SpelEvaluationException when initiating GET on a SftpOutboundGateway - spring

Question

I have a Spring Integration Flow starting with a SFTPOutboundGateway. It should get a file from a SFTP server. The file contains Event objects in JSON format. My configuration is:
#Bean
public DirectChannelSpec sftpGetInputChannel() {
return MessageChannels.direct();
}
#Bean
public QueueChannelSpec remoteFileOutputChannel() {
return MessageChannels.queue();
}
#Bean(name = PollerMetadata.DEFAULT_POLLER)
public PollerMetadata defaultPoller() {
PollerMetadata pollerMetadata = new PollerMetadata();
pollerMetadata.setTrigger(new PeriodicTrigger(5000));
return pollerMetadata;
}
#Bean
public IntegrationFlow sftpGetFlow(TransferContext context) {
return IntegrationFlows.from("sftpGetInputChannel")
.handle(Sftp.outboundGateway(sftpSessionFactory(context.getChannel()),
AbstractRemoteFileOutboundGateway.Command.GET, "payload")
.remoteDirectoryExpression(context.getRemoteDir())
.localDirectory(new File(context.getLocalDir()))
.localFilenameExpression(context.getLocalFilename())
)
.channel("remoteFileOutputChannel")
.transform(Transformers.fromJson(Event[].class))
.get();
}
To get a file from the SFTP server I send a message to the gateway's input channel "sftpGetInputChannel":
boolean sent = sftpGetInputChannel.send(new GenericMessage<>(env.getRemoteDir() + "/" + env.getRemoteFilename()));
An SpelEvaluationException is thrown when trying to interprete the given filename. Both fields, remoteDir and remoteFilename are of type String:
org.springframework.messaging.MessageHandlingException: error occurred in message handler [bean 'sftpGetFlow.sftp:outbound-gateway#0' for component 'sftpGetFlow.org.springframework.integration.config.ConsumerEndpointFactoryBean#0'; defined in: 'class path resource [com/harry/potter/job/config/SftpConfiguration.class]'; from source: 'bean method sftpGetFlow']; nested exception is org.springframework.messaging.MessagingException: Failed to execute on session; nested exception is org.springframework.expression.spel.SpelEvaluationException: EL1001E: Type conversion problem, cannot convert from org.springframework.messaging.support.GenericMessage<?> to java.lang.String
at org.springframework.integration.support.utils.IntegrationUtils.wrapInHandlingExceptionIfNecessary(IntegrationUtils.java:192)
at org.springframework.integration.handler.AbstractMessageHandler.handleMessage(AbstractMessageHandler.java:79)
at org.springframework.integration.dispatcher.AbstractDispatcher.tryOptimizedDispatch(AbstractDispatcher.java:115)
at org.springframework.integration.dispatcher.UnicastingDispatcher.doDispatch(UnicastingDispatcher.java:133)
at org.springframework.integration.dispatcher.UnicastingDispatcher.dispatch(UnicastingDispatcher.java:106)
at org.springframework.integration.channel.AbstractSubscribableChannel.doSend(AbstractSubscribableChannel.java:72)
at org.springframework.integration.channel.AbstractMessageChannel.send(AbstractMessageChannel.java:570)
at org.springframework.integration.channel.AbstractMessageChannel.send(AbstractMessageChannel.java:520)
at com.harry.potter.job.MyTask.getFile(MyEventsTask.java:170)
at com.harry.potter.job.myTask.runAsTask(MyEventsTask.java:112)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at org.springframework.scheduling.support.ScheduledMethodRunnable.run(ScheduledMethodRunnable.java:84)
at org.springframework.scheduling.support.DelegatingErrorHandlingRunnable.run(DelegatingErrorHandlingRunnable.java:54)
at org.springframework.scheduling.concurrent.ReschedulingRunnable.run(ReschedulingRunnable.java:93)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:836)
Caused by: org.springframework.messaging.MessagingException: Failed to execute on session; nested exception is org.springframework.expression.spel.SpelEvaluationException: EL1001E: Type conversion problem, cannot convert from org.springframework.messaging.support.GenericMessage<?> to java.lang.String
at org.springframework.integration.file.remote.RemoteFileTemplate.execute(RemoteFileTemplate.java:448)
at org.springframework.integration.file.remote.gateway.AbstractRemoteFileOutboundGateway.doGet(AbstractRemoteFileOutboundGateway.java:680)
at org.springframework.integration.file.remote.gateway.AbstractRemoteFileOutboundGateway.handleRequestMessage(AbstractRemoteFileOutboundGateway.java:584)
at org.springframework.integration.handler.AbstractReplyProducingMessageHandler.handleMessageInternal(AbstractReplyProducingMessageHandler.java:134)
at org.springframework.integration.handler.AbstractMessageHandler.handleMessage(AbstractMessageHandler.java:62)
... 21 common frames omitted
Caused by: org.springframework.expression.spel.SpelEvaluationException: EL1001E: Type conversion problem, cannot convert from org.springframework.messaging.support.GenericMessage<?> to java.lang.String
at org.springframework.expression.spel.support.StandardTypeConverter.convertValue(StandardTypeConverter.java:75)
at org.springframework.expression.common.ExpressionUtils.convertTypedValue(ExpressionUtils.java:57)
at org.springframework.expression.spel.standard.SpelExpression.getValue(SpelExpression.java:377)
at org.springframework.integration.file.remote.gateway.AbstractRemoteFileOutboundGateway.generateLocalFileName(AbstractRemoteFileOutboundGateway.java:1316)
at org.springframework.integration.file.remote.gateway.AbstractRemoteFileOutboundGateway.get(AbstractRemoteFileOutboundGateway.java:1081)
at org.springframework.integration.file.remote.gateway.AbstractRemoteFileOutboundGateway.lambda$doGet$6(AbstractRemoteFileOutboundGateway.java:681)
at org.springframework.integration.file.remote.gateway.AbstractRemoteFileOutboundGateway$$Lambda$30183/0x0000000000000000.doInSession(Unknown Source)
at org.springframework.integration.file.remote.RemoteFileTemplate.execute(RemoteFileTemplate.java:439)
... 25 common frames omitted
Caused by: org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type [org.springframework.messaging.support.GenericMessage<?>] to type [java.lang.String]
at org.springframework.core.convert.support.GenericConversionService.handleConverterNotFound(GenericConversionService.java:322)
at org.springframework.core.convert.support.GenericConversionService.convert(GenericConversionService.java:195)
at org.springframework.expression.spel.support.StandardTypeConverter.convertValue(StandardTypeConverter.java:70)
... 32 common frames omitted
What do I wrong?

