Java 为什么我的Spring Boot转换器在其他转换器不工作时不工作

我一直无法理解为什么我的一些Spring Boot转换器不能工作。我已经制作了两个转换器，它们实现了convert方法，扩展了webmvcconfiguer，覆盖了addFormatters方法，并在那里添加了所有转换器。一些th转换器正在工作，但我必须在转换器类中包含一些repo，因为转换中使用了来自它们的数据。 一些示例代码

    //this one does work
@Component
class ReviewToDtoConverter: Converter<Review, ReviewDto> {
    override fun convert(review: Review): ReviewDto {
        return ReviewDto(review)
    }
}

//this one does not work
@Component
class DtoToReviewConverter: Converter<ReviewDto,Review> {

    @field:Autowired
    lateinit var userRepo: UserRepo

    @field:Autowired
    lateinit var productRepo: ProductRepo

    override fun convert(reviewDto: ReviewDto): Review? {

        return Review(
            reviewDto = reviewDto,
            user = try {userRepo.findByIdUser(reviewDto.userId ?: throw UserNotProvidedException("The User was not provided"))}
            catch (e: EmptyResultDataAccessException)
            { throw UserNotFoundException("The user could not be found")},
            product = try {productRepo.findByUpc(reviewDto.upc)}
            catch (e: EmptyResultDataAccessException)
            {throw ProductNotFoundException("The product could not be found")}
        )
    }
}

我不得不添加MyConversionService类，因为我在spring前后遇到了一个错误，不知道使用哪个bean，这是我发现唯一有效的解决方案

我在哪里使用转换服务

    @RestController
@RequestMapping("/review")
class ReviewController(val reviewService: ReviewService, val conversionService: MyConversionService) {

    @PutMapping(params = ["upc", "userId"])
    fun updateReview(@RequestParam("upc") upc: Int, @RequestParam("userId") userId: Int, @RequestBody reviewDto: ReviewDto): ReviewDto {
        reviewDto.userId = userId
        reviewDto.upc = upc
        conversionService.addConverter(DtoToReviewConverter())
        println("can convert " + conversionService.canConvert(ReviewDto::class.java, Review::class.java))

        return conversionService.convert(reviewService.updateReview(upc, userId, conversionService.convert(reviewDto, Review::class.java) ?: throw CustomConversionException("There was a problem")), ReviewDto::class.java) ?: throw CustomConversionException("There was a problem")

    }

    @PostMapping(params = ["upc", "userId"])
    fun saveReview(@RequestParam("upc") upc: Int, @RequestParam("userId") userId: Int, @RequestBody reviewDto: ReviewDto): ReviewDto {
        reviewDto.userId = userId
        reviewDto.upc = upc
        return conversionService.convert(reviewService.saveReview(
            upc = upc,
            userId = userId,
            review = conversionService.convert(reviewDto, Review::class.java) ?: throw CustomConversionException("There was a problem")
        ), ReviewDto::class.java) ?: throw CustomConversionException("There was a problem")
    }

    @GetMapping(params = ["userId"])
    fun getReviewsByUser(@RequestParam("userId") userId: Int): List<ReviewDto> {
        return reviewService.getReviewsByUser(userId).map { conversionService.convert(it, ReviewDto::class.java) ?: throw CustomConversionException("There was a problem") }
    }

    @GetMapping(params = ["upc"])
    fun getReviewsByProduct(@RequestParam("upc") upc: Int): List<ReviewDto> {
        return reviewService.getReviewsByProduct(upc).map { conversionService.convert(it, ReviewDto::class.java) ?: throw CustomConversionException("There was a problem") }
    }
}

我尝试将repos添加到一个工作的转换器类中，认为它可能会停止工作，但它仍然工作

不知道去哪里，因为堆栈跟踪对我没有帮助

---

更新我认为我已经取得了一些进展，我非常确定这个问题与spring实例化bean的顺序有关。我只是不知道现在如何正确设置一切。似乎如果我能改变spring执行自动布线的方式，我就能解决这个问题，我相信可能的原因是类的签名与转换器的返回类型不匹配。因此，即使您已将转换器定义为返回类型为

Review

的对象，您的转换器方法仍返回类型为

Review？

的对象。可为null的类型与Kotlin中的不可为null的类型有着本质上的不同。要解决此问题，您可以将转换器的通用类型更新为

Review？

，或确保转换器函数的返回类型为

Review

---

本文讨论Kotlin中的可空性和泛型，看看这是否有帮助：

您能发布转换器的定义吗？不确定您的意思。你在找什么？我想我把定义放在了您发布的第一个代码块中，您发布了适用于订单的

ordertoConverter

和

dtoOrderConverter

，但错误是关于

Review

，所以我们需要查看

Review

相关转换器。在你的代码中，我相信这就是所谓的

reviewToToConverter

。哇，我真的没注意到。发布的订单和评论的实现和错误基本相同。谢谢，我也对此提出了质疑，并尝试使用转换器返回可选值和非可选值。我两个都得到了同样的结果。查看我的最新更新。我认为这个问题与bean被实例化的顺序以及spring如何自动连接它们有关

