在Google App Engine上返回空列表的行为在开发服务器上和部署时有所不同 [英] Returning an empty list on Google App Engine behaves differently on the dev server and when deployed

问题描述

我创建了一个返回项目列表的端点。当列表为空时，我期待在JSON中看到一个空列表，但列表字段被省略。这不是在开发服务器上发生的事情。

I've created an endpoint that returns a list of items. When the list is empty, I was expecting to see an empty list in the JSON, but the list field was instead omitted. That's not what happens on the dev server.

例：

Ex:

@ApiMethod(name = "udinic", path = "udinic")
public List<UdinicResponse> getUdinics() {
    List<UdinicResponse> list = new ArrayList<>();

    UdinicResponse res = new UdinicResponse();
    res.bla = "sds";
    list.add(res);

    return list;
}

static class UdinicResponse {
    String bla;

    public String getBla() {
        return bla;
    }

    public void setBla(String bla) {
        this.bla = bla;
    }
}

当我在dev服务器上运行这个时，我得到的答复：

When I run this on the dev server, that's the response I get:

{
items: [ ]
}

当它位于部署的服务器上时，这就是我得到的结果：

When it's on the deployed server, that's what I get:

{
kind: "udinicEndpoint#resourcesItem",
etag: ""3Ms41gaYW9qnDr8JAXr8FIDhu9jVetg""
}

任何想法如何获得一致的行为？我希望获得一个空列表，而不是省略该字段。

Any ideas how can I get a consistent behavior? I prefer to get an empty list instead of omitting the field.

推荐答案

预期的行为是空列表将被省略根据文档[1]：

The expected behavior is that empty lists will be omitted, as per the documentation [1]:

返回的空列表将作为客户端的空值到达。
记得检查这些。

Empty Lists that are returned will arrive as nulls on the client-side. Remember to check for those.

所以实际的问题是开发服务器与生产不一致。作为开发服务器一致性的解决方法，您可以添加对空列表的检查，并返回null。

So the actual issue is the development server is not consistent with production. As a workaround for consistency on the development server, you can add a check for an empty list and return null instead.

return list.isEmpty() ? null : list;

[1] https://cloud.google.com/solutions/mobile/google-cloud-endpoints-for-android/

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