java 如何将 byte[] 转换为带有下载对话框的文件？
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How to convert a byte[] into a file with a download dialog box?
提问by Freakyuser
I have a table with blob content in it, in which I store different file types(text, audio, image, etc). After retrieving the byte []successfully, I don't have any idea of how to convert the [] in such a way as to convert it into a download dialog box.
Here is my code
我有一个包含 blob 内容的表，我在其中存储了不同的文件类型(text, audio, image, etc)。byte []成功检索后，我不知道如何将[]转换为将其转换为下载对话框。
这是我的代码
trns = session.beginTransaction();
Query query = session.createQuery("from FileDownload as fu where fu.Id =:Id");
query.setInteger("Id", id);
FileDownload fileDownload = (FileDownload) query.iterate().next();
byte[] byteArray = fileDownload.getFile();
The above code works fine and I receive a byte []. But I don't know how to proceed further in order to convert it into a file with the dialog appearing.
上面的代码工作正常，我收到一个byte []. 但我不知道如何进一步将其转换为出现对话框的文件。
Can anyone please help me?
谁能帮帮我吗？
回答by Moritz Petersen
Assuming you know the mimeTypeand filenameof your file, you can set the content type and the HTTP header Content-Disposition.
假设您知道文件的mimeType和filename，您可以设置内容类型和 HTTP 标头 Content-Disposition。
Just write the byte array to the OutputStream:
只需将字节数组写入OutputStream：
// The response from your servlet.
HttpServletResponse resp;
resp.setContentType(mimeType);
resp.setHeader("Content-Disposition", "attachment;filename=" + filename);
resp.getOutputStream().write(byteArray);
回答by Sean Connolly
The byte array can be sent to the client from a servlet. You can find many discussions on the topic here and elsewhere.
字节数组可以从 servlet 发送到客户端。您可以在此处和其他地方找到有关该主题的许多讨论。
Here are folks discussing efficiency of streaming(with code). Here is a discussion on how to map the servlet to a url(with examples).
这里有人在讨论流的效率（带代码）。这里讨论如何将 servlet 映射到 url（带有示例）。
The last thing for you to do is just link the user to the servlet's URL when they click the button.
您要做的最后一件事就是在用户单击按钮时将用户链接到 servlet 的 URL。
You'll also want to look into what additional info you can provide in the header before streaming the byte array. For example, if you provide a mime type the browser then has a clue what to do with the file; open PDFs in the browser, display images in the browser; open xls files in Excel.
在流式传输字节数组之前，您还需要查看可以在标头中提供哪些附加信息。例如，如果您提供 MIME 类型，浏览器就会知道如何处理该文件；在浏览器中打开PDF，在浏览器中显示图片；在 Excel 中打开 xls 文件。
