Mapped IO : Input Output Stream « File Input Output « Java
Mapped IO
// : c12:MappedIO.java
// {Clean: temp.tmp}
// From 'Thinking in Java, 3rd ed.' (c) Bruce Eckel 2002
// www.BruceEckel.com. See copyright notice in CopyRight.txt.
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 long runTest() {
System.out.print(name + ": ");
try {
long startTime = System.currentTimeMillis();
test();
long endTime = System.currentTimeMillis();
return (endTime - startTime);
} catch (IOException e) {
throw new RuntimeException(e);
}
}
public abstract void test() throws IOException;
}
private static Tester[] tests = { new Tester("Stream Write") {
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") {
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") {
public void test() throws IOException {
DataInputStream dis = new DataInputStream(new BufferedInputStream(
new FileInputStream("temp.tmp")));
for (int i = 0; i < numOfInts; i++)
dis.readInt();
dis.close();
}
}, new Tester("Mapped Read") {
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();
}
}, new Tester("Stream Read/Write") {
public void test() throws IOException {
RandomAccessFile raf = new RandomAccessFile(new File("temp.tmp"),
"rw");
raf.writeInt(1);
for (int i = 0; i < numOfUbuffInts; i++) {
raf.seek(raf.length() - 4);
raf.writeInt(raf.readInt());
}
raf.close();
}
}, new Tester("Mapped Read/Write") {
public void test() throws IOException {
FileChannel fc = new RandomAccessFile(new File("temp.tmp"), "rw")
.getChannel();
IntBuffer ib = fc.map(FileChannel.MapMode.READ_WRITE, 0, fc.size())
.asIntBuffer();
ib.put(0);
for (int i = 1; i < numOfUbuffInts; i++)
ib.put(ib.get(i - 1));
fc.close();
}
} };
public static void main(String[] args) {
for (int i = 0; i < tests.length; i++)
System.out.println(tests[i].runTest());
}
} ///:~
