<!--在SDCard中创建与删除文件权限 -->
<uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
<!-- 往SDCard写入数据权限 -->
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<!-- 从SDCard读取数据权限 -->
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

/**
* Environment.getExternalStorageDirectory()得到：“、mnt/sdcard” 即找到了sd卡的根目录
*/
private String path=Environment.getExternalStorageDirectory()+"client/tile/1.jpg";

File mFile=new File(path);
//若该文件存在
if (mFile.exists()) {
  Bitmap bitmap=BitmapFactory.decodeFile(path);
  return bitmap;
}

/**
* Environment.getExternalStorageState()获取路径是否成功
*/
if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
  String path=Environment.getExternalStorageDirectory().getPath();
}

private String path=Environment.getExternalStorageDirectory()+"client";
File file=new File(path);
if (file.canRead()) {
  Log.v("TAG", "可读");
}
if (file.canWrite()) {
  Log.v("TAG", "可写");
}