Java nio

[jubin kart]

Hi,
I was trying out java nio and I wanted to see the difference between nio and the normal file stream.
I tried copying over 115MB using both methods and they both got the job done in 3 sec. Am i not supossed to see considerable difference in copying or is this for only very large files in GB.
Should I try something else to see a difference.

Jubin

[jubin kart]

Hi,

I was trying to run the following code for memory mapped copying of files but it kept giving me java.io.IOException: Map failed. The file is about 700MB and does get copied only thing its corrupted and this exception is thrown.

  
 
 public static void main(String[] args) {
   
    try {
      copy("C:\\Users\\jubin\\Documents\\LimeWire\\Saved\\EdwardScissorhands.avi", "C:\\Users\\jubin\\workspace\\EdwardScissorhands.avi");
    }
    catch (IOException e) {
      System.err.println(e);
    }
 
  }
 
  public static void copy(String inFile, String outFile) 
   throws IOException {
 
    FileInputStream fin = null;
    RandomAccessFile fout = null;
    
    try {
      fin  = new FileInputStream(inFile);
      fout = new RandomAccessFile(outFile, "rw");
      
      FileChannel in = fin.getChannel();
      FileChannel out = fout.getChannel();
      
      MappedByteBuffer input = in.map(FileChannel.MapMode.READ_ONLY, 0, in.size());
      MappedByteBuffer output = out.map(FileChannel.MapMode.READ_WRITE, 0, in.size());
      output.put(input);
      
    }catch(IOException e){
    System.out.println(e);
    }
    
    
   
}

any ideas... ?

[Rob Spoor]

"being_nice",

Please read your private messages regarding an important announcement.

Thank you,

Rob

[jubin kart]

done...

[Bear Bibeault]

Not done. "jubin", please check your private messages again. And read carefully.

[Carey Evans]

The JavaDoc for the map() methods says:

The behavior of this method when the requested region is not completely contained within this channel's file is unspecified.

If the output file doesn't already exist, you should probably make it the right length first.

I don't think this will work very well though. As far as I can tell, the put() method you're calling will copy the file byte by byte. Copying from a FileInputStream to a FileOutputStream using a large enough byte array as a buffer should work better.

[Norm Radder]

You are not seeing the TRUE cause of the problem.
Add a printStackTrace() call to all the catch(){} blocks and you'll see!

[jubin kart]

thanks guys,
Printing out the stack trace helped. So how would I know how much memory I can copy over for a system , can I can I do it in parts?

java.io.IOException: Map failed
at sun.nio.ch.FileChannelImpl.map(Unknown Source)
at com.jtk.nio.FastCopy.copy(FastCopy.java:36)
at com.jtk.nio.FastCopy.main(FastCopy.java:14)
[B]Caused by: java.lang.OutOfMemoryError: Map failed[/B]
at sun.nio.ch.FileChannelImpl.map0(Native Method)
... 3 more

[jubin kart]

I did this in the end. Although it copied, the file came out corrupt and there isn't much difference between stream copy and nio.

  
  FileInputStream fin = null;
    RandomAccessFile fout = null;
    
    try {
      long time = System.currentTimeMillis();
      fin  = new FileInputStream(inFile);
      fout = new RandomAccessFile(outFile, "rw");
      
      FileChannel in = fin.getChannel();
      FileChannel out = fout.getChannel();
      MappedByteBuffer input = in.map(FileChannel.MapMode.READ_ONLY, 0, in.size());
      //out.write(input); very slow.
      ByteBuffer byteBuffer = ByteBuffer.allocate(2048);
      
      byte buffer[] = new byte[2048];
      byteBuffer.wrap(buffer);
      int offset=0;
      int length = buffer.length;
      while(input.remaining() > 0){
      byteBuffer.clear();
      if(input.remaining() < length){
      buffer = new byte[input.remaining()];
      byteBuffer.wrap(buffer);
      }
      input.get(buffer);
     out.write(byteBuffer);
      
      }
      
      System.out.println("Time to Copy: " + (System.currentTimeMillis() - time)/1000 +"s");
      in.close();
      out.close();
    }catch(IOException e){
    e.printStackTrace();
    }
 

[Mike Simmons]

Unfortunately, the API tells us nothing about whether memory-mapped files can ever be freed up after the mapping occurs. Depending on the operating system, the memory usage may be permanent. There's no particular reason to expect that it should be possible to map part of the file, free it up, and then map another part. Maybe it will work, or maybe not. But I wouldn't count on it.

