java nio学习笔记<一>

package nio;

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;

/**
 * 关于NIO的其他内容可以参考：http://www.iteye.com/topic/834447
 * @author Administrator
 *
 */
public class ChannelDemo1 {
	public static void main(String[] args) throws IOException {
		// writeFile("c:\\aaaa.txt");
		// readFile("c:\\aaaa.txt");
		// readFileByReader("c:\\aaaa.txt");
		copy("c:\\aaaa.txt", "c:\\aaaa2.txt");
	}

	public static void writeFile(String fileName) throws IOException {
		/*
		 * Channel是一个对象(通道)，可以通过它读取或写入数据。拿NIO和IO相比较通道就像是流。
		 * 所有的数据都是通过Buffer来处理，您永远不会将字节直接写入通道中，而是将数据写入缓冲区，读取的话也是将数据读取到缓冲区。
		 */
		FileChannel fileOutChannel = (new FileOutputStream(fileName, true))
				.getChannel();
		// 将经过UTF-8编码的字符写入到buffer中，然后通道负责把buffer写入到输出流。
		fileOutChannel.write(Charset.forName("utf-8").encode(
				CharBuffer.wrap("北京 您好！\n")));
		fileOutChannel.close();
	}

	/*
	 * 指定InputStreamReader的解析字符集读取文件
	 */
	public static void readFileByReader(String fileName) throws IOException {
		BufferedReader buff = new BufferedReader(new InputStreamReader(
				new FileInputStream(fileName), Charset.forName("utf-8")));
		String s;
		while ((s = buff.readLine()) != null) {
			System.out.println(s);
		}
		buff.close();
	}

	// nio读取文件
	public static void readFile(String fileName) throws IOException {
		FileChannel fileInChannel = (new FileInputStream(fileName))
				.getChannel();
		Charset charset = Charset.forName("UTF-8");
		CharsetDecoder decoder = charset.newDecoder();
		// CharsetEncoder encoder = charset.newEncoder();
		/*
		 * allocateDirect：直接缓冲区，allocate非直接缓冲区， 直接缓冲区是一块连续的内存区域，适合长期驻留内存的数据，
		 * 非直接缓冲区适合相当于一次性的，适合用完就扔。
		 */
		ByteBuffer buff = ByteBuffer.allocateDirect(1024);
		CharBuffer charBuff = CharBuffer.allocate(1024);
		while (fileInChannel.read(buff) != -1) {
			// flip用于反转
			buff.flip();
			// 将字节数组转换成字符数组
			decoder.decode(buff, charBuff, false);
			charBuff.flip();
			System.out.println("read:" + charBuff);
			buff.clear();
			charBuff.clear();
		}
		fileInChannel.close();

		// 下面代码证明关闭FileChannel也完全关闭了文件句柄
		FileChannel fileInChannel11 = (new FileInputStream(fileName))
				.getChannel();
		System.out.println(fileInChannel11.isOpen());
		fileInChannel11.close();
		System.out.println(fileInChannel11.isOpen());
	}

	// nio copy文件
	public static void copy(String src, String dest) throws IOException {
		FileChannel srcChannel = (new FileInputStream(src)).getChannel();
		FileChannel destChannel = (new FileOutputStream(dest)).getChannel();
		ByteBuffer buff = ByteBuffer.allocate(1024);
		while (true) {
			//清空缓冲区，使其可以接受数据
			buff.clear();
			if (srcChannel.read(buff) == -1) {
				break;
			}
			//将数据读取到缓冲区后，如果要把缓冲区的数据写到通道就要先反转
			buff.flip();
			destChannel.write(buff);
		}
		srcChannel.close();
		destChannel.close();
	}
}