    @RestController
@RequestMapping("/review")
class ReviewController(val reviewService: ReviewService, val conversionService: MyConversionService) {

    @PutMapping(params = ["upc", "userId"])
    fun updateReview(@RequestParam("upc") upc: Int, @RequestParam("userId") userId: Int, @RequestBody reviewDto: ReviewDto): ReviewDto {
        reviewDto.userId = userId
        reviewDto.upc = upc
        conversionService.addConverter(DtoToReviewConverter())
        println("can convert " + conversionService.canConvert(ReviewDto::class.java, Review::class.java))

        return conversionService.convert(reviewService.updateReview(upc, userId, conversionService.convert(reviewDto, Review::class.java) ?: throw CustomConversionException("There was a problem")), ReviewDto::class.java) ?: throw CustomConversionException("There was a problem")

    }

    @PostMapping(params = ["upc", "userId"])
    fun saveReview(@RequestParam("upc") upc: Int, @RequestParam("userId") userId: Int, @RequestBody reviewDto: ReviewDto): ReviewDto {
        reviewDto.userId = userId
        reviewDto.upc = upc
        return conversionService.convert(reviewService.saveReview(
            upc = upc,
            userId = userId,
            review = conversionService.convert(reviewDto, Review::class.java) ?: throw CustomConversionException("There was a problem")
        ), ReviewDto::class.java) ?: throw CustomConversionException("There was a problem")
    }

    @GetMapping(params = ["userId"])
    fun getReviewsByUser(@RequestParam("userId") userId: Int): List<ReviewDto> {
        return reviewService.getReviewsByUser(userId).map { conversionService.convert(it, ReviewDto::class.java) ?: throw CustomConversionException("There was a problem") }
    }

    @GetMapping(params = ["upc"])
    fun getReviewsByProduct(@RequestParam("upc") upc: Int): List<ReviewDto> {
        return reviewService.getReviewsByProduct(upc).map { conversionService.convert(it, ReviewDto::class.java) ?: throw CustomConversionException("There was a problem") }
    }
}

org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type [com.example.demo.datatranferobjects.ReviewDto] to type [com.example.demo.entities.Review]
    at org.springframework.core.convert.support.GenericConversionService.handleConverterNotFound(GenericConversionService.java:322) ~[spring-core-5.3.6.jar:5.3.6]
    at org.springframework.core.convert.support.GenericConversionService.convert(GenericConversionService.java:195) ~[spring-core-5.3.6.jar:5.3.6]
    at org.springframework.core.convert.support.GenericConversionService.convert(GenericConversionService.java:175) ~[spring-core-5.3.6.jar:5.3.6]
    at com.example.demo.controllers.ReviewController.updateReview(ReviewController.kt:18) ~[classes/:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:567) ~[na:na]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:197) ~[spring-web-5.3.6.jar:5.3.6]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:141) ~[spring-web-5.3.6.jar:5.3.6]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:106) ~[spring-webmvc-5.3.6.jar:5.3.6]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:894) ~[spring-webmvc-5.3.6.jar:5.3.6]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808) ~[spring-webmvc-5.3.6.jar:5.3.6]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.3.6.jar:5.3.6]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1060) ~[spring-webmvc-5.3.6.jar:5.3.6]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:962) ~[spring-webmvc-5.3.6.jar:5.3.6]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.3.6.jar:5.3.6]
    at org.springframework.web.servlet.FrameworkServlet.doPut(FrameworkServlet.java:920) ~[spring-webmvc-5.3.6.jar:5.3.6]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:655) ~[tomcat-embed-core-9.0.45.jar:4.0.FR]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.3.6.jar:5.3.6]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:733) ~[tomcat-embed-core-9.0.45.jar:4.0.FR]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.45.jar:9.0.45]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.3.6.jar:5.3.6]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.6.jar:5.3.6]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.3.6.jar:5.3.6]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.6.jar:5.3.6]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter.doFilterInternal(WebMvcMetricsFilter.java:93) ~[spring-boot-actuator-2.4.5.jar:2.4.5]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.6.jar:5.3.6]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.3.6.jar:5.3.6]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.6.jar:5.3.6]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:143) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:357) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:893) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1707) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130) ~[na:na]
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630) ~[na:na]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.45.jar:9.0.45]
    at java.base/java.lang.Thread.run(Thread.java:831) ~[na:na]