我知道已经太迟了，但我认为这里有更清晰的解决方案，更易于阅读……

/**
 * method converts {@link InputStream} Object into byte[] array.
 * 
 * @param stream the {@link InputStream} Object.
 * @return the byte[] array representation of received {@link InputStream} Object.
 * @throws IOException if an error occurs.
 */
public static byte[] streamToByteArray(InputStream stream) throws IOException {

    byte[] buffer = new byte[1024];
    ByteArrayOutputStream os = new ByteArrayOutputStream();

    int line = 0;
    // read bytes from stream, and store them in buffer
    while ((line = stream.read(buffer)) != -1) {
        // Writes bytes from byte array (buffer) into output stream.
        os.write(buffer, 0, line);
    }
    stream.close();
    os.flush();
    os.close();
    return os.toByteArray();
}

你可以试试仙人掌:

byte[] array = new BytesOf(stream).bytes();

你可以完全避免缓冲。

从http://www.exampledepot.com/egs/java.io/File2ByteArray.html复制的代码(是的，它非常冗长，但需要的内存大小是其他解决方案的一半)。

// Returns the contents of the file in a byte array.
public static byte[] getBytesFromFile(File file) throws IOException {
    InputStream is = new FileInputStream(file);

    // Get the size of the file
    long length = file.length();

    // You cannot create an array using a long type.
    // It needs to be an int type.
    // Before converting to an int type, check
    // to ensure that file is not larger than Integer.MAX_VALUE.
    if (length > Integer.MAX_VALUE) {
        // File is too large
    }

    // Create the byte array to hold the data
    byte[] bytes = new byte[(int)length];

    // Read in the bytes
    int offset = 0;
    int numRead = 0;
    while (offset < bytes.length
           && (numRead=is.read(bytes, offset, bytes.length-offset)) >= 0) {
        offset += numRead;
    }

    // Ensure all the bytes have been read in
    if (offset < bytes.length) {
        throw new IOException("Could not completely read file "+file.getName());
    }

    // Close the input stream and return bytes
    is.close();
    return bytes;
}

如果你使用ByteArrayOutputStream，你会做一个额外的拷贝。如果你在开始读取流之前知道它的长度(例如，InputStream实际上是FileInputStream，你可以在文件上调用file.length()，或者InputStream是一个zipfile条目InputStream，你可以调用zipEntry.length())，那么直接写入byte[]数组会更好——它使用一半的内存，并节省时间。

// Read the file contents into a byte[] array
byte[] buf = new byte[inputStreamLength];
int bytesRead = Math.max(0, inputStream.read(buf));

// If needed: for safety, truncate the array if the file may somehow get
// truncated during the read operation
byte[] contents = bytesRead == inputStreamLength ? buf
                  : Arrays.copyOf(buf, bytesRead);

注意:上面的最后一行处理的是在读取流时被截断的文件，如果你需要处理这种可能性，但是如果在读取流时文件变长了，byte[]数组中的内容将不会被延长以包括新的文件内容，数组将简单地被截断为旧的长度inputStreamLength。

我知道已经太迟了，但我认为这里有更清晰的解决方案，更易于阅读……

/**
 * method converts {@link InputStream} Object into byte[] array.
 * 
 * @param stream the {@link InputStream} Object.
 * @return the byte[] array representation of received {@link InputStream} Object.
 * @throws IOException if an error occurs.
 */
public static byte[] streamToByteArray(InputStream stream) throws IOException {

    byte[] buffer = new byte[1024];
    ByteArrayOutputStream os = new ByteArrayOutputStream();

    int line = 0;
    // read bytes from stream, and store them in buffer
    while ((line = stream.read(buffer)) != -1) {
        // Writes bytes from byte array (buffer) into output stream.
        os.write(buffer, 0, line);
    }
    stream.close();
    os.flush();
    os.close();
    return os.toByteArray();
}

Java 8方式(感谢BufferedReader和Adam Bien)

private static byte[] readFully(InputStream input) throws IOException {
    try (BufferedReader buffer = new BufferedReader(new InputStreamReader(input))) {
        return buffer.lines().collect(Collectors.joining("\n")).getBytes(<charset_can_be_specified>);
    }
}

注意，这个解决方案删除回车符('\r')，可能是不合适的。