读取Assets所存在的所有文件(遍历每一个文件夹)，并存入sdcard里面

private void CopyAssets(String assetDir, String dir) {
        String[] files;
        try {
            // 获得Assets一共有几多文件
            files = this.getResources().getAssets().list(assetDir);
        } catch (IOException e1) {
            return;
        }
        File mWorkingPath = new File(dir);
        // 如果文件路径不存在
        if (!mWorkingPath.exists()) {
            // 创建文件夹
            if (!mWorkingPath.mkdirs()) {
                // 文件夹创建不成功时调用
            }
        }

        for (int i = 0; i < files.length; i++) {
            try {
                // 获得每个文件的名字
                String fileName = files[i];
                // 根据路径判断是文件夹还是文件
                if (!fileName.contains(".")) {
                    if (0 == assetDir.length()) {
                        CopyAssets(fileName, dir + fileName + "/");
                    } else {
                        CopyAssets(assetDir + "/" + fileName, dir + "/"
                                + fileName + "/");
                    }
                    continue;
                }
                File outFile = new File(mWorkingPath, fileName);
                if (outFile.exists())
                    outFile.delete();
                InputStream in = null;
                if (0 != assetDir.length())
                    in = getAssets().open(assetDir + "/" + fileName);
                else
                    in = getAssets().open(fileName);
                OutputStream out = new FileOutputStream(outFile);

                // 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();
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }

            catch (IOException e) {
                e.printStackTrace();
            }
        }

    }