java - GSON 如何决定它在反序列化过程中使用哪个 TypeAdapter？

Question

我遇到了问题，App Engine 将 Long/long 值返回为“String”。这是返回的 JSON 文件的一部分:

  "stringObject" : "This is a string.",
  "integerPrimitive" : -3,
  "intergerObject" : 3333,
  "longPrimitive" : "1234567890123456789",
  "longObject" : "1234567890123456789",

以及产生它的服务器端数据类型:

private String stringObject = "This is a string.";
private int integerPrimitive = -3;
private Integer intergerObject = 3333;
private long longPrimitive = 1234567890123456789L;
private Long longObject = 1234567890123456789L;

我已经写了一个 TypeAdapter 来处理 Long，但是在反序列化过程中，GSON 似乎并不看目标变量，而是看 JSON 本身。换句话说:它似乎仍然为 Long/long 调用 String TypeAdapter，至少我的 TypeAdapter 中的断点从未达到(不过这也可能是反射的产物)。这是可能的还是我的 TypeAdapter 有其他问题？ GSON 如何确定它调用哪个适配器。

public class LongTypeAdapter extends TypeAdapter<Long> {

    // Long/long is converted to String by AppEngine 0L -> "0"

    @Override public void write(JsonWriter writer, Long value) throws IOException {
        if (value == null) {
            writer.nullValue();
            return;
        }
        String text = "\"" + String.valueOf(value) + "\"";
        writer.value(text);
    }

    @Override public Long read(JsonReader reader) throws IOException {
        if (reader.peek() == JsonToken.NULL) {
            reader.nextNull();
            return null;
        }
        String text = reader.nextString();
        text = text.replaceAll("\"", "");
        Long value = Long.parseLong(text);
        return value;
    }

}

我调试到 GSON 并且我的适配器已正确注册，所以我很可能会在此处排除注册问题。

---

适配器是这样注册的:

public class Backend {

    // Singleton
    private static volatile BackendInterface service = null;
    private Backend() {} // exists only to defeat instantiation

    public static BackendInterface api() {
        if (service == null) { // lazy initialization

            final Gson gson = new GsonBuilder()
                    .registerTypeAdapter(Long.class, new LongTypeAdapter())
                    .create();

            RestAdapter restAdapter = new RestAdapter.Builder()
                    .setEndpoint(Constants.BACKEND_API_ENDPOINT)
                    .setClient(new OkClient())
                    .setLogLevel(RestAdapter.LogLevel.FULL) // TODO remove full logging for production
                    .setConverter(new GsonConverter(gson))
                    .build();

            service = restAdapter.create(BackendInterface.class);

        }
        return service;
    }

}

下面是我如何使用它:

Test test = Backend.api().getTest(2L);

Answer 1

那么您必须注册新型适配器:

final Gson gson = new GsonBuilder().registerTypeAdapter(Long.class,
                    new LongTypeAdapter()).create();

希望对你有帮助