递归：

5，复制一个文件夹里面的所有内容到另外一个文件夹，包括里面的子文件夹 

package com.studyjava.chapter5;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class Practice5 {
	public static void main(String[] args) {
		
		copyFilesWithsubFloder("D:\\dev\\test\\bw\\2\\", "D:\\dev\\test\\bw\\3\\");
	}
	
	public static void copyFilesWithsubFloder(String source, String target) {
		File src = new File(source);
		File dest = new File(target);
		
		if (src.isDirectory()) {
			for(File f: src.listFiles()) {
				if(f.isFile())
					copyFile(f, new File(target, f.getName()));//通过目标路径和文件名构造目标File文件对象,然后copy
				else {
					File newFloder = new File(target, f.getName());
					if(!newFloder.exists())
						newFloder.mkdir();//根据目标文件夹路径和源文件夹名称在目标文件夹路径建立文件夹
					copyFilesWithsubFloder(f.getAbsolutePath(),newFloder.getAbsolutePath());//复制动作
				}
			}
		}
		else {
			System.out.println("the source should be a floder.");
		}
	}
	
	public static void copyFile(File src, File dest) {
		BufferedInputStream bis = null;
		BufferedOutputStream bos = null;
		
		try {
			bis = new BufferedInputStream(new FileInputStream(src));
			bos = new BufferedOutputStream(new FileOutputStream(dest));
			
			byte[] bys = new byte[1024];
			int length = -1;
			while ((length = bis.read(bys))!=-1) {
				bos.write(bys, 0, length);
			}
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}finally {
			
			try {
				if(bis!=null)
					bis.close();
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			try {
				if(bos!=null)
					bos.close();
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}
}