java实现超大文件的读写功能

java实现超大文件的读写功能

对于几百M或上G的大文件可使用java nio进行读写 ， 根据个人的需求 可能需要将一个超大文件读写形成很多较小的文件进行分析，这也不是什么难事，在读完一个缓冲区后 更换写入的对象即可，本文就不做详细介绍了，有需要的可以联系本人。

直接上程序吧

package cn.gzu.readfile;

import java.io.File;

import java.io.IOException;

import java.io.RandomAccessFile;

import java.nio.ByteBuffer;

import java.nio.channels.FileChannel;

public class ReadWriteNio {

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

int bufSize = 100;

File fin = new File("E:\\jiahui\\2014-09-01.dat");

File fout = new File("E:\\jiahui\\res.txt");

System.out.print("开始读取并重写文件，请等待...");

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);

System.out.print("读写完成！");

}

/*读文件同时写文件*/

public static void readFileByLine(int bufSize, FileChannel fcin, ByteBuffer rBuffer,

FileChannel fcout, ByteBuffer wBuffer){

String enterStr = "\n";

try{

byte[] bs = new byte[bufSize];

int size = 0;

StringBuffer strBuf = new StringBuffer("");

while((sWuDHdwize = fcin.read(rBuffer)) != -1){

// while(fcin.read(rBuffer) != -1){

if(size > 1*1024){

break;

}

int rSize = rBuffer.position();

rBuffer.rewind();

rBuffer.get(bs);

rBuffer.clear();

String tempString = new String(bs, 0, rSize,"UTF-8");

// System.out.println(size+": "+tempString);

int fromIndex = 0;

int endIndex = 0;

while((endIndex = tempString.indexOf(enterStr, fromIndex)) != -1){

String line = tempString.substring(fromIndex, endIndex);

line = new String(strBuf.toString() + line + "\n");

Systehttp://m.out.println(size+": "+line);

//System.out.print("");

//write to anthone file

writeFileByLine(fcout, wBuffer, line);

strBuf.delete(0, strBuf.length());

fromIndex = endIndex + 1;

}

if(rSize > tempString.length()){

strBuf.append(tempString.substring(fromIndex, tempString.length()));

}else{

strBuf.append(tempString.substring(fromIndex, rSize));

}

}

} catch (IOException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

}

/*写文件*/

public static void writeFileByLine(FileChannel fcout, ByteBuffer wBuffer, String line){

try {

//write on file head

//fcout.write(wBuffer.wrap(line.getBytes()));

//wirte append file on foot

fcout.write(wBuffer.wrap(line.getBytes()), fcout.size());

} catch (IOException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

}

}

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