java7 NIO2(7) random access file API

java7NIO2 随机文件访问API

package com.mime;import java.io.IOException;import java.nio.ByteBuffer;import java.nio.CharBuffer;import java.nio.MappedByteBuffer;import java.nio.channels.FileChannel;import java.nio.channels.FileLock;import java.nio.channels.SeekableByteChannel;import java.nio.charset.CharacterCodingException;import java.nio.charset.Charset;import java.nio.charset.CharsetDecoder;import java.nio.file.Files;import java.nio.file.Path;import java.nio.file.Paths;import java.nio.file.StandardOpenOption;import java.nio.file.attribute.FileAttribute;import java.nio.file.attribute.PosixFilePermission;import java.nio.file.attribute.PosixFilePermissions;import java.util.EnumSet;import java.util.Set;public class NIO2RandomAccessFile {/** * @param args */public static void main(String[] args) {Path path = Paths.get("/tmp", "story.txt");// create the custom permissions attribute for the email.txt fileSet<PosixFilePermission> perms = PosixFilePermissions.fromString("rw-r------");FileAttribute<Set<PosixFilePermission>> attr = PosixFilePermissions.asFileAttribute(perms);// write a file using SeekableByteChanneltry (SeekableByteChannel seekableByteChannel = Files.newByteChannel(path, EnumSet.of(StandardOpenOption.WRITE,StandardOpenOption.TRUNCATE_EXISTING), attr)) {ByteBuffer buffer = ByteBuffer.wrap("Rafa Nadal produced another masterclass of clay-court tennis to win his fifth French Open title ...".getBytes());int write = seekableByteChannel.write(buffer);System.out.println("Number of written bytes: " + write);buffer.clear();} catch (IOException ex) {System.err.println(ex);}// read a file using SeekableByteChanneltry (SeekableByteChannel seekableByteChannel = Files.newByteChannel(path, EnumSet.of(StandardOpenOption.READ), attr)) {ByteBuffer buffer = ByteBuffer.allocate(12);String encoding = System.getProperty("file.encoding");buffer.clear();//随机访问定位API//seekableByteChannel.position();//seekableByteChannel.truncate(100);while (seekableByteChannel.read(buffer) > 0) {buffer.flip();System.out.print(Charset.forName(encoding).decode(buffer));buffer.clear();}// seekableByteChannel.position(seekableByteChannel.size()/2);} catch (IOException ex) {System.err.println(ex);}MappedByteBuffer buffer = null;try (FileChannel fileChannel = (FileChannel.open(path,EnumSet.of(StandardOpenOption.READ)))) {//文件锁FileLock lock = fileChannel.lock();buffer = fileChannel.map(FileChannel.MapMode.READ_ONLY, 0,fileChannel.size());//文件channel操作，从一个channel通道把数据传输到另外一个channel//fileChannel_from.transferTo(0L, fileChannel_from.size(), fileChannel_to);lock.release();} catch (IOException ex) {System.err.println(ex);}if (buffer != null) {try {Charset charset = Charset.defaultCharset();CharsetDecoder decoder = charset.newDecoder();CharBuffer charBuffer = decoder.decode(buffer);String content = charBuffer.toString();System.out.println(content);buffer.clear();} catch (CharacterCodingException ex) {System.err.println(ex);}}}}