Convert byte array to OutputStream

Question

I have following code to write byte array to OutputStream in Java program.

public static void write(OutputStream out, ArrayList<byte[]> buffer) throws IOException {
    for (byte[] packet: buffer) {
        out.write(packet);
    }
}

When buffer size is 770,000 and the max length of each element is 40, this loop takes 2840 millisecond.

Is there a more optimized / faster way of doing that convertion?

how big are those packets? if your packets are 8 bytes size total then you should build larger packets and write less times — Martín Zaragoza
– Martín Zaragoza, Commented Aug 18, 2018 at 18:32
You can try a) wrap the output stream into a buffered stream, or b) if memory is not an issue, copy X small arrays into one large and write large arrays. — khachik
– khachik, Commented Aug 18, 2018 at 18:32
Seems fairly fast to me: ideone.com/M8sZhw Convert the array of arrays to a single array and write that to the output stream all in one shot.. 30ms at most. — Brandon
– Brandon, Commented Aug 18, 2018 at 18:58

khachik · Accepted Answer · 2018-08-18 18:46:56Z

Although the use-case is not completely clear - what is the underlying stream, etc, but among a few options you have wrapping the output stream into a buffered one seems to make sense, please see a short example below. On FileOutputStream, with 400k small arrays, it gives 20x performance boost:

// Buffered write, time elapsed: 51
// Raw write, time elapsed: 1050

import java.io.*;
import java.util.*;


public class Test {
    public static void main(String [] args) throws Exception {
        int max = 400000;
        List<byte[]> arrays = new ArrayList<>(max);
        for(int i=0; i< max; i++) {
            arrays.add(new byte[40]);
        }

        try(FileOutputStream fout = new FileOutputStream("/tmp/deleteme")) {
            long start = System.currentTimeMillis();
            writeBuffered(arrays, fout);
            System.out.println("Buffered write, time elapsed: " + (System.currentTimeMillis() - start));
        }
        try(FileOutputStream fout = new FileOutputStream("/tmp/deleteme")) {
            long start = System.currentTimeMillis();
            writeRaw(arrays, fout);
            System.out.println("Raw write, time elapsed: " + (System.currentTimeMillis() - start));
        }
    }

    static void writeRaw(List<byte[]> arrays, OutputStream out) throws IOException {
        for (byte[] packet: arrays) {
            out.write(packet);
        }
    }

    static void writeBuffered(List<byte[]> arrays, OutputStream out) throws IOException {
        BufferedOutputStream bout = new BufferedOutputStream(out);
        for (byte[] packet: arrays) {
            bout.write(packet);
        }
    }
}

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