import java.io.*;

public class CopyFolder {

  public static void main(String[] args) {
      File srcDir = new File("F:/test");
      File dstDir = new File("G:/test");
      try {
        copyDirectory(srcDir, dstDir);
      } catch (IOException ioe) {
        ioe.printStackTrace();
      }
  }

    // Copies all files under srcDir to dstDir.
    // If dstDir does not exist, it will be created.
    static void copyDirectory(File srcDir, File dstDir) throws IOException {
        if (srcDir.isDirectory()) {  // 1.判断File是否文件夹，是则跳到步骤3
            if (!dstDir.exists()) {
                dstDir.mkdir();
            }
    
// 3.遍历文件夹下的所有文件（夹），以每个文件（夹）的File作为条件进入到步骤1（递归） 
            String[] children = srcDir.list();
            for (int i=0; i<children.length; i++) {
                copyDirectory(new File(srcDir, children[i]),
                                     new File(dstDir, children[i]));
            }
        } else {
// ~2.[构造目标文件的URL，并] 通过IO进行文件复制
            // This method is implemented in e1071 Copying a File
            copyFile(srcDir, dstDir);
        }
    }
    
    // Copies src file to dst file.
    // If the dst file does not exist, it is created
    static void copyFile(File src, File dst) throws IOException {
        InputStream in = new FileInputStream(src);
        OutputStream out = new FileOutputStream(dst);
    
        // Transfer bytes from in to out
        byte[] buf = new byte[1024];
        int len;
        while ((len = in.read(buf)) > 0) {
            out.write(buf, 0, len);
        }
        in.close();
        out.close();
    }
}

import java.io.*;

public class CopyFolder {

  public static void main(String[] args) {
      CopyFolder cf = new CopyFolder();

      File srcDir = new File("C:/temp/1");
      File dstDir = new File("C:/temp/2");
      try {
        cf.copyDirectory(srcDir, dstDir);
      } catch (IOException ioe) {
        ioe.printStackTrace();
      }
  }

    // Copies all files under srcDir to dstDir.
    // If dstDir does not exist, it will be created.
    void copyDirectory(File srcDir, File dstDir) throws IOException {
... 
    }
    
    // Copies src file to dst file.
    // If the dst file does not exist, it is created
    void copyFile(File src, File dst) throws IOException {
...
    }
}