我已经定义了数据类，配置了gson并创建了路由器来处理post请求，如下所示：

data class PurchaseOrder(val buyer: String, val seller: String, 
val poNumber: String, val date: String,
                     val vendorReference: String)

 install(ContentNegotiation) {
    gson {
        setDateFormat(DateFormat.LONG)
        setPrettyPrinting()
    }

    post("/purchaseOrder"){
        val po = call.receive<PurchaseOrder>()
        println("purchase order: ${po.toString()}")
        call.respondText("post received", contentType = 
        ContentType.Text.Plain)

在POST请求中发送以下JSON

{
"PurchaseOrder" : {
"buyer": "buyer a",
"seller": "seller A",
"poNumber": "PO1234",
"date": "27-Jun-2018",
"vendorReference": "Ref1234"
}
}

输出显示所有空值。

purchase order: PurchaseOrder(buyer=null, seller=null, poNumber=null, 
date=null, vendorReference=null)

从call.request.receiveChannel（）阅读数据时显示的JSON是正确的。因此，我正在接收数据，但call.receive（）似乎没有产生预期的结果。
手动获取JSON，并尝试创建PurchaseOrder，如下所示，但没有成功：

val channel = call.request.receiveChannel()
        val ba = ByteArray(channel.availableForRead)
        channel.readFully(ba)
        val s = ba.toString(Charset.defaultCharset())

        println(s) // prints JSON

        val gson = Gson()
        val po = gson.fromJson(s, PurchaseOrder::class.java)

        println("buyer = ${po.buyer}"  //prints null