Spring Boot REST 服务：JSON 反序列化不起作用

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【中文标题】Spring Boot REST 服务：JSON 反序列化不起作用【英文标题】：Spring Boot REST Service: JSON Deserialization Not Working 【发布时间】：2016-11-16 19:20:06 【问题描述】：

我正在使用 spring-boot 和 Kotlin 开发 REST 服务。 （我应该提到这是我第一次同时使用这两种方法。）我无法让 Jackson 使用以下代码从 POST 请求中反序列化 JSON：

@RequestMapping("cloudservice/login/uuid", method = arrayOf(RequestMethod.POST))
fun login(@PathVariable(value="uuid")uuid: String, @RequestBody user: CloudServiceUser ) : ResponseEntity<CloudServiceUser> 

    val cloudServiceFactory : Class<CloudServiceFactory> = cloudServiceRepository.cloudServiceExtensions[UUID.fromString(uuid)] ?: throw InvalidPathVariableException("Invalid UUID.")
    var token : String
    try 
        token = cloudServiceFactory.newInstance().authenticationService.login(user.userId, user.password)
     catch (e:Exception )
        throw CloudServiceException(e.message)
    

    return ResponseEntity(CloudServiceUser(userId=user.userId, password = "", token = token),HttpStatus.OK)

用户对象很简单：

data class CloudServiceUser(val userId: String, val password:String, val token:String)

我得到了错误

org.springframework.http.converter.HttpMessageNotReadableException: Could not read document: Can not construct instance of com.irotsoma.cloudbackenc.cloudservice.CloudServiceUser: no suitable constructor found, can not deserialize from Object value (missing default constructor or creator, or perhaps need to add/enable type information?)
 at [Source: java.io.PushbackInputStream@682b15d6; line: 1, column: 2]; nested exception is com.fasterxml.jackson.databind.JsonMappingException: Can not construct instance of com.irotsoma.cloudbackenc.cloudservice.CloudServiceUser: no suitable constructor found, can not deserialize from Object value (missing default constructor or creator, or perhaps need to add/enable type information?)
 at [Source: java.io.PushbackInputStream@682b15d6; line: 1, column: 2]
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:229) ~[spring-web-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.read(AbstractJackson2HttpMessageConverter.java:213) ~[spring-web-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodArgumentResolver.readWithMessageConverters(AbstractMessageConverterMethodArgumentResolver.java:197) ~[spring-webmvc-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.readWithMessageConverters(RequestResponseBodyMethodProcessor.java:147) ~[spring-webmvc-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.resolveArgument(RequestResponseBodyMethodProcessor.java:125) ~[spring-webmvc-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.springframework.web.method.support.HandlerMethodArgumentResolverComposite.resolveArgument(HandlerMethodArgumentResolverComposite.java:99) ~[spring-web-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.springframework.web.method.support.InvocableHandlerMethod.getMethodArgumentValues(InvocableHandlerMethod.java:161) [spring-web-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:128) [spring-web-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:110) [spring-webmvc-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:832) [spring-webmvc-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:743) [spring-webmvc-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85) [spring-webmvc-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:961) [spring-webmvc-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:895) [spring-webmvc-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:967) [spring-webmvc-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:869) [spring-webmvc-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:648) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:843) [spring-webmvc-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) [tomcat-embed-websocket-8.0.33.jar:8.0.33]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.springframework.boot.actuate.autoconfigure.EndpointWebMvcAutoConfiguration$ApplicationContextHeaderFilter.doFilterInternal(EndpointWebMvcAutoConfiguration.java:261) [spring-boot-actuator-1.3.5.RELEASE.jar:1.3.5.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.springframework.boot.actuate.trace.WebRequestTraceFilter.doFilterInternal(WebRequestTraceFilter.java:115) [spring-boot-actuator-1.3.5.RELEASE.jar:1.3.5.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) [spring-web-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:87) [spring-web-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77) [spring-web-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:121) [spring-web-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.springframework.boot.actuate.autoconfigure.MetricsFilter.doFilterInternal(MetricsFilter.java:103) [spring-boot-actuator-1.3.5.RELEASE.jar:1.3.5.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:522) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1095) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:672) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1502) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1458) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_92]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_92]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.0.33.jar:8.0.33]
    at java.lang.Thread.run(Thread.java:745) [na:1.8.0_92]
Caused by: com.fasterxml.jackson.databind.JsonMappingException: Can not construct instance of com.irotsoma.cloudbackenc.cloudservice.CloudServiceUser: no suitable constructor found, can not deserialize from Object value (missing default constructor or creator, or perhaps need to add/enable type information?)
 at [Source: java.io.PushbackInputStream@682b15d6; line: 1, column: 2]
    at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:261) ~[jackson-databind-2.8.0.jar:2.8.0]
    at com.fasterxml.jackson.databind.DeserializationContext.instantiationException(DeserializationContext.java:1420) ~[jackson-databind-2.8.0.jar:2.8.0]
    at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1011) ~[jackson-databind-2.8.0.jar:2.8.0]
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1201) ~[jackson-databind-2.8.0.jar:2.8.0]
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:314) ~[jackson-databind-2.8.0.jar:2.8.0]
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:148) ~[jackson-databind-2.8.0.jar:2.8.0]
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3789) ~[jackson-databind-2.8.0.jar:2.8.0]
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2913) ~[jackson-databind-2.8.0.jar:2.8.0]
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:226) ~[spring-web-4.2.6.RELEASE.jar:4.2.6.RELEASE]
    ... 66 common frames omitted

