Java SE 7新特性之文件操作（7） - 随机访问文件

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

                String s = "I was here!\n";
                byte data[] = s.getBytes();
                ByteBuffer out = ByteBuffer.wrap(data);

                ByteBuffer copy = ByteBuffer.allocate(12);
                FileChannel fc = null;
                Path file = Paths.get("c:\\testChannel.txt");

                try {
                    fc = (FileChannel)file.newByteChannel(StandardOpenOption.READ, StandardOpenOption.WRITE);

                    //Read the first 12 bytes of the file.
                    int nread;
                    do {
                        nread = fc.read(copy);
                    } while (nread != -1 && copy.hasRemaining());

                    //Write "I was here!" at the beginning of the file.
                    fc.position(0);
                    while (out.hasRemaining())
                        fc.write(out);
                    out.rewind();

                    /*Move to the end of the file, write "I was here!" again,then copy the first 12 bytes to the end of the file.*/
                    long length = fc.size();
                    fc.position(length);
                    while (out.hasRemaining())
                        fc.write(out);
                    copy.flip();
                    while (copy.hasRemaining())
                        fc.write(copy);
                } catch (IOException x) {
                    System.out.println("I/O Exception: " + x);
                } finally {
                    //Close the file.
                    if (fc != null) fc.close();
                    System.out.println(file + " has been modified!");
                }