com.google.gson.internal.LinkedTreeMap不能转换到我的类(com.google.gson.internal.LinkedTreeMap cannot be cast to my class)
I have some problems with getting my object from a JSON string.
I got the class Product
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);}}
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"}]
This String is generated like this:
public static <T> String arrayToString(ArrayList<T> list) {Gson g = new Gson();return g.toJson(list);}
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;}
But when calling
String name = Util.stringToArray(message).get(i).getName();
I get the errorcom.google.gson.internal.LinkedTreeMap cannot be cast to object.Product
What am I doing wrong? It looks like it created a List of LinkedTreeMaps but how do i convert those into my Product Object?
解决方案
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.
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}
And call it like:
String name = stringToArray(message, Product[].class).get(0).getName();
翻译：
问 题
从JSON字串取得我的物件时发生问题。
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：
[{“mBarcode”：“123”，“mName”：“Apfel”，“mPrice”：“ “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：
public static< T> ArrayList< T> stringToArray（String s）{Gson g = new Gson（）; 类型listType = new TypeToken< ArrayList< T>>（）{}。getType（）; ArrayList< T> list = g.fromJson（s，listType）; return list; }
但是当调
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？
解决方案
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。
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。
public static< T>列表< T> stringToArray（String s，Class< T []> clazz）{T [] arr = new Gson（）。fromJson（s，clazz）; return Arrays.asList（arr）; //或者返回Arrays.asList（new Gson（）。fromJson（s，clazz））; }
并像这样调用：
字符串名称= stringToArray（消息，Product []类）.get（0）.getName
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