是否有更好的方法将文件的全部内容写入OutputStream? [英] Is there a better way to write the full contents of a file to an OutputStream?

问题描述

当我想将文件的全部内容写入OutputStream时，我通常将缓冲区分配为byte[]，然后进行for循环以将文件InputStream中的read数据写入缓冲区，并将缓冲区内容写入OutputStream，直到InputStream没有更多字节可用.

When I want to write the full contents of a file into an OutputStream, I usually allocate a buffer as a byte[], then make a for loop to read data from the file's InputStream into the buffer and write the buffer contents into the OutputStream, until the InputStream has no more bytes available.

对我来说，这似乎很笨拙.有更好的方法吗?

This seems rather clumsy to me. Is there a better way to do this?

此外，我始终不确定缓冲区的大小.通常，我分配1024个字节，因为感觉很好.有没有更好的方法来确定合理的缓冲区大小?

Also, I am always unsure about the buffer size. Usually, I am allocating 1024 bytes, because it just feels good. Is there a better way to determine a reasonable buffer size?

在当前情况下，我想将文件的全部内容复制到写入HTTP响应内容的输出流中.因此，这不是关于如何在文件系统上复制文件的问题.

In my current case, I want to copy the full contents of a file into the output stream that writes the contents of an HTTP response. So, this is not a question about how to copy files on the file system.

推荐答案

对于Java 1.7+，您可以使用

For Java 1.7+ you can use the Files.copy(Path, OutputStream), e.g.

HttpServletResponse response = // ...
File toBeCopied = // ...

try (OutputStream out = response.getOutputStream()) {
    Path path = toBeCopied.toPath();
    Files.copy(path, out);
    out.flush();
} catch (IOException e) {
    // handle exception
}

注意，由于您正在处理HttpServletResponse也是设置正确响应头的好主意.在将实际文件数据复制到响应之前，在 之前添加以下行:

Note, since you are dealing with HttpServletResponse is is also a good idea to set correct response headers. Add the following lines before you copy the actual file data to the response:

String mimeType = URLConnection.guessContentTypeFromName(toBeCopied.getName());
String contentDisposition = String.format("attachment; filename=%s", toBeCopied.getName());
int fileSize = Long.valueOf(toBeCopied.length()).intValue();

response.setContentType(mimeType);
response.setHeader("Content-Disposition", contentDisposition);
response.setContentLength(fileSize);

请注意，传递给内容处置的文件名的编码很重要，请参见

Note, the encoding of the file name passed to the content disposition is important, see this question.

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