如何将文件保存在内存中并读取文件输出流? [英] How to save file in memory and read file output stream?

问题描述

保存文件时，我使用:

File file = new File(filename);

但是，由于我不再具有写文件夹的权限，我想将其保存到内存中，然后再将文件读取到FileOutputStream.

But, since I no longer have privileges to write to folders, I would like rather to save it to memory and then read file to FileOutputStream.

我已经读过我可以用这种方法将文件保存到内存中

I have read I can save file to memory with this approach:

new ByteArrayOutputStream(); 

整个代码看起来如何?上传完成后，我无法弄清楚如何正确编写它.

How would whole code look like? I can't figure it out how to write it properly after upload is done.

我正在使用Vaadins上传插件:

I'm using Vaadins upload plugin:

public File file;

    public OutputStream receiveUpload(String filename,
                                      String mimeType) {

        // Create upload stream
        FileOutputStream fos = null; // Stream to write to
        file = null;

        if(StringUtils.containsIgnoreCase(filename, ".csv")){
            try {

                file = new File(filename);
                fos = new FileOutputStream(file);
            } catch (final java.io.FileNotFoundException e) {

                new Notification("Error", e.getMessage(), Notification.Type.WARNING_MESSAGE)
                    .show(Page.getCurrent());
                return null;
            }
        } else {

            new Notification("Document is not .csv file", Notification.Type.WARNING_MESSAGE)
                .show(Page.getCurrent());
            return null;
        }
        return fos; // Return the output stream to write to
    }

推荐答案

public OutputStream receiveUpload(String filename,
                                  String mimeType) {

    ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();

    return byteArrayOutputStream;
}

您可以使用以下方法将内容写入流中:

You can get the content written in the stream using:

byte[] dataWrittenInTheOutputStream = byteArrayOutputStream.toByteArray();

或者您可以将内容写入另一个OutputStream:

Or you can write the contents to another OutputStream:

byteArrayOutputStream.writeTo(System.out);

或者:

file = new File(filename);    
fos = new FileOutputStream(file);
byteArrayOutputStream.writeTo(fos);

这篇关于如何将文件保存在内存中并读取文件输出流?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！