Generally, if you want to copy files quickly using NIO, don't use map() - use transferTo():

FileChannel in = fin.getChannel();
try {
  FileChannel out = fout.getChannel();
  try {
    final long length = fin.size();
    for (long pos = 0; pos < length; ) 
      pos += out.transferFrom(in, pos, length - pos);
  }
  finally { out.close(); }
}
finally { in.close(); }

Depending on your operating system and hardware, you may see substantial improvement with this code - or not. In many cases NIO is not significantly faster than regular IO, because many of the improvements of NIO have already been incorporated into IO beneath the covers. In some cases, however, further improvements are still possible. You won't really know until you try.
[ July 22, 2008: Message edited by: Mike Simmons ]

[jubin kart]

Thanks mike there is a very good difference in copy.

[Norm Radder]

I tried a few different methods and file sizes to see which way was fastest to copy a file. I used 3 files of about: 53M, 280M and 680M.
It appears no one way is fastest. Depended on the size of the file.
I'm on XP with 512M ram.
The program:

 
import java.nio.*;
import java.io.*;
import java.nio.channels.*;
 
public class FileCopyTest {
 
  static  String[][] Src_Trgt = new String[][] {
        {"E:\\Downloads\\Miscellaneous\\CentOS-5.1-i386-LiveCD.iso",    // 687M
           "C:\\Temp\\Testing.iso"},
        {"E:\\Downloads\\Java\\jdk-6-doc.zip",        // 53M
           "C:\\Temp\\jdk6doc.zip"},
        {"E:\\Downloads\\Java.zip",                   // 280M
           "C:\\Temp\\java.zip"}}; 
 
   final static int Ix687M = 0;
   final static int Ix280M = 2;
   final static int Ix53M = 1;
 

   //------------------------------------------------------------------------
   static int ix = Ix280M;                   // Select which file to copy
   //------------------------------------------------------------------------
 
public static void main(String[] args) throws Exception {
       if(args.length > 0 ) {
         copy0(args);
       } // have index to read
   
 
      // Copy a file
    try {
         long start = System.currentTimeMillis();
         long size = copy1(Src_Trgt[ix][0], Src_Trgt[ix][1]);
         long dur = System.currentTimeMillis() - start;
         System.out.println("copy time=" + dur + ", rate=" + (size/dur));
    }
    catch (Exception e) {
      System.err.println("copy err " + e);
         e.printStackTrace();
    }
 
  } // end main()
 
     //---------------------------------------------------------------------------
     // Special test - read some bytes from a file at given displacement
     // args = displacement into file to read from
     static void copy0(String[] args) throws Exception {
         int loc = Integer.parseInt(args[0]);
         RandomAccessFile  fin  = new RandomAccessFile(Src_Trgt[ix][0], "r");
 
         // Time the seek
         long start = System.currentTimeMillis();
         fin.seek(loc);
         long dur = System.currentTimeMillis() - start;
         System.out.println("copy0 - seek time=" + dur);
 
         // Time the read
         int lineLen = 16;
         int bufLen = (int)(((fin.length() - loc) < lineLen) ? (fin.length() - loc) : lineLen);
         System.out.println("reading " + bufLen + " bytes from " +  Src_Trgt[ix][0] 
                                          + " at " + loc + ", length=" + fin.length());
         if(bufLen < 1) {
            // past the end
            System.out.println("loc past end");
            System.exit(0);
         }
 
         byte[] buf = new byte[bufLen];
         start = System.currentTimeMillis();
         fin.readFully(buf);
         // Add code here to show what was read
         System.out.println("bytes read:" + bytesToHex(buf));
 
         dur = System.currentTimeMillis() - start;
         System.out.println("read time=" + dur);
 
         // Time the close
         start = System.currentTimeMillis();
         fin.close();
         dur = System.currentTimeMillis() - start;
         System.out.println("close time=" + dur);
         System.exit(0);
     } // end copy0()
 
// Java.zip in hex
//00000000 504B 0304 1400 0000 0800 F66E F334 6D31 PK.........n.4m1
//00000010 44C6 527A 0100 9889 0100 1500 0000 4272 D.Rz..........Br
//00000020 6964 6765 5374 7564 696F 2D53 7263 2E7A idgeStudio-Src.z
 
   static String HexChars = "0123456789ABCDEF";
   // Convert bytes to hex 2-pules with blank spacer 
   static String bytesToHex(byte[] buf) {
      StringBuffer sb = new StringBuffer((buf.length/2)*5+3);
      for(int i=0; i < buf.length; i++ ) {
         byte b = buf[i];
         b = (byte)(b >> 4);     // Hit to bottom
         b = (byte)(b & 0x0F);   // get HI byte
         sb.append(HexChars.charAt(b));
         b = buf[i];             // refresh
         b = (byte)(b & 0x0F);   // get LOW byte
         sb.append(HexChars.charAt(b));
         if(i % 2 == 1)
            sb.append(' ');
      }
      return sb.toString();
   } // end bytesToHex()
 
