一直在处理爬虫，经常能遇到读写文件的操作，很多时候都是读写超大文件，记录如下：一、读文件import java.io.BufferedOutputStream;import  java.io.BufferedReader;import java.io.File;import java.io.FileOutputStream;import java.io.FileReader;import java.io.FileWriter;import java.io.IOException;import java.io.OutputStreamWriter;public void ReadFile(String filename) {File file=new File(filename);BufferedReader reader=null;try{reader=new BufferedReader(new FileReader(file));   //如果是读大文件  则  new BufferedReader(new FileReader(file),5*1024*1024);  即，设置缓存
String tempString=null;while((tempString=reader.readLine())!=null){//进行操作.....
}reader.close();}catch(IOException e){e.printStackTrace();}finally{if(reader!=null){try{reader.close();}catch(IOException e){e.printStackTrace();}}}}二、写文件import java.io.BufferedOutputStream;import  java.io.BufferedReader;import  java.io.BufferedWriter;import java.io.File;import java.io.FileOutputStream;import java.io.FileReader;import java.io.FileWriter;import java.io.IOException;import java.io.OutputStreamWriter;public void method1(String file,String content){BufferedWriter out=null;try{out=new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file,true)));  //追加的方法
out.write(content);out.write("\r\n");}catch(IOException e){e.printStackTrace();}finally{try{out.close();}catch(IOException e){e.printStackTrace();}}}public void main(String[] args){String filename="D:\a.txt";File f=new File(filename);if(f.exists()){f.delete();}f.createNewFile();String ss="sssssss";method1(filename,ss);}===========================华丽丽的分隔符=============================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：下面的代码转自【http://www.oschina.net/code/snippet_54100_7938】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();
}
} }