Google Gson会将每个JSON本地文件都视为字符串，即使不是

问题描述

我不断收到Expected BEGIN_TYPE but was STRING at line 1 column 1 path $错误.我已经读过有关该错误的信息，但是遇到了一些不同的情况.

I am constantly getting Expected BEGIN_TYPE but was STRING at line 1 column 1 path $ error. I've read about that error, but I am experiencing something different.

当我尝试在我在应用程序中创建的JSON字符串上使用gson.fromJson()时，它可以很好地编译.

When I try to use gson.fromJson() on a JSON string I've created in my app it compiles fine.

     ArrayList<MyCar> cars = new ArrayList<>();
     cars.add(new MyCar());
     cars.add(new MyCar());
     String json = gson.toJson(cars);

这会编译.

     Type carList = new TypeToken<ArrayList<MyCar>>(){}.getType();
     ArrayList<MyCar> myCars = gson.fromJson(json, carList);

这也可以编译.

我的问题是，当我尝试读取自己写的本地文件或从Web下载的本地文件时(我已经在JsonLint上运行了所有本地文件，并且它们是有效的).

My problem is when I try to read from a local file I've either written myself or downloaded from the web (I have run all local files on JsonLint and they're valid).

这是写入名为testingArray.json的文件时的JSON:

Here is the JSON when written to a file named testingArray.json:

[{
    "model": "I3",
    "manufacturer": "Audi",
    "features": ["wifi", "bluetooth", "charging"]
}, {
    "model": "I3",
    "manufacturer": "Audi",
    "features": ["wifi", "bluetooth", "charging"]
}, {
    "model": "I3",
    "manufacturer": "Audi",
    "features": ["wifi", "bluetooth", "charging"]
}]

它显然以方括号而不是引号开头.

It clearly begins with brackets and not quotes.

但是这个:

 Type carList = new TypeToken<ArrayList<MyCar>>(){}.getType();
 ArrayList<MyCar> myCars = gson.fromJson(basePath + "testingArray.json", carList);

不编译并给出上述错误.

Doesn't compile and gives the aforementioned error.

为什么我傻眼了，因为当我在JSON之类的POJO上运行fromJson时，它可以工作.但是，如果我从本地文件运行SAME JSON数据，它将无法正常工作.即使它以方括号开头，它也始终将其读取为字符串.

I am dumbfounded as to why, because when I run fromJson on a POJO like JSON it works. But if I run the SAME JSON data from a local file it doesn't work. It always reads it as a string even if it begins with brackets.

推荐答案

指向文件的路径在字面上被视为JSON有效负载，因此这就是为什么您看到此异常的原因.您需要根据文件的路径创建Reader:

Path to the file is treated literally as JSON payload, so this why you see this exception. You need to create Reader based on path to the file:

try (FileReader jsonReader = new FileReader(basePath + "testingArray.json")) {
    Type carList = new TypeToken<ArrayList<MyCar>>(){}.getType();
    List<MyCar> myCars = gson.fromJson(jsonReader, carList);
}

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