Determine the size of an InputStream

问题

My current situation is: I have to read a file and put the contents into InputStream. Afterwards I need to place the contents of the InputStream into a byte array which requires (as far as I know) the size of the InputStream. Any ideas?

As requested, I will show the input stream that I am creating from an uploaded file

InputStream uploadedStream = null;
FileItemFactory factory = new DiskFileItemFactory();
ServletFileUpload upload = new ServletFileUpload(factory);
java.util.List items = upload.parseRequest(request);      
java.util.Iterator iter = items.iterator();

while (iter.hasNext()) {
    FileItem item = (FileItem) iter.next();
    if (!item.isFormField()) {
        uploadedStream = item.getInputStream();
        //CHANGE uploadedStreambyte = item.get()
    }
}

The request is a HttpServletRequest object, which is like the FileItemFactory and ServletFileUpload is from the Apache Commons FileUpload package.

回答1:

I just wanted to add, Apache Commons IO has stream support utilities to perform the copy. (Btw, what do you mean by placing the file into an inputstream? Can you show us your code?)

Edit:

Okay, what do you want to do with the contents of the item? There is an item.get() which returns the entire thing in a byte array.

Edit2

item.getSize() will return the uploaded file size.

回答2:

This is a REALLY old thread, but it was still the first thing to pop up when I googled the issue. So I just wanted to add this:

InputStream inputStream = conn.getInputStream();
int length = inputStream.available();

Worked for me. And MUCH simpler than the other answers here.

回答3:

I would read into a ByteArrayOutputStream and then call toByteArray() to get the resultant byte array. You don't need to define the size in advance (although it's possibly an optimisation if you know it. In many cases you won't)

回答4:

You can't determine the amount of data in a stream without reading it; you can, however, ask for the size of a file:

http://java.sun.com/javase/6/docs/api/java/io/File.html#length()

If that isn't possible, you can write the bytes you read from the input stream to a ByteArrayOutputStream which will grow as required.

回答5:

For InputStream

org.apache.commons.io.IoUtils.toByteArray(inputStream).length

For Optional < MultipartFile >

Stream.of(multipartFile.get()).mapToLong(file->file.getSize()).findFirst().getAsLong()

回答6:

you can get the size of InputStream using getBytes(inputStream) of Utils.java check this following link

Get Bytes from Inputstream

回答7:

When explicitly dealing with a ByteArrayInputStream then contrary to some of the comments on this page you can use the .available() function to get the size. Just have to do it before you start reading from it.

From the JavaDocs:

Returns the number of remaining bytes that can be read (or skipped over) from this input stream. The value returned is count - pos, which is the number of bytes remaining to be read from the input buffer.

https://docs.oracle.com/javase/7/docs/api/java/io/ByteArrayInputStream.html#available()

回答8:

If you know that your InputStream is a FileInputStream or a ByteArrayInputStream, you can use a little reflection to get at the stream size without reading the entire contents. Here's an example method:

static long getInputLength(InputStream inputStream) {
    try {
        if (inputStream instanceof FilterInputStream) {
            FilterInputStream filtered = (FilterInputStream)inputStream;
            Field field = FilterInputStream.class.getDeclaredField("in");
            field.setAccessible(true);
            InputStream internal = (InputStream) field.get(filtered);
            return getInputLength(internal);
        } else if (inputStream instanceof ByteArrayInputStream) {
            ByteArrayInputStream wrapper = (ByteArrayInputStream)inputStream;
            Field field = ByteArrayInputStream.class.getDeclaredField("buf");
            field.setAccessible(true);
            byte[] buffer = (byte[])field.get(wrapper);
            return buffer.length;
        } else if (inputStream instanceof FileInputStream) {
            FileInputStream fileStream = (FileInputStream)inputStream;
            return fileStream.getChannel().size();
        }
    } catch (NoSuchFieldException | IllegalAccessException | IOException exception) {
        // Ignore all errors and just return -1.
    }
    return -1;
}

This could be extended to support additional input streams, I am sure.

回答9:

Use this method, you just have to pass the InputStream

public String readIt(InputStream is) {
    if (is != null) {
        BufferedReader reader = new BufferedReader(new InputStreamReader(is, "utf-8"), 8);

        StringBuilder sb = new StringBuilder();
        String line;
        while ((line = reader.readLine()) != null) {
            sb.append(line).append("\n");
        }
        is.close();
        return sb.toString();
    }
    return "error: ";
}

回答10:

    try {
        InputStream connInputStream = connection.getInputStream();
    } catch (IOException e) {
        e.printStackTrace();
    }

    int size = connInputStream.available();

int available () Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream. The next invocation might be the same thread or another thread. A single read or skip of this many bytes will not block, but may read or skip fewer bytes.

InputStream - Android SDK | Android Developers

来源：https://stackoverflow.com/questions/1119332/determine-the-size-of-an-inputstream

标签

java

arrays

size

inputstream