Simple method of replicating the file structure inc files from one drive/directory to another.

Backup.java

package backup;

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

public class Backup {
	
	
	private File SourceDrive;
	private File TargetDrive;

	public static void main(String[] args) {
		// TODO Auto-generated method stub

		Backup process = new Backup();
		process.start();
	}
	
	public Backup(){
		this.SourceDrive =  new File("H:\\");
		this.TargetDrive = new File("I:\\");
	}
	
	public void start(){
		
		if(SourceDrive == null || !SourceDrive.exists()){
			System.out.println("ERROR: The source drive/directory does not exist.");
			System.exit(0);
		}
		
		if(TargetDrive == null || !TargetDrive.exists()){
			System.out.println("ERROR: The target drive/directory does not exist.");
			System.exit(0);
		}
		
		long start = System.nanoTime();
		
		processSource(SourceDrive);
		processTarget(TargetDrive);
		
		long finish = System.nanoTime();
		System.out.println("Execution time = " + (finish-start)/1000000f + " milliseconds ");
	}
	
	/**
	 * get relative path in respect to either the source directory
	 * or the target directory.
	 * 
	 * @param path
	 * @return
	 */
	private String getRelativePath(String path){

		String result = null;
		
		if(path.startsWith(SourceDrive.getAbsolutePath())){
			result = path.substring(SourceDrive.getAbsolutePath().length());
		}else if(path.startsWith(TargetDrive.getAbsolutePath())){
			result = path.substring(TargetDrive.getAbsolutePath().length());
		}
		
		return result;
	}
	
	
	public void processSource(File source){
		
		File targetFile = new File(TargetDrive+getRelativePath(source.getAbsolutePath()));
		
		if(source.isFile()){
			
			
			if(targetFile.exists()){
				if(targetFile.lastModified() < source.lastModified()){
					//replace file
					System.out.println("Replaced in target: "+getRelativePath(source.getAbsolutePath()));
					try {
						copyFile(source, targetFile);
					} catch (IOException e) {
						e.printStackTrace();
						System.exit(0);
					}
				}
			}else{
				//create and copy file/directory
				System.out.println("Created in target: "+getRelativePath(source.getAbsolutePath()));
				try {
					copyFile(source, targetFile);
				} catch (IOException e) {
					e.printStackTrace();
					System.exit(0);
				}
			}
			
			
		}else{
			
			targetFile.mkdirs();
			
			for(File f: source.listFiles()){
				processSource(f);
			}
		}
		
	}
	
	
	/**
	 * this method will delete any files stored on the target
	 * that are not present in the source
	 */
	public void processTarget(File target){
		
		File sourceFile = new File(SourceDrive+getRelativePath(target.getAbsolutePath()));
			
		if(target.isDirectory()){
			for(File f: target.listFiles()){
				processTarget(f);
			}	
		}
		
		if(!sourceFile.exists()){
			System.out.println("Removed from target: "+getRelativePath(target.getAbsolutePath()));
			target.delete();
		}
					
	}

	
	public static void copyFile(File sourceFile, File destFile) throws IOException {
	    if(!destFile.exists()) {
	        destFile.createNewFile();
	    }

	    FileChannel source = null;
	    FileChannel destination = null;

	    try {
	        source = new FileInputStream(sourceFile).getChannel();
	        destination = new FileOutputStream(destFile).getChannel();
	        destination.transferFrom(source, 0, source.size());
	    }
	    finally {
	        if(source != null) {
	            source.close();
	        }
	        if(destination != null) {
	            destination.close();
	        }
	    }
	}
	

}