Gson - 从 Json 转换为类型化的 ArrayList<T> [英] Gson - convert from Json to a typed ArrayList<T>
问题描述
使用 Gson 库，如何将 JSON 字符串转换为自定义类 JsonLog 的 ArrayList?基本上，JsonLog 是由我的 Android 应用程序制作的不同类型的日志实现的接口——短信日志、通话日志、数据日志——而这个 ArrayList 是一个集合他们都.我一直在第 6 行收到错误.
Using the Gson library, how do I convert a JSON string to an ArrayList of a custom class JsonLog? Basically, JsonLog is an interface implemented by different kinds of logs made by my Android app--SMS logs, call logs, data logs--and this ArrayList is a collection of all of them. I keep getting an error in line 6.
public static void log(File destination, JsonLog log) {
Collection<JsonLog> logs = null;
if (destination.exists()) {
Gson gson = new Gson();
BufferedReader br = new BufferedReader(new FileReader(destination));
logs = gson.fromJson(br, ArrayList<JsonLog>.class); // line 6
// logs.add(log);
// serialize "logs" again
}
}
似乎编译器不理解我指的是类型化的 ArrayList.我该怎么办?
It seems the compiler doesn't understand I'm referring to a typed ArrayList. What do I do?
推荐答案
您可以使用 TypeToken 将 json 字符串加载到自定义对象中.
You may use TypeToken to load the json string into a custom object.
logs = gson.fromJson(br, new TypeToken<List<JsonLog>>(){}.getType());
文档:
代表一个泛型类型T.
Java 还没有提供表示泛型类型的方法，所以这个类提供了.强制客户端创建此类的子类，即使在运行时也可以检索类型信息.
Java doesn't yet provide a way to represent generic types, so this class does. Forces clients to create a subclass of this class which enables retrieval the type information even at runtime.
例如，要为 List 创建类型字面量，您可以创建一个空的匿名内部类:
For example, to create a type literal for List<String>, you can create an empty anonymous inner class:
TypeToken
此语法不能用于创建具有通配符参数的类型文字，例如 Class 或 List.
This syntax cannot be used to create type literals that have wildcard parameters, such as Class<?> or List<? extends CharSequence>.
科特林:
如果您需要在 Kotlin 中执行此操作，您可以这样做:
If you need to do it in Kotlin you can do it like this:
val myType = object : TypeToken<List<JsonLong>>() {}.type
val logs = gson.fromJson<List<JsonLong>>(br, myType)
或者您可以查看此答案以了解各种替代方案.
Or you can see this answer for various alternatives.
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