Write an InputStream to an HttpServletResponse

Question

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.

Answer 1

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());

• Michael Brewer-Davis: Of course many utility packages have this method already defined, so once you start using Guava... docs.guava-libraries.googlecode.com/git/javadoc/com/google/…, java.io.OutputStream)
• Roy Lee: +1 @BalusC Do we need to set its ContentType? If yes, what would it be?
• BalusC: @Roylee: yes, that's recommended. Just set the content type to the type of the content :) freeformatter.com/mime-types-list.html
• vvavepacket: i tried this,, why is that my stream will return an error like this: org.apache.catalina.connector.ClientAbortException: java.io.IOException: An established connection was aborted by the software in your host machine at org.apache.catalina.connector.OutputBuffer.realWriteBytes(OutputBuffer.java:356) at org.apache.catalina.connector.OutputBuffer.appendByteArray(OutputBuffer.java:778) at org.apache.catalina.connector.OutputBuffer.append(OutputBuffer.java:707) at org.apache.catalina.connector.OutputBuffer.writeBytes(OutputBuffer.java:391)
• Pramod Gaikwad: how to getContentLenght() of input Stream?

Answer 2

BufferedInputStream in = null;
BufferedOutputStream out = null;
OutputStream os;
os = new BufferedOutputStream(response.getOutputStream());
in = new BufferedInputStream(new FileInputStream(file));
out = new BufferedOutputStream(os);
byte[] buffer = new byte[1024 * 8];
int j = -1;
while ((j = in.read(buffer)) != -1) {
 out.write(buffer, 0, j);
}

• Sabry Shawally: I wan to avoid the usage of byte[], if possible
• Luiggi Mendoza: @MuhammadSabry there's no way to read the InputStream w/o using byte[]
• MTilsted: What's wrong with byte[]. You need to store the data someware :}

Answer 3

I think that is very close to the best way, but I would suggest the following change. Use a fixed size buffer(Say 20K) and then do the read/write in a loop.

For the loop do something like

byte[] buffer=new byte[20*1024];
outputStream=response.getOutputStream();
while(true) {
 int readSize=is.read(buffer);
 if(readSize==-1)
 break;
 outputStream.write(buffer,0,readSize);
}

ps: Your program will not always work as is, because read don't always fill up the entire array you give it.

• Sabry Shawally: what exactly do you mean by read doesn't fill up the entire array you give it?
• MTilsted: Read does not always fill up the input array. So you need to check the value which read return which is the number of bytes read. (See docs.oracle.com/javase/6/docs/api/java/io/…)