Tuning the performance of reading a large InputStream in java

Question

I want to read a large InputStream and return it as a String. This InputStream is a large one. So, normally it takes much time and a lot of memory while it is excuting. The following code is the one that I've developed so far. I need to convert this code as it does the job in a lesser time consuming lesser memory.

Can you give me any idea to do this.

BufferedReader br =
    new BufferedReader(
        new InputStreamReader(
            connection.getInputStream(),
            "UTF-8")
        );

StringBuilder response = new StringBuilder(1000);

char[] buffer = new char[4096];

int n = 0;
while(n >= 0){
    n = br.read(buffer, 0, buffer.length);
    if(n > 0){
        response.append(buffer, 0, n);
    }
}
return response.toString();

Thank you!

Answer 1

When you are doing buffered I/O you can just read one char at a time from the buffered reader. Then build up the string, and do a toString() at the end.

Answer 2

You may find that for large files on some operating systems, mmaping the file via FileChannel.map will give you better performance - map the file and then create a string out of the mapped ByteBuffer. You'll have to benchmark though, as it may be that 'traditional' IO is faster in some cases.