com.google.gson.internal.LinkedTreeMap不能转换到我的类

问题描述

从JSON字串取得我的物件时发生问题。

I have some problems with getting my object from a JSON string.

我有产品

public class Product {
    private String mBarcode;
    private String mName;
    private String mPrice;

    public Product(String barcode, String name, String price) {
        mBarcode = barcode;
        mName = name;
        mPrice = price;
    }

    public int getBarcode() {
        return Integer.parseInt(mBarcode);
    }

    public String getName() {
        return mName;
    }

    public double getPrice() {
        return Double.parseDouble(mPrice);
    }
}    

从我的服务器，我得到一个 ArrayList< Product> in JSON字符串表示形式。例如：

From my server I get an ArrayList<Product> in JSON String representation. For example:

[{"mBarcode":"123","mName":"Apfel","mPrice":"2.7"},
{"mBarcode":"456","mName":"Pfirsich","mPrice":"1.1111"},
{"mBarcode":"89325982","mName":"Birne","mPrice":"1.5555"}] 

public static <T> String arrayToString(ArrayList<T> list) {
    Gson g = new Gson();
    return g.toJson(list);
}

要使我的对象回来，我使用这个函数：

To get my Object back I use this function:

public static <T> ArrayList<T> stringToArray(String s) {
    Gson g = new Gson();
    Type listType = new TypeToken<ArrayList<T>>(){}.getType();
    ArrayList<T> list = g.fromJson(s, listType);
    return list;
}

但是当调用

String name = Util.stringToArray(message).get(i).getName();

我得到错误
com.google.gson.internal.LinkedTreeMap不能被投射到对象。产品

我做错了什么？看起来它创建了一个LinkedTreeMaps列表，但是如何将它转换为我的产品对象？

What am I doing wrong? It looks like it created a List of LinkedTreeMaps but how do i convert those into my Product Object?

推荐答案

为了进行类型擦除，解析器不能在运行时获取真实类型T.一种解决方法是提供类类型作为方法的参数。

In my opinion, due to type erasure, the parser can't fetch the real type T at runtime. One workaround would be to provide the class type as parameter to the method.

这样的工作原理，当然还有其他可能的解决方法，但我觉得这个很清楚简洁。

Something like this works, there are certainly other possible workarounds but I find this one very clear and concise.

public static <T> List<T> stringToArray(String s, Class<T[]> clazz) {
    T[] arr = new Gson().fromJson(s, clazz);
    return Arrays.asList(arr); //or return Arrays.asList(new Gson().fromJson(s, clazz)); for a one-liner
}

并像这样调用：

String name = stringToArray(message, Product[].class).get(0).getName();

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