   //-------------------------------------------------------------------
   // Copy one large chunk of a file & time it
 
   public static long copy3(String inFile, String outFile) throws IOException {
      System.out.println("copy3 of " + inFile + " to " + outFile);
 
   RandomAccessFile fin  = new RandomAccessFile(inFile, "r");
   RandomAccessFile fout = new RandomAccessFile(outFile, "rw");
 
      long copySize = 0x3FFFFFF;          /* FFFFFF=16M*/
      long seekPt = fin.length() - copySize;
      if(seekPt < 0) {
         seekPt = 0;
         copySize = fin.length();
      }
      byte[] buf = new byte[(int)copySize];
 
      // Set length of output file
      long start = System.currentTimeMillis();
      fout.setLength(fin.length());
      long dur = System.currentTimeMillis() - start;
      System.out.println("setLength took=" + dur + ", length=" + fin.length()
                           + ", copySize=" + copySize);
 

      do {
         // Seek to end of input
         start = System.currentTimeMillis();
         fin.seek(seekPt);
         dur = System.currentTimeMillis() - start;
         System.out.println("i/p seek took=" + dur + ", seekPt=" + seekPt);
   
         // Seek to end of output file
         start = System.currentTimeMillis();
         fout.seek(seekPt);
         dur = System.currentTimeMillis() - start;
         System.out.println("o/p seek took=" + dur);
   
         // Read end of input file
         start = System.currentTimeMillis();
         fin.readFully(buf);
         dur = System.currentTimeMillis() - start;
         System.out.println("read took=" + dur);
   
         //Write out buffer
         start = System.currentTimeMillis();
         fout.write(buf);
         dur = System.currentTimeMillis() - start;
         System.out.println("write took=" + dur);
   
         // Now close the file
         start = System.currentTimeMillis();
         fin.close();
         fout.close();
         dur = System.currentTimeMillis() - start;
         System.out.println("Close took=" + dur);
   
         // Backup to next chunk
         seekPt = seekPt - copySize;
         if(seekPt < 0) {
            if(seekPt == -copySize)
               break;                  // Done
            seekPt = 0;
         }
         start = System.currentTimeMillis();
         fin  = new RandomAccessFile(inFile, "r");
         fout = new RandomAccessFile(outFile, "rw");
         dur = System.currentTimeMillis() - start;
         System.out.println("opens took=" + dur);
      }while(seekPt >= 0);
 
      return (int)copySize;
   } // end copy3()
 
   //-----------------------------------------------------------------------------
   // NB:  THis code hangs the system/makes it very SLOOOOOOOOOOOOW   <<<<<<<<<<<<<<<<
   // Code copied from "e172. Copying One File to Another"
   public static long copy2(String srcFilename, String destFilename) {         
       try {
           // Create channel on the source
           FileChannel srcChannel = new FileInputStream(srcFilename).getChannel();
       
           // Create channel on the destination
           FileChannel dstChannel = new FileOutputStream(destFilename).getChannel();
       
           System.out.println("copy2 of " + srcFilename + " size=" + srcChannel.size());
           long size = srcChannel.size();
           // Copy file contents from source to destination
           dstChannel.transferFrom(srcChannel, 0, srcChannel.size());
       
           // Close the channels
           srcChannel.close();
           dstChannel.close();
           System.out.println("copy2 done");
           return size;
       } catch (IOException e) {
         e.printStackTrace();
       }
       return -1;
   } // end copy2()
 
   //-----------------------------------------------------------------------------
   // Use MappedByteBuffer and Channels
public static long copy1(String inFile, String outFile) throws IOException {
 
    RandomAccessFile fin = null;
    RandomAccessFile fout = null;
       Runtime rt = Runtime.getRuntime();
 
       long ix = 0;
    long start = System.currentTimeMillis();
 
    try {
      fin  = new RandomAccessFile(inFile, "r");
      fout = new RandomAccessFile(outFile, "rw");
//      System.out.println("freeMemory=" + rt.freeMemory()+ ", totalMemory=" + rt.totalMemory());
      FileChannel in = fin.getChannel();
      FileChannel out = fout.getChannel();
      
         long dur = System.currentTimeMillis() - start;
 
