package com.chillax.imp;
import java.io.File;

import java.io.IOException;

import java.io.RandomAccessFile;

import java.nio.ByteBuffer;

import java.nio.channels.FileChannel;

import java.util.ArrayList;

import java.util.Date;

import java.util.List;
/**

• NIO读取百万级别文件
• @author Chillax

*/
public class NIO {

public static void main(String args[]) throws Exception {

	int bufSize = 1000000;//一次读取的字节长度
	File fin = new File("D:\test\20160622_627975.txt");//读取的文件
	File fout = new File("D:\test\20160622_627975_1.txt");//写出的文件
	Date startDate = new Date();
	FileChannel fcin = new RandomAccessFile(fin, "r").getChannel();
	ByteBuffer rBuffer = ByteBuffer.allocate(bufSize);

	FileChannel fcout = new RandomAccessFile(fout, "rws").getChannel();
	ByteBuffer wBuffer = ByteBuffer.allocateDirect(bufSize);

	readFileByLine(bufSize, fcin, rBuffer, fcout, wBuffer);
	Date endDate = new Date();
	
	System.out.print(startDate+"|"+endDate);//测试执行时间
	if(fcin.isOpen()){
		fcin.close();
	}
	if(fcout.isOpen()){
		fcout.close();
	}
}

public static void readFileByLine(int bufSize, FileChannel fcin,
		ByteBuffer rBuffer, FileChannel fcout, ByteBuffer wBuffer) {
	String enter = "
";
	List<String> dataList = new ArrayList<String>();//存储读取的每行数据
	byte[] lineByte = new byte[0];
	
	String encode = "GBK";

// String encode = "UTF-8";
try {
//temp：由于是按固定字节读取，在一次读取中，第一行和最后一行经常是不完整的行，因此定义此变量来存储上次的最后一行和这次的第一行的内容，
//并将之连接成完成的一行，否则会出现汉字被拆分成2个字节，并被提前转换成字符串而乱码的问题
byte[] temp = new byte[0];
while (fcin.read(rBuffer) != -1) {//fcin.read(rBuffer)：从文件管道读取内容到缓冲区(rBuffer)
int rSize = rBuffer.position();//读取结束后的位置，相当于读取的长度
byte[] bs = new byte[rSize];//用来存放读取的内容的数组
rBuffer.rewind();//将position设回0,所以你可以重读Buffer中的所有数据,此处如果不设置,无法使用下面的get方法
rBuffer.get(bs);//相当于rBuffer.get(bs,0,bs.length())：从position初始位置开始相对读,读bs.length个byte,并写入bs[0]到bs[bs.length-1]的区域
rBuffer.clear();

			int startNum = 0;
			int LF = 10;//换行符
			int CR = 13;//回车符
			boolean hasLF = false;//是否有换行符
			for(int i = 0; i < rSize; i++){
				if(bs[i] == LF){
					hasLF = true;
					int tempNum = temp.length;
					int lineNum = i - startNum;
					lineByte = new byte[tempNum + lineNum];//数组大小已经去掉换行符
					
					System.arraycopy(temp, 0, lineByte, 0, tempNum);//填充了lineByte[0]~lineByte[tempNum-1]
					temp = new byte[0];
					System.arraycopy(bs, startNum, lineByte, tempNum, lineNum);//填充lineByte[tempNum]~lineByte[tempNum+lineNum-1]
					
					String line = new String(lineByte, 0, lineByte.length, encode);//一行完整的字符串(过滤了换行和回车)
					dataList.add(line);

// System.out.println(line);
writeFileByLine(fcout, wBuffer, line + enter);

					//过滤回车符和换行符
					if(i + 1 < rSize && bs[i + 1] == CR){
						startNum = i + 2;
					}else{
						startNum = i + 1;
					}
					
				}
			}
			if(hasLF){
				temp = new byte[bs.length - startNum];
				System.arraycopy(bs, startNum, temp, 0, temp.length);
			}else{//兼容单次读取的内容不足一行的情况
				byte[] toTemp = new byte[temp.length + bs.length];
				System.arraycopy(temp, 0, toTemp, 0, temp.length);
				System.arraycopy(bs, 0, toTemp, temp.length, bs.length);
				temp = toTemp;
			}
		}
		if(temp != null && temp.length > 0){//兼容文件最后一行没有换行的情况
			String line = new String(temp, 0, temp.length, encode);
			dataList.add(line);

// System.out.println(line);
writeFileByLine(fcout, wBuffer, line + enter);
}
} catch (IOException e) {
e.printStackTrace();
}
}

/**
 * 写到文件上
 * @param fcout
 * @param wBuffer
 * @param line
 */
@SuppressWarnings("static-access")
public static void writeFileByLine(FileChannel fcout, ByteBuffer wBuffer,
		String line) {
	try {
		fcout.write(wBuffer.wrap(line.getBytes("UTF-8")), fcout.size());
	} catch (IOException e) {
		e.printStackTrace();
	}
}

}

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