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【Java】 Java NIO 按行读写大文件
作者:Dezai.CN / 发布于2013/7/13/ 1030

	import java.io.BufferedReader;
	import java.io.File;
	import java.io.FileInputStream;
	import java.io.IOException;
	import java.io.RandomAccessFile;
	import java.nio.ByteBuffer;
	import java.nio.channels.FileChannel;

	public class TestNio {

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

	 //String infile = "D:\\workspace\\test\\usagetracking.log";
	 //FileInputStream fin= new FileInputStream(infile);
	 //FileChannel fcin = fin.getChannel();

	 int bufSize = 100;
	 File fin = new File("D:\\workspace\\test\\usagetracking.log");
	 File fout = new File("D:\\workspace\\test\\usagetracking2.log");

	 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("OK!!!");
	 }

	 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(buffer)) != -1){
	 while(fcin.read(rBuffer) != -1){
	 int rSize = rBuffer.position();
	 rBuffer.rewind();
	 rBuffer.get(bs);
	 rBuffer.clear();
	 String tempString = new String(bs, 0, rSize);
	 //System.out.print(tempString);
	 //System.out.print("<200>");

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

	 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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