右边的json formatting string为：

{"clinetId":12345,"clientName":"digital","payload":"xyz"}

所以这是正确的方法得到它：

val json = gson.toJson(invoiceAdditionalAttribute)

如果要将字符串格式化为以下格式：

{"clinetId"=12345, "clientName"="digital", "payload"="xyz"}

只需将:替换为=：

val json = gson.toJson(invoiceAdditionalAttribute).replace(":", "=")

但是如果你真的想让一个字符串中有反斜杠，并且clinetId值在引号内：

val invoiceAdditionalAttribute = mutableMapOf<String, Any?>()
invoiceAdditionalAttribute["clinetId"] = 12345.toString()
invoiceAdditionalAttribute["clientName"] = "digital"
invoiceAdditionalAttribute["payload"] = "xyz"

val json = gson.toJson(invoiceAdditionalAttribute)
        .replace(":", "=")
        .replace("\"", "\\\"")

编辑：
正如注解中指出的，如果某些字符串值包含“：“字符，.replace(":", "=")可能是脆弱的。为了避免这种情况，我将在Map<String, Any?>上编写一个自定义扩展函数：

fun Map<String, Any?>.toCustomJson(): String = buildString {
    append("{")
    var isFirst = true
    this@toCustomJson.forEach {
        it.value?.let { value ->
            if (!isFirst) {
                append(",")
            }
            isFirst = false
            append("\\\"${it.key}\\\"=\\\"$value\\\"")
        }
    }

    append("}")
}

// Using extension function

val customJson = invoiceAdditionalAttribute.toCustomJson()