Gson 预期为 BEGIN_ARRAY，但在第 1 行第 62 列处为 STRING [英] Gson Expected BEGIN_ARRAY but was STRING at line 1 column 62

问题描述

我有以下课程:

final class CFS {
    public Map<String, String> files = new HashMap<String, String>();
    public List<String> directories = new ArrayList<String>();
}

这段代码应该解析json:

And this code which should parse the json :

CFS cfs = JStorage.getGson().fromJson(JSON_STRING, CFS.class);

哪里

JSON_STRING = "{\"directories\" : [\"folder1\", \"folder1/folder2\"], \"files\" : [{\"folder1\" : \"file.txt\"}, {\"folder1/folder2\" : \"file.cfg\"}]}"

JSON 是:

{
  "directories": ["folder1", "folder1/folder2"],
  "files": [
    {
      "folder1": "file.txt"
    }, 
    {
      "folder1/folder2": "file.cfg"
    }
  ]
}

我得到的错误是:预期为 BEGIN_ARRAY 但在第 1 行第 62 列处为 STRING

但我不知道为什么，json 根据 jsonlint 是有效的.

But I have no idea why, the json is valid according to jsonlint.

知道为什么我会收到此错误吗?

Any idea on why I am getting this error?

推荐答案

您的 JSON 有效 - 但您的映射类无效(部分不匹配).特别是，您的类的 files 属性无法从给定的 JSON 映射为 Map.很难在没有看到更大样本的情况下推荐用于存储数据的替代结构，但通常您可以在以下情况下遵循本指南JSON 结构和 Java 类之间的映射.这个 JSON:

Your JSON is valid - but your mapping class isn't (parts of it don't match). In particular, the files property of your class cannot be mapped as a Map<String, String> from the given JSON. It's hard to recommend an alternate structure for storing the data without seeing a larger sample, but in general you can follow this guide when mapping between JSON structures and Java classes. This JSON:

"files": [
    {
        "folder1": "file.txt"
    }, 
    {
        "folder1/folder2": "file.cfg"
    }
]

表示一个包含对象的数组，其中每个对象最好表示为一个映射.所以本质上是一个地图列表.因此，您的 Java 对象应该是:

represents an array containing objects, where each object is best represented as a map. So in essence, a list of maps. Consequently your Java object should be:

public class CFS {
    private List<Map<String, String>> files = new ArrayList<Map<String, String>>(
            4);
    private List<String> directories = new ArrayList<String>(4);

    // Constructors, setters/getters
}

请注意，我已通过将它们设为私有并添加 getter/setter 来更正您的属性.使用上面定义的类，您的程序应该可以正常工作.

Note that I've corrected your properties by making them private and adding getters/setters. With the above defined class your program should work just fine.

final Gson gson = new GsonBuilder().create();
final CFS results = gson.fromJson(json, CFS.class);
Assert.assertNotNull(results);
Assert.assertNotNull(results.getFiles());
System.out.println(results.getFiles());

产生:

[{folder1=file.txt}, {folder1/folder2=file.cfg}]

如果您发现自己需要保留当前的 ​​CFS 结构，则需要手动将 JSON 解析到其中.

If you find yourself needing to retain the current CFS structure though, you would need to manually parse the JSON into it.

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