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使用gson反序列化json数组

发布于 2024-09-14 08:46:15 字数 3017 浏览 2 评论 0 原文

我在反序列化以下 json 数组时遇到问题（抱歉，大小）：

"geometry": { "type": "Polygon", "coordinates": [ [ [ 771230.894373, 4422896.962001 ],
 [ 804804.852796, 4451159.130080 ], [ 876828.563339, 4417873.954498 ], [ 959794.979827, 
4430944.287708 ], [ 910992.515063, 4372980.866944 ], [ 932488.308736, 4357684.778349 ], 
[ 918573.372386, 4115663.286966 ], [ 834059.614976, 4013708.358795 ], [ 929360.231044, 
3833522.241529 ], [ 1008029.715188, 3776446.653183 ], [ 1061663.445852, 3533717.758754      
], [ 1035703.740599, 3519308.069656 ], [ 1095348.723766, 3396028.487184 ], [ 
1108462.159782, 3230455.268230 ], [ 1083571.121640, 3163122.508021 ], [ 1103953.720405, 
3082716.041755 ], [ 1045722.494771, 3020215.642212 ], [ 1117367.719045, 2915275.458735 
], [ 1141268.013718, 2827405.304519 ], [ 1286729.192338, 2790314.754276 ], [ 
1334329.406601, 2695307.513404 ], [ 829417.592210, 2374337.277646 ], [ 647042.870444, 
2207530.090128 ], [ 370914.873531, 2152159.656850 ], [ 346669.488436, 2173360.227237 ], 
[ 359905.375891, 2251757.174668 ], [ 199905.871774, 2309591.361246 ], [ 129963.835709, 
2361036.252651 ], [ 130208.738589, 2404106.913263 ], [ -964785.432600, 3159802.671416 
], [ -964829.960396, 3338713.127631 ], [ -851005.781060, 3424742.002477 ], [ -
616522.405653, 3491025.523892 ], [ -547749.224241, 3569019.334331 ], [ -403724.067052, 
3628920.873754 ], [ -423973.082428, 3724062.779415 ], [ -333893.350478, 3741450.793542 
], [ -317696.364567, 3774909.265404 ], [ -131414.328674, 3777826.527844 ], [ -
112467.751341, 3830221.719769 ], [ -185682.580436, 3930014.456814 ], [ -194499.084106, 
4129581.855629 ], [ -245950.952751, 4175549.526399 ], [ -42303.076294, 4287174.981681 
], [ -11222.674464, 4271148.905617 ], [ 131633.628071, 4371332.547494 ], [ 
433220.392528, 4427574.250017 ], [ 593119.709103, 4389089.571176 ], [ 719645.442339, 
4451856.882422 ], [ 771230.894373, 4422896.962001 ] ] ] }

如果我将其粘贴到 json 查看器中，我会得到以下结构：

[geometry]
...
[coordinates] => Array
    (
        [0] => Array
            (
                [0] => Array
                    (
                        [0] => 771230.894373
                        [1] => 4422896.962001
                    )
                [1] => Array
                    (
                        [0] => 804804.852796
                        [1] => 4451159.13008
                    )
                ...
                [n] => Array
        [n] => Array

现在，包含带有坐标的数组的数组具有可变大小。所以我想在java中，整个对象应该是一个数组，包含数组的集合，每个数组包含一个Collection。类似于 Collection[][].

但 gson 不接受这一点。我收到以下错误消息：

Exception in thread "main" com.google.gson.JsonParseException: Expecting object but     
found array: 2.963610

这看起来很奇怪，因为 2.963610 对我来说看起来不像数组。但这可能让我感到困惑，以至于我或多或少迷失了……

原文

Continuing from this question.