Answer 1

Okay, the problem is not within the message to get the file but in the configuration of the gateway:
.localFilenameExpression(context.getLocalFilename())
Just to set the local filename as expression is not allowed because dots - often part of the filename - is a SpEL delimiter to separate bean from method name. Hence the expression becomes invalid.
Possible expression would be:
.localFilenameExpression("#remoteFileName")

Answer 2

See its JavaDocs:
/**
* Specify a SpEL expression for local files renaming after downloading.
* #param localFilenameExpression the SpEL expression to use.
* #return the Spec.
*/
public S localFilenameExpression(String localFilenameExpression) {
And here is some code snippet how it works:
private String generateLocalFileName(Message<?> message, String remoteFileName) {
if (this.localFilenameGeneratorExpression != null) {
EvaluationContext evaluationContext = ExpressionUtils.createStandardEvaluationContext(getBeanFactory());
evaluationContext.setVariable("remoteFileName", remoteFileName);
return this.localFilenameGeneratorExpression.getValue(evaluationContext, message, String.class);
}
return remoteFileName;
}
The expression you can provide should somehow be in the context of the currently downloaded remote file. Not sure what is yours static context.getLocalFilename(). You can build a local file name based on the request message and that remoteFileName variable contexts.
See more in docs: https://docs.spring.io/spring-integration/docs/current/reference/html/sftp.html#configuring-with-the-java-dsl-3
The sample over there is like this:
.localDirectoryExpression("'myDir/' + #remoteDirectory")
.localFilenameExpression("#remoteFileName.replaceFirst('sftpSource', 'localTarget')"))