Spring 如何调试HttpMessageTreadableException？

我有这样一个DTO对象：

data class ClientDto(
        var uuid: String,
        var ip: String,
        var lastSeen: Date? = Date()
) {
    internal fun toEntity() = Client(uuid=uuid, ip=ip, lastSeen=Date())
}

@RestController
internal class ClientController {

    @Autowired
    private lateinit var service : ClientService

    @GetMapping("/clients")
    internal fun getClients() =  service.findAll()

    @PostMapping("/clients")
    internal fun postClient(@RequestBody client: ClientDto) = service.add(client)
}

。。。还有这样一个控制器：

data class ClientDto(
        var uuid: String,
        var ip: String,
        var lastSeen: Date? = Date()
) {
    internal fun toEntity() = Client(uuid=uuid, ip=ip, lastSeen=Date())
}

@RestController
internal class ClientController {

    @Autowired
    private lateinit var service : ClientService

    @GetMapping("/clients")
    internal fun getClients() =  service.findAll()

    @PostMapping("/clients")
    internal fun postClient(@RequestBody client: ClientDto) = service.add(client)
}

现在我在httpie上发布如下内容：

http POST localhost:8080/clients uuid=my-uuid ip=192.123.31:8080

并获得：

{
    "error": "Bad Request",
    "exception": "org.springframework.http.converter.HttpMessageNotReadableException",
    "message": "JSON parse error: Can not construct instance of awesome.discovery.domain.dto.ClientDto: no suitable constructor found, can not deserialize from Object value (missing default constructor or creator, or perhaps need to add/enable type information?); nested exception is com.fasterxml.jackson.databind.JsonMappingException: Can not construct instance of awesome.discovery.domain.dto.ClientDto: no suitable constructor found, can not deserialize from Object value (missing default constructor or creator, or perhaps need to add/enable type information?)\n at [Source: java.io.PushbackInputStream@71c6ae97; line: 1, column: 2]",
    "path": "/clients",
    "status": 400,
    "timestamp": 1519587678605
}

这个帖子怎么了

更重要的是，我如何调试它，例如，知道它尝试了什么，以及如何理解它出错的地方

---

1-DTO需要提供默认构造函数（没有参数的空构造函数）。错误就是这么说的

---

2-Spring将Jackson配置为根据

RequestParam

的类型使用反射自动反序列化JSON。您可以通过实现

JsonDeserializer

自定义此行为。如果您想调试，可以在带有

PostMapping

注释的方法上设置断点。我知道kotlins默认构造函数的设置与我在数据类中所做的相同。啊，您是对的。这里有一个关于Java中默认构造函数的可视性的答案：没错，我没有使用kotlin，但我在ProjectLombok的

数据

和

值

注释中遇到了类似的问题