Most effective way to write File to ServletOutputStream

Question

ServletOutputStream output = response.getOutputStream();
output.write(byte[]);

What is the most effective way to write File to javax.servlet.ServletOutputStream?

EDIT:

won't this be more effective if the NIO was used?

Solution 1

IOUtils.copy(in, out);
out.flush();
//...........
out.close(); // depends on your application

Where in is the FileInputStream and out is the SocketOutputStream. IOUtils is a utility from Commons IO module in Apache Commons.

Solution 2

You have a ServletOutputStream. The only way you can write to that is via java.io.*. You can't use NIO on it at all (other than via wrapping with Channels, which is pointless: it's still an OutputStream underneath and you are just adding processing over the top). The actual I/O is network-bound, and your writes are being buffered anyway by the servlet container (so that it can set the Content-Length) header so looking for performance tweaks here is pointless.

Solution 3

First of all, this is unrelated to servlets. This applies to Java IO in general. You have after all just an InputStream and an OutputStream.

As to the answer, you're not the only one who wondered about this. On the interwebs you can find others who wondered about the same but took the effort to test/benchmark it themselves:

• Java tip: How to read files quickly?
• File copy in Java - Benchmark

In general, a FileChannel with a 256K byte array which is read through a wrapped ByteBuffer and written directly from the byte array is the fastest way. Indeed, NIO.

FileInputStream input = new FileInputStream("/path/to/file.ext");
FileChannel channel = input.getChannel();
byte[] buffer = new byte[256 * 1024];
ByteBuffer byteBuffer = ByteBuffer.wrap(buffer);

try {
    for (int length = 0; (length = channel.read(byteBuffer)) != -1;) {
        System.out.write(buffer, 0, length);
        byteBuffer.clear();
    }
} finally {
    input.close();
}

Comments

[Bozho]

+1, but two notes - it's "apache commons", and you can use IOUtils.closeQuitely(..)

[Sean Patrick Floyd]

@Bozho it used to be called Jakarta Commons many years ago :-)

[IAdapter]

that doesn't work for me, I don't want to add Commons IO jar just for that functionality.

[IAdapter]

won't this be more effective if the NIO was used?

[IAdapter]

won't this be more effective if the NIO was used?

[Mihai Toader]

i had mixed results with nio :). It might be better or it might not. The code is definitely a little more complex and you really need to test the results on your machine to make sure is good enough. Look here for some code: thomaswabner.wordpress.com/2007/10/09/…

[Bozho]

@01 adding a dependency on apache commons rarely has any downsides ;)

[IAdapter]

Bozho it has a very huge downside, i will have to fight with my boss, because of it. i rather reinvent the wheel than fight with him.

[AngerClown]

The first link actually seems to recommend an 8K buffer since the time to copy difference between 8 and 256K is minimal. That seems to make sense given that most file systems still use 4KB pages and 4KB disk clusters.

[BalusC]

Difference is indeed minimal. OP is however asking for "effective way" not "efficient way". 8K is still fast but less memory consuming in case of a busy site.

[IAdapter]

What about using channels and Channel.transferTo ?

[user207421]

@01: Yes, you can use NIO's channels if you use Channels.newChannel(OutputStream). Which wraps the output stream in a channel. It is still talking to an underlying ByteArrayOutputStream. There is no efficiency gain in this situation. It is pointless.

[Adam Rabung]

+1 ymmv, but i've had a hard time making the nio version faster than good old streams

[brady]

@IAdapter In general, using transferTo() will give the best performance; unfortunately, the Servlet API doesn't expose the SocketChannel, so the optimization isn't available.

[user207421]

@JerylCook I addessed that in comments five and a half years ago and have so far attracted 5 comment votes for having done so. Look.