Spring Boot 简明教程

Spring Boot - File Handling

在本章中，您将学习如何使用 Web 服务上传和下载文件。

File Upload

对于上传文件，您可以使用 MultipartFile 作为请求参数，并且此 API 应使用多部分表单数据值。观察下面给出的代码 −

@RequestMapping(value = "/upload", method = RequestMethod.POST, consumes = MediaType.MULTIPART_FORM_DATA_VALUE)

public String fileUpload(@RequestParam("file") MultipartFile file) {
   return null;
}

完整的代码如下 −

package com.tutorialspoint.demo.controller;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;

import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.multipart.MultipartFile;

@RestController
public class FileUploadController {
   @RequestMapping(value = "/upload", method = RequestMethod.POST,
      consumes = MediaType.MULTIPART_FORM_DATA_VALUE)

   public String fileUpload(@RequestParam("file") MultipartFile file) throws IOException {
      File convertFile = new File("/var/tmp/"+file.getOriginalFilename());
      convertFile.createNewFile();
      FileOutputStream fout = new FileOutputStream(convertFile);
      fout.write(file.getBytes());
      fout.close();
      return "File is upload successfully";
   }
}

File Download

对于文件下载，您应该使用 InputStreamResource 下载文件。我们需要在响应中设置 Content-Disposition 的 HttpHeader，并且需要指定应用程序的响应媒体类型。

Note − 在以下示例中，文件应可在应用程序正在运行的指定路径上获得。

@RequestMapping(value = "/download", method = RequestMethod.GET)
public ResponseEntity<Object> downloadFile() throws IOException  {
   String filename = "/var/tmp/mysql.png";
   File file = new File(filename);
   InputStreamResource resource = new InputStreamResource(new FileInputStream(file));
   HttpHeaders headers = new HttpHeaders();

   headers.add("Content-Disposition", String.format("attachment; filename=\"%s\"", file.getName()));
   headers.add("Cache-Control", "no-cache, no-store, must-revalidate");
   headers.add("Pragma", "no-cache");
   headers.add("Expires", "0");

   ResponseEntity<Object>
   responseEntity = ResponseEntity.ok().headers(headers).contentLength(file.length()).contentType(
      MediaType.parseMediaType("application/txt")).body(resource);

   return responseEntity;
}

完整的代码如下 −

package com.tutorialspoint.demo.controller;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

import org.springframework.core.io.InputStreamResource;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class FileDownloadController {
   @RequestMapping(value = "/download", method = RequestMethod.GET)
   public ResponseEntity<Object> downloadFile() throws IOException  {
      String filename = "/var/tmp/mysql.png";
      File file = new File(filename);
      InputStreamResource resource = new InputStreamResource(new FileInputStream(file));
      HttpHeaders headers = new HttpHeaders();

      headers.add("Content-Disposition", String.format("attachment; filename=\"%s\"", file.getName()));
      headers.add("Cache-Control", "no-cache, no-store, must-revalidate");
      headers.add("Pragma", "no-cache");
      headers.add("Expires", "0");

      ResponseEntity<Object>
      responseEntity = ResponseEntity.ok().headers(headers).contentLength(
         file.length()).contentType(MediaType.parseMediaType("application/txt")).body(resource);

      return responseEntity;
   }
}

Spring Boot 的主应用程序如下 −

package com.tutorialspoint.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication {
   public static void main(String[] args) {
      SpringApplication.run(DemoApplication.class, args);
   }
}

Maven 构建的代码 - pom.xml 如下 −

<?xml version = "1.0" encoding = "UTF-8"?>
<project xmlns = "http://maven.apache.org/POM/4.0.0"
   xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation = "http://maven.apache.org/POM/4.0.0
   http://maven.apache.org/xsd/maven-4.0.0.xsd">

   <modelVersion>4.0.0</modelVersion>
   <groupId>com.tutorialspoint</groupId>
   <artifactId>demo</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <packaging>jar</packaging>
   <name>demo</name>
   <description>Demo project for Spring Boot</description>

   <parent>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-parent</artifactId>
      <version>1.5.8.RELEASE</version>
      <relativePath/>
   </parent>

   <properties>
      <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
      <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
      <java.version>1.8</java.version>
   </properties>

   <dependencies>
      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-web</artifactId>
      </dependency>

      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-test</artifactId>
         <scope>test</scope>
      </dependency>
   </dependencies>

   <build>
      <plugins>
         <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
         </plugin>
      </plugins>
   </build>

</project>

Gradle 构建的代码 - build.gradle 如下 −

buildscript {
   ext {
      springBootVersion = '1.5.8.RELEASE'
   }
   repositories {
      mavenCentral()
   }
   dependencies {
      classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
   }
}

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'org.springframework.boot'

group = 'com.tutorialspoint'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = 1.8

repositories {
   mavenCentral()
}
dependencies {
   compile('org.springframework.boot:spring-boot-starter-web')
   testCompile('org.springframework.boot:spring-boot-starter-test')
}

现在，您可以创建可执行 JAR 文件，并使用以下给出的 Maven 或 Gradle 命令运行 Spring Boot 应用程序 −

对于 Maven，使用以下给出的命令 −

mvn clean install

在“构建成功”后，您可以在 target 目录下找到 JAR 文件。

对于 Gradle，您可以使用以下所示命令 −

sgradle clean build

在 “BUILD SUCCESSFUL” 后，你可以在 build/libs 目录下找到 JAR 文件。

现在，通过使用以下命令运行 JAR 文件 −

java –jar <JARFILE>

这将启动 8080 端口上的应用程序，如下所示 −

started application on tomcat port 8080

现在在 POSTMAN 应用程序中点击下方 URL，你就可以看到如下图所示的输出：

文件上传 − http://localhost:8080/upload

postman application file upload

文件下载 − http://localhost:8080/upload