Admin: 1 версия

2010-06-01T06:04:40Z

1 версия

в 18:01, 31 мая 2010

2010-05-31T18:01:43Z

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== A ByteBuffer is a fixed-capacity buffer that holds byte values. ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {

byte[] bytes = new byte[10];
ByteBuffer buf = ByteBuffer.wrap(bytes);
}
}

</source>



== Applying Regular Expressions on the Contents of a File ==



<source lang="java">

import java.io.FileInputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.Charset;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Main {
public static CharSequence fromFile(String filename) throws IOException {
FileInputStream fis = new FileInputStream(filename);
FileChannel fc = fis.getChannel();
// Create a read-only CharBuffer on the file
ByteBuffer bbuf = fc.map(FileChannel.MapMode.READ_ONLY, 0, (int) fc.size());
CharBuffer cbuf = Charset.forName("8859_1").newDecoder().decode(bbuf);
return cbuf;
}
public static void main(String[] argv) throws Exception {
// Create matcher on file
Pattern pattern = Pattern.rupile("pattern");
Matcher matcher = pattern.matcher(fromFile("infile.txt"));
// Find all matches
while (matcher.find()) {
// Get the matching string
String match = matcher.group();
}
}
}
</source>



== Converting Between a ByteBuffer an a Byte Array ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
// Create a ByteBuffer from a byte array
byte[] bytes = new byte[10];
ByteBuffer buf = ByteBuffer.wrap(bytes);
}
}

</source>



== Convert interchangeably between a ByteBuffer and a byte array ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
// Create a ByteBuffer from a byte array
byte[] bytes = new byte[10];
ByteBuffer buffer = ByteBuffer.wrap(bytes);
// Retrieve bytes between the position and limit
bytes = new byte[buffer.remaining()];
buffer.get(bytes, 0, bytes.length);
// Retrieve all bytes in the buffer
buffer.clear();
bytes = new byte[buffer.capacity()];
buffer.get(bytes, 0, bytes.length);
}
}

</source>



== Create a ByteBuffer ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
// Create a ByteBuffer using a byte array
byte[] bytes = new byte[10];
ByteBuffer buffer = ByteBuffer.wrap(bytes);
// Create a non-direct ByteBuffer with a 10 byte capacity
// The underlying storage is a byte array.
buffer = ByteBuffer.allocate(10);
// Create a memory-mapped ByteBuffer with a 10 byte capacity.
buffer = ByteBuffer.allocateDirect(10);
}
}

</source>



== Create a ByteBuffer using a byte array ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {

byte[] bytes = new byte[10];
ByteBuffer buf = ByteBuffer.wrap(bytes);
}
}

</source>



== Create a character ByteBuffer ==



<source lang="java">

import java.nio.ByteBuffer;
import java.nio.CharBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocate(15);
CharBuffer cbuf = buf.asCharBuffer();
}
}

</source>



== Create a direct (memory-mapped) ByteBuffer with a 10 byte capacity. ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocateDirect(10);
}
}

</source>



== Create a double ByteBuffer ==



<source lang="java">

import java.nio.ByteBuffer;
import java.nio.DoubleBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocate(15);
DoubleBuffer dbuf = buf.asDoubleBuffer();
}
}

</source>



== Create a float ByteBuffer ==



<source lang="java">

import java.nio.ByteBuffer;
import java.nio.FloatBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocate(15);
FloatBuffer fbuf = buf.asFloatBuffer();
}
}

</source>



== Create a long ByteBuffer ==



<source lang="java">

import java.nio.ByteBuffer;
import java.nio.LongBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocate(15);
LongBuffer lbuf = buf.asLongBuffer();
}
}

</source>



== Create an integer ByteBuffer ==



<source lang="java">

import java.nio.ByteBuffer;
import java.nio.IntBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocate(15);
IntBuffer ibuf = buf.asIntBuffer();
}
}

</source>



== Create a non-direct ByteBuffer with a 10 byte capacity ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocate(10);
}
}

</source>



== Create a short ByteBuffer ==



<source lang="java">

import java.nio.ByteBuffer;
import java.nio.ShortBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocate(15);
ShortBuffer sbuf = buf.asShortBuffer();
}
}

</source>



== Determining If a ByteBuffer Is Direct ==



<source lang="java">

//Contents in a non-direct ByteBuffer are stored in the normal memory.
//Contents in a direct ByteBuffer are stored in some I/O device.
import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer bbuf = ByteBuffer.wrap(new byte[10]);
boolean isDirect = bbuf.isDirect(); // false
bbuf = ByteBuffer.allocate(10);
isDirect = bbuf.isDirect(); // false
bbuf = ByteBuffer.allocateDirect(10);
isDirect = bbuf.isDirect(); // true
}
}

