Spring Boot 与 Kotlin 上传文件的示例代码

如果我们做一个小型的web站，而且刚好选择的kotlin 和Spring Boot技术栈，那么上传文件的必不可少了，当然，如果你做一个中大型的web站，那建议你使用云存储，能省不少事情。

构建工程

如果对于构建工程还不是很熟悉的可以参考《我的第一个Kotlin应用》

完整 build.gradle 文件

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的默认无参构造函数，默认把所有的类设置open类插件
   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"
}

创建文件上传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

/**
* 文件上传控制器
* 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>()
 }

}

上传文件服务的接口

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()

}

上传文件服务

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)
   }

}
}

自定义异常

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)
}

配置文件上传目录

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

@ConfigurationProperties("storage")
class StorageProperties {

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

}

启动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)
   }
 }
}

创建一个简单的 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}" rel="external nofollow" th:text="${file}"/>
   </li>
 </ul>
</div>

</body>
</html>

配置文件 application.yml

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

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源码：

https://github.com/quanke/spring-boot-with-kotlin-in-action/

参考:

https://spring.io/guides/gs/uploading-files/

来源：https://www.jianshu.com/p/d4952e71360b