java实现超大文件的读写

来源：互联网发布：杭州大数据培训编辑：程序博客网时间：2024/05/05 03:32

一、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((size = 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");   System.out.println(size+": "+line);   //System.out.print("</over/>");   //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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