java noi读取文件

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要利用nio进行文件的去读需要明白缓冲区的原理可以通过以下的链接进行了解~

http://www.ibm.com/developerworks/cn/education/java/j-nio/j-nio.html#

以下是几种读取利用noi读取和写入文件的几种方法.

import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.RandomAccessFile;import java.nio.ByteBuffer;import java.nio.MappedByteBuffer;import java.nio.channels.FileChannel;/*参考网址 * http://www.ibm.com/developerworks/cn/education/java/j-nio/j-nio.html * */public class NFile{/**/public static StringBuilder readFile(String dir) throws Exception{FileInputStream input = new FileInputStream(dir);//获取通道FileChannel fc = input.getChannel();//创建缓冲区.ByteBuffer buffer = ByteBuffer.allocate(2048);int n = -1;StringBuilder sb = new StringBuilder("");while((n = fc.read(buffer)) != -1){//System.out.println(buffer);System.out.println(n);buffer.flip();/*flip,将limit设置为当前的position的位置,position=0*///sb.append(new String(buffer.array(),0,n));byte[] b = new byte[n] ;buffer.get(b);sb.append(new String(b));System.out.println(buffer);/*清空缓冲区让缓冲区可以重新进入读取数据,设置当前的limit为capacity,position为0*/buffer.clear();}if(null != input) {input.close();}return sb;}public static void readFile() throws Exception{RandomAccessFile aFile = new RandomAccessFile("d:\\text\\group.txt", "rw");FileChannel inChannel = aFile.getChannel();ByteBuffer buf = ByteBuffer.allocate(2048);int bytesRead = inChannel.read(buf);while (bytesRead != -1) {System.out.print(bytesRead);buf.flip();while(buf.hasRemaining()){/*利用get进行直接的读取,也可以get一个byte数组*/    System.out.print((char) buf.get());}buf.clear();bytesRead = inChannel.read(buf);}aFile.close();}public static boolean writeFile(String dir,String content ) throws Exception{FileOutputStream output = new FileOutputStream(dir);FileChannel fout = output.getChannel();byte[] contenByte = content.getBytes("GBK");//byte[] contenByte = content.getBytes();//方法1://ByteBuffer buffer = ByteBuffer.allocate(contenByte.length);//buffer.put(contenByte);//buffer.flip();//方法二:ByteBuffer buffer = ByteBuffer.wrap(contenByte);fout.write(buffer);fout.close();output.close();return true;}/*文件直接映射到内存中进行读取.*/public static StringBuilder FileMap(String dir) throws Exception{/*打开文件刘*/FileInputStream input = new FileInputStream(dir);/*获取管道*/FileChannel fc = input.getChannel();MappedByteBuffer mbb = fc.map( FileChannel.MapMode.READ_ONLY,     0, fc.size() );StringBuilder sb = new StringBuilder("");byte[] b = new byte[(int)fc.size()] ;mbb.get(b);sb.append(new String(b));input.close();return sb;}public static void main(String[] args) throws Exception{StringBuilder sb = null;//sb = FileMap("d:\\text\\group.txt");readFile();// sb = readFile("d:\\text\\group.txt");//writeFile("d:\\text\\group_cpy.txt",sb.toString());System.out.println("");System.out.println(sb);}}

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