public static void main(String[] args) throws Exception {
 int bufSize = 1024;
 byte[] bs = new byte[bufSize];
 ByteBuffer byteBuf = ByteBuffer.allocate(1024);
 FileChannel channel = new RandomAccessFile("d:\\filename","r").getChannel();
 while(channel.read(byteBuf) != -1) {
 int size = byteBuf.position();
 byteBuf.rewind();
 byteBuf.get(bs);
 // 把文件當(dāng)字符串處理，直接打印做為一個例子。
 System.out.print(new String(bs, 0, size));
 byteBuf.clear();
 }
 }

package com.okey.util;
 
import java.io.*;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
 
/**
 * Created with Okey
 * User: Okey
 * Date: 13-3-14
 * Time: 上午11:29
 * 讀取文件工具
 */
public class NIOFileReader {
 
 // 每次讀取文件內(nèi)容緩沖大小,默認(rèn)為1024個字節(jié)
 private int bufSize = 1024;
 // 換行符
 private byte key = "\n".getBytes()[0];
 // 當(dāng)前行數(shù)
 private long lineNum = 0;
 // 文件編碼,默認(rèn)為gb2312
 private String encode = "gb2312";
 // 具體業(yè)務(wù)邏輯監(jiān)聽器
 private ReaderListener readerListener;
 
 /**
 * 設(shè)置回調(diào)方法
 * @param readerListener
 */
 public NIOFileReader(ReaderListener readerListener) {
 this.readerListener = readerListener;
 }
 
 /**
 * 設(shè)置回調(diào)方法,并指明文件編碼
 * @param readerListener
 * @param encode
 */
 public NIOFileReader(ReaderListener readerListener, String encode) {
 this.encode = encode;
 this.readerListener = readerListener;
 }
 
 /**
 * 普通io方式讀取文件
 * @param fullPath
 * @throws Exception
 */
 public void normalReadFileByLine(String fullPath) throws Exception {
 File fin = new File(fullPath);
 if (fin.exists()) {
 BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream(fin), encode));
 String lineStr;
 while ((lineStr = reader.readLine()) != null) {
 lineNum++;
 readerListener.outLine(lineStr.trim(), lineNum, false);
 }
 readerListener.outLine(null, lineNum, true);
 reader.close();
 }
 }
 
 /**
 * 使用NIO逐行讀取文件
 *
 * @param fullPath
 * @throws java.io.FileNotFoundException
 */
 public void readFileByLine(String fullPath) throws Exception {
 File fin = new File(fullPath);
 if (fin.exists()) {
 FileChannel fcin = new RandomAccessFile(fin, "r").getChannel();
 try {
 ByteBuffer rBuffer = ByteBuffer.allocate(bufSize);
 // 每次讀取的內(nèi)容
 byte[] bs = new byte[bufSize];
 // 緩存
 byte[] tempBs = new byte[0];
 String line = "";
 while (fcin.read(rBuffer) != -1) {
  int rSize = rBuffer.position();
  rBuffer.rewind();
  rBuffer.get(bs);
  rBuffer.clear();
  byte[] newStrByte = bs;
  // 如果發(fā)現(xiàn)有上次未讀完的緩存,則將它加到當(dāng)前讀取的內(nèi)容前面
  if (null != tempBs) {
  int tL = tempBs.length;
  newStrByte = new byte[rSize + tL];
  System.arraycopy(tempBs, 0, newStrByte, 0, tL);
  System.arraycopy(bs, 0, newStrByte, tL, rSize);
  }
  int fromIndex = 0;
  int endIndex = 0;
  // 每次讀一行內(nèi)容，以 key（默認(rèn)為\n） 作為結(jié)束符
  while ((endIndex = indexOf(newStrByte, fromIndex)) != -1) {
  byte[] bLine = substring(newStrByte, fromIndex, endIndex);
  line = new String(bLine, 0, bLine.length, encode);
  lineNum++;
  // 輸出一行內(nèi)容，處理方式由調(diào)用方提供
  readerListener.outLine(line.trim(), lineNum, false);
  fromIndex = endIndex + 1;
  }
  // 將未讀取完成的內(nèi)容放到緩存中
  tempBs = substring(newStrByte, fromIndex, newStrByte.length);
 }
 // 將剩下的最后內(nèi)容作為一行，輸出，并指明這是最后一行
 String lineStr = new String(tempBs, 0, tempBs.length, encode);
 readerListener.outLine(lineStr.trim(), lineNum, true);
 } catch (Exception e) {
 e.printStackTrace();
 } finally {
 fcin.close();
 }
 
 } else {
 throw new FileNotFoundException("沒有找到文件：" + fullPath);
 }
 }
 
 /**
 * 查找一個byte[]從指定位置之后的一個換行符位置
 * @param src
 * @param fromIndex
 * @return
 * @throws Exception
 */
 private int indexOf(byte[] src, int fromIndex) throws Exception {
 
 for (int i = fromIndex; i < src.length; i++) {
 if (src[i] == key) {
 return i;
 }
 }
 return -1;
 }
 
 /**
 * 從指定開始位置讀取一個byte[]直到指定結(jié)束位置為止生成一個全新的byte[]
 * @param src
 * @param fromIndex
 * @param endIndex
 * @return
 * @throws Exception
 */
 private byte[] substring(byte[] src, int fromIndex, int endIndex) throws Exception {
 int size = endIndex - fromIndex;
 byte[] ret = new byte[size];
 System.arraycopy(src, fromIndex, ret, 0, size);
 return ret;
 }
 
}

package com.okey.util;
 
import java.util.ArrayList;
import java.util.List;
 
/**
 * Created with Okey
 * User: Okey
 * Date: 13-3-14
 * Time: 下午3:19
 * NIO逐行讀數(shù)據(jù)回調(diào)方法
 */
public abstract class ReaderListener {
 
 // 一次讀取行數(shù)，默認(rèn)為500
 private int readColNum = 500;
 
 private List<String> list = new ArrayList<String>();
 
 /**
 * 設(shè)置一次讀取行數(shù)
 * @param readColNum
 */
 protected void setReadColNum(int readColNum) {
 this.readColNum = readColNum;
 }
 
 /**
 * 每讀取到一行數(shù)據(jù)，添加到緩存中
 * @param lineStr 讀取到的數(shù)據(jù)
 * @param lineNum 行號
 * @param over 是否讀取完成
 * @throws Exception
 */
 public void outLine(String lineStr, long lineNum, boolean over) throws Exception {
 if(null != lineStr)
 list.add(lineStr);
 if (!over && (lineNum % readColNum == 0)) {
 output(list);
 list.clear();
 } else if (over) {
 output(list);
 list.clear();
 }
 }
 
 /**
 * 批量輸出
 *
 * @param stringList
 * @throws Exception
 */
 public abstract void output(List<String> stringList) throws Exception;
 
}

package com.okey.util;
 
 
import java.io.File;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
 
 
/**
 * Created with IntelliJ IDEA.
 * User: Okey
 * Date: 14-3-6
 * Time: 上午11:02
 * To change this template use File | Settings | File Templates.
 */
public class ReadTxt {
 public static void main(String[] args) throws Exception{
 String filename = "E:/address_city.utf8.txt";
 ReaderListener readerListener = new ReaderListener() {
 @Override
 public void output(List<String> stringList) throws Exception {
 for (String s : stringList) {
  System.out.println("s = " + s);
 }
 }
 };
 readerListener.setReadColNum(100000);
 NIOFileReader nioFileReader = new NIOFileReader(readerListener,"utf-8");
 nioFileReader.readFileByLine(filename);
 }
}