利用java内存映射文件机制实现CRC循环冗余校验

import java.nio.MappedByteBuffer;   
import java.nio.channels.FileChannel;   
import java.util.zip.CRC32;   
public static void main(String[] args){   
            try {                               //对

import java.nio.MappedByteBuffer;   import java.nio.channels.FileChannel;   import java.util.zip.CRC32;   public static void main(String[] args){               try {                               //对文件进行crc校验               long begin = System.currentTimeMillis();               FileInputStream in = new FileInputStream("code.py");//指定目标文件               FileChannel channel = in.getChannel(); //从文件中获取一个通道               CRC32 crc = new CRC32();               int length = (int)channel.size();               MappedByteBuffer buffer = channel.map(FileChannel.MapMode.READ_ONLY, 0, length); //用只读模式从该通道获取字节缓冲，实现文件到内存的映射               for(int i = 0;i<length;i++)               {                   int c = buffer.get(i);                   crc.update(c);//按字节做crc               }               System.out.println("crc校验和："+(Long.toHexString(crc.getValue())).toUpperCase());               long end = System.currentTimeMillis();               System.out.println("运行"+(end-begin)+"ms");           } catch (Exception e) {               // TODO Auto-generated catch block               e.printStackTrace();           }   }  import java.nio.MappedByteBuffer; import java.nio.channels.FileChannel; import java.util.zip.CRC32; public static void main(String[] args){    try {              //对文件进行crc校验    long begin = System.currentTimeMillis();    FileInputStream in = new FileInputStream("code.py");//指定目标文件    FileChannel channel = in.getChannel(); //从文件中获取一个通道    CRC32 crc = new CRC32();    int length = (int)channel.size();    MappedByteBuffer buffer = channel.map(FileChannel.MapMode.READ_ONLY, 0, length); //用只读模式从该通道获取字节缓冲，实现文件到内存的映射    for(int i = 0;i<length;i++)    {     int c = buffer.get(i);     crc.update(c);//按字节做crc    }    System.out.println("crc校验和："+(Long.toHexString(crc.getValue())).toUpperCase());    long end = System.currentTimeMillis();    System.out.println("运行"+(end-begin)+"ms");   } catch (Exception e) {    // TODO Auto-generated catch block    e.printStackTrace();   } } 运行结果： crc校验和：4831ACAC 运行16ms