Java实现文件的下载功能

首先呢，我们先建立一个Springboot项目：

<?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>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.5.RELEASE</version>
        <relativePath/>
    </parent>

    <groupId>fun.gosuncn</groupId>
    <artifactId>download</artifactId>
    <version>1.0</version>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </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>

然后呢，为了方便我们直接将端口设置为80：

server:
  port: 80

接下来，写Controller下载的处理器：

package fun.gosuncn.controller;

import org.apache.tomcat.util.http.fileupload.IOUtils;
import org.springframework.core.io.ClassPathResource;
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.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.InputStream;

@RestController
public class DownloadController {

    @GetMapping("/1")
    public void download1(HttpServletResponse response) throws IOException {
        String filename = "abc.jpg";
        InputStream inputStream = ClassLoader.getSystemClassLoader().getResourceAsStream(filename);
        response.setHeader("Content-Disposition", "attachment;filename=" + filename);
        response.addHeader("Content-Length", String.valueOf(inputStream.available()));
        response.setContentType(MediaType.APPLICATION_OCTET_STREAM_VALUE);
        ServletOutputStream outputStream = response.getOutputStream();
        IOUtils.copy(inputStream, outputStream);
        inputStream.close();
    }

    @GetMapping("/2")
    public ResponseEntity<InputStreamResource> download2() throws IOException {
        String filename = "abc.jpg";
        ClassPathResource resource = new ClassPathResource(filename);
        HttpHeaders headers = new HttpHeaders();
        headers.add("Cache-Control", "no-cache, no-store, must-revalidate");
        headers.add("Content-Disposition", String.format("attachment; filename=\"%s\"", filename));
        headers.add("Pragma", "no-cache");
        headers.add("Expires", "0");
        return ResponseEntity.ok().headers(headers).contentLength(resource.contentLength())
                .contentType(MediaType.APPLICATION_OCTET_STREAM).body(new InputStreamResource(resource.getInputStream()));
    }

}

提供了两种方式，第一种呢，是Servlet原生的方式，第二种是Springboot 的方式，看你喜欢哪种，你就用那种。