java實現(xiàn)超大文件的讀寫功能

更新時間：2019年05月04日 13:29:41 作者：只要你能好

這篇文章主要為大家詳細介紹了java實現(xiàn)超大文件的讀寫功能，具有一定的參考價值，感興趣的小伙伴們可以參考一下

對于幾百M或上G的大文件可使用java nio進行讀寫，根據(jù)個人的需求可能需要將一個超大文件讀寫形成很多較小的文件進行分析，這也不是什么難事，在讀完一個緩沖區(qū)后更換寫入的對象即可，本文就不做詳細介紹了，有需要的可以聯(lián)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("開始讀取并重寫文件，請等待...");
 
 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("讀寫完成！"); 
} 
 
 /*讀文件同時寫文件*/
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(); 
 } 
} 
 
 /*寫文件*/
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(); 
 } 
} 
 
 
}

以上就是本文的全部內(nèi)容，希望對大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。

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