由於專案中存在自定義型別，而Jackson的序列化與反序列化又不太會玩，轉而使用Gson，由於有生成Restful API文件的需求，使用Swagger2，最終api-docs無法正常顯示(使用Jackson一切正常)：

{
"value": "{\"swagger\":\"2.0\",\"info\":{\"description\":\"this is restful api document\",\"version\":\"1.0.0\",\"title\":\"MyApp API文件\",\"contact\":{\"name\":\"xxx\",\"url\":\"http://xxxx.com\",\"email\":\"
 
[email protected]\"}},\"host\":\"localhost:8080\",\"basePath\":\"/\",\"tags\":[{\"name\":\"login-controller\",\"description\":\"Login Controller\"},{\"name\":\"user-controller\",\"description\":\"User Controller\"}],\"paths\"
......

同時也導致/swagger-ui.html無法正常顯示。

原因：Gson的序列化問題
解決方法：自定義Gson序列化

//***注意***：這裡的`Json
 
`是`springfox.documentation.spring.web.json.Json`包下的類

class springfoxJsonToGsonAdapter : JsonSerializer<Json> {
        override fun serialize(json: Json, type: Type, jsc: JsonSerializationContext): JsonElement
                = JsonParser().parse(json.value())
}

接下來註冊到GsonHttpMessageConverter

//***注意***：`Json`同上，為`springfox.documentation.spring.web.json.Json`包下的類

class IGsonHttpMessageConverter : GsonHttpMessageConverter() {
    init {
        //自定義Gson介面卡
        super.setGson(GsonBuilder()
                .registerTypeAdapter(Json::class.java, springfoxJsonToGsonAdapter())
                .create())
    }
}

接下來訪問http://localhost:8080/v2/api-docs，得到正常結果

{
    "swagger": "2.0",
    "info": {
        "description": "this is restful api document",
        "version": "1.0.0",
        "title": "MyApp API文件",
        "contact": {
            "name": "userName",
            "url": "http://xxxuri.com",
            "email": "[email protected]"
        }
    },
    "host": "localhost:8080",
    "basePath": "/",
    "tags": [{
        "name": "login-controller",
        "description": "Login Controller"
    }, {
        "name": "user-controller",
        "description": "User Controller"
    }],
    "paths": {
        "/login/verify/{userId}": {
            "get": {
                "tags": [
                    "login-controller"
                ],
                "summary": "askGroupsAndRoles",
                "operationId": "askGroupsAndRolesUsingGET",
                "consumes": [
                    "application/json"
                ],
                "produces": [
                    "*/*"
                ],
                "parameters": [{
                    "name": "userId",
                    "in": "path",
                    "description": "userId",
                    "required": true,
                    "type": "string"
                }],
                "responses": {
                    "200": {
                        "description": "OK"
                    },
                    "401": {
                        "description": "Unauthorized"
                    },
                    "403": {
                        "description": "Forbidden"
                    },
                    "404": {
                        "description": "Not Found"
                    }
                }
            }
        }
}

Swagger UI 也正常顯示。

問題解決。