我用这个。

public static byte[] toByteArray(InputStream is) throws IOException {
        ByteArrayOutputStream output = new ByteArrayOutputStream();
        try {
            byte[] b = new byte[4096];
            int n = 0;
            while ((n = is.read(b)) != -1) {
                output.write(b, 0, n);
            }
            return output.toByteArray();
        } finally {
            output.close();
        }
    }

如果你碰巧使用谷歌Guava，它将像使用ByteStreams一样简单:

byte[] bytes = ByteStreams.toByteArray(inputStream);

你可以使用Cactoos(我是它的开发者之一):

import org.cactoos.bytes.BytesOf;
byte[] array = new BytesOf(stream).asBytes();

你也可以将流转换为字符串:

import org.cactoos.text.TextOf;
String txt = new TextOf(stream).asString();

asBytes()和asString()方法都会抛出checked Exception。如果你不想捕获它，使用Unchecked*装饰器，例如:

import org.cactoos.bytes.BytesOf;
import org.cactoos.bytes.UncheckedBytes;
byte[] array = new UncheckedBytes(new BytesOf(stream)).asBytes();

这对我很有用，

if(inputStream != null){
                ByteArrayOutputStream contentStream = readSourceContent(inputStream);
                String stringContent = contentStream.toString();
                byte[] byteArr = encodeString(stringContent);
            }

readSourceContent ()

public static ByteArrayOutputStream readSourceContent(InputStream inputStream) throws IOException {
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        int nextChar;
        try {
            while ((nextChar = inputStream.read()) != -1) {
                outputStream.write(nextChar);
            }
            outputStream.flush();
        } catch (IOException e) {
            throw new IOException("Exception occurred while reading content", e);
        }

        return outputStream;
    }

encodeString（）

public static byte[] encodeString(String content) throws UnsupportedEncodingException {
        byte[] bytes;
        try {
            bytes = content.getBytes();

        } catch (UnsupportedEncodingException e) {
            String msg = ENCODING + " is unsupported encoding type";
            log.error(msg,e);
            throw new UnsupportedEncodingException(msg, e);
        }
        return bytes;
    }

Kotlin中的解决方案(当然也可以在Java中工作)，其中包括当你知道大小时的两种情况:

    fun InputStream.readBytesWithSize(size: Long): ByteArray? {
        return when {
            size < 0L -> this.readBytes()
            size == 0L -> ByteArray(0)
            size > Int.MAX_VALUE -> null
            else -> {
                val sizeInt = size.toInt()
                val result = ByteArray(sizeInt)
                readBytesIntoByteArray(result, sizeInt)
                result
            }
        }
    }

    fun InputStream.readBytesIntoByteArray(byteArray: ByteArray,bytesToRead:Int=byteArray.size) {
        var offset = 0
        while (true) {
            val read = this.read(byteArray, offset, bytesToRead - offset)
            if (read == -1)
                break
            offset += read
            if (offset >= bytesToRead)
                break
        }
    }

如果您知道大小，那么与其他解决方案相比，它可以节省两倍的内存(在很短的时间内，但仍然可能有用)。这是因为您必须将整个流读到末尾，然后将其转换为字节数组(类似于将数组转换为数组的ArrayList)。

例如，如果你在Android上，你有一些Uri要处理，你可以尝试用这个来获取大小:

    fun getStreamLengthFromUri(context: Context, uri: Uri): Long {
        context.contentResolver.query(uri, arrayOf(MediaStore.MediaColumns.SIZE), null, null, null)?.use {
            if (!it.moveToNext())
                return@use
            val fileSize = it.getLong(it.getColumnIndex(MediaStore.MediaColumns.SIZE))
            if (fileSize > 0)
                return fileSize
        }
        //if you wish, you can also get the file-path from the uri here, and then try to get its size, using this: https://stackoverflow.com/a/61835665/878126
        FileUtilEx.getFilePathFromUri(context, uri, false)?.use {
            val file = it.file
            val fileSize = file.length()
            if (fileSize > 0)
                return fileSize
        }
        context.contentResolver.openInputStream(uri)?.use { inputStream ->
            if (inputStream is FileInputStream)
                return inputStream.channel.size()
            else {
                var bytesCount = 0L
                while (true) {
                    val available = inputStream.available()
                    if (available == 0)
                        break
                    val skip = inputStream.skip(available.toLong())
                    if (skip < 0)
                        break
                    bytesCount += skip
                }
                if (bytesCount > 0L)
                    return bytesCount
            }
        }
        return -1L
    }

ByteArrayOutputStream out = new ByteArrayOutputStream();
byte[] buffer = new byte[1024];
while (true) {
    int r = in.read(buffer);
    if (r == -1) break;
    out.write(buffer, 0, r);
}

byte[] ret = out.toByteArray();