Ktor Server在Postman中返回406错误的技术求助

我正在开发Android笔记应用的后端服务，测试/v1/users/register路由的POST请求时遇到问题：调用http://127.0.0.1:8080/v1/users/register接口，Postman返回406错误，数据库无新增数据（已通过Ktor创建数据表）。

相关代码与日志 #

路由代码 #

fun Route.userRoutes(db: repo, jwtService: JwtService, hashFunction: (String) -> String) {
    route("/v1/users") {
        post("/register") {
            try {
                val registerRequest = call.receive<RegisterRequest>()

                // Handle registration logic
                val user = User(registerRequest.email, hashFunction(registerRequest.password), registerRequest.name)
                db.addUser(user)
                call.respond(HttpStatusCode.OK, SimpleResponse(true, jwtService.generateToken(user)))

            } catch (e: Exception) {
                // Handle registration errors
                call.respond(HttpStatusCode.BadRequest, SimpleResponse(false, "Missing Some Fields or Registration Failed"))
            }
        }
    }
}

RegisterRequest类 #

data class RegisterRequest(
    val email: String,
    val name: String,
    val password: String
)

SimpleResponse类 #

package com.example.data.model

data class SimpleResponse(
    val success: Boolean,
    val message: String
)

控制台日志 #

2023-12-29 21:42:28.514 [eventLoopGroupProxy-4-1] TRACE io.ktor.server.routing.Routing - Trace for [v1, users, register]
/, segment:0 -> SUCCESS @ /
  /session, segment:0 -> FAILURE "Selector didn't match" @ /session
  /json, segment:0 -> FAILURE "Selector didn't match" @ /json
  /, segment:0 -> SUCCESS @ /
    /(method:GET), segment:0 -> FAILURE "Selector didn't match" @ /(method:GET)
  /v1, segment:1 -> SUCCESS @ /v1
    /v1/users, segment:2 -> SUCCESS @ /v1/users
      /v1/users/register, segment:3 -> SUCCESS @ /v1/users/register
        /v1/users/register/(method:POST), segment:3 -> SUCCESS @ /v1/users/register/(method:POST)
      /v1/users/login, segment:2 -> FAILURE "Selector didn't match" @ /v1/users/login
Matched routes:
  "" -> "v1" -> "users" -> "register" -> "(method:POST)"
Route resolve result:
  SUCCESS @ /v1/users/register/(method:POST)
2023-12-30 21:04:26.349 [eventLoopGroupProxy-4-1] TRACE i.k.server.engine.DefaultTransform - No Default Transformations found for class io.ktor.utils.io.ByteBufferChannel and expected type TypeInfo(type=class com.example.data.model.RegisterRequest, reifiedType=class com.example.data.model.RegisterRequest, kotlinType=com.example.data.model.RegisterRequest) for call /v1/users/register
2023-12-30 21:04:26.375 [eventLoopGroupProxy-4-1] TRACE i.k.s.p.c.ContentNegotiation - No suitable content converter found for request type class com.example.data.model.RegisterRequest
2023-12-30 21:04:26.384 [eventLoopGroupProxy-4-1] TRACE io.ktor.server.sessions.Sessions - Sending session data for /v1/users/register: MY_SESSION
2023-12-30 21:04:26.407 [eventLoopGroupProxy-4-1] TRACE i.k.s.p.c.ContentNegotiation - No suitable content converter found for response type class com.example.data.model.SimpleResponse and body SimpleResponse(success=false, message=Missing Some Fields)

Postman请求体 #

{
    "name": "john",
    "email": "abcd@gmail.com",
    "password": "pass"
}

序列化配置代码 #

fun Application.configureSerialization() {

    install(ContentNegotiation) {

            Json {
                prettyPrint = true
                isLenient = true
                encodeDefaults = false
            }

    }

    routing {
        get("/json/gson") {
            call.respond(mapOf("hello" to "world"))
        }
    }
}

已确认信息 #

• Postman请求头包含Content-Type: application/json和Accept: */*
• Gradle使用最新版本依赖

问题分析与解决方案 #

从日志里的No suitable content converter found for request type class com.example.data.model.RegisterRequest可以明确，问题出在Ktor的ContentNegotiation插件没有正确配置序列化转换器，导致无法将请求的JSON数据反序列化为RegisterRequest对象，也无法将SimpleResponse序列化为JSON响应。

具体修复步骤： #

1. 添加序列化依赖：
   如果使用Kotlinx Serialization，确保Gradle中添加以下依赖（替换$ktor_version为你使用的Ktor版本）：

   implementation("io.ktor:ktor-serialization-kotlinx-json-jvm:$ktor_version")
   implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.6.0")
   

2. 修正ContentNegotiation配置：
   明确指定使用Kotlinx Json转换器，修改configureSerialization函数：

   import io.ktor.serialization.kotlinx.json.*
   import kotlinx.serialization.json.Json
   
   fun Application.configureSerialization() {
       install(ContentNegotiation) {
           json(Json {
               prettyPrint = true
               isLenient = true
               encodeDefaults = false
               ignoreUnknownKeys = true // 可选，忽略请求中多余字段
           })
       }
   
       routing {
           get("/json/gson") {
               call.respond(mapOf("hello" to "world"))
           }
       }
   }
   

3. 为数据类添加序列化注解：
   给RegisterRequest和SimpleResponse添加@Serializable注解，Kotlinx Serialization需要该注解生成序列化代码：

   import kotlinx.serialization.Serializable
   
   @Serializable
   data class RegisterRequest(
       val email: String,
       val name: String,
       val password: String
   )
   

   package com.example.data.model
   
   import kotlinx.serialization.Serializable
   
   @Serializable
   data class SimpleResponse(
       val success: Boolean,
       val message: String
   )
   

4. 确认Application调用序列化配置：
   检查主Application类是否调用了configureSerialization()，示例：

   fun main(args: Array<String>): Unit = io.ktor.server.netty.EngineMain.main(args)
   
   fun Application.module() {
       configureSerialization()
       // 其他配置：configureRouting、configureDatabase等
   }
   

完成以上步骤后重启服务，再次测试注册接口，即可正常完成JSON序列化/反序列化，406错误会消失，数据库也会新增用户数据。

内容的提问来源于stack exchange，提问作者Mr Sir