Although the performance of "old" stream I/O has been improved by implementing it with nio,
mapped file access tends to be dramatically faster, this program does a simple performance comparison:
package think.in.java.io;
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.IntBuffer;
import java.nio.channels.FileChannel;
public class MappedIO {
private static int numOfInts = 4000000;
private static int numOfUbuffInts = 200000;
private abstract static class Tester{
private String name;
public Tester(String name){
this.name = name;
}
public void runTest(){
System.out.print(name + ": ");
try {
long start = System.nanoTime();
test();
double duration = System.nanoTime() - start;
System.out.format("%.2f\n", duration/1.0e9);
} catch (IOException e) {
throw new RuntimeException(e);
}
}
public abstract void test() throws IOException;
}
private static Tester[] tests = {
new Tester("Stream Write") {
@Override
public void test() throws IOException {
DataOutputStream dos = new DataOutputStream(
new BufferedOutputStream(
new FileOutputStream(new File("temp.tmp"))));
for(int i=0; i<numOfInts; i++){
dos.writeInt(i);
}
dos.close();
}
},
new Tester("Mapped Write") {
@Override
public void test() throws IOException {
FileChannel fc = new RandomAccessFile("temp.tmp", "rw").getChannel();
IntBuffer ib = fc.map(
FileChannel.MapMode.READ_WRITE, 0, fc.size()).asIntBuffer();
for(int i=0; i<numOfInts; i++){
ib.put(i);
}
fc.close();
}
},
new Tester("Stream Read"){
@Override
public void test() throws IOException {
DataInputStream dis = new DataInputStream(
new BufferedInputStream(
new FileInputStream(new File("temp.tmp"))));
for(int i=0; i<numOfInts; i++){
dis.readInt();
}
dis.close();
}
},
new Tester("Mapped Read") {
@Override
public void test() throws IOException {
FileChannel fc = new FileInputStream(new File("temp.tmp")).getChannel();
IntBuffer ib = fc.map(
FileChannel.MapMode.READ_ONLY, 0, fc.size()).asIntBuffer();
while(ib.hasRemaining()){
ib.get();
}
fc.close();
}
}
};
/**
* @param args
*/
public static void main(String[] args) {
for(Tester test : tests){
test.runTest();
}
}
}
// Output:
Stream Write: 0.73
Mapped Write: 0.06
Stream Read: 0.70
Mapped Read: 0.06