package kddcup2012.task2.FileSystem;  import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;  public class FileSplit
{     public static void main(String[] args) throws IOException  {  long timer = System.currentTimeMillis();  int bufferSize = 20 * 1024 * 1024;//设读取文件的缓存为20MB   //建立缓冲文本输入流   File file = new File("/media/Data/毕业设计/kdd cup/数据/userid_profile.txt");  FileInputStream fileInputStream = new FileInputStream(file);  BufferedInputStream bufferedInputStream = new BufferedInputStream(fileInputStream);  InputStreamReader inputStreamReader = new InputStreamReader(bufferedInputStream);  BufferedReader input = new BufferedReader(inputStreamReader, bufferSize);  int splitNum = 112-1;//要分割的块数减一   int fileLines = 23669283;//输入文件的行数   long perSplitLines = fileLines / splitNum;//每个块的行数   for (int i = 0; i <= splitNum; ++i)  {  //分割   //每个块建立一个输出   FileWriter output = new FileWriter("/home/haoqiong/part" + i + ".txt");  String line = null;  //逐行读取，逐行输出   for (long lineCounter = 0; lineCounter < perSplitLines && (line = input.readLine()) != null; ++lineCounter)  {  output.append(line + "\r");  }  output.flush();  output.close();  output = null;  }  input.close();  timer = System.currentTimeMillis() - timer;  System.out.println("处理时间：" + timer);  }
}  

package helloword.helloword;import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;public class ReadBig {public static String fff = "C:\\mq\\read\\from.xml";public static void main1(String[] args) throws Exception {final int BUFFER_SIZE = 0x300000;// 缓冲区大小为3M
File f = new File(fff);MappedByteBuffer inputBuffer = new RandomAccessFile(f, "r").getChannel().map(FileChannel.MapMode.READ_ONLY,f.length() / 2, f.length() / 2);byte[] dst = new byte[BUFFER_SIZE];// 每次读出3M的内容long start = System.currentTimeMillis();for (int offset = 0; offset < inputBuffer.capacity(); offset += BUFFER_SIZE) {if (inputBuffer.capacity() - offset >= BUFFER_SIZE) {for (int i = 0; i < BUFFER_SIZE; i++)dst[i] = inputBuffer.get(offset + i);} else {for (int i = 0; i < inputBuffer.capacity() - offset; i++)dst[i] = inputBuffer.get(offset + i);}int length = (inputBuffer.capacity() % BUFFER_SIZE == 0) ? BUFFER_SIZE: inputBuffer.capacity() % BUFFER_SIZE;System.out.println(new String(dst, 0, length));// new// String(dst,0,length)这样可以取出缓存保存的字符串，可以对其进行操作
}long end = System.currentTimeMillis();System.out.println("读取文件文件一半内容花费：" + (end - start) + "毫秒");}public static void main2(String[] args) throws Exception {int bufSize = 1024;byte[] bs = new byte[bufSize];ByteBuffer byteBuf = ByteBuffer.allocate(1024);FileChannel channel = new RandomAccessFile(fff, "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();}}public static void main3(String[] args) throws Exception {BufferedReader br = new BufferedReader(new FileReader(fff));String line = null;while ((line = br.readLine()) != null) {System.out.println(line);}}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 helloword.helloword;import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.RandomAccessFile;
import java.util.Scanner;public class TestPrint {public static void main(String[] args) throws IOException {String path = "你要读的文件的路径";RandomAccessFile br = new RandomAccessFile(path, "rw");// 这里rw看你了。要是之都就只写rString str = null, app = null;int i = 0;while ((str = br.readLine()) != null) {i++;app = app + str;if (i >= 100) {// 假设读取100行i = 0;// 这里你先对这100行操作，然后继续读app = null;}}br.close();}// 当逐行读写大于2G的文本文件时推荐使用以下代码void largeFileIO(String inputFile, String outputFile) {try {BufferedInputStream bis = new BufferedInputStream(new FileInputStream(new File(inputFile)));BufferedReader in = new BufferedReader(new InputStreamReader(bis, "utf-8"), 10 * 1024 * 1024);// 10M缓存FileWriter fw = new FileWriter(outputFile);while (in.ready()) {String line = in.readLine();fw.append(line + " ");}in.close();fw.flush();fw.close();} catch (IOException ex) {ex.printStackTrace();}}
}

File file = new File(filepath);
BufferedInputStream fis = new BufferedInputStream(new FileInputStream(file));
BufferedReader reader = new BufferedReader(new InputStreamReader(fis,"utf-8"),5*1024*1024);// 用5M的缓冲读取文本文件  

String line = "";
while((line = reader.readLine()) != null){
   //TODO: write your business
}