Spring Boot中4种文件下载方法的实现

ycyin2023年5月19日大约 5 分钟

本篇文章介绍Spring Boot中分别返回ResponseEntity<InputStreamResource>、ResponseEntity<Resource>、ResponseEntity<StreamingResponseBody>、HttpServletResponse.getOutputStream()4种文件下载方法的实现。

先看看Controller比较直观的展示效果：

@RestController
@RequestMapping("v1/api/file")
public class FileController {
    // spring 注入泛型接口实现
    private final DownLoadFileService<InputStreamResource> isrDownLoadFileService;
    private final DownLoadFileService<Resource> rDownLoadFileService;
    private final DownLoadFileService<StreamingResponseBody> srbDownLoadFileService;
    private final DownLoadFileService srDownLoadFileService;

    public FileController(DownLoadFileService<InputStreamResource> isrDownLoadFileService, DownLoadFileService<Resource> rDownLoadFileService, DownLoadFileService<StreamingResponseBody> srbDownLoadFileService, DownLoadFileService srDownLoadFileService) {
        this.isrDownLoadFileService = isrDownLoadFileService;
        this.rDownLoadFileService = rDownLoadFileService;
        this.srbDownLoadFileService = srbDownLoadFileService;
        this.srDownLoadFileService = srDownLoadFileService;
    }
    
    @RequestMapping(value = "/download1", method = RequestMethod.GET,produces = {MediaType.APPLICATION_OCTET_STREAM_VALUE})
    @SneakyThrows
    public ResponseEntity<InputStreamResource> downloadFile1(String id){
        return isrDownLoadFileService.downloadFile(id);
    }

    @RequestMapping(value = "/download2", method = RequestMethod.GET, produces = MediaType.APPLICATION_OCTET_STREAM_VALUE)
    @SneakyThrows
    public ResponseEntity<Resource> downloadFile2(String id) {
        return rDownLoadFileService.downloadFile(id);
    }

    @GetMapping(value = "/download3", produces = MediaType.APPLICATION_OCTET_STREAM_VALUE)
    public ResponseEntity<StreamingResponseBody> downloadFile3(@RequestParam(name = "id") String id) {
        return srbDownLoadFileService.downloadFile(id);
    }

    @GetMapping(value = "/download4")
    public void downloadFile4(@RequestParam(name = "id") String id) {
        srDownLoadFileService.downloadFile(id);
    }

}

前言

springboot：2.3.9.RELEASE

mybatis-plus: 3.5.2

本文的文件访问依赖使用minioClient，所有的InputStream都来自minioTemplate.get(thirdFile.getName());，篇幅有限，访问minio具体实现也比较简单就不在本文中介绍，也可以使用其它方式比如本地文件获取文件输入流InputStream。

其实本文介绍的这几种方式原理都是一样的，最终都是往HttpServletResponse输出流，由此还可以做出更多的变通，比如还可以返回ResponseEntity<ByteArrayResource> 、ResponseEntity<byte[]>等，这里可以去看看ResponseEntity的原理：

ResponseEntity对应一个http请求或者响应，可以用在controller的返回值里，方便处理header及status。而通常使用的@ResponseBody注解，只能处理body部分。这也是为什么通常在下载场景中会使用ResponseEntity，因为下载需要设置header里的content-type以及特殊的status（比如206）。

ResponseEntity类型的返回值由一个特殊的HttpEntityMethodProcessor类型的returnTypeHandler来处理，主要是将ResponseEntity里设置的header和status写入到httpResponse中，body部分调用的是父类的模板方法。

必需的配置

添加HttpMessageConverter转换器配置
不添加会报错：springboot no converter for [class org.springframework.core.io.inputstreamresource] with preset content-type '.....']
报这个错误的原因大概就是我们在Controller层使用@RestController注解，这个注解包含@ResponseBody注解，AbstractMessageConverterMethodProcessor类的子类RequestResponseBodyMethodProcessor是用来处理@Responsebody注解的，而HttpEntityMethodProcessor是AbstractMessageConverterMethodProcessor的另一个子类，该processor专门处理返回值类型是ResponseEntity类型的controller返回值。
所以按照原理来说，不使用@RestController和@Responsebody注解就可以不用添加这个HttpMessageConverter转换器配置，但是我这里不知道为啥即使不使用@RestController注解还是要必须添加这个转换器配置才行。有懂的老铁欢迎评论。
```
@Configuration
public class WebMVCConfig implements WebMvcConfigurer {

    public void    configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        ResourceHttpMessageConverter resHttpMessageConverter = new ResourceHttpMessageConverter();
        final List<MediaType> list = new ArrayList<>();
        list.add(MediaType.IMAGE_JPEG);
        list.add(MediaType.IMAGE_PNG);
        list.add(MediaType.APPLICATION_OCTET_STREAM);
        resHttpMessageConverter.setSupportedMediaTypes(list);
        converters.add(resHttpMessageConverter);
    }
}
```

使用到的实体和Mapper

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import org.apache.ibatis.annotations.Mapper;