I'm having trouble deserializing the following json array (Sorry for the size):

"geometry": { "type": "Polygon", "coordinates": [ [ [ 771230.894373, 4422896.962001 ],
 [ 804804.852796, 4451159.130080 ], [ 876828.563339, 4417873.954498 ], [ 959794.979827, 
4430944.287708 ], [ 910992.515063, 4372980.866944 ], [ 932488.308736, 4357684.778349 ], 
[ 918573.372386, 4115663.286966 ], [ 834059.614976, 4013708.358795 ], [ 929360.231044, 
3833522.241529 ], [ 1008029.715188, 3776446.653183 ], [ 1061663.445852, 3533717.758754      
], [ 1035703.740599, 3519308.069656 ], [ 1095348.723766, 3396028.487184 ], [ 
1108462.159782, 3230455.268230 ], [ 1083571.121640, 3163122.508021 ], [ 1103953.720405, 
3082716.041755 ], [ 1045722.494771, 3020215.642212 ], [ 1117367.719045, 2915275.458735 
], [ 1141268.013718, 2827405.304519 ], [ 1286729.192338, 2790314.754276 ], [ 
1334329.406601, 2695307.513404 ], [ 829417.592210, 2374337.277646 ], [ 647042.870444, 
2207530.090128 ], [ 370914.873531, 2152159.656850 ], [ 346669.488436, 2173360.227237 ], 
[ 359905.375891, 2251757.174668 ], [ 199905.871774, 2309591.361246 ], [ 129963.835709, 
2361036.252651 ], [ 130208.738589, 2404106.913263 ], [ -964785.432600, 3159802.671416 
], [ -964829.960396, 3338713.127631 ], [ -851005.781060, 3424742.002477 ], [ -
616522.405653, 3491025.523892 ], [ -547749.224241, 3569019.334331 ], [ -403724.067052, 
3628920.873754 ], [ -423973.082428, 3724062.779415 ], [ -333893.350478, 3741450.793542 
], [ -317696.364567, 3774909.265404 ], [ -131414.328674, 3777826.527844 ], [ -
112467.751341, 3830221.719769 ], [ -185682.580436, 3930014.456814 ], [ -194499.084106, 
4129581.855629 ], [ -245950.952751, 4175549.526399 ], [ -42303.076294, 4287174.981681 
], [ -11222.674464, 4271148.905617 ], [ 131633.628071, 4371332.547494 ], [ 
433220.392528, 4427574.250017 ], [ 593119.709103, 4389089.571176 ], [ 719645.442339, 
4451856.882422 ], [ 771230.894373, 4422896.962001 ] ] ] }

If I paste it into a json-viewer, I get this structure:

[geometry]
...
[coordinates] => Array
    (
        [0] => Array
            (
                [0] => Array
                    (
                        [0] => 771230.894373
                        [1] => 4422896.962001
                    )
                [1] => Array
                    (
                        [0] => 804804.852796
                        [1] => 4451159.13008
                    )
                ...
                [n] => Array
        [n] => Array

Now, the array containing the arrays with the coordinates has a variable size. So I figured that in java, this whole object whould be an array, containing a collection of arrays, with each array containing a Collection<double[]>. Something like Collection<double[]>[][].

But gson does not accept this. I get the following error message:

Exception in thread "main" com.google.gson.JsonParseException: Expecting object but     
found array: 2.963610

Which seems weird, as 2.963610 doesnt look like an array to me. But it might have confused me to the point where I'm lost, more or less...

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﹂绝世的画 2024-09-21 08:46:16

我认为我们需要更多细节，例如您为反序列化编写的内容。

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自我难过 2024-09-21 08:46:15

我想我知道你的问题来自哪里，阅读 Gson API ：

如果你的对象是
序列化/反序列化是
ParameterizedType（即包含在
至少一个类型参数，并且可以是
数组）那么你必须使用
toJson(对象，类型) 或
fromJson(String, Type) 方法。这是
序列化和的示例
反序列化 ParameterizedType：

Type listType = new TypeToken<LinkedList>() {}.getType();
List target = new LinkedList();
target.add("blah");

Gson gson = new Gson();
String json = gson.toJson(target, listType);
List target2 = gson.fromJson(json, listType);

