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2010-06-01T05:19:54Z

1 версия

в 17:44, 31 мая 2010

2010-05-31T17:44:27Z

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== Create MappedByteBuffer from FileInputStream ==



<source lang="java">
import java.io.FileInputStream;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
public class MainClass {
private static final int LENGTH = 100; // Small
public static void main(String[] args) throws Exception {
MappedByteBuffer in = new FileInputStream("test.txt").getChannel().map(
FileChannel.MapMode.READ_ONLY, 0, LENGTH);
int i = 0;
while (i < LENGTH)
System.out.print((char) in.get(i++));
System.out.println((char) in.get(i++));
}
}</source>



== Create Read only buffer ==



<source lang="java">
import java.io.FileInputStream;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
public class MainClass {
private static final int LENGTH = 100; // Small
public static void main(String[] args) throws Exception {
MappedByteBuffer in = new FileInputStream("test.txt").getChannel().map(
FileChannel.MapMode.READ_ONLY, 0, LENGTH);
int i = 0;
while (i < LENGTH)
System.out.print((char) in.get(i++));
System.out.println((char) in.get(i++));
}
}</source>



== Creating a very large file using mapping ==



<source lang="java">
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
public class MainClass {
static int length = 0x8FFFFFF; // 128 Mb
public static void main(String[] args) throws Exception {
MappedByteBuffer out = new RandomAccessFile("test.dat", "rw").getChannel().map(
FileChannel.MapMode.READ_WRITE, 0, length);
for (int i = 0; i < length; i++)
out.put((byte) "x");
System.out.println("Finished writing");
for (int i = length / 2; i < length / 2 + 6; i++)
System.out.print((char) out.get(i));
}
}</source>



== Get MappedByteBuffer from FileChannel ==



<source lang="java">
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
public class MainClass {
public static void main(String[] argv) throws Exception {
RandomAccessFile raf = new RandomAccessFile("test.txt", "r");
FileChannel fc = raf.getChannel();
MappedByteBuffer buffer = fc.map(FileChannel.MapMode.READ_ONLY, 0, fc.size());
buffer.clear();
buffer.flip();
System.out.println("hasArray=" + buffer.hasArray());
System.out.println(buffer.toString());
System.out.flush();
}
}</source>



== Locking portions of a mapped file ==



<source lang="java">
// From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002
// www.BruceEckel.ru. See copyright notice in CopyRight.txt.
// Locking portions of a mapped file.
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
public class MainClass {
static final int LENGTH = 0x8FFFFFF; // 128 Mb
static FileChannel fc;
public static void main(String[] args) throws Exception {
fc = new RandomAccessFile("test.dat", "rw").getChannel();
MappedByteBuffer out = fc.map(FileChannel.MapMode.READ_WRITE, 0, LENGTH);
for (int i = 0; i < LENGTH; i++)
out.put((byte) "x");
new LockAndModify(out, 0, 0 + LENGTH / 3);
new LockAndModify(out, LENGTH / 2, LENGTH / 2 + LENGTH / 4);
}
private static class LockAndModify extends Thread {
private ByteBuffer buff;
private int start, end;
LockAndModify(ByteBuffer mbb, int start, int end) {
this.start = start;
this.end = end;
mbb.limit(end);
mbb.position(start);
buff = mbb.slice();
start();
}
public void run() {
try {
FileLock fl = fc.lock(start, end, false);
System.out.println("Locked: " + start + " to " + end);
while (buff.position() < buff.limit() - 1){
buff.put((byte) (buff.get() + 1));
}
fl.release();
System.out.println("Released: " + start + " to " + end);
} catch (IOException e) {
throw new RuntimeException(e);
}
}
}
}</source>



== Mapping an entire file into memory for reading ==



<source lang="java">
import java.io.File;
import java.io.FileInputStream;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
public class MainClass {
public static void main(String[] args) throws Exception {
long length = new File("test.txt").length();
MappedByteBuffer in = new FileInputStream("test.txt").getChannel().map(
FileChannel.MapMode.READ_ONLY, 0, length);
int i = 0;
while (i < length)
System.out.print((char) in.get(i++));
}
}</source>



== Read file upside/down with RandomAccessFile ==



<source lang="java">
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
public class Main {
public static void main(String[] args) throws Exception {
RandomAccessFile f = new RandomAccessFile("hello.txt", "rw");
FileChannel fc = f.getChannel();
MappedByteBuffer mbb = fc.map(FileChannel.MapMode.READ_WRITE, 0, f.length());
int len = (int) f.length();
for (int i = 0, j = len - 1; i < j; i++, j--) {
byte b = mbb.get(i);
mbb.put(i, mbb.get(j));
mbb.put(j, b);
}
fc.close();
}
}</source>



== What happens when the entire file isn"t in your mapping region? ==



<source lang="java">
import java.io.FileInputStream;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
public class MainClass {
private static final int LENGTH = 100; // Small
public static void main(String[] args) throws Exception {
MappedByteBuffer in = new FileInputStream("test.txt").getChannel().map(
FileChannel.MapMode.READ_ONLY, 0, LENGTH);
int i = 0;
while (i < LENGTH)
System.out.print((char) in.get(i++));
System.out.println((char) in.get(i++));
}
}</source>

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Admin: 1 версия

в 17:44, 31 мая 2010