无法获取与正确的格式JSON对象 [英] can't fetch json object with correct format

问题描述

假如我从一个API获取一些 JSON 数组等等

<$p$p><$c$c>[{\"id\":1,\"title\":\"title\",\"description\":\"description\",\"vote\":null,\"created_at\":\"2013-11-12T21:08:10.922Z\",\"updated_at\":\"2013-11-12T21:08:10.922Z\"}]

我想检索该 JSON 为一些对象 URL_Some 网​​址

 公共类的一些实现Serializable {    私人字符串ID;
    私人字符串称号;
    私人字符串描述;
    私人字符串投票;
    私人字符串created_at;
    私人字符串的updated_at;
    } //所有的getter和setter
 

 公开名单＆LT;有的＆GT; getSome（）抛出IOException
        尝试{
            HTT prequest请求=执行（HTT prequest.get（URL_Some））;
            SomeWrapper响应= fromJson（请求，SomeWrapper.class）;
            现场[]栏= response.getClass（）getDeclaredFields（）。
            的for（int i = 0; I＆LT; fields.length;我++）
            {
                尝试{
                    Log.i（TAG，（串）域[I]获得（响应））;
                }赶上（IllegalAccessException E）{
                    e.printStackTrace（）; //改变catch语句使用文件的身体|设置|文件模板。
                }
                Log.i（TAG，字段[I] .getName（））;
            }
            如果（响应= NULL＆放大器;！＆安培;！response.results = NULL）
                返回response.results;
            返回Collections.emptyList（）;
        }赶上（HTT prequestException E）{
            扔e.getCause（）;
        }
    }
 

和 SomeWrapper 只是

 私有静态类SomeWrapper {        私人列表＆LT;有的＆GT;结果;
    }
 

问题是，我不断收到此消息。

  java.lang.IllegalStateException：预期BEGIN_OBJECT但BEGIN_ARRAY
 

PS：我用

 进口com.google.gson.Gson;进口com.google.gson.GsonBuilder;进口com.google.gson.JsonParseException;
 

解决方案

您应该JSON实际上是这样的：

{成果： [{\"id\":1,\"title\":\"title\",\"description\":\"description\",\"vote\":null,\"created_at\":\"2013-11-12T21:08:10.922Z\",\"updated_at\":\"2013-11-12T21:08:10.922Z\"}]}

GSON将尝试解析JSON并创建一个SomeWrapper对象。仅此一点就告诉他GSON将等待这种格式 {...} A JSON，因为他期待的对象。然而，你传递一个数组来代替，这就是为什么它抱怨期待BEGIN_OBJECT（ {），但越来越BEGIN_ARRAY代替（ [） 。在此之后，它会想到这个JSON对象有一个结果字段，这将持有对象的数组。

您可以创建列表＆LT;有的＆GT; 直接，而不需要一但包装类。这样做，这样做，而不是：

 键入类型=新TypeToken＆LT;名单，LT;有的＆GT;＆GT;（）{} .getType（）;
清单＆LT;有的＆GT; someList =新GsonBuilder（）创建（）fromJson（jsonArray，类型）。;
 

在这种情况下，您可以使用您发布的原始JSON阵列。

Suppose I am fetching from an api some json array as so

[{"id":1,"title":"title","description":"description","vote":null,"created_at":"2013-11-12T21:08:10.922Z","updated_at":"2013-11-12T21:08:10.922Z"}]

I want to retrieve this json as an Some object from URL_Some url

public class Some implements Serializable {

    private String id;
    private String title;
    private String description;
    private String vote;
    private String created_at;
    private String updated_at;
    }//with all getters and setters

.

public List<Some> getSome() throws IOException {
        try {
            HttpRequest request = execute(HttpRequest.get(URL_Some));
            SomeWrapper response = fromJson(request, SomeWrapper.class);
            Field[] fields = response.getClass().getDeclaredFields();
            for (int i=0; i<fields.length; i++)
            {
                try {
                    Log.i("TAG", (String) fields[i].get(response));
                } catch (IllegalAccessException e) {
                    e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
                }
                Log.i("TAG", fields[i].getName());
            }
            if (response != null && response.results != null)
                return response.results;
            return Collections.emptyList();
        } catch (HttpRequestException e) {
            throw e.getCause();
        }
    }

and SomeWrapper is simply

private static class SomeWrapper {

        private List<Some> results;
    }

The problem is that I keep on getting this message

java.lang.IllegalStateException: Expected BEGIN_OBJECT but was BEGIN_ARRAY

PS : I use

import com.google.gson.Gson;

import com.google.gson.GsonBuilder;

import com.google.gson.JsonParseException;

解决方案

Your json should actually be like this:

{"results": [{"id":1,"title":"title","description":"description","vote":null,"created_at":"2013-11-12T21:08:10.922Z","updated_at":"2013-11-12T21:08:10.922Z"}]}

Gson will try to parse the json and create a SomeWrapper object. This alone tells Gson he will wait for a json with this format {...} since he's expecting an object. However you passed an array instead, that's why it complains about expecting BEGIN_OBJECT ({) but getting BEGIN_ARRAY instead ([). After that, it will expect this json object to have a results field, which will hold an array of objects.

You can create List<Some> directly without the need of a wrapper class however. To do so do this instead:

Type type= new TypeToken<List<Some>>() {}.getType();
List<Some> someList = new GsonBuilder().create().fromJson(jsonArray, type);

In this case, you can use the original json array you posted.

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