Copy a file

http://www.javapractices.com/topic/TopicAction.do?Id=246

In JDK 7+, copying a file is a simple operation, involving a single call to File.copy.

Example 

import java.io.IOException;import java.nio.file.CopyOption;import java.nio.file.Files;import java.nio.file.Path;import java.nio.file.Paths;import java.nio.file.StandardCopyOption;/** JDK 7+. */public final class CopyFilesNew {    public static void main(String... aArgs) throws IOException {    Path FROM = Paths.get("C:\\Temp\\from.txt");    Path TO = Paths.get("C:\\Temp\\to.txt");    //overwrite existing file, if exists    CopyOption[] options = new CopyOption[]{      StandardCopyOption.REPLACE_EXISTING,      StandardCopyOption.COPY_ATTRIBUTES    };     Files.copy(FROM, TO, options);  }} 

In older JDKs, however, copying a file involves a lot more code. It can be done either with FileChannels or with basic streams. The FileChanneltechnique is usually faster.

Here's an example showing both techniques. 

import java.io.BufferedInputStream;import java.io.BufferedOutputStream;import java.io.File;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;import java.nio.channels.FileChannel;/**  Copy files, using two techniques, FileChannels and streams. Using FileChannels is usually faster than using streams. JDK 6-.*/public final class CopyFiles {    /* Change these settings before running this class. */    /** The file to be copied. */  public static final String INPUT_FILE = "C:\\TEMP\\cottage.jpg";    /**   The name of the copy to be created by this class.     If this file doesn't exist, it will be created, along with any    needed parent directories.    */  public static final String COPY_FILE_TO = "C:\\TEMP10\\cottage_2.jpg";    /** Run the example. */  public static void main(String... aArgs) throws IOException{    File source = new File(INPUT_FILE);    File target = new File(COPY_FILE_TO);    CopyFiles test = new CopyFiles();    test.copyWithChannels(source, target, false);    //test.copyWithStreams(source, target, false);    log("Done.");  }  /** This may fail for VERY large files. */  private void copyWithChannels(File aSourceFile, File aTargetFile, boolean aAppend) {    log("Copying files with channels.");    ensureTargetDirectoryExists(aTargetFile.getParentFile());    FileChannel inChannel = null;    FileChannel outChannel = null;    FileInputStream inStream = null;    FileOutputStream outStream = null;    try{      try {        inStream = new FileInputStream(aSourceFile);        inChannel = inStream.getChannel();        outStream = new  FileOutputStream(aTargetFile, aAppend);                outChannel = outStream.getChannel();        long bytesTransferred = 0;        //defensive loop - there's usually only a single iteration :        while(bytesTransferred < inChannel.size()){          bytesTransferred += inChannel.transferTo(0, inChannel.size(), outChannel);        }      }      finally {        //being defensive about closing all channels and streams         if (inChannel != null) inChannel.close();        if (outChannel != null) outChannel.close();        if (inStream != null) inStream.close();        if (outStream != null) outStream.close();      }    }    catch (FileNotFoundException ex){      log("File not found: " + ex);    }    catch (IOException ex){      log(ex);    }  }    private void copyWithStreams(File aSourceFile, File aTargetFile, boolean aAppend) {    log("Copying files with streams.");    ensureTargetDirectoryExists(aTargetFile.getParentFile());    InputStream inStream = null;    OutputStream outStream = null;    try{      try {        byte[] bucket = new byte[32*1024];        inStream = new BufferedInputStream(new FileInputStream(aSourceFile));        outStream = new BufferedOutputStream(new FileOutputStream(aTargetFile, aAppend));        int bytesRead = 0;        while(bytesRead != -1){          bytesRead = inStream.read(bucket); //-1, 0, or more          if(bytesRead > 0){            outStream.write(bucket, 0, bytesRead);          }        }      }      finally {        if (inStream != null) inStream.close();        if (outStream != null) outStream.close();      }    }    catch (FileNotFoundException ex){      log("File not found: " + ex);    }    catch (IOException ex){      log(ex);    }  }    private void ensureTargetDirectoryExists(File aTargetDir){    if(!aTargetDir.exists()){      aTargetDir.mkdirs();    }  }    private static void log(Object aThing){    System.out.println(String.valueOf(aThing));  }}