HttpServletResponse和 ResponseEntity下载文件预览图片

直接上菜，然后在点评一波：

import org.springframework.http.*;
import org.springframework.web.bind.annotation.*;

import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.net.URLEncoder;


@RestController
@RequestMapping(value = "/test")
public class KeyController {

    /**
     * ResponseEntity图片预览
     *
     * @return
     * @throws Exception
     */
    @GetMapping("/responseEntityView")
    public ResponseEntity responseEntityView() throws Exception {
        File file = new File("E:\\图片\\bpic4828.jpg");
        InputStream inputStream = new FileInputStream(file);
        byte[] bytes = null;
        bytes = readInputStream(inputStream);

        HttpHeaders httpHeaders = new HttpHeaders();
        // 不是用缓存
        httpHeaders.setCacheControl(CacheControl.noCache());
        httpHeaders.setPragma("no-cache");
        httpHeaders.setExpires(0L);
        httpHeaders.setContentType(MediaType.IMAGE_JPEG);
        ResponseEntity responseEntity = new ResponseEntity<>(bytes, httpHeaders, HttpStatus.OK);
        return responseEntity;
    }

    /**
     * ResponseEntity文件下载Post请求
     * （如果不会参数不多就最好使用get,post请求不会解码文件名，如果不编码中文就会成一个_，没有中文用那个都可以）
     *
     * @return
     * @throws Exception
     */
    @PostMapping("/responseEntityDownloadPost")
    public ResponseEntity responseEntityDownloadPost() throws Exception {
        File file = new File("C:\\Users\\Administrator\\Desktop\\tt\\小儿喜.zip");
        InputStream inputStream = new FileInputStream(file);
        byte[] bytes = null;
        bytes = readInputStream(inputStream);
        String fileName = URLEncoder.encode(file.getName(), "UTF-8");

        HttpHeaders httpHeaders = new HttpHeaders();
        httpHeaders.setContentDispositionFormData("attachment", fileName);
        httpHeaders.setContentType(MediaType.APPLICATION_OCTET_STREAM);
        ResponseEntity responseEntity = new ResponseEntity<>(bytes, httpHeaders, HttpStatus.OK);
        return responseEntity;
    }

    /**
     * ResponseEntity文件下载Get请求
     *
     * @return
     * @throws Exception
     */
    @GetMapping("/responseEntityDownloadGet")
    public ResponseEntity responseEntityDownloadGet() throws Exception {
        File file = new File("C:\\Users\\Administrator\\Desktop\\tt\\小儿喜.zip");
        InputStream inputStream = new FileInputStream(file);
        byte[] bytes = null;
        bytes = readInputStream(inputStream);
        String fileName = URLEncoder.encode(file.getName(), "UTF-8");

        HttpHeaders httpHeaders = new HttpHeaders();
        httpHeaders.setContentDispositionFormData("attachment", fileName);
        httpHeaders.setContentType(MediaType.APPLICATION_OCTET_STREAM);
        ResponseEntity responseEntity = new ResponseEntity<>(bytes, httpHeaders, HttpStatus.OK);
        return responseEntity;
    }

    /**
     * ResponseEntity文件下载Get请求PostPost请求不会自动解码，所以使用get请求转一下就没有问题了
     *
     * @return
     * @throws Exception
     */
    @GetMapping("/responseEntityDownloadGetByPost")
    public ResponseEntity responseEntityDownloadGetByPost() throws Exception {
        ResponseEntity responseEntity = this.responseEntityDownloadPost();
        return responseEntity;
    }

    /**
     * HttpServletResponse图片预览
     *
     * @param response
     * @return
     * @throws Exception
     */
    @GetMapping("/httpServletResponseView")
    public String httpServletResponseView(HttpServletResponse response) throws Exception {
        File file = new File("E:\\图片\\bpic4828.jpg");
        InputStream inputStream = new FileInputStream(file);
        byte[] bytes = null;
        OutputStream outputStream = response.getOutputStream();
        response.setContentType(MediaType.IMAGE_JPEG_VALUE);
        // 不使用缓存
        response.setHeader("Cache-Control", "no-cache");
        response.setHeader("Pragma", "no-cache");
        response.setDateHeader("expires", -1);
        response.setHeader("Content-Disposition", "inline");
        readInputStreamToOutStream(inputStream, outputStream);
        return null;
    }


