java各种IO读取文件对比

本文对比java几种读取文件常用的方式，有普通的IO、BufferIO、RandomAccessFile、普通的NIO、MappedByteBuffer和DirectByteBuffer。如下：

package com.io.nio;import java.io.BufferedInputStream;import java.io.File;import java.io.FileInputStream;import java.io.FileReader;import java.io.IOException;import java.io.RandomAccessFile;import java.nio.ByteBuffer;import java.nio.MappedByteBuffer;import java.nio.channels.FileChannel;public class IOComparison {      static final int BUFFER_SIZE = 1024*10;        public static void testMappedByteBuffer() throws IOException{    File file = new File("E:\\AllLog.log");      FileChannel channel = new FileInputStream(file).getChannel();          MappedByteBuffer buff = channel.map(FileChannel.MapMode.READ_ONLY, 0, channel.size());          byte[] b = new byte[BUFFER_SIZE];          long begin = System.currentTimeMillis();          while (buff.remaining() > 0) {        if(buff.limit()-buff.position()>BUFFER_SIZE){        buff.get(b);        }else{        buff.get(new byte[buff.limit()-buff.position()]);          }//较慢        //buff.get();//较快}        long end = System.currentTimeMillis();          System.out.println("testMappedByteBuffer time is:" + (end - begin));      }        public static void testNormalNIO() throws IOException{    File file = new File("E:\\AllLog.log");      FileChannel channel = new FileInputStream(file).getChannel();      ByteBuffer buff = ByteBuffer.allocate(BUFFER_SIZE);       long begin = System.currentTimeMillis();      while (channel.read(buff) != -1) {          buff.flip();  //make ready to read        //do something        buff.clear();  //make ready to write    }      long end = System.currentTimeMillis();      System.out.println("testNormalNIO time is:" + (end - begin));      }        public static void testDirectByteBuffer() throws IOException{    File file = new File("E:\\AllLog.log");      FileChannel channel = new FileInputStream(file).getChannel();    ByteBuffer buff = ByteBuffer.allocateDirect(BUFFER_SIZE);       long begin = System.currentTimeMillis();      while (channel.read(buff) != -1) {          buff.flip();          buff.clear();      }      long end = System.currentTimeMillis();      System.out.println("testDirectByteBuffer time is:" + (end - begin));    }        public static void testNormalIO()throws IOException{    File file = new File("E:\\AllLog.log");      FileInputStream inputStream = new FileInputStream(file);    byte[] buff=new byte[BUFFER_SIZE];    long begin = System.currentTimeMillis();      while(inputStream.read(buff)>0){//inputStream.read()会慢很多        }    long end = System.currentTimeMillis();      System.out.println("testNormalIO time is:" + (end - begin));    }        public static void testNormalBufferIO()throws IOException{    File file = new File("E:\\AllLog.log");      BufferedInputStream inputStream = new BufferedInputStream(new FileInputStream(file)) ;    byte[] buff=new byte[BUFFER_SIZE];    long begin = System.currentTimeMillis();      while(inputStream.read(buff)>0){//inputStream.read()会快，因为其本身就预读到内置的buf[]里面了        }    long end = System.currentTimeMillis();      System.out.println("testNormalBufferIO time is:" + (end - begin));    }        public static void testRandomAccessFile()throws IOException{    File file = new File("E:\\AllLog.log");    RandomAccessFile raf=new RandomAccessFile(file, "r");    long begin = System.currentTimeMillis();     String line;    while((line=raf.readLine())!=null){        }    long end = System.currentTimeMillis();      System.out.println("testRandomAccessFile time is:" + (end - begin));    }        public static void main(String[] args) throws Exception {     testNormalIO();    testNormalBufferIO();    testNormalNIO();    testMappedByteBuffer();    testDirectByteBuffer();    testRandomAccessFile();    }  }  

读取的文件大小为1.21G，运行结果如下所示：

testNormalIO time is:943testNormalBufferIO time is:993testNormalNIO time is:1023testMappedByteBuffer time is:251testDirectByteBuffer time is:703