但是，return 语句中的序列化可以很好地序列化为 JSON 对象并发送响应。只是反序列化不起作用。

如果我将 body 变量更改为 String 并手动创建映射器，它也可以正常工作。像这样：

@RequestMapping("cloudservice/login/uuid", method = arrayOf(RequestMethod.POST))
fun login(@PathVariable(value="uuid")uuid: String, @RequestBody user: String ) : ResponseEntity<CloudServiceUser> 

    val mapper = ObjectMapper().registerModule(KotlinModule())
    val mapperData: CloudServiceUser = mapper.readValue(user)


    val cloudServiceFactory : Class<CloudServiceFactory> = cloudServiceRepository.cloudServiceExtensions[UUID.fromString(uuid)] ?: throw InvalidPathVariableException("Invalid UUID.")
    var token : String
    try 
        token = cloudServiceFactory.newInstance().authenticationService.login(mapperData.userId, mapperData.password)
     catch (e:Exception )
        throw CloudServiceException(e.message)
    

    return ResponseEntity(CloudServiceUser(userId=mapperData.userId, password = "", token = token),HttpStatus.OK)

有什么想法吗？

这是一个开源项目，如果您需要更多信息，请随时浏览：https://github.com/irotsoma/cloudbackenc。请注意，它目前处于非常早期的状态。

编辑：只是想添加一条关于我在集成测试中遇到的麻烦的注释，如 cmets 中所接受的答案中所述。我最终没有得到能够反序列化响应的集成测试（尽管 REST 控制器方面的工作就像在生产中一样）。所以我找到了一个使用 Map 对象的解决方法，由于某种原因它能够反序列化，然后手动处理它而不是使用类对象。由于这只是测试的问题，而不是正在测试的代码，这对我来说很好。

val returnValue = template.postForEntity("REQUEST URL", httpEntity, Map::class.java)

【问题讨论】：

【参考方案1】：

您需要帮助 Jackson 反序列化数据类，如错误消息中所示。您可以通过在ObjectMapper 中注册jackson-module-kotlin 来做到这一点，如下所示：

val mapper = ObjectMapper().registerModule(KotlinModule())

告诉spring你自己定制的ObjectMapperdefine a @Bean and mark it as @Primary：

@Configuration
open class ObjectMapperConfiguration 
  @Bean
  @Primary
  open fun objectMapper() = ObjectMapper().apply  
    registerModule(KotlinModule())

进一步阅读：

How to use jackson to deserialize to Kotlin collections How do I deserialize JSON into a List<SomeType> with Kotlin + Jackson

【讨论】：

效果很好！关于让它与集成测试一起工作的任何建议？我遇到了同样的错误。我使用 JSON MediaType 创建了一个带有标头的 HttpEntity，并使用了 TestRestTemplate.postForEntity。似乎对请求进行了反序列化，但 REST 服务抛出了同样的错误，即使它在 REST 客户端正常运行时也能正常工作。 @irotsoma 确保您在测试中自定义 ObjectMapperConfiguration 是 @Imported。 我尝试的第一件事是将@Import(ObjectMapperConfiguration::class) 和@RunWith(SpringJUnit4ClassRunner::class) @SpringApplicationConfiguration(CentralController::class) @WebIntegrationTest 添加到测试类中。关于还有什么要检查的任何想法？ @irotsoma 你找到测试解决方案了吗？ 该错误也可能源于控制器参数上缺少@RequestBody。

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