几种IO读文件性能对比

文件大小19M，10万行左右的数据。堆内存设置如下：

一，NIO，无内存溢出，耗时220毫秒左右。缺点是实现起来太复杂，要考虑汉字等。

package myWeb.test.nio;

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;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Date;
import java.util.List;

public class NIOReadFile1 {
       public static void main(String args[]) throws Exception {  
           long begin = System.currentTimeMillis();
            int bufSize = 30000;//一次读取的字节长度  
            File fin = new File("/Users/yp-tc-m-2777/Desktop/CCB_NET_B2C_JHBZ1012all.txt");//读取的文件  
           // File fout = new File("/Users/yp-tc-m-2777/Desktop/22.txt");//写出的文件  
            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, null, wBuffer);  
            long end = System.currentTimeMillis();
            System.out.print(end-begin);//测试执行时间  
            if(fcin.isOpen()){  
                fcin.close();  
            }  
//            if(fcout.isOpen()){  
//                fcout.close();  
//            }  
        }  
      
        public static void readFileByLine(int bufSize, FileChannel fcin,  
                ByteBuffer rBuffer, FileChannel fcout, ByteBuffer wBuffer) {  
            String enter = "
";  
         //   List<String> dataList = new ArrayList<String>();//存储读取的每行数据  
            byte[] lineByte = new byte[0];  
              
            String encode = "utf-8";  
//          String encode = "UTF-8";  
            try {  
                //temp：由于是按固定字节读取，在一次读取中，第一行和最后一行经常是不完整的行，因此定义此变量来存储上次的最后一行和这次的第一行的内容，  
                //并将之连接成完成的一行，否则会出现汉字被拆分成2个字节，并被提前转换成字符串而乱码的问题  
                byte[] temp = new byte[0];  
                while (fcin.read(rBuffer) != -1) {//fcin.read(rBuffer)：从文件管道读取内容到缓冲区(rBuffer)  
                    int rSize = rBuffer.position();//读取结束后的位置，相当于读取的长度  
                    byte[] bs = new byte[rSize];//用来存放读取的内容的数组  
                    rBuffer.rewind();//将position设回0,所以你可以重读Buffer中的所有数据,此处如果不设置,无法使用下面的get方法  
                    rBuffer.get(bs);//相当于rBuffer.get(bs,0,bs.length())：从position初始位置开始相对读,读bs.length个byte,并写入bs[0]到bs[bs.length-1]的区域  
                    rBuffer.clear();  
                      
                    int startNum = 0;  
                    int LF = 10;//换行符  
                    int CR = 13;//回车符  
                    boolean hasLF = false;//是否有换行符  
                    for(int i = 0; i < rSize; i++){  
                        if(bs[i] == LF){  
                            hasLF = true;  
                            int tempNum = temp.length;  
                            int lineNum = i - startNum;  
                            lineByte = new byte[tempNum + lineNum];//数组大小已经去掉换行符  
                              
                            System.arraycopy(temp, 0, lineByte, 0, tempNum);//填充了lineByte[0]~lineByte[tempNum-1]  
                            temp = new byte[0];  
                            System.arraycopy(bs, startNum, lineByte, tempNum, lineNum);//填充lineByte[tempNum]~lineByte[tempNum+lineNum-1]  
                              
                            String line = new String(lineByte, 0, lineByte.length, encode);//一行完整的字符串(过滤了换行和回车)  
                       //     dataList.add(line);  
    //                      System.out.println(line);  
//                            writeFileByLine(fcout, wBuffer, line + enter);  
                              
                            //过滤回车符和换行符  
                            if(i + 1 < rSize && bs[i + 1] == CR){  
                                startNum = i + 2;  
                            }else{  
                                startNum = i + 1;  
                            }  
                              
