用 FileChannel 拷贝文件

原文链接：http://www.2cto.com/kf/201108/102100.html

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.
 */
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);
		}
	}

	public 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));
	}
}