         System.out.println("copy1 " + inFile  + " size is " + in.size() + ", dur=" + dur);
//      System.out.println("Before-freeMemory=" + rt.freeMemory()+ ", totalMemory=" + rt.totalMemory());
 
//      MappedByteBuffer input = in.map(FileChannel.MapMode.READ_ONLY, 0, in.size());
//      System.out.println("After0-freeMemory=" + rt.freeMemory()+ ", totalMemory=" + rt.totalMemory());
 
         // >>>>>THE Following causes the out of memory problem!!!!!!!!!!!!!!!!
//      MappedByteBuffer output = out.map(FileChannel.MapMode.READ_WRITE, 0, in.size());
//      output.put(input);
 
         // Try doing it in chunks
         long MaxRec = 0x3FFFFFF;          /* FFFFFF=16M*/
         long fileSize = in.size();
         MaxRec = Math.min(MaxRec, fileSize);  // incase too small
         System.out.println("MaxRec=" + MaxRec);
 
         for(ix = 0; ix < in.size(); ix += MaxRec) {
            // Copy file MaxRec bytes at a time
            if(ix + MaxRec > in.size())
               ix = in.size() - MaxRec;
            System.out.print("ix=" + ix + " at " + System.currentTimeMillis());  // show intermediate values
            start = System.currentTimeMillis();
         MappedByteBuffer input = in.map(FileChannel.MapMode.READ_ONLY, ix, MaxRec);
            dur = System.currentTimeMillis() - start;
            System.out.print(", map input=" + dur);
            start = System.currentTimeMillis();
         MappedByteBuffer output = out.map(FileChannel.MapMode.READ_WRITE, ix, MaxRec);
            dur = System.currentTimeMillis() - start;
            System.out.print(", map output=" + dur);
            start = System.currentTimeMillis();
            output.put(input);
            dur = System.currentTimeMillis() - start;
            System.out.println(", put=" + dur);
         } // end for(i)
 
         start = System.currentTimeMillis();
         in.close();
         out.close();
         dur = System.currentTimeMillis() - start;
         System.out.println(" close=" + dur);
         return fileSize;
      
    }catch(Exception e){
//     System.out.println(e);
          e.printStackTrace();
       System.out.println("ix=" + ix + ",  freeMemory=" + rt.freeMemory()+ ", totalMemory=" 
                                   + rt.totalMemory());
    }
       return -1;
    
} // end copy()   
} // end class
   

Results in next post

[Norm Radder]

The system rejected this when I had it tagged as QUOTE.

Fastest way to copy a large file

After reading the nio post I tried some experiments trying various ways to copy a large file.
Using


** copy2 - FileChannel 53M in 1.2 sec / 280M in 17.8-21 sec / 687M in 90-100 sec(79 w/128M)
D:\JavaDevelopment\Testing>java FileCopyTest
copy2 of E:\Downloads\Java\jdk-6-doc.zip size=54898268
copy2 done
copy time=1203, rate=45634
D:\JavaDevelopment\Testing>java FileCopyTest
copy2 of E:\Downloads\Java\jdk-6-doc.zip size=54898268
copy2 done
copy time=1031, rate=53247

D:\JavaDevelopment\Testing>java FileCopyTest
copy2 of E:\Downloads\Java.zip size=281183548
copy2 done
copy time=20969, rate=13409

D:\JavaDevelopment\Testing>java FileCopyTest
copy2 of E:\Downloads\Java.zip size=281183548
copy2 done
copy time=17656, rate=15925

D:\JavaDevelopment\Testing>java FileCopyTest
copy2 of E:\Downloads\Java.zip size=281183548
copy2 done
copy time=18985, rate=14810

D:\JavaDevelopment\Testing>java FileCopyTest
copy2 of E:\Downloads\Miscellaneous\CentOS-5.1-i386-LiveCD.iso size=720766976
copy2 done
copy time=89984, rate=8009

D:\JavaDevelopment\Testing>java -Xmx128M FileCopyTest
copy2 of E:\Downloads\Miscellaneous\CentOS-5.1-i386-LiveCD.iso size=720766976
copy2 done
copy time=79922, rate=9018

D:\JavaDevelopment\Testing>java FileCopyTest
copy2 of E:\Downloads\Miscellaneous\CentOS-5.1-i386-LiveCD.iso size=720766976
copy2 done
copy time=100703, rate=7157
>>>>>>>>>>>>> System now very sluggish/slow - effected first copy test below

