参考：

1. https://github.com/yole/jkid
2. https://github.com/cbeust/klaxon

通过测试，我们发现jkad不支持map属性的json序列化，为此我们将此功能添加上去；

1. List 与 Set 考虑

因为List与Set同属于 Collection的子类，所以，修改以下serializePropertyValue方法：
将 serializeList 重名为 serializeCollection，同时新增分支 serializeMap

private fun StringBuilder.serializePropertyValue(value: Any?) {
    when (value) {
        null -> append("null")
        is String -> serializeString(value)
        is Boolean, is Number -> append(value.toString())
        is Collection<*> -> serializeCollection(value)
        is Map<*,*> -> serializeMap(value)
        else -> serializeObj(value)
    }
}

2. 属性为Map的解析方法serializeMap

map 其实就是一个JsonObject，所以大括号括起来即可，新增方法如下：
对于Map中的key，json只能使用String类型的key，所以使用toString方法；

/**
 * Map 实际上是一个 Object
 */
private fun StringBuilder.serializeMap(data: Map<*, *>) {
    data.entries.joinToStringBuilder(this, separator = ", ", prefix = "{", postfix = "}") { it ->
        serializeString(it.key.toString())       // force to String
        append(":")
        serializePropertyValue(it.value as Any)
    }
}

2.1 测试Map类型属性

data class Person(val name: String, val age: Int) {
    val map = HashMap<String, Map<String, County>>()
    init {
        val county1 = County("湘潭", 20)
        val county2 = County("长沙", 100)
        val map1 = mapOf("JavaEE" to county1, "JavaSE" to county2)

        map["Java"] = map1
        map["Kotlin"] = map1
    }
}

class MyJsonToolsTest {
    @Test
    fun testMapToJson() {
        val person = Person("Alice", 29)
        val result = serialize(person)
        println(result)
    }
}

输出如下：

{
    "age": 29,
    "map": {
        "Java": {
            "JavaEE": {
                "name": "湘潭",
                "peopleCount": 20
            },
            "JavaSE": {
                "name": "长沙",
                "peopleCount": 100
            }
        },
        "Kotlin": {
            "JavaEE": {
                "name": "湘潭",
                "peopleCount": 20
            },
            "JavaSE": {
                "name": "长沙",
                "peopleCount": 100
            }
        }
    },
    "name": "Alice"
}