java读取大文件

import java.io.File;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

public class FileUtils {
	 public static void main(String[] args) throws Exception {
	        final int BUFFER_SIZE = 0x300000; // 缓冲区为3M
	        File f = new File("c:/backupfile.sql"); 
	        int len = 0;
	        Long start = System.currentTimeMillis();
	        for (int z = 8; z >0; z--) {
	            MappedByteBuffer inputBuffer = new RandomAccessFile(f , "r"  )
	                    .getChannel().map(FileChannel.MapMode.READ_ONLY ,
	                            f.length() * (z-1) / 8, f.length() * 1 / 8) ;
	           
	            byte[] dst = new byte[BUFFER_SIZE];// 每次读出3M的内容
	            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;
	                String line = new String(dst, 0, length , "UTF-8" ) ;  
	                len += length ;
	                System.out.println( length +"-"+(z-1)+"-"+(8-z+1));  
	            }
	        }
	        System.out.println( len ) ; 
	        long end = System.currentTimeMillis();
	        System.out.println("读取文件文件花费：" + (end - start) + "毫秒");
	    }
}