-----------------------------------------------------------------------------
** copy3 - RandomAccessFile w/64M blocks 53M in 1.4-6.5sec / 280M in 23.5 sec / 687M in 65.5
D:\JavaDevelopment\Testing>java FileCopyTest
copy3 of E:\Downloads\Java\jdk-6-doc.zip to C:\Temp\jdk6doc.zip
setLength took=47, length=54898268, copySize=54898268
i/p seek took=0, seekPt=0
output seek took=0
read took=4875
write took=1078
Close took=0
copy time=6484, rate=8466

>>>>>>>>> System response time more normal
D:\JavaDevelopment\Testing>java FileCopyTest
copy3 of E:\Downloads\Java\jdk-6-doc.zip to C:\Temp\jdk6doc.zip
setLength took=0, length=54898268, copySize=54898268
i/p seek took=0, seekPt=0
output seek took=0
read took=219
write took=1047
Close took=0
copy time=1359, rate=40396 <<<<<<<<< 1.4 sec

D:\JavaDevelopment\Testing>java -Xmx128M FileCopyTest <<<<<<<<<< NB took 128M
copy3 of E:\Downloads\Java.zip to C:\Temp\java.zip
setLength took=15, length=281183548, copySize=67108863
i/p seek took=0, seekPt=214074685
output seek took=0
read took=2172
write took=5531
Close took=0
opens took=0
i/p seek took=0, seekPt=146965822
output seek took=0
read took=1938
write took=2703
Close took=0
opens took=0
i/p seek took=0, seekPt=79856959
output seek took=0
read took=1844
write took=2547
Close took=0
opens took=0
i/p seek took=0, seekPt=12748096
output seek took=0
read took=1797
write took=2672
Close took=0
opens took=0
i/p seek took=0, seekPt=0
output seek took=0
read took=593
write took=1578
Close took=0
copy time=23531, rate=2851

D:\JavaDevelopment\Testing>java -Xmx128M FileCopyTest
copy3 of E:\Downloads\Java.zip to C:\Temp\java.zip
setLength took=0, length=281183548, copySize=67108863
i/p seek took=0, seekPt=214074685
output seek took=0
read took=1890
write took=5516
Close took=0
opens took=16
i/p seek took=0, seekPt=146965822
output seek took=0
read took=1860
write took=2593
Close took=0
opens took=0
i/p seek took=0, seekPt=79856959
output seek took=0
read took=1828
write took=2672
Close took=0
opens took=0
i/p seek took=0, seekPt=12748096
output seek took=0
read took=1797
write took=2640
Close took=0
opens took=0
i/p seek took=0, seekPt=0
output seek took=0
read took=609
write took=1500
Close took=0
copy time=23093, rate=2906

D:\JavaDevelopment\Testing>java -Xmx128M FileCopyTest
copy3 of E:\Downloads\Miscellaneous\CentOS-5.1-i386-LiveCD.iso to C:\Temp\Testing.iso
setLength took=0, length=720766976, copySize=67108863
i/p seek took=0, seekPt=653658113
output seek took=0
read took=2078
write took=15672
Close took=0
opens took=0
i/p seek took=0, seekPt=586549250
output seek took=0
read took=2671
write took=2750
Close took=0
opens took=0
i/p seek took=0, seekPt=519440387
output seek took=0
read took=2063
write took=2765
Close took=0
opens took=0
i/p seek took=0, seekPt=452331524
output seek took=0
read took=2063
write took=2656
Close took=0
opens took=0
i/p seek took=0, seekPt=385222661
output seek took=0
read took=1984
write took=2625
Close took=16
opens took=0
i/p seek took=0, seekPt=318113798
output seek took=0
read took=2000
write took=2640
Close took=0
opens took=0
i/p seek took=0, seekPt=251004935
output seek took=0
read took=2000
write took=2625
Close took=0
opens took=0
i/p seek took=0, seekPt=183896072
output seek took=0
read took=2000
write took=2656
Close took=0
opens took=0
i/p seek took=0, seekPt=116787209
output seek took=0
read took=2000
write took=2578
Close took=0
opens took=0
i/p seek took=0, seekPt=49678346
output seek took=0
read took=2015
write took=2563
Close took=0
opens took=0
i/p seek took=0, seekPt=0
output seek took=0
read took=2031
write took=2891
Close took=0
copy time=65531, rate=1024

-----------------------------------------------------------------------------
** copy1 MappedByteBuffer 53M in 0.15-2.3 sec / 280M in 20-24 sec
??? Was first one slow because System sluggish from above??? 2nd&3rd VERY FAST
D:\JavaDevelopment\Testing>java -Xmx128M FileCopyTest
copy1 E:\Downloads\Java\jdk-6-doc.zip size is 54898268, dur=484
MaxRec=54898268
ix=0 at 1216742943687, map input=31, map output=78, put=1609
close=0
copy time=2281, rate=24067 <<<<<<<<<<<<<<<???

