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importjava.io.BufferedOutputStream;importjava.io.BufferedReader;importjava.io.File;importjava.io.FileOutputStream;importjava.io.FileReader;importjava.io.FileWriter;importjava.io.IOException;importjava.io.OutputStreamWriter;public voidReadFile(String filename) {
File file=newFile(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importjava.io.BufferedOutputStream;importjava.io.BufferedReader;importjava.io.BufferedWriter;importjava.io.File;importjava.io.FileOutputStream;importjava.io.FileReader;importjava.io.FileWriter;importjava.io.IOException;importjava.io.OutputStreamWriter;public voidmethod1(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 voidmain(String[] args)
{
String filename="D:\a.txt";
File f=newFile(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】
importjava.io.BufferedReader;importjava.io.File;importjava.io.FileInputStream;importjava.io.IOException;importjava.io.RandomAccessFile;importjava.nio.ByteBuffer;importjava.nio.channels.FileChannel;public classTestNio {public static void main(String args[]) throwsException{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(intbufSize, 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("");//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 voidwriteFileByLine(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();
}
}
}
