java 将数据库中的文件下载到PC

Question

我从数据库获取图像(jpeg 或 pdf)并希望将其下载到 PC。但是，!file.exists() 无法识别该图像。这表明 File file = new File(resourceDetail.getResourseImage()); 不正确。请问正确的编码方法是什么？

注意:resourceDetail.getResourseImage()是实际图像而不是路径。

我的代码是:

        resourceDetail = MySQLConnection.resourceDownload(fileID);

        FileInputStream stream = null;
        try {
            File file = new File(resourceDetail.getResourseImage());
            System.out.println("resourceDetail.getResourseImage(): " + resourceDetail.getResourseImage());

            if (!file.exists()) {
                System.out.println("File does not exist: ");
//              context.addMessage(new ErrorMessage("msg.file.notdownloaded"));
//              context.setForwardName("failure");
            } else {
                System.out.println("File exist: ");
                if (resourceDetail.getResourseImageType().equals("pdf")){
                    System.out.println("pdf: ");
                    response.setContentType("application/pdf");
                    response.setHeader("Content-Disposition", "attachment; filename='myfile.pdf'");
                }else{
                    System.out.println("jpeg: ");
                    response.setContentType("image/jpeg");
                    response.setHeader("Content-Disposition", "attachment; filename='myfile.jpg'");
                }
//              response.setHeader("Content-Disposition", "attachment; filename=" + file.getName());
                System.out.println("stream: ");
                stream = new FileInputStream(file);
                response.setContentLength(stream.available());
                OutputStream os = response.getOutputStream();      
                os.close();
                response.flushBuffer();
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (stream != null) {
                try {
                    stream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

Answer 1

resourceDetail.getResourseImage() 得到字符串数据，可以直接使用:OuputStream#write(bytes) 将数据写入响应。在您的情况下，只需使用·os.write(resourceDetail.getResourseImage().getByets());`来执行此操作。

示例代码:

resourceDetail = MySQLConnection.resourceDownload(fileID);
try {
    System.out.println(
            "resourceDetail.getResourseImage(): " + resourceDetail.getResourseImage());

        if (resourceDetail.getResourseImageType().equals("pdf")) {
            System.out.println("pdf: ");
            response.setContentType("application/pdf");
            response.setHeader("Content-Disposition", "attachment; filename='myfile.pdf'");
        } else {
            System.out.println("jpeg: ");
            response.setContentType("image/jpeg");
            response.setHeader("Content-Disposition", "attachment; filename='myfile.jpg'");
        }
        response.setContentLength(resourceDetail.getResourseImage().length());
        OutputStream os = response.getOutputStream();
        os.write(resourceDetail.getResourseImage().getBytes());
        os.close();
        response.flushBuffer();
} catch (IOException e) {
    e.printStackTrace();
} finally {
    if (stream != null) {
        try {
            stream.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}