知道

Type typeOfCollectionOfFoo = new TypeToken<Collection<Foo>>(){}.getType()

希望这会有所帮助。

I think I know where your problem comes from, reading the Gson API :

If the object that your are
serializing/deserializing is a
ParameterizedType (i.e. contains at
least one type parameter and may be an
array) then you must use the
toJson(Object, Type) or
fromJson(String, Type) method. Here is
an example for serializing and
deserialing a ParameterizedType:

Type listType = new TypeToken<LinkedList>() {}.getType();
List target = new LinkedList();
target.add("blah");

Gson gson = new Gson();
String json = gson.toJson(target, listType);
List target2 = gson.fromJson(json, listType);

Knowing that

Type typeOfCollectionOfFoo = new TypeToken<Collection<Foo>>(){}.getType()

Hope this helps.

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澜川若宁 2024-09-21 08:46:15

JSON 中的坐标是一个三维矩阵。使用 Collection[][] 你在一维上走得太远了。 Collection 本身已经是一维的，因此您基本上已经声明了一个四维矩阵。

通过错误消息，Gson 基本上是在告诉您它正在等待第四维的对象，但它遇到了一个双精度对象。

以下代表有效的三维矩阵，应该由 Gson 完美处理：

private double[][][]坐标；（推荐）
private Collection[]坐标;
私有集合坐标;
private Collection>坐标;
private Collection>>>也就是说

，我更喜欢列表 >集合 在这种特殊情况下。使用List，您可以保证它已填充插入订单，并且您将能够按索引获取元素。

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满栀 2024-09-21 08:46:15

根据 Gson 用户指南：

序列化和反序列化通用类型
当您调用 toJson(obj) 时，Gson 会调用 obj.getClass() 来获取有关要序列化的字段的信息。同样，您通常可以在 fromJson(json, MyClass.class) 方法中传递 MyClass.class 对象。只要对象是非泛型类型，这种方法就可以正常工作。但是，如果对象是泛型类型，则由于 Java 类型擦除。下面是一个说明这一点的示例：

List<String> myStrings = new List<String>();
gson.toJson(myStrings); // Will cause a runtime exception

gson.fromJson(json, myStrings.getClass());

上面的调用会导致运行时异常，因为 Gson 调用 myStrings.getClass() 来获取其类信息，但此方法返回一个原始类 List。类。这意味着 Gson 无法知道这是一个字符串列表，而不是普通对象。

您可以通过为泛型类型指定正确的参数化类型来解决此问题。您可以使用 TypeToken 类来完成此操作。

Type listType = new TypeToken<List<String>>() {}.getType();
gson.toJson(myStrings, listType);

gson.fromJson(json, listType);

用于获取listType的习惯用法实际上定义了一个匿名本地内部类，其中包含一个返回完全参数化类型的方法getType()。

希望这有帮助。

According to Gson user guide:

Serializing and Deserializing Generic Types
When you call toJson(obj), Gson calls obj.getClass() to get information about the fields to serialize. Similarly, you can typically pass MyClass.class object in the fromJson(json, MyClass.class) method. This works fine as long as the object is a non-generic type. However, if the object is of a generic type, then the generic type information is lost because of Java Type Erasure. Here is an example illustrating the point:

List<String> myStrings = new List<String>();
gson.toJson(myStrings); // Will cause a runtime exception

gson.fromJson(json, myStrings.getClass());

The above call results in a runtime exception because Gson invokes myStrings.getClass() to get its class information, but this method returns a raw class, List.class. This means that Gson has no way of knowing that this is a list of Strings, and not plain objects.

You can solve this problem by specifying the correct parameterized type for your generic type. You can do this by using the TypeToken class.

Type listType = new TypeToken<List<String>>() {}.getType();
gson.toJson(myStrings, listType);

gson.fromJson(json, listType);

The idiom used to get listType actually defines an anonymous local inner class containing a method getType() that returns the fully parameterized type.

Hope this helps.

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