Spring Boot 教程：文件处理

tech2023-01-13 102

【注】本文译自： https://www.tutorialspoint.com/spring_boot/spring_boot_file_handling.htm

本文学习如何使用 web 服务进行文件上传和下载。

文件上传

上传一个文件，可以使用 MultipartFile 作为请求参数，并且这个 API 应当消费 Multi-Part 表单数据值。示例代码如下：

@RequestMapping(value = "/upload", method = RequestMethod.POST, consumes = MediaType.MULTIPART_FORM_DATA_VALUE) public String fileUpload(@RequestParam("file") MultipartFile file) { return null; }

完整代码如下：

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"; } }

文件下载

文件下载应当使用 InputStreamResource。我们要在响应中设置 HttpHeader Content-Disposition，并且要指定应用的响应媒体类型（Media Type）。

注意：以下面的例子中，在应用运行时指定路径上的文件应当是可用的。

@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; } }

主 Spring Boot 应用类如下：

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 build – pom.xml 代码如下：

<?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 Build – build.gradle 代码如下：

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') }

现在你可以使用 Maven 或 Gradle 命令创建可执行 executable JAR 文件并运行 Spring Boot 应用了：

Maven 命令如下：

mvn clean install

在 “BUILD SUCCESS” 之后，你可以在 target 目录下找到 JAR 文件。

Gradle 可以使用以下命令：

gradle clean build

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

现在，使用以下命令运行 JAR 文件：

java –jar <JARFILE>

应用将在 Tomcat 8080 端口启动，如下所示：

现在在 POSTMAN 应用中输入以下 URL’s in POSTMAN，可以看到下图所示的输出：

文件上传： http://localhost:8080/upload

文件下载： http://localhost:8080/download

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