java讀寫檔案，讀超大檔案
一直在處理爬蟲，經常能遇到讀寫檔案的操作，很多時候都是讀寫超大檔案，記錄如下：
一、讀檔案
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)); //如果是讀大檔案 則 new BufferedReader(new FileReader(file),5*1024*1024); 即，設定快取
String tempString=null;
while((tempString=reader.readLine())!=null)
{
//進行操作.....
}
reader.close();
}catch(IOException e){
e.printStackTrace();
}finally{
if(reader!=null)
{
try{
reader.close();
}catch(IOException e)
{
e.printStackTrace();
}
}
}
}
二、寫檔案
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);
}
===========================華麗麗的分隔符=============================
在實踐中發現上面的方法最多也就能處理10M以內的資料，從而編輯此文章。
想要真正處理上百M，甚至上G的檔案，那就要用到java的nio包：
下面的程式碼轉自【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!!!");
}
/*讀檔案同時寫檔案*/
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();
}
}
/*寫檔案*/
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();
}
}
}