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);
 // 把文件当字符串处理，直接打印做为一个例子。
 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
 * 读取文件工具
 */
public class NIOFileReader {
 
 // 每次读取文件内容缓冲大小,默认为1024个字节
 private int bufSize = 1024;
 // 换行符
 private byte key = "\n".getBytes()[0];
 // 当前行数
 private long lineNum = 0;
 // 文件编码,默认为gb2312
 private String encode = "gb2312";
 // 具体业务逻辑监听器
 private ReaderListener readerListener;
 
 /**
 * 设置回调方法
 * @param readerListener
 */
 public NIOFileReader(ReaderListener readerListener) {
 this.readerListener = readerListener;
 }
 
 /**
 * 设置回调方法,并指明文件编码
 * @param readerListener
 * @param encode
 */
 public NIOFileReader(ReaderListener readerListener, String encode) {
 this.encode = encode;
 this.readerListener = readerListener;
 }
 
 /**
 * 普通io方式读取文件
 * @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逐行读取文件
 *
 * @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);
  // 每次读取的内容
  byte[] bs = new byte[bufSize];
  // 缓存
  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;
   // 如果发现有上次未读完的缓存,则将它加到当前读取的内容前面
   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;
   // 每次读一行内容，以 key（默认为\n） 作为结束符
   while ((endIndex = indexOf(newStrByte, fromIndex)) != -1) {
   byte[] bLine = substring(newStrByte, fromIndex, endIndex);
   line = new String(bLine, 0, bLine.length, encode);
   lineNum++;
   // 输出一行内容，处理方式由调用方提供
   readerListener.outLine(line.trim(), lineNum, false);
   fromIndex = endIndex + 1;
   }
   // 将未读取完成的内容放到缓存中
   tempBs = substring(newStrByte, fromIndex, newStrByte.length);
  }
  // 将剩下的最后内容作为一行，输出，并指明这是最后一行
  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("没有找到文件：" + fullPath);
 }
 }
 
 /**
 * 查找一个byte[]从指定位置之后的一个换行符位置
 * @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;
 }
 
 /**
 * 从指定开始位置读取一个byte[]直到指定结束位置为止生成一个全新的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逐行读数据回调方法
 */
public abstract class ReaderListener {
 
 // 一次读取行数，默认为500
 private int readColNum = 500;
 
 private List<String> list = new ArrayList<String>();
 
 /**
 * 设置一次读取行数
 * @param readColNum
 */
 protected void setReadColNum(int readColNum) {
 this.readColNum = readColNum;
 }
 
 /**
 * 每读取到一行数据，添加到缓存中
 * @param lineStr 读取到的数据
 * @param lineNum 行号
 * @param over 是否读取完成
 * @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();
 }
 }
 
 /**
 * 批量输出
 *
 * @param stringList
 * @throws Exception
 */
 public abstract void output(List<String> stringList) throws Exception;
 
}

ReadTxt(具体业务逻辑)


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);
 }
}