如何使用Spring Integration dsl在子流路径中转换字符串

Question

我在Spring集成转换中使用路由编写了一个非常简单的示例，但是它给出了SpelEvaluationException。

代码网关：

@MessagingGateway
@Component
interface ApiGateway {

  @Gateway(requestChannel = "integrateAttributeChannel")
  fun integrateAttributes(message: String)

}

我的流程：

IntegrationFlows
            .from("integrateAttributeChannel")
            .route<String, Boolean>({ sellerId -> sellerId.isBlank() },
                    { m ->
                        m.subFlowMapping(true) { sf ->
                            sf.transform<String, String> { t -> t.toUpperCase() }
                        }
                        m.subFlowMapping(false) { sf ->
                            sf.transform<String, String> { t -> t.reversed() }
                        }
                    })
            .handle { t -> println(t) }
            .get()

异常跟踪：

Caused by: org.springframework.expression.spel.SpelEvaluationException: EL1004E: Method call: Method transform(java.lang.String) cannot be found on type br.com.gubee.config.AttributeFlow$flow$2$2$1
    at org.springframework.expression.spel.ast.MethodReference.findAccessorForMethod(MethodReference.java:225)
    at org.springframework.expression.spel.ast.MethodReference.getValueInternal(MethodReference.java:134)
    at org.springframework.expression.spel.ast.MethodReference.access$000(MethodReference.java:54)
    at org.springframework.expression.spel.ast.MethodReference$MethodValueRef.getValue(MethodReference.java:390)
    at org.springframework.expression.spel.ast.CompoundExpression.getValueInternal(CompoundExpression.java:90)
    at org.springframework.expression.spel.ast.SpelNodeImpl.getTypedValue(SpelNodeImpl.java:114)
    at org.springframework.expression.spel.standard.SpelExpression.getValue(SpelExpression.java:365)
    at org.springframework.integration.util.AbstractExpressionEvaluator.evaluateExpression(AbstractExpressionEvaluator.java:172)
    at org.springframework.integration.util.AbstractExpressionEvaluator.evaluateExpression(AbstractExpressionEvaluator.java:160)
    at org.springframework.integration.handler.support.MessagingMethodInvokerHelper.invokeExpression(MessagingMethodInvokerHelper.java:664)
    at org.springframework.integration.handler.support.MessagingMethodInvokerHelper.invokeHandlerMethod(MessagingMethodInvokerHelper.java:655)
    at org.springframework.integration.handler.support.MessagingMethodInvokerHelper.processInternal(MessagingMethodInvokerHelper.java:491)
    at org.springframework.integration.handler.support.MessagingMethodInvokerHelper.process(MessagingMethodInvokerHelper.java:362)
    at org.springframework.integration.handler.MethodInvokingMessageProcessor.processMessage(MethodInvokingMessageProcessor.java:106)
    at org.springframework.integration.transformer.AbstractMessageProcessingTransformer.transform(AbstractMessageProcessingTransformer.java:113)
    at org.springframework.integration.transformer.MessageTransformingHandler.handleRequestMessage(MessageTransformingHandler.java:109)
    at org.springframework.integration.handler.AbstractReplyProducingMessageHandler.handleMessageInternal(AbstractReplyProducingMessageHandler.java:123)
    at org.springframework.integration.handler.AbstractMessageHandler.handleMessage(AbstractMessageHandler.java:162)
    at org.springframework.integration.dispatcher.AbstractDispatcher.tryOptimizedDispatch(AbstractDispatcher.java:115)

Answer 1

[当我们执行SpEL调用的后备时，它看起来像是一个错误，它只是找不到具有预期参数类型的方法来调用。请针对Spring Integration提出问题。即使是普通的Java，我们也有同样的问题，不仅是Kotlin。

作为一种解决方法，我建议使用filter()而不是transform()，因为默认情况下PayloadMethodArgumentResolver的InvocableHandlerMethod不允许空有效负载：

if (isEmptyPayload(payload)) {
        if (ann == null || ann.required()) {
            String paramName = getParameterName(parameter);
            BindingResult bindingResult = new BeanPropertyBindingResult(payload, paramName);
            bindingResult.addError(new ObjectError(paramName, "Payload value must not be empty"));
            throw new MethodArgumentNotValidException(message, parameter, bindingResult);
        }