@Mapper
public interface FileMapper extends BaseMapper<ThirdFile> {
}

import com.alibaba.fastjson.annotation.JSONField;
import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.Builder;
import lombok.Data;

@TableName("third_file")
@Data
@Builder
public class ThirdFile {
    @TableId(value = "id",type = IdType.INPUT)
    private String id;

    @TableField("name")
    private String name;

    @TableField("size")
    private Long size;

    @TableField("version")
    private Integer version;

    @TableField("create_time")
    @JSONField(name = "create_time")
    private Long createTime;

    @TableField("update_time")
    @JSONField(name = "update_time")
    private Long updateTime;
}

定义泛型接口

import org.springframework.http.HttpHeaders;
import org.springframework.http.ResponseEntity;

import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import java.nio.charset.StandardCharsets;

public interface DownLoadFileService<T> {

    ResponseEntity<T> downloadFile(String id);

    default HttpHeaders getHttpHeaders(String filename) throws UnsupportedEncodingException {
        HttpHeaders headers = new HttpHeaders();
        headers.add(HttpHeaders.CONTENT_DISPOSITION, String.format("attachment; filename=\"%s\"", URLEncoder.encode(filename, StandardCharsets.UTF_8.name())));
        headers.add(HttpHeaders.CACHE_CONTROL, "no-cache, no-store, must-revalidate");
        headers.add(HttpHeaders.PRAGMA, "no-cache");
        headers.add(HttpHeaders.EXPIRES, "0");
        return headers;
    }
}

具体实现

第一种:返回InputStreamResource

import lombok.SneakyThrows;
import lombok.extern.log4j.Log4j2;
import org.springframework.core.io.InputStreamResource;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Service;

import javax.servlet.ServletContext;
import java.io.InputStream;

@Log4j2
@Service
public class InputStreamResourceDownService implements DownLoadFileService<InputStreamResource> {


    private final MinioTemplate minioTemplate;
    private final FileMapper fileMapper;
    private final ServletContext servletContext;

    public InputStreamResourceDownService(MinioTemplate minioTemplate, FileMapper fileMapper, ServletContext servletContext) {
        this.minioTemplate = minioTemplate;
        this.fileMapper = fileMapper;
        this.servletContext = servletContext;
    }

    @SneakyThrows
    @Override
    public ResponseEntity<InputStreamResource> downloadFile(String id) {
        ThirdFile thirdFile = fileMapper.selectById(id);
        InputStream inputStream = minioTemplate.get(thirdFile.getName());
        InputStreamResource inputStreamResource = new InputStreamResource(inputStream);

        String fileName = thirdFile.getName();
        MediaType mediaType = MediaTypeUtils.getMediaTypeForFileName(this.servletContext, fileName);
        log.info("fileName: " + fileName);
        log.info("mediaType: " + mediaType);

        return ResponseEntity
                .ok()
                .headers(getHttpHeaders(fileName))
                .contentLength(thirdFile.getSize())
                .contentType(mediaType)
                .body(inputStreamResource);
    }
}

第二种:返回Resource

import lombok.SneakyThrows;
import org.springframework.core.io.ByteArrayResource;
import org.springframework.core.io.Resource;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Service;
import java.io.ByteArrayOutputStream;
import java.io.InputStream;

@Service
public class ResourceDownLoadService implements DownLoadFileService<Resource> {

    private final MinioTemplate minioTemplate;
    private final FileMapper fileMapper;

    public ResourceDownLoadService(MinioTemplate minioTemplate, FileMapper fileMapper) {
        this.minioTemplate = minioTemplate;
        this.fileMapper = fileMapper;
    }

    @SneakyThrows
    @Override
    public ResponseEntity<Resource> downloadFile(String id) {
        ThirdFile thirdFile = fileMapper.selectById(id);
        InputStream inputStream = minioTemplate.get(thirdFile.getName());
        // 读取 InputStream 的数据到字节数组中
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        byte[] buffer = new byte[4096];
        int bytesRead;
        while ((bytesRead = inputStream.read(buffer)) != -1) {
            outputStream.write(buffer, 0, bytesRead);
        }
        byte[] fileBytes = outputStream.toByteArray();

        return ResponseEntity.ok()
                .headers(getHttpHeaders(thirdFile.getName()))
                .contentLength(fileBytes.length)
                .contentType(MediaType.APPLICATION_OCTET_STREAM)
                .body(new ByteArrayResource(fileBytes));
    }
}

第三种:返回StreamingResponseBody

import lombok.SneakyThrows;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Service;
import org.springframework.util.StreamUtils;
import org.springframework.web.servlet.mvc.method.annotation.StreamingResponseBody;

import java.io.IOException;
import java.io.InputStream;

@Service
public class StreamingResponseBodyDownLoadService implements DownLoadFileService<StreamingResponseBody> {
    private final MinioTemplate minioTemplate;
    private final FileMapper fileMapper;

    public StreamingResponseBodyDownLoadService(MinioTemplate minioTemplate, FileMapper fileMapper) {
        this.minioTemplate = minioTemplate;
        this.fileMapper = fileMapper;
    }