</source>



== Fast Copy File ==



<source lang="java">

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class Main {
static public void main(String args[]) throws Exception {
FileInputStream fin = new FileInputStream("infile.txt");
FileOutputStream fout = new FileOutputStream("outfile.txt");
FileChannel inc = fin.getChannel();
FileChannel outc = fout.getChannel();
ByteBuffer bb = ByteBuffer.allocateDirect(1024);
while (true) {
int ret = inc.read(bb);
if (ret == -1)
break;
bb.flip();
outc.write(bb);
bb.clear();
}
}
}

</source>



== Get and Set char type data in a ByteBuffer ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocate(100);
// Put values of different types
buf.putChar((char) 123);
// Reset position for reading
buf.flip();
// Retrieve the values
char c = buf.getChar();
}
}

</source>



== Get and Set double type data in a ByteBuffer ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocate(100);
// Put values of different types
buf.putDouble(12.3D);
// Reset position for reading
buf.flip();
// Retrieve the values
double d = buf.getDouble();
}
}

</source>



== Get and Set float type data in a ByteBuffer ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocate(100);
// Put values of different types
buf.putFloat(12.3F);
// Reset position for reading
buf.flip();
// Retrieve the values
float f = buf.getFloat();
}
}

</source>



== Get and Set int type data in a ByteBuffer ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocate(100);
// Put values of different types
buf.putInt(123);
// Reset position for reading
buf.flip();
// Retrieve the values
int i = buf.getInt();
}
}

</source>



== Get and Set long type data in a ByteBuffer ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocate(100);
// Put values of different types
buf.putLong(123L);
// Reset position for reading
buf.flip();
// Retrieve the values
long l = buf.getLong();
}
}

</source>



== Get and Set short type data in a ByteBuffer ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocate(100);
buf.putShort((short) 123);
// Reset position for reading
buf.flip();
// Retrieve the values
short s = buf.getShort();
}
}

</source>



== Get a substring ==



<source lang="java">

import java.nio.ByteBuffer;
import java.nio.CharBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocate(100);
CharBuffer cbuf = buf.asCharBuffer();
cbuf.put("a string");
int start = 2; // start is relative to cbuf"s current position
int end = 5;
CharSequence sub = cbuf.subSequence(start, end); // str
}
}

</source>



== Get default byte ordering ==



<source lang="java">

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocate(10);

ByteOrder order = buf.order(); // ByteOrder.BIG_ENDIAN
}
}

</source>



== Get remaining byte count in a ByteBuffer ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocateDirect(10);
int rem = buf.remaining();
}
}

</source>



== Get the ByteBuffer"s capacity ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocateDirect(10);
int capacity = buf.capacity(); // 10
}
}

</source>



== How to get bytes from a ByteBuffer ==



<source lang="java">

public class Main{
public static void main(String[] argv) throws Exception{
// Create an empty ByteBuffer with a 10 byte capacity
ByteBuffer bbuf = ByteBuffer.allocate(10);

// Retrieve the capacity of the ByteBuffer
int capacity = bbuf.capacity(); // 10

// The position is not affected by the absolute get() method.
byte b = bbuf.get(5); // position=0

// Set the position
bbuf.position(5);

// Use the relative get()
b = bbuf.get();

// Get the new position
int pos = bbuf.position();

// Get remaining byte count
int rem = bbuf.remaining();

// Set the limit
bbuf.limit(7); // remaining=1

// This convenience method sets the position to 0
bbuf.rewind(); // remaining=7

}}

</source>



== Put a multibyte value ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocate(10);
buf.putShort(0, (short) 123);
buf.get(0); // 0
buf.get(1); // 123
}
}

</source>



== Put bytes into a ByteBuffer ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
// Create an empty ByteBuffer with a 10 byte capacity
ByteBuffer bbuf = ByteBuffer.allocate(10);
// Retrieve the capacity of the ByteBuffer
int capacity = bbuf.capacity(); // 10
// The position is not affected by the absolute get() method.
byte b = bbuf.get(5); // position=0
// Set the position
bbuf.position(5);
// Use the relative get()
b = bbuf.get();
// Get the new position
int pos = bbuf.position(); // 6
// Get remaining byte count
int rem = bbuf.remaining(); // 4
// Set the limit
bbuf.limit(7); // remaining=1
// This convenience method sets the position to 0
bbuf.rewind(); // remaining=7
}
}

</source>



== Putting Bytes into a ByteBuffer ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer bbuf = ByteBuffer.allocate(10);
int capacity = bbuf.capacity(); // 10
System.out.println(capacity);
bbuf.put((byte) 0xFF);
bbuf.position(5);
bbuf.put((byte) 0xFF);
int pos = bbuf.position();
int rem = bbuf.remaining();
bbuf.limit(7);
bbuf.rewind();
}
}

