer> indices = new ArrayList<Integer>();
ArrayList<String> weights = new ArrayList<String>();

indices.add(2);
indices.add(5);

weights.add("fifty");
weights.add("twenty");

IndicesAndWeightsParams iaw = new IndicesAndWeightsParams(indices, weights);

Gson gson = new Gson();
String string = gson.toJson(iaw);

System.out.println(string);

IndicesAndWeightsParams fromJson = gson.fromJson(string, IndicesAndWeightsParams.class);

System.out.println(fromJson.indicesParams);
System.out.println(fromJson.weightsParams);

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