D:\JavaDevelopment\Testing>java -Xmx128M FileCopyTest
copy1 E:\Downloads\Java\jdk-6-doc.zip size is 54898268, dur=0
MaxRec=54898268
ix=0 at 1216743046937, map input=0, map output=0, put=141
close=0
copy time=157, rate=349670

D:\JavaDevelopment\Testing>java -Xmx128M FileCopyTest
copy1 E:\Downloads\Java\jdk-6-doc.zip size is 54898268, dur=16
MaxRec=54898268
ix=0 at 1216743171734, map input=0, map output=0, put=156
close=0
copy time=188, rate=292012

D:\JavaDevelopment\Testing>java -Xmx128M FileCopyTest
copy1 E:\Downloads\Java.zip size is 281183548, dur=31
MaxRec=67108863
ix=0 at 1216743254265, map input=0, map output=31, put=2000
ix=67108863 at 1216743256296, map input=0, map output=0, put=1688
ix=134217726 at 1216743257984, map input=0, map output=0, put=4875
ix=201326589 at 1216743264140, map input=31, map output=0, put=9922
ix=214074685 at 1216743274109, map input=0, map output=31, put=3594
close=562
copy time=24141, rate=11647

D:\JavaDevelopment\Testing>java -Xmx128M FileCopyTest
copy1 E:\Downloads\Java.zip size is 281183548, dur=234
MaxRec=67108863
ix=0 at 1216743448265, map input=31, map output=32, put=6172
ix=67108863 at 1216743454500, map input=0, map output=0, put=1046
ix=134217726 at 1216743455546, map input=0, map output=0, put=4344
ix=201326589 at 1216743460578, map input=78, map output=0, put=2625
ix=214074685 at 1216743464437, map input=266, map output=0, put=2547
close=625
copy time=19906, rate=14125

D:\JavaDevelopment\Testing>java -Xmx128M FileCopyTest
copy1 E:\Downloads\Java.zip size is 281183548, dur=235
MaxRec=67108863
ix=0 at 1216743575750, map input=31, map output=31, put=1734
ix=67108863 at 1216743577546, map input=0, map output=32, put=6906
ix=134217726 at 1216743585781, map input=156, map output=16, put=56250
ix=201326589 at 1216743643828, map input=203, map output=234, put=57891
ix=214074685 at 1216743704968, map input=546, map output=266, put=8750
close=500
copy time=139688, rate=2012 <<<<<<<<<<<<< OS went away ???

[Carey Evans]

I don�t know how it compares to mapping the files, but you can gain quite a bit of performance by using file channels with a direct byte buffer. For example:

final ByteBuffer buffer = ByteBuffer
.allocateDirect(Integer.parseInt(args[1]));
final FileChannel in = new FileInputStream(args[0]).getChannel();
final FileChannel out = new FileOutputStream("out.zip").getChannel();
while (in.read(buffer) > 0) {
buffer.flip();
out.write(buffer);
buffer.clear();
}
out.close();
in.close();

[Mike Simmons]

[Carey]: I don�t know how it compares to mapping the files

Or more pertinently, how it compares to using transferTo() or perhaps transferFrom(). The key here is: if you don't need to change or analyze anything about the content - if you only need to copy the bytes and nothing else: use a technique that communicates this basic intent. And trust that it may be implemented by people who aren't total morons, and are capable of being efficient once they realize that we don't care about the content, as long as it's transferred accurately. Most other APIs (really, all other Java APIs I'm aware of) try to transfer the content to some intermediate form - most commonly, a byte[] array. Which would allow our program to read individual bytes, and analyze them. If we cared to do so. But often, we don't. Why waste time transferring bytes to an intermediate readable data structure if you don't need to read the bytes? Just tell the underlying system what you want: move content from foo to bar, and don't waste time making those bytes available to our Java program (located somewhere else entirely). We don't care. Just move the bytes. That's what transferTo() and transferFrom() can accomplish.
[ July 24, 2008: Message edited by: Mike Simmons ]