</source>



== Reading from a Channel with a ByteBuffer ==



<source lang="java">

import java.io.FileInputStream;
import java.nio.ByteBuffer;
import java.nio.channels.ReadableByteChannel;
public class Main {
public static void main(String[] argv) throws Exception {
ReadableByteChannel channel = new FileInputStream("infile").getChannel();
ByteBuffer buf = ByteBuffer.allocateDirect(10);
int numRead = 0;
while (numRead >= 0) {
buf.rewind();
numRead = channel.read(buf);
buf.rewind();
// Read bytes from ByteBuffer; see also
for (int i = 0; i < numRead; i++) {
byte b = buf.get();
}
}
}
}

</source>



== Retrieve all bytes in the buffer ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
byte[] bytes = new byte[10];
ByteBuffer buf = ByteBuffer.wrap(bytes);
buf.clear();
bytes = new byte[buf.capacity()];
buf.get(bytes, 0, bytes.length);
}
}

</source>



== Retrieve bytes between the position and limit ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
byte[] bytes = new byte[10];
ByteBuffer buf = ByteBuffer.wrap(bytes);
bytes = new byte[buf.remaining()];
buf.get(bytes, 0, bytes.length);
}
}

</source>



== Set the limit for ByteBuffer ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocateDirect(10);
buf.limit(7); // remaining=1
}
}

</source>



== Set the position ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocateDirect(10);
buf.position(5);
}
}

</source>



== Set to little endian ==



<source lang="java">

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocate(10);
buf.order(ByteOrder.LITTLE_ENDIAN);
}
}

</source>



== This convenience method sets the position to 0 ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocateDirect(10);
buf.rewind(); // remaining=7
}
}

</source>



== use FileChannel and ByteBuffer ==



<source lang="java">

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class Main {
static public void main(String args[]) throws Exception {
FileInputStream fin = new FileInputStream("infile.txt");
FileOutputStream fout = new FileOutputStream("outfile.txt");
FileChannel inc = fin.getChannel();
FileChannel outc = fout.getChannel();
ByteBuffer bb = ByteBuffer.allocate(1024);
while (true) {
int ret = inc.read(bb);
if (ret == -1)
break;
bb.flip();
outc.write(bb);
bb.clear();
}
}
}

</source>



== Use NIO to read a text file. ==



<source lang="java">

import java.io.FileInputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class ExplicitChannelRead {
public static void main(String args[]) {
FileInputStream fIn;
FileChannel fChan;
long fSize;
ByteBuffer mBuf;
try {
fIn = new FileInputStream("test.txt");
fChan = fIn.getChannel();
fSize = fChan.size();
mBuf = ByteBuffer.allocate((int) fSize);
fChan.read(mBuf);
mBuf.rewind();
for (int i = 0; i < fSize; i++)
System.out.print((char) mBuf.get());
fChan.close();
fIn.close();
} catch (IOException exc) {
System.out.println(exc);
System.exit(1);
}
}
}

</source>



== Use the absolute get(). ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocateDirect(10);
byte b = buf.get(5); // position=0
}
}

</source>



== Use the relative get() ==



<source lang="java">

import java.nio.ByteBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocateDirect(10);
byte b = buf.get();
}
}

</source>



== Using a ByteBuffer to Store Strings ==



<source lang="java">

import java.nio.ByteBuffer;
import java.nio.CharBuffer;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer buf = ByteBuffer.allocate(100);
CharBuffer cbuf = buf.asCharBuffer();
cbuf.put("a string");
cbuf.flip();
String s = cbuf.toString(); // a string
}
}

</source>



== View buffers ==



<source lang="java">

import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.FloatBuffer;
public class Buffers {
public static void main(String[] args) {
try {
float[] floats = { 6.61E-39F, 9.918385E-39F};
ByteBuffer bb = ByteBuffer.allocate(floats.length * 4);
FloatBuffer fb = bb.asFloatBuffer();
fb.put(floats);
CharBuffer cb = bb.asCharBuffer();
System.out.println(cb.toString());
} catch (Exception e) {
System.out.println(e.getMessage());
e.printStackTrace();
}
}
}

</source>



== Write with ByteBuffer ==



<source lang="java">

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class Main {
public static void main(String[] args) throws Exception {
String fromFileName = "from.txt";
String toFileName = "to.txt";
FileChannel in = new FileInputStream(fromFileName).getChannel();
FileChannel out = new FileOutputStream(toFileName).getChannel();
ByteBuffer buff = ByteBuffer.allocateDirect(32 * 1024);
while (in.read(buff) > 0) {
buff.flip();
out.write(buff);
buff.clear();
}
in.close();
out.close();
}
}

</source>



== Writing and Appending a ByteBuffer to a File ==



<source lang="java">

import java.io.File;
import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class Main {
public static void main(String[] argv) throws Exception {
ByteBuffer bbuf = ByteBuffer.allocate(100);
File file = new File("filename");
boolean append = false;
FileChannel wChannel = new FileOutputStream(file, append).getChannel();
wChannel.write(bbuf);
wChannel.close();
}
}

</source>

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Admin: 1 версия

в 18:01, 31 мая 2010