如何在Spring Websocket中为@Header值创建自定义转换器/反序列化器

解决方案 #

方法一：注册自定义转换器（推荐） #

• 第一步：实现字符串到Context的转换器，假设你Header中传的context是JSON序列化字符串，示例代码如下：

import org.springframework.core.convert.converter.Converter
import com.fasterxml.jackson.databind.ObjectMapper
import com.barbarus.gameserver.websocket.Context

class StringToContextConverter(private val objectMapper: ObjectMapper) : Converter<String, Context> {
    override fun convert(source: String): Context {
        return objectMapper.readValue(source, Context::class.java)
    }
}

注意：如果你的Context是Kotlin数据类，需要引入jackson-datatype-kotlin依赖并给ObjectMapper注册Kotlin模块，避免反序列化无参构造报错
对应的ObjectMapper配置示例：

import com.fasterxml.jackson.module.kotlin.KotlinModule
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration

@Configuration
class JacksonConfig {
    @Bean
    fun objectMapper(): ObjectMapper {
        return ObjectMapper()
            .registerModule(KotlinModule())
    }
}

• 第二步：将转换器注册到WebSocket Messaging的参数解析器中，在你已有的@EnableWebSocketMessageBroker配置类中添加如下配置：

import org.springframework.core.convert.support.DefaultConversionService
import org.springframework.messaging.handler.annotation.support.HeaderMethodArgumentResolver
import org.springframework.messaging.handler.invocation.HandlerMethodArgumentResolver
import org.springframework.web.socket.config.annotation.EnableWebSocketMessageBroker
import org.springframework.web.socket.config.annotation.WebSocketMessageBrokerConfigurer

@Configuration
@EnableWebSocketMessageBroker
class WebSocketConfig(
    private val stringToContextConverter: StringToContextConverter
) : WebSocketMessageBrokerConfigurer {

    override fun addArgumentResolvers(resolvers: MutableList<HandlerMethodArgumentResolver>) {
        val conversionService = DefaultConversionService()
        conversionService.addConverter(stringToContextConverter)
        resolvers.add(HeaderMethodArgumentResolver(conversionService, null))
    }

    // 保留你原有WebSocket的其他配置，比如端点注册、消息代理配置等
}

配置完成后重启服务即可正常通过@Header context: Context直接注入转换后的对象。

方法二：临时手动转换（快速验证用） #

如果不想额外配置转换器，可以先将Header以字符串形式接收，再手动反序列化：

@MessageMapping("/gather/{resource}")
fun emitGatherEvent(
    @DestinationVariable resource: String,
    @Header context: String,
    private val objectMapper: ObjectMapper
) {     
    val contextObj = objectMapper.readValue(context, Context::class.java)
    LOG.debug("gather endpoint called for client ${contextObj.clientId} and character ${contextObj.characterId} with resource '$resource'")
    eventDispatcher.dispatchEvent(Gather(resource), contextObj.characterId)
}

内容的提问来源于stack exchange，提问作者xetra11