如果我們做一個小型的web站，而且剛好選擇的kotlin 和Spring Boot技術棧，那麼上傳檔案的必不可少了，當然，如果你做一箇中大型的web站，那建議你使用雲端儲存，能省不少事情。

這篇文章就介紹怎麼使用kotlin 和Spring Boot上傳檔案

構建工程

完整build.gradle檔案

group 'name.quanke.kotlin'
version '1.0-SNAPSHOT'

buildscript {
    ext.kotlin_version = '1.2.10'
    ext.spring_boot_version = '1.5.4.RELEASE'
 

    repositories {
        mavenCentral()
    }
    dependencies {
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
        classpath("org.springframework.boot:spring-boot-gradle-plugin:$spring_boot_version")

//        Kotlin整合SpringBoot的預設無參建構函式，預設把所有的類設定open類外掛
        classpath("org.jetbrains.kotlin:kotlin-noarg:$kotlin_version
 
")
        classpath("org.jetbrains.kotlin:kotlin-allopen:$kotlin_version")

    }
}

apply plugin: 'kotlin'
apply plugin: "kotlin-spring" // See https://kotlinlang.org/docs/reference/compiler-plugins.html#kotlin-spring-compiler-plugin
apply plugin: 'org.springframework.boot'


jar {
    baseName = 'chapter11-5-6-service'
 

    version = '0.1.0'
}
repositories {
    mavenCentral()
}


dependencies {
    compile "org.jetbrains.kotlin:kotlin-stdlib-jre8:$kotlin_version"
    compile "org.springframework.boot:spring-boot-starter-web:$spring_boot_version"
    compile "org.springframework.boot:spring-boot-starter-thymeleaf:$spring_boot_version"

    testCompile "org.springframework.boot:spring-boot-starter-test:$spring_boot_version"
    testCompile "org.jetbrains.kotlin:kotlin-test-junit:$kotlin_version"

}

compileKotlin {
    kotlinOptions.jvmTarget = "1.8"
}
compileTestKotlin {
    kotlinOptions.jvmTarget = "1.8"
}

建立檔案上傳controller

import name.quanke.kotlin.chaper11_5_6.storage.StorageFileNotFoundException
import name.quanke.kotlin.chaper11_5_6.storage.StorageService
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.core.io.Resource
import org.springframework.http.HttpHeaders
import org.springframework.http.ResponseEntity
import org.springframework.stereotype.Controller
import org.springframework.ui.Model
import org.springframework.web.bind.annotation.*
import org.springframework.web.multipart.MultipartFile
import org.springframework.web.servlet.mvc.method.annotation.MvcUriComponentsBuilder
import org.springframework.web.servlet.mvc.support.RedirectAttributes

import java.io.IOException
import java.util.stream.Collectors


/**
 * 檔案上傳控制器
 * Created by http://quanke.name on 2018/1/12.
 */

@Controller
class FileUploadController @Autowired
constructor(private val storageService: StorageService) {

    @GetMapping("/")
    @Throws(IOException::class)
    fun listUploadedFiles(model: Model): String {

        model.addAttribute("files", storageService
                .loadAll()
                .map { path ->
                    MvcUriComponentsBuilder
                            .fromMethodName(FileUploadController::class.java, "serveFile", path.fileName.toString())
                            .build().toString()
                }
                .collect(Collectors.toList()))

        return "uploadForm"
    }

    @GetMapping("/files/{filename:.+}")
    @ResponseBody
    fun serveFile(@PathVariable filename: String): ResponseEntity<Resource> {

        val file = storageService.loadAsResource(filename)
        return ResponseEntity
                .ok()
                .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + file.filename + "\"")
                .body(file)
    }

    @PostMapping("/")
    fun handleFileUpload(@RequestParam("file") file: MultipartFile,
                         redirectAttributes: RedirectAttributes): String {

        storageService.store(file)
        redirectAttributes.addFlashAttribute("message",
                "You successfully uploaded " + file.originalFilename + "!")

        return "redirect:/"
    }

    @ExceptionHandler(StorageFileNotFoundException::class)
    fun handleStorageFileNotFound(exc: StorageFileNotFoundException): ResponseEntity<*> {
        return ResponseEntity.notFound().build<Any>()
    }

}

上傳檔案服務的介面

import org.springframework.core.io.Resource
import org.springframework.web.multipart.MultipartFile

import java.nio.file.Path
import java.util.stream.Stream

interface StorageService {

    fun init()

    fun store(file: MultipartFile)

    fun loadAll(): Stream<Path>

    fun load(filename: String): Path

    fun loadAsResource(filename: String): Resource

    fun deleteAll()

