package testNew;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

public class Test {
    public final static Map<String,String> fileMap = new HashMap<String,String>();
    public final static String readFileName = "D:" + File.separator + "hello";
    public final static String writeFileName = "D:" + File.separator + "back";
    public static void main(String[] args) {
        ReadThread read = new ReadThread();
        WriteThread write = new WriteThread();
        read.start();
        write.start();
    }
    /**
     *返回目录下文件 
     */
    public static List<String> printfFile(String fileName){
        File file = new File(fileName);
        String[] fileList  = file.list();//获得该目录下所有文件的名字，包含隐藏文件
        for(String s : fileList){
            System.out.println(s);
        }
        return Arrays.asList(fileList);
    }
    /**
     *拷贝文件 
     */
    public static void copyFile(String fileName,String fileName1) throws IOException {
        File file = new File(fileName);
        File file1 = new File(fileName1);
        FileInputStream fileStream = new FileInputStream(file);
        FileOutputStream fileOutStream = new FileOutputStream(file1);
        byte[] byteArray = new byte[1024];
        int temp = 0;
        while((temp = fileStream.read(byteArray))!=-1){
            fileOutStream.write(byteArray, 0, temp);
        }
        fileStream.read(byteArray);
        fileStream.close();
        fileOutStream.close();
    }
    
} 
class ReadThread extends Thread{
    
    public void run() {
        while(true){
            List<String> readList = Test.printfFile(Test.readFileName);
            for(String str : readList){
                if(Test.fileMap.containsKey(str)){
                    continue;
                } else
                    Test.fileMap.put(str, str);
            }
            try {
                Thread.sleep(5000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    
}
class WriteThread extends Thread{
    
    public void run() {
        while(true){
            try {
                Thread.sleep(5000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            List<String> writeList =Test.printfFile(Test.writeFileName);
            for(Iterator it = Test.fileMap.keySet().iterator();it.hasNext();){
                String     key = (String)it.next();
                boolean flag = false;
                for(String str : writeList){
                    if(str.equalsIgnoreCase(key)){
                        flag = true;
                        break;
                    }
                }
                if(!flag){
                    try {
                        Test.copyFile(Test.readFileName + File.separator + key,Test.writeFileName + File.separator + key);
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }
}

------解决方案--------------------

基本逻辑是这样的，楼主发现问题，或者可以根据自己需求自己改一改。

Java code
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.util.HashSet;
import java.util.Set;

public class FilesListener implements Runnable{

    private String fileDir = "d://from";
    private String newFileDir = "d://to";
    private Set<String> oldFiles = new HashSet<String>();
    
    public FilesListener(){
        File[] files = new File(fileDir).listFiles();
        if(files != null){
            for(File file : files){
                oldFiles.add(file.getName());
            }
        }
    }
    
    private Set<String> checkNewFiles(){
        Set<String> nowFiles = new HashSet<String>();
        File[] files = new File(fileDir).listFiles();
        if(files != null){
            for(File file : files){
                nowFiles.add(file.getName());
            }
        }
        
        if(nowFiles.size() > oldFiles.size()){
            Set<String> addFiles = new HashSet<String>();
            addFiles.addAll(nowFiles);
            addFiles.removeAll(oldFiles);
            
            oldFiles.addAll(addFiles);
            return addFiles;
        }
        return null;
    }
    
    private void copyFiles(Set<String> addFiles) {
        
        for (String file : addFiles) {
            try {
                String oldFileName = fileDir + "//" + file;
                BufferedInputStream bis = new BufferedInputStream(new FileInputStream(oldFileName));
                String newFileName = newFileDir + "//" + file;
                BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(newFileName));
                byte[] buf = new byte[1024];
                int read = -1;
                while((read = bis.read(buf)) > 0){
                    bos.write(buf,0,read);
                }

                bos.close();
                bis.close();
                System.out.println("复制文件：" + file);
            }
            catch (Exception e) {
                e.printStackTrace();
            }
        }

    }
    
    public void run() {
        Set<String> addFiles = checkNewFiles();
        if (addFiles != null) {
            copyFiles(addFiles);
        }
        try {
            Thread.sleep(3000);
            run();
        }
        catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    public static void main(String[] args) {
        FilesListener fl = new FilesListener();
        new Thread(fl).start();
    }
}