                        }  
                    }  
                    if(hasLF){  
                        temp = new byte[bs.length - startNum];  
                        System.arraycopy(bs, startNum, temp, 0, temp.length);  
                    }else{//兼容单次读取的内容不足一行的情况  
                        byte[] toTemp = new byte[temp.length + bs.length];  
                        System.arraycopy(temp, 0, toTemp, 0, temp.length);  
                        System.arraycopy(bs, 0, toTemp, temp.length, bs.length);  
                        temp = toTemp;  
                    }  
                }  
                if(temp != null && temp.length > 0){//兼容文件最后一行没有换行的情况  
                    String line = new String(temp, 0, temp.length, encode);  
             //       dataList.add(line);  
//                  System.out.println(line);  
//                    writeFileByLine(fcout, wBuffer, line + enter);  
                } 
             //   System.out.println(dataList.size());
            } catch (IOException e) {  
                e.printStackTrace();  
            }   
        }  
      
        /** 
         * 写到文件上 
         * @param fcout 
         * @param wBuffer 
         * @param line 
         */  
        @SuppressWarnings("static-access")  
        private static void writeFileByLine(FileChannel fcout, ByteBuffer wBuffer,  
                String line) {  
            try {  
                fcout.write(wBuffer.wrap(line.getBytes("UTF-8")), fcout.size());  
            } catch (IOException e) {  
                e.printStackTrace();  
            }  
        }  
}

二，BIO使用BUFFER，180毫秒左右竟然是最高效，代码最简洁的方式。

package myWeb.test.nio;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;

public class OfOldIO1 {
    public static void main(String[] args) throws IOException {
        long begin = System.currentTimeMillis();
        BufferedReader read = new BufferedReader(new InputStreamReader(new FileInputStream(new File("/Users/yp-tc-m-2777/Desktop/CCB_NET_B2C_JHBZ1012all.txt"))));
        String line = null;
    //     List<String> dataList = new ArrayList<String>();//存储读取的每行数据 
        while((line = read.readLine())!=null){
            //System.out.println(line);
        //    dataList.add(line);
        }
        if(read!=null){
            read.close();
        }
        long end = System.currentTimeMillis();
    //    System.out.println(dataList.size());
        System.out.print(end-begin);//测试执行时间 
    }
}

 三，Scanner，惨不忍睹。

package myWeb.test.nio;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class ScannerReadFile {
    public static void main(String[] args) throws IOException {
        long begin = System.currentTimeMillis();
        FileInputStream inputStream = null;
        Scanner sc = null;
    //     List<String> dataList = new ArrayList<String>();//存储读取的每行数据 
        try {
            inputStream = new FileInputStream("/Users/yp-tc-m-2777/Desktop/CCB_NET_B2C_JHBZ1012all.txt");
            sc = new Scanner(inputStream, "UTF-8");
            while (sc.hasNextLine()) {
                String line = sc.nextLine();
          //      dataList.add(line);
                // System.out.println(line);
            }
            if (sc.ioException() != null) {
                throw sc.ioException();
            }
        } finally {
            if (inputStream != null) {
                inputStream.close();
            }
            if (sc != null) {
                sc.close();
            }
        }
        long end = System.currentTimeMillis();
    //     System.out.println(dataList.size());
            System.out.print(end-begin);//测试执行时间  
    }
}

四，CommonIO,与NIO类似。

package myWeb.test.nio;

import java.io.File;
import java.io.IOException;

import org.apache.commons.io.FileUtils;
import org.apache.commons.io.LineIterator;

public class CommonIOReadFile {
    public static void main(String[] args) throws Exception {
        long begin = System.currentTimeMillis();
        LineIterator it = FileUtils.lineIterator(new File("/Users/yp-tc-m-2777/Desktop/CCB_NET_B2C_JHBZ1012all.txt"), "UTF-8");
        try {
            while (it.hasNext()) {
                String line = it.nextLine();
                // do something with line
            }
        } finally {
            LineIterator.closeQuietly(it);
        }
        long end = System.currentTimeMillis();
        //     System.out.println(dataList.size());
                System.out.print(end-begin);//测试执行时间  
    }
}