    /**
     * HttpServletResponse文件下载Post请求
     *
     * @param response
     * @return
     * @throws Exception
     */
    @PostMapping("/httpServletResponseDownloadPost")
    public String httpServletResponseDownloadPost(HttpServletResponse response) throws Exception {
        File file = new File("C:\\Users\\Administrator\\Desktop\\tt\\小儿喜.zip");
        InputStream inputStream = new FileInputStream(file);
        response.setContentType(MediaType.APPLICATION_OCTET_STREAM_VALUE);
        response.setCharacterEncoding("UTF-8");
        OutputStream outputStream = response.getOutputStream();
        String fileName = URLEncoder.encode(file.getName(), "UTF-8");
        response.setHeader("Content-Disposition", "attachment;filename=" + fileName);
        readInputStreamToOutStream(inputStream, outputStream);
        return null;
    }

    /**
     * HttpServletResponse文件下载Get请求
     *
     * @param response
     * @return
     * @throws Exception
     */
    @GetMapping("/httpServletResponseDownloadGet")
    public String httpServletResponseDownloadGet(HttpServletResponse response) throws Exception {
        File file = new File("C:\\Users\\Administrator\\Desktop\\tt\\小儿喜.zip");
        InputStream inputStream = new FileInputStream(file);
        response.setContentType(MediaType.APPLICATION_OCTET_STREAM_VALUE);
        response.setCharacterEncoding("UTF-8");
        OutputStream outputStream = response.getOutputStream();
        String fileName = URLEncoder.encode(file.getName(), "UTF-8");
        response.setHeader("Content-Disposition", "attachment;filename=" + fileName);
        readInputStreamToOutStream(inputStream, outputStream);
        return null;
    }

    /**
     * HttpServletResponse文件下载Get请求通过Post生成数据
     * @param response
     * @return
     * @throws Exception
     */
    @GetMapping("/httpServletResponseDownloadGetByPost")
    public String httpServletResponseDownloadGetByPost(HttpServletResponse response) throws Exception {
        this.httpServletResponseDownloadPost(response);
        return null;
    }


    /**
     * 输入流装成字节数组
     *
     * @param inStream
     * @return
     * @throws Exception
     */
    private byte[] readInputStream(InputStream inStream) throws Exception {
        ByteArrayOutputStream outStream = new ByteArrayOutputStream();
        byte[] buffer = new byte[1024];
        int len = 0;
        while ((len = inStream.read(buffer)) != -1) {
            outStream.write(buffer, 0, len);
        }
        inStream.close();
        return outStream.toByteArray();
    }

    /**
     * 输入流写进输出流
     *
     * @param inStream
     * @param outStream
     * @throws Exception
     */
    private void readInputStreamToOutStream(InputStream inStream, OutputStream outStream) throws Exception {
        byte[] buffer = new byte[1024];
        int len = 0;
        while ((len = inStream.read(buffer)) != -1) {
            outStream.write(buffer, 0, len);
        }
        inStream.close();
        outStream.close();
    }

}

 

结论：

1、HttpServletResponse 和 ResponseEntity的使用主要看个人了，如果使用Spring的项目就可以选择使用ResponseEntity，没有用Spring就可以直接使用HttpServletResponse。

2、不管用那个来下载文件，如果这个文件名是中文就要编码（不编码中文会变成_，没有中文就可以不编码的哦），但是编码也有一个问题，post请求不会自动解码，目前我是没有找到解决的方法（如果您有就可以写在评论区），get就会自动解码，所以有时候后台直接可以使用post请求（需要组装后台其他服务的多个参数的时候），前端获取的使用用get转一下就可以了。建议尽量使用get请求。

3、ResponseEntity其实可以看做是把HttpServletResponse封装了，但是功能比HttpServletResponse多，推介使用。

4、contentType的类型如果没有具体的类型就可以使用"application/octet-stream(MediaType.APPLICATION_OCTET_STREAM)",如果有具体类型建议使用具体类型。

5、如有不对请在评论区进行评论，谢谢。

《………………………………………………菜鸟起飞中，请各位走过路过的多多指教……………………………………》