Java复制文件夹下所有内容

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;

public class Test {

    public static void main(String[] args) {
        try {
            new Test().copyDir("demo", "test");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void copyDir(String from, String to) throws IOException {
        File folder = new File(to);
        if(!folder.exists() && !folder.isDirectory()) folder.mkdir();
        File f = new File(from);
        File[] it = f.listFiles();
        for (int i = 0; i < it.length; i++) {
            String str1 = it[i].toString();
            String str2 = str1.replace(from, to);
            if (new File(str1).isDirectory()) {
                new File(str2).mkdir();
                copyDir(str1,str2);
            } else {
                InputStream input = null;
                OutputStream output = null;
                try {
                    input = new FileInputStream(str1);
                    output = new FileOutputStream(str2);
                    byte[] buf = new byte[1024];
                    int bytesRead;
                    while ((bytesRead = input.read(buf)) > 0) {
                        output.write(buf, 0, bytesRead);
                    }
                } finally {
                    input.close();
                    output.close();
                }
            }
        }
    }

}