java - 如果 blob 超过 2MB，getBlob() 会崩溃，substr 方法不起作用

Question

我正在尝试使用 getBlob 方法将图片检索到 byte[]。

但是，如果 blob 超过 2MB，我注意到它会崩溃。

我发现一篇文章说使用 substr 函数来分段获取它，但这不