Java讀取大文件

import java.io.BufferedReader; 
import java.io.File; 
import java.io.FileReader; 
import java.io.RandomAccessFile; 
import java.nio.ByteBuffer; 
import java.nio.MappedByteBuffer; 
import java.nio.channels.FileChannel; 
 
public class ReadBig { 
 
    public static String fff = "D:\\report\\inbound\\Citi_OrderLines.csv"; 
 
    public static void main1(String[] args) throws Exception { 
 
        final int BUFFER_SIZE = 0x300000;// 緩衝區大小爲3M 
 
        File f = new File(fff); 
 
        /**
         * map(FileChannel.MapMode mode,long position, long size) mode -
         * 根據是按只讀、讀取/寫入或專用（寫入時拷貝）來映射文件，分別爲 FileChannel.MapMode 類中所定義的
         * READ_ONLY、READ_WRITE 或 PRIVATE 之一 position - 文件中的位置，映射區域今後位置開始；必須爲非負數
         * size - 要映射的區域大小；必須爲非負數且不大於 Integer.MAX_VALUE
         * 因此若想讀取文件後半部份內容，如例子所寫；若想讀取文本後1
         * /8內容，須要這樣寫map(FileChannel.MapMode.READ_ONLY,
         * f.length()*7/8,f.length()/8)
         * 想讀取文件全部內容，須要這樣寫map(FileChannel.MapMode.READ_ONLY, 0,f.length())
         */ 
 
        MappedByteBuffer inputBuffer = new RandomAccessFile(f, "r").getChannel().map(FileChannel.MapMode.READ_ONLY, 
                f.length() / 2, f.length() / 2); 
 
        byte[] dst = new byte[BUFFER_SIZE];// 每次讀出3M的內容 
 
        long start = System.currentTimeMillis(); 
 
        for (int offset = 0; offset < inputBuffer.capacity(); offset += BUFFER_SIZE) { 
 
            if (inputBuffer.capacity() - offset >= BUFFER_SIZE) { 
 
                for (int i = 0; i < BUFFER_SIZE; i++) 
 
                    dst[i] = inputBuffer.get(offset + i); 
 
            } else { 
 
                for (int i = 0; i < inputBuffer.capacity() - offset; i++) 
 
                    dst[i] = inputBuffer.get(offset + i); 
 
            } 
 
            int length = (inputBuffer.capacity() % BUFFER_SIZE == 0) ? BUFFER_SIZE : inputBuffer.capacity() 
                    % BUFFER_SIZE; 
 
            System.out.println(new String(dst, 0, length));// new 
            // String(dst,0,length)這樣能夠取出緩存保存的字符串，能夠對其進行操做 
 
        } 
 
        long end = System.currentTimeMillis(); 
 
        System.out.println("讀取文件文件一半內容花費：" + (end - start) + "毫秒"); 
 
    } 
}