Java implements the preview and download functions of file pictures

    @ApiOperation("Access File")
    @GetMapping("/download/{name}")
    public void getImage(HttpServletResponse response, @PathVariable("name") String name) throws IOException {
        // Dynamically obtain the image storage location        // String path = getUploadPath();//Get the current system path        String path = upload;
        String imagePath = path +  + name;
        if (!new File(imagePath).exists()) {
            return;
        }
        if (("jpg") || ("png") || ("gif") || ("jpeg")) {
            //Do not set Content-Disposition during preview            ("image/jpeg;charset=utf-8");//picture        }else {
            //download        ("application/octet-stream");//document        ("Content-Disposition", "inline; filename=" + (name, "UTF-8"));
        }
        ServletOutputStream outputStream = ();
        (((path).resolve(name)));
        ();
        ();
    }

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@RestController
@RequestMapping("/api/files")
public class FileDownloadController {

    @GetMapping("/download")
    public ResponseEntity<Resource> downloadFile() {
        String fileName = ""; // File name to download        
        try {
            // Load the file from the resources directory            ClassPathResource resource = new ClassPathResource(fileName);
            
            if (!()) {
                return ().build();
            }

            // Set response header            HttpHeaders headers = new HttpHeaders();
            (HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=" + ());

            // Return the file as a response            return ()
                    .headers(headers)
                    .contentType(.APPLICATION_OCTET_STREAM)
                    .body(resource);
        } catch (IOException e) {
            return (HttpStatus.INTERNAL_SERVER_ERROR).build();
        }
    }
}

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/**
 * @author long
 * @version 1.0.0
 * @ClassName FileController
 * @Description TODO
 * @createTime 2022.03.18 18:47
 */
@RestController
@RequestMapping("/demo")
public class FileController {


    @GetMapping("/file")
    public void filePreviewOrDownload(HttpServletRequest request, HttpServletResponse response) throws Exception {
        String fileName = ("fileName");
        //type.p preview, d download        String type = ("type");
        ();
        ("UTF-8");

        File file = new File("C:\\Users\\long\\Desktop\\" + fileName);
        FileInputStream fis = new FileInputStream(file);

        if ("d".equalsIgnoreCase(type)) {
            //download            ("application/octet-stream");
            ("Content-Disposition", "attachment;filename*=utf-8''" + () + ((".")));

        } else {
            //Do not set Content-Disposition during preview//            ("application/octet-stream");
//            ("text/html;charset=UTF-8");
//            ("Content-Disposition","inline;filename=" + () + ((".")));
        }
        OutputStream os = ();
        byte[] bytes = new byte[1024];
        int length = 0;
        while ((length = (bytes)) != -1) {
            (bytes, 0, length);
        }
        ();
        ();
    }


}

@GetMapping("/downFile")
    public void downFile(HttpServletResponse response, HttpServletRequest request) {
        try {
// File file = new File("C:\\Users\\hnsh\\Pictures\\Tieshankui.png");            File file = new File("F:\\BaiduNetdiskDownload\\activitiTutorial (1).pdf");
            String filename = ();
            String fileType = ((".") + 1);

            // Download the file in stream form.            FileInputStream fileInputStream = new FileInputStream(file);
            InputStream fis = new BufferedInputStream(fileInputStream);
            byte[] buffer = new byte[1024];
            int len = 0;
            // Clear response            ();
            // Set the response header            // Solve cross-domain            ("Access-Control-Allow-Origin", "*");
            boolean b = "jpg".equalsIgnoreCase(fileType) || "png".equalsIgnoreCase(fileType) || "gif".equalsIgnoreCase(fileType);
            // Picture preview            if (b) {
                ("image/" + fileType);
            } else if ("pdf".equalsIgnoreCase(fileType)) {
                // pdf preview                ("application/pdf");
            } else {
                // Download directly                ("application/text;chartset=utf-8");
                ("Content-Disposition", "attachment;filename=" + (filename, "UTF-8"));
                ("Content-Length", "" + ());
            }
            OutputStream toClient = new BufferedOutputStream(());
            int a = 0;
            while ((len = (buffer)) != -1) {
                a = len + a;
                (buffer, 0, len);
            }
            ();
            ();
        } catch (IOException ex) {
            ();
        }
    }