}

上傳檔案服務

import org.springframework.beans.factory.annotation.Autowired
import org.springframework.core.io.Resource
import org.springframework.core.io.UrlResource
import org.springframework.stereotype.Service
import org.springframework.util.FileSystemUtils
import org.springframework.util.StringUtils
import org.springframework.web.multipart.MultipartFile
import java.io.IOException
import java.net.MalformedURLException
import java.nio.file.Files
import java.nio.file.Path
import java.nio.file.Paths
import java.nio.file.StandardCopyOption
import java.util.stream.Stream

@Service
class FileSystemStorageService @Autowired
constructor(properties: StorageProperties) : StorageService {

    private val rootLocation: Path

    init {
        this.rootLocation = Paths.get(properties.location)
    }

    override fun store(file: MultipartFile) {
        val filename = StringUtils.cleanPath(file.originalFilename)
        try {
            if (file.isEmpty) {
                throw StorageException("Failed to store empty file " + filename)
            }
            if (filename.contains("..")) {
                // This is a security check
                throw StorageException(
                        "Cannot store file with relative path outside current directory " + filename)
            }
            Files.copy(file.inputStream, this.rootLocation.resolve(filename),
                    StandardCopyOption.REPLACE_EXISTING)
        } catch (e: IOException) {
            throw StorageException("Failed to store file " + filename, e)
        }

    }

    override fun loadAll(): Stream<Path> {
        try {
            return Files.walk(this.rootLocation, 1)
                    .filter { path -> path != this.rootLocation }
                    .map { path -> this.rootLocation.relativize(path) }
        } catch (e: IOException) {
            throw StorageException("Failed to read stored files", e)
        }

    }

    override fun load(filename: String): Path {
        return rootLocation.resolve(filename)
    }

    override fun loadAsResource(filename: String): Resource {
        try {
            val file = load(filename)
            val resource = UrlResource(file.toUri())
            return if (resource.exists() || resource.isReadable) {
                resource
            } else {
                throw StorageFileNotFoundException(
                        "Could not read file: " + filename)

            }
        } catch (e: MalformedURLException) {
            throw StorageFileNotFoundException("Could not read file: " + filename, e)
        }

    }

    override fun deleteAll() {
        FileSystemUtils.deleteRecursively(rootLocation.toFile())
    }

    override fun init() {
        try {
            Files.createDirectories(rootLocation)
        } catch (e: IOException) {
            throw StorageException("Could not initialize storage", e)
        }

    }
}

自定義異常

open class StorageException : RuntimeException {

    constructor(message: String) : super(message)

    constructor(message: String, cause: Throwable) : super(message, cause)
}

class StorageFileNotFoundException : StorageException {

    constructor(message: String) : super(message)

    constructor(message: String, cause: Throwable) : super(message, cause)
}

配置檔案上傳目錄

import org.springframework.boot.context.properties.ConfigurationProperties

@ConfigurationProperties("storage")
class StorageProperties {

    /**
     * Folder location for storing files
     */
    var location = "upload-dir"

}

啟動Spring Boot

/**
 * Created by http://quanke.name on 2018/1/9.
 */

@SpringBootApplication
@EnableConfigurationProperties(StorageProperties::class)
class Application {

    @Bean
    internal fun init(storageService: StorageService) = CommandLineRunner {
        storageService.deleteAll()
        storageService.init()
    }

    companion object {

        @Throws(Exception::class)
        @JvmStatic
        fun main(args: Array<String>) {
            SpringApplication.run(Application::class.java, *args)
        }
    }
}

建立一個簡單的 html模板 src/main/resources/templates/uploadForm.html

<html xmlns:th="http://www.thymeleaf.org">
<body>

<div th:if="${message}">
    <h2 th:text="${message}"/>
</div>

<div>
    <form method="POST" enctype="multipart/form-data" action="/">
        <table>
            <tr>
                <td>File to upload:</td>
                <td><input type="file" name="file"/></td>
            </tr>
            <tr>
                <td></td>
                <td><input type="submit" value="Upload"/></td>
            </tr>
        </table>
    </form>
</div>

<div>
    <ul>
        <li th:each="file : ${files}">
            <a th:href="${file}" th:text="${file}"/>
        </li>
    </ul>
</div>

</body>
</html>

配置檔案application.yml

spring:
  http:
    multipart:
      max-file-size: 128KB
      max-request-size: 128KB

原始碼：

參考: