Spring Boot 文件处理

在本章中，我们将学习如何使用 Web 服务上传和下载文件。

文件上传

对于上传文件，我们可以使用 MultipartFile 作为请求参数，此 API 应使用 Multi-Part 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;
}

下面给出了相同的完整代码

package com.study.controller;

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;

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

/**
 * @author jiyik.com
 */
@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("/tmp/"+file.getOriginalFilename());
        convertFile.createNewFile();

        FileOutputStream fout = new FileOutputStream(convertFile);

        fout.write(file.getBytes());

        fout.close();

        return "文件上传成功";
    }
}

文件下载

对于文件下载，我们应该使用 InputStreamResource 下载文件。 我们需要在 Response 中设置HttpHeader Content-Disposition ，并且需要指定应用的响应Media Type。

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

@RequestMapping(value = "/download", method = RequestMethod.GET)
public ResponseEntity<Object> downloadFile() throws IOException {
        String filename = "/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;
}

下面给出了主要的 Spring Boot 应用程序

package com.study;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

/**
 * @author jiyik.com
 */
@SpringBootApplication
public class MyApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyApplication.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.spring</groupId>
    <artifactId>springBootProject</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.6.6</version>
    </parent>

    <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 的代码如下

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.study'
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')
}

这里我们使用 IDEA 来启动服务（读者也可以使用 mvn clean install 或者 gradle clean build 生成可执行jar包）

现在访问以下 URL，我们可以看到如下所示的输出

文件下载 - http://localhost:8080/download