How can you improve Java I/O performance?

Java applications that utilise Input/Output are excellent candidates for performance  tuning. Profiling of Java applications that handle significant volumes of data will show significant time spent in I/O operations. This means substantial gains can be had from I/O performance tuning. Therefore, I/O efficiency should be a high priority for developers looking to optimally increase performance.
The basic rules for speeding up I/O performance are

• Minimise accessing the hard disk.
• Minimise accessing the underlying operating system.
• Minimise processing bytes and characters individually.   

Let us look at some of the techniques to improve I/O performance.

Use bufferingto minimise disk access and underlying operating system. As shown below, with buffering large chunks of a file are read from a disk and then accessed a byte or character at a time.

Without buffering : inefficient code
try{
File f = new File("myFile.txt");
FileInputStream fis = new FileInputStream(f);
int count = 0;
int b = ;
while((b = fis.read()) != -1){
if(b== '\n') {
count++;
}
}
// fis should be closed in a finally block.
fis.close() ;
}
catch(IOException io){}
Note: fis.read() is a native method call to the underlying system.
With Buffering:yields better performance
try{
File f = new File("myFile.txt");
FileInputStream fis = new FileInputStream(f);
BufferedInputStream bis = new BufferedInputStream(fis);
int count = 0;
int b = ;
while((b = bis.read()) != -1){
if(b== '\n') {
count++;
}
}
//bis should be closed in a finally block.
bis.close() ;
}
catch(IOException io){}
Note:bis.read() takes the next byte from the input buffer and only
rarely access the underlying operating system.

Instead of reading a character or a byte at a time, the above code with buffering can be improved further by reading one line at a time as shown below:

FileReader fr = new FileReader(f);
BufferedReader br = new BufferedReader(fr);
While (br.readLine() != null) count++;