    @SneakyThrows
    @Override
    public ResponseEntity<StreamingResponseBody> downloadFile(String id) {

        ThirdFile thirdFile = fileMapper.selectById(id);
        InputStream inputStream = minioTemplate.get(thirdFile.getName());

        return ResponseEntity.ok()
                .headers(getHttpHeaders(thirdFile.getName()))
                .contentType(MediaType.APPLICATION_OCTET_STREAM)
                .body(outputStream -> {
                    try (InputStream inputStream2 = inputStream) {
                        StreamUtils.copy(inputStream2, outputStream);
                    } catch (IOException ignored) {

                    }
                });
    }
}

第四种:返回HttpServletResponse输出流

import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Service;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletResponse;
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.InputStream;
import java.net.URLEncoder;
import java.nio.charset.StandardCharsets;


@Log4j2
@Service("srDownLoadFileService")
public class ServletResponseDownService implements DownLoadFileService {

    private final MinioTemplate minioTemplate;
    private final FileMapper fileMapper;
    private final ServletContext servletContext;
    private final HttpServletResponse response;

    public ServletResponseDownService(MinioTemplate minioTemplate, FileMapper fileMapper, ServletContext servletContext, HttpServletResponse response) {
        this.minioTemplate = minioTemplate;
        this.fileMapper = fileMapper;
        this.servletContext = servletContext;
        this.response = response;
    }

    @SneakyThrows
    @Override
    public ResponseEntity downloadFile(String id) {
        ThirdFile thirdFile = fileMapper.selectById(id);
        InputStream inputStream = minioTemplate.get(thirdFile.getName());
        String fileName = thirdFile.getName();
        MediaType mediaType = MediaTypeUtils.getMediaTypeForFileName(this.servletContext, fileName);
        log.info("fileName: " + fileName);
        log.info("mediaType: " + mediaType);

        // Content-Type, eg: application/pdf
        response.setContentType(mediaType.getType());

        // Content-Disposition
        response.setHeader(HttpHeaders.CONTENT_DISPOSITION, "attachment;filename=" + URLEncoder.encode(fileName, StandardCharsets.UTF_8.name()));

        // Content-Length
        response.setContentLength(Math.toIntExact(thirdFile.getSize()));

        BufferedInputStream inStream = new BufferedInputStream(inputStream);
        BufferedOutputStream outStream = new BufferedOutputStream(response.getOutputStream());

        byte[] buffer = new byte[1024];
        int bytesRead = 0;
        while ((bytesRead = inStream.read(buffer)) != -1) {
            outStream.write(buffer, 0, bytesRead);
        }
        outStream.flush();
        inStream.close();
        return null;
    }
}

Spring注入泛型接口使用

@Log4j2
@RestController
@RequestMapping("v1/api/file")
public class FileController {

    // 泛型接口注入
    private final DownLoadFileService<InputStreamResource> isrDownLoadFileService;
    private final DownLoadFileService<Resource> rDownLoadFileService;
    private final DownLoadFileService<StreamingResponseBody> srbDownLoadFileService;
    private final DownLoadFileService srDownLoadFileService;

    public FileController(DownLoadFileService<InputStreamResource> isrDownLoadFileService, DownLoadFileService<Resource> rDownLoadFileService, DownLoadFileService<StreamingResponseBody> srbDownLoadFileService, DownLoadFileService srDownLoadFileService) {
        this.isrDownLoadFileService = isrDownLoadFileService;
        this.rDownLoadFileService = rDownLoadFileService;
        this.srbDownLoadFileService = srbDownLoadFileService;
        this.srDownLoadFileService = srDownLoadFileService;
    }

    @RequestMapping(value = "/download1", method = RequestMethod.GET,produces = {MediaType.APPLICATION_OCTET_STREAM_VALUE})
    @SneakyThrows
    public ResponseEntity<InputStreamResource> downloadFile1(String id){
        return isrDownLoadFileService.downloadFile(id);
    }

    @RequestMapping(value = "/download2", method = RequestMethod.GET, produces = MediaType.APPLICATION_OCTET_STREAM_VALUE)
    @SneakyThrows
    public ResponseEntity<Resource> downloadFile2(String id) {
        return rDownLoadFileService.downloadFile(id);
    }

    @GetMapping(value = "/download3", produces = MediaType.APPLICATION_OCTET_STREAM_VALUE)
    public ResponseEntity<StreamingResponseBody> downloadFile3(@RequestParam(name = "id") String id) {
        return srbDownLoadFileService.downloadFile(id);
    }


    @GetMapping(value = "/download4")
    public void downloadFile4(@RequestParam(name = "id") String id) {
        srDownLoadFileService.downloadFile(id);
    }


}

参考：

some ways for creating the file downloading function

How to solve "No converter for class B with preset Content-Type 'image/png'" error in Spring when trying to serve an image?

ResponseEntity 使用及原理

springboot 使用ResponseEntity实现文件流下载

SpringBoot中文件二进制流下载功能Api

Java- 泛型机制详解

java 泛型详解

Spring 框架：泛型接口的自动注入