[FIXED] Write an InputStream to an HttpServletResponse

Issue

I have an InputStream that I want written to a HttpServletResponse. There's this approach, which takes too long due to the use of byte[]

InputStream is = getInputStream();
int contentLength = getContentLength();

byte[] data = new byte[contentLength];
is.read(data);

//response here is the HttpServletResponse object
response.setContentLength(contentLength);
response.write(data);

I was wondering what could possibly be the best way to do it, in terms of speed and efficiency.

Solution

Just write in blocks instead of copying it entirely into Java's memory first. The below basic example writes it in blocks of 10KB. This way you end up with a consistent memory usage of only 10KB instead of the complete content length. Also the enduser will start getting parts of the content much sooner.

response.setContentLength(getContentLength());
byte[] buffer = new byte[10240];

try (
    InputStream input = getInputStream();
    OutputStream output = response.getOutputStream();
) {
    for (int length = 0; (length = input.read(buffer)) > 0;) {
        output.write(buffer, 0, length);
    }
}

---

As creme de la creme with regard to performance, you could use NIO Channels and a directly allocated ByteBuffer. Create the following utility/helper method in some custom utility class, e.g. Utils:

public static long stream(InputStream input, OutputStream output) throws IOException {
    try (
        ReadableByteChannel inputChannel = Channels.newChannel(input);
        WritableByteChannel outputChannel = Channels.newChannel(output);
    ) {
        ByteBuffer buffer = ByteBuffer.allocateDirect(10240);
        long size = 0;

        while (inputChannel.read(buffer) != -1) {
            buffer.flip();
            size += outputChannel.write(buffer);
            buffer.clear();
        }

        return size;
    }
}

Which you then use as below:

response.setContentLength(getContentLength());
Utils.stream(getInputStream(), response.getOutputStream());

Answered By - BalusC