android编程实现sd卡读取数据库的方法

<uses-permission android:name="android.permission.write_external_storage" />
<uses-permission android:name="android.permission.mount_unmount_filesystems" />

sqlitedatabase db;
private final string database_path = android.os.environment
 .getexternalstoragedirectory().getabsolutepath() + "/vote";
private string database_filename = "db_vote.db";
// 初始化数据库
private sqlitedatabase opendatabase() {
  try {
   string databasefilename = database_path + "/" + database_filename;
   file dir = new file(database_path);
   if (!dir.exists())
    dir.mkdir();
   if (!(new file(databasefilename)).exists()) {
    inputstream is = getresources().openrawresource(r.raw.db_vote);
    fileoutputstream fos = new fileoutputstream(databasefilename);
    byte[] buffer = new byte[8192];
    int count = 0;
    while ((count = is.read(buffer)) > 0) {
     fos.write(buffer, 0, count);
    }
    fos.close();
    is.close();
   }
   db = sqlitedatabase.openorcreatedatabase(databasefilename, null);
   return db;
  } catch (exception e) {
   e.printstacktrace();
  }
  return null;
}