Spring Boot - 文件处理

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在本章中，您将学习如何使用 Web 服务上传和下载文件。

文件上传

要上传文件，您可以使用MultipartFile作为请求参数，并且此 API 应该使用多部分表单数据值。请观察以下代码：

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

完整的代码如下所示：

FileUploadController.java

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.PostMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.multipart.MultipartFile;

@RestController
public class FileUploadController {
   @PostMapping(value = "/upload", 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

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

注意 - 在以下示例中，文件应该在应用程序运行的指定路径上可用。

@GetMapping(value = "/download") 
public ResponseEntity<Object> downloadFile() throws IOException  {
   String filename = "/var/tmp/logo.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;
}

完整的代码如下所示：

FileDownloadController.java

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/logo.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 主应用程序如下所示：

DemoApplication.java

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 构建代码 - pom.xml 如下所示：

pom.xml

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
   <modelVersion>4.0.0</modelVersion>
   <parent>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-parent</artifactId>
      <version>3.3.3</version>
      <relativePath/> <!-- lookup parent from repository -->
   </parent>
   <groupId>com.tutorialspoint</groupId>
   <artifactId>demo</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <name>demo</name>
   <description>Demo project for Spring Boot</description>
   <url/>
   <licenses>
      <license/>
   </licenses>
   <developers>
      <developer/>
   </developers>
   <scm>
      <connection/>
      <developerConnection/>
      <tag/>
      <url/>
   </scm>
   <properties>
      <java.version>21</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 构建代码 - build.gradle 如下所示：

build.gradle

buildscript {
   ext {
      springBootVersion = '3.3.3'
   }
   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 = 21

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

现在您可以创建一个可执行的 JAR 文件，并使用以下 Maven 或 Gradle 命令运行 Spring Boot 应用程序：

对于 Maven，使用以下命令：

mvn clean install

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

对于 Gradle，您可以使用以下命令：

sgradle clean build

“BUILD SUCCESSFUL”之后，您可以在 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>

这将在 Tomcat 端口 8080 上启动应用程序，如下所示：

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/

[32m :: Spring Boot :: [39m              [2m (v3.3.3)[0;39m

[2024-09-06T11:55:39Z] [org.springframework.boot.StartupInfoLogger] [main] [50] [INFO ] Starting DemoApplication using Java 21.0.3 with PID 4648 (E:\Dev\demo\target\classes started by Tutorialspoint in E:\Dev\demo)
[2024-09-06T11:55:39Z] [org.springframework.boot.SpringApplication] [main] [654] [INFO ] No active profile set, falling back to 1 default profile: "default"
[2024-09-06T11:55:40Z] [org.springframework.boot.web.embedded.tomcat.TomcatWebServer] [main] [111] [INFO ] Tomcat initialized with port 8080 (http)
[2024-09-06T11:55:40Z] [org.apache.juli.logging.DirectJDKLog] [main] [173] [INFO ] Initializing ProtocolHandler ["http-nio-8080"]
[2024-09-06T11:55:40Z] [org.apache.juli.logging.DirectJDKLog] [main] [173] [INFO ] Starting service [Tomcat]
[2024-09-06T11:55:40Z] [org.apache.juli.logging.DirectJDKLog] [main] [173] [INFO ] Starting Servlet engine: [Apache Tomcat/10.1.28]
[2024-09-06T11:55:40Z] [org.apache.juli.logging.DirectJDKLog] [main] [173] [INFO ] Initializing Spring embedded WebApplicationContext
[2024-09-06T11:55:40Z] [org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext] [main] [296] [INFO ] Root WebApplicationContext: initialization completed in 1857 ms
[2024-09-06T11:55:41Z] [org.apache.juli.logging.DirectJDKLog] [main] [173] [INFO ] Starting ProtocolHandler ["http-nio-8080"]
[2024-09-06T11:55:41Z] [org.springframework.boot.web.embedded.tomcat.TomcatWebServer] [main] [243] [INFO ] Tomcat started on port 8080 (http) with context path '/'
[2024-09-06T11:55:41Z] [org.springframework.boot.StartupInfoLogger] [main] [56] [INFO ] Started DemoApplication in 3.638 seconds (process running for 5.691)

现在在 POSTMAN 应用程序中点击以下 URL，您将看到以下输出：

文件下载 - https://:8080/download

POSTMAN application File Upload

文件上传 - https://:8080/upload

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