Save and get large objects (BLOB) to postgresql using hibernate and Spring Data JPA

I found a solution: I should use the Large Object API for PostgreSQL instead of using bytea and Blob in my entities. Thanks to Andrey, who provided a very useful resource in the comments.

Here's working code that allows you to get a stream from a database object. To avoid the "slow client" problem and connection pool exhaustion, the file from the database is read into a temporary file on disk and a stream from this file is returned to the client. After reading, the file will be deleted.

//the service level is deliberately omitted 
@RestController  
class LargeFileController(  
    private val fileRepo: LargeFileContentRepo,  
    private val dataSource: DataSource,  
) {  
    @PostMapping("large/file", consumes = [MediaType.MULTIPARTFORMDATAVALUE])  
    @Transactional //working with lage object requires active transaction  
    fun saveFile(@RequestBody file: MultipartFile) {  
        val conn = DataSourceUtils.getConnection(dataSource)  
        try {  
            val pgConn = conn.unwrap(org.postgresql.PGConnection::class.java)  
            val lobj = pgConn.largeObjectAPI  
            val oid = lobj.createLO(LargeObjectManager.WRITE)  
            val obj = lobj.open(oid, LargeObjectManager.WRITE)  
            file.inputStream.use { input ->  
                input.copyTo(obj.outputStream)  
            }  
            obj.close()  
            val entity = LargeFile(  
                oid = oid,  
                fileName = file.originalFilename,  
                size = file.size,  
                mimeType = file.contentType  
            )  
            fileRepo.save(entity)  
        } finally {  
            DataSourceUtils.releaseConnection(conn, dataSource)  
        }  
    }  
    @GetMapping("large/file/{id}", produces = [MediaType.APPLICATIONOCTETSTREAMVALUE])  
    @Transactional  
    fun getFileById(@PathVariable("id") id: Long, response: HttpServletResponse): ResponseEntity {  
        val file = fileRepo.findById(id).orElseThrow()  
        val tempFile = Files.createTempFile(UUID.randomUUID().toString(),file.fileName!!)  
        return try {  
            val conn: Connection = DataSourceUtils.getConnection(dataSource)  
            try {  
                val pgConn = conn.unwrap(org.postgresql.PGConnection::class.java)  
                val lobj = pgConn.largeObjectAPI  
                val obj = lobj.open(file.oid, LargeObjectManager.READ)  
                val inputStream = obj.inputStream  
                inputStream.use { lois ->  
                    tempFile.outputStream().use { fileOutputStream ->  
                        IOUtils.copy(lois, fileOutputStream)  
                    }  
                }  
                obj.close()  
                val contentDisposition = ContentDisposition.builder("attachment")  
                        .filename(file.fileName, StandardCharsets.UTF8)  
                        .build()  
                ResponseEntity.ok()  
                    .header(HttpHeaders.CONTENTDISPOSITION, contentDisposition.toString())  
                    .header(HttpHeaders.CONTENTLENGTH, tempFile.fileSize().toString())  
                    .contentType(MediaType.APPLICATIONOCTETSTREAM)  
                    .body(InputStreamResource(tempFile.inputStream()))  
                //or  
                /*tempFile.inputStream().use { input ->                   
                 val contentDisposition = ContentDisposition.builder("attachment")                        .filename(file.fileName, StandardCharsets.UTF8)                                       .build()                    
                 response.contentType = MediaType.MULTIPARTFORMDATAVALUE                             response.addHeader(HttpHeaders.CONTENTDISPOSITION, contentDisposition.toString())  
                 response.outputStream.use { output ->                        
                    IOUtils.copy(input, output)                    
                 }                
                }*/            
            } finally {  
                DataSourceUtils.releaseConnection(conn, dataSource)  
            }  
        } finally {  
            try {  
                if (Files.exists(tempFile)) {  
                    Files.deleteIfExists(tempFile)  
                }  
            } catch (ex: Exception) {  
                log.warn("Failed to delete temp file: ${tempFile.toAbsolutePath()}", ex)  
            }  
        }  
    }  
    companion object {  
        private val log = LoggerFactory.getLogger(LargeFileController::class.java)  
    }  
}

Full example here

UPDATE:

My mistake was that I was trying to store a Blob in my table in a bytea column. All I had to do was change the column type in the database from bytea to bigint for this column. JPA works correctly with Blobs in this case (it stores the file's oid in the column).

Here is a complete correct example:

@Entity
@Table(name = "filecontent")
class FileContent (
    //The field type in the database must be bigint, not bytea. This field will store the OID of the created file.
    @Lob
    val oid: Blob,
    val name: String?,
    val mimeType: String?,
    val size: Long,
    @OneToMany(cascade = [CascadeType.ALL], mappedBy = "file")
    @BatchSize(size = 20)
    val tags: List,
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    val id: Long?=null,
) {
    constructor(file: MultipartFile) : this(
        oid = BlobProxy.generateProxy(file.inputStream, file.size),
        name = file.originalFilename!!,
        mimeType = file.contentType!!,
        size = file.size,
        tags = listOf()
    )
}
@Service
class FileService(
    private val fileRepo: FileRepo
) {
    @Transactional
    fun getFile(id: Long): Pair {
        val fileInfo = fileRepo.findById(id).orElseThrow { RuntimeException("File not found") }.content
        val largeObj = fileInfo.oid
        val tmpFile = Files.createTempFile(fileInfo.name, null)
        tmpFile.outputStream().use { out ->
            largeObj.binaryStream.use {
                it.copyTo(out)
            }
        }
        return fileInfo to tmpFile.toFile()
    }
    fun saveFile(file: MultipartFile): Long {
        return fileRepo.save(FileMetadata(file)).id!!
    }
}
@RestController
class BlobObjectController(
    val fileService: FileService
) {
    @GetMapping("/file/{id}", produces = [MediaType.APPLICATIONOCTETSTREAMVALUE])
    fun getFileById(@PathVariable("id") id: Long): ResponseEntity {
        val (metadata, tempFile) = fileService.getFile(id)
        val contentDisposition = ContentDisposition.builder("attachment")
            .filename(metadata.name, StandardCharsets.UTF8)
            .build()
        val contentType = metadata.mimeType
            ?.let { runCatching { MediaType.valueOf(it) }.getOrNull() }
            ?: MediaType.APPLICATIONOCTETSTREAM
        val responseBody = StreamingResponseBody { outputStream ->
            tempFile.inputStream().use { input ->
                input.copyTo(outputStream)
            }
            val deleted = Files.deleteIfExists(tempFile.toPath())
            log.info("File ${if (deleted) "was deleted" else "WAS NOT DELETED"} after response sent: ${tempFile.name}")
        }
        return ResponseEntity.ok()
            .header(HttpHeaders.CONTENTDISPOSITION, contentDisposition.toString())
            .contentLength(metadata.size)
            .contentType(contentType)
            .body(responseBody)
    }
    @PostMapping("/file", consumes = [MediaType.MULTIPARTFORMDATA_VALUE])
    fun saveFile(@RequestBody file: MultipartFile) {
        fileService.saveFile(file)
    }
    companion object {
        private val log = LoggerFactory.getLogger(BlobObjectController::class.java)
    }
}