filecopy.java

拷贝文件的java程序

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.nio.channels.FileChannel;

public class FileCopy{
	public static void main(String[] args){
		if(args.length == 0){
			System.out.println("No file to copy. Application usage is:\n" +
													"java -classpath . FileCopy \"filepath\"");
			System.exit(1);
		}
		File fromFile = new File(args[0]);
		if(!fromFile.exists()){
			System.out.printf("File to copy, %s, does not exist.",fromFile.getAbsolutePath());
			System.exit(1);
		}
		
		File toFile = createBackupFile(fromFile);
		FileInputStream inFile = null;
		FileOutputStream outFile = null;
		try{
			inFile = new FileInputStream(fromFile);
			outFile = new FileOutputStream(toFile);
		}catch(FileNotFoundException e){
			e.printStackTrace(System.err);
			assert false;
		}
		
		FileChannel inChannel = inFile.getChannel();
		FileChannel outChannel = outFile.getChannel();
		
		try{
			int bytesWritten = 0;
			long byteCount = inChannel.size();
			while(bytesWritten < byteCount){
				bytesWritten += inChannel.transferTo(bytesWritten,
																						 byteCount - bytesWritten,
																						 outChannel);
			}
			System.out.printf("File copy complete. %d bytes copied to %s%n",
																			byteCount,toFile.getAbsolutePath());
			inFile.close();
			outFile.close();
		}catch(IOException e){
			e.printStackTrace(System.err);
			System.exit(1);
		}
		System.exit(0);
	}
	
	//Method to create a unique backup File object
	public static File createBackupFile(File aFile){
		aFile = aFile.getAbsoluteFile();            //Ensure you have an absolute path
		File parentDir = new File(aFile.getParent());    //Get the parent directory
		String name = aFile.getName();                   //Get the file name
		int period = name.indexOf(".");             //Find the extension separator
		if(period == -1){                           //If there isn't one
			period = name.length();                   //set it to the end of the string
		}
		String nameAdd = "_backup";                 //String to be appended
		
		//Create a File Object that is unique
		File backup = aFile;
		while(backup.exists()){                     //If the name already exists...
			name = backup.getName();                  //Get the current name of the file
			backup = new File(parentDir,name.substring(0,period)  // add _backup again
												+ nameAdd + name.substring(period));
			period += nameAdd.length();               //Increment separator index
		}
		return backup;
	}
}