Spring Integration SFTP多文件夹跟踪下载遇remoteDirectoryExpression非空异常

基于Spring Boot 3.2.0、Spring Integration 6.2.0技术栈开发应用，需实现跟踪SFTP多个文件夹并下载文件。按照官方指引，移除了Sftp入站适配器的remoteDirectory配置，给轮询器添加RotatingServerAdvice，相关配置代码如下：

@Bean
fun advice(): RotatingServerAdvice {
    val keyDirectories = listOf(
        RotationPolicy.KeyDirectory(
            "foo",
            sftpProperties.remoteDirectory
        ),
        RotationPolicy.KeyDirectory(
            "foo",
            sftpProperties.remoteFooDirectory
        )
    )
    return RotatingServerAdvice(DelegatingSessionFactory { sftpSessionFactory() }, keyDirectories, true)
}


@Bean
fun sftpInboundFlow(): IntegrationFlow {
    return IntegrationFlow
        .from(
            Sftp.inboundAdapter(sftpSessionFactory())
                .preserveTimestamp(true)
                .deleteRemoteFiles(true) // 传输完成后删除远程文件
                // 通过advice切换多个文件夹，因此注释了该行
                //.remoteDirectory(sftpProperties.remoteDirectory)
                .regexFilter(".*\\.csv$")
                // 本地配置
                .localFilenameExpression("#this.toUpperCase() + '.csv'")
                .autoCreateLocalDirectory(true)
                .localDirectory(File("./sftp-inbound"))
        ) { e: SourcePollingChannelAdapterSpec ->
            e.id("sftpInboundAdapter")
                .autoStartup(true)
                .poller(Pollers.fixedDelay(5000).advice(advice()))
        }

运行测试时抛出如下异常：

'remoteDirectoryExpression' must not be null
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:608)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:523)
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:325)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:323)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:973)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:946)

1. 解决初始化校验问题 #

Sftp入站适配器初始化时必须指定remoteDirectory或remoteDirectoryExpression，即使后续会通过RotatingServerAdvice切换目录，也需要设置一个默认值通过校验。

可选两种方式：

• 设置临时默认目录（比如/dummy），轮询时RotatingServerAdvice会覆盖该值：

Sftp.inboundAdapter(sftpSessionFactory())
    // ...其他配置
    .remoteDirectory("/dummy") // 添加默认目录
    // ...其他配置

• 通过配置项设置默认目录表达式：

Sftp.inboundAdapter(sftpSessionFactory())
    // ...其他配置
    .remoteDirectoryExpression("\${sftp.remote-directory}") // 用配置的主目录作为默认
    // ...其他配置

2. 修正RotatingServerAdvice的Key配置 #

当前keyDirectories中两个目录使用了同一个key（"foo"），会导致轮换逻辑混乱，应为每个目录分配唯一的key：

val keyDirectories = listOf(
    RotationPolicy.KeyDirectory("main", sftpProperties.remoteDirectory),
    RotationPolicy.KeyDirectory("foo", sftpProperties.remoteFooDirectory)
)

内容的提问来源于stack exchange，提问作者Hantsy