call.receive<List<User>>() throws cannot cast exception when accessing elements. The so...

# ktor

[Nikola]

call.receive<List<User>>() throws cannot cast exception when accessing elements.

The solution is to wrap the list inside an object and call like this:
call.receive<Users>()

But what if I need array to be the root of the JSON? What can I do?

P.S. I'm using gson.

[Deactivated User]

I guess it is this issue, right? https://github.com/ktorio/ktor/issues/365

[Nikola]

Right. Thanks.

[Nikola]

I was wrong, that's ktor-client issue, my is ktor-server.

[Nikola]

This sample https://gist.github.com/nikolajakshic/0a7ea29a53fab557e40deb14d7d201be

[Nikola]

Throws this exception https://gist.github.com/nikolajakshic/0cba31c828c8b970da8d4e399396e0ad

[mp]

🤷 try using Jackson?

[mp]

Yep, works fine with Jackson.

post("/foo") {
                call.respond(call.receive<List<String>>().size)
            }

echo '["foo", "bar"]' | http POST 127.0.0.1:9080/foo
HTTP/1.1 200 OK
Connection: keep-alive
Content-Length: 1
Content-Type: application/json; charset=UTF-8

2

[Nikola]

try to access the element from the list, thats when the exception happens

[Nikola]

https://github.com/ktorio/ktor/issues/377

[mp]

Worked fine to get the first element too.

[mp]

Granted, I was only trying to get a List<String>

[mp]

In the short term you could use a wrapper class with a @JsonUnwrapped List field (for Jackson)