SpringFileChangedIntegrationFlow.kt

import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration
import org.springframework.core.io.ClassPathResource
import org.springframework.integration.config.EnableIntegration
import org.springframework.integration.dsl.integrationFlow
import org.springframework.integration.file.FileHeaders
import org.springframework.integration.file.dsl.Files
import org.springframework.integration.file.filters.ChainFileListFilter
import org.springframework.integration.file.filters.FileListFilter
import org.springframework.integration.file.filters.SimplePatternFileListFilter
import org.springframework.integration.file.transformer.FileToStringTransformer
import java.io.File

class ChangedFileFilter : FileListFilter<File> {
    private val seen = mutableMapOf<File, Long>()

    override fun filterFiles(files: Array<out File>?): MutableList<File> {
        println(seen)
        return files?.filterNot { file ->
            val isSeen = seen[file] == file.lastModified()
            if (!isSeen) seen[file] = file.lastModified()
            isSeen
        }?.toMutableList() ?: mutableListOf()
    }
}

@Configuration
@EnableIntegration
class ApplicationConfig {
    @Bean
    fun processFileFlow() = integrationFlow(
        Files.inboundAdapter(ClassPathResource("manifest.json").file.parentFile)
            .filter(
                ChainFileListFilter<File>()
                    .addFilter(SimplePatternFileListFilter("*.json"))
                    .addFilter(ChangedFileFilter()),
            ),
        { poller { it.fixedRate(1000) } }
    ) {
        transform(FileToStringTransformer())
        handle { msg ->
            val filename = msg.headers[FileHeaders.FILENAME] as String
            val content: String = msg.payload.toString()
            println("FILE CONTENTS")
            println(filename)
            println(content)
        }
    }
}

Polls a file (files) in the Spring resource directory for changes at given interval and emits file contents when changed.