如何用 Gson 序列化 java.nio.file.Path？

Question

我在尝试序列化包含java.nio.file.Path 的Object 时收到java.lang.StackOverflowError

即使我写了：

public class PathConverter implements JsonDeserializer<Path>, JsonSerializer<Path> {
    @Override
    public Path deserialize(JsonElement jsonElement, Type type, JsonDeserializationContext jsonDeserializationContext) throws JsonParseException {
        return Paths.get(jsonElement.getAsString());
    }

    @Override
    public JsonElement serialize(Path path, Type type, JsonSerializationContext jsonSerializationContext) {
        return new JsonPrimitive(path.toString());
    }
}

并应用它：

    String json = new GsonBuilder()
            .registerTypeAdapter(Path.class, new PathConverter())
            .create()
            .toJson(constructorSetup, new TypeToken<ConstructorSetup>() {}.getType());

我还是不能序列化这个类：

public class ConstructorSetup {

    private Path appIconMimmapDirPathOnPc;

}

Stacktrace：（pastebin 已满）

Exception in thread "main" java.lang.StackOverflowError
    at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
    at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
    at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
        ...
    at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
    at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:355)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:117)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:72)
    at com.google.gson.Gson.getAdapter(Gson.java:356)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.<init>(ReflectiveTypeAdapterFactory.java:82)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:81)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:118)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:72)
    at com.google.gson.Gson.getAdapter(Gson.java:356)
        ...
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.<init>(ReflectiveTypeAdapterFactory.java:82)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:81)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:118)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:72)
    at com.google.gson.Gson.getAdapter(Gson.java:356)

有什么办法吗？

Answer 1

您的问题是Path 是interface。假设您使用了Paths.get("/")，它将在我的Windows PC 上创建类似WindowsPath 的实例。现在，你必须告诉 GSON 如何反序列化这个类型：

ConstructorSetup setup = new ConstructorSetup();
setup.setAppIconMimmapDirPathOnPc(Paths.get("/"));

// here we get actual class type of our Path object
Class classT = setup.getAppIconMimmapDirPathOnPc().getClass();

Gson gson = new GsonBuilder().registerTypeAdapter(classT, new MyPathConverter())

您可以使用的另一种方法是registerTypeHierarchyAdapter：

.registerTypeHierarchyAdapter(Path.class, new MyPathConverter())

typeHierarchyAdapter 的目的是涵盖当您希望某个类型的所有子类型具有相同表示的情况，这正是您使用 Path 的情况。