java超大文件

在实践中发现上面的方法最多也就能处理10M以内的数据,从而编辑此文章。

想要真正处理上百M,甚至上G的文件,那就要用到java的nio包:

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{
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!!!”);
}

/*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(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();
}
}

/*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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