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
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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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