JavaNio 文件按行读写

最新推荐文章于 2024-11-28 20:44:42 发布

cynthia831224

最新推荐文章于 2024-11-28 20:44:42 发布

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分类专栏： java 文章标签： java nio bytebuffer

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本文介绍了一个使用Java NIO进行文件读写的示例程序。该程序通过直接操作ByteBuffer来提高文件读取效率，并实现了逐行读取及写入文件的功能。文章详细展示了如何创建FileChannel、分配缓冲区以及进行数据的读取与写入。

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package alex;

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{

//String infile = "D:\\workspace\\test\\usagetracking.log";
//FileInputStream fin= new FileInputStream(infile);
//FileChannel fcin = fin.getChannel();

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!!!");
}

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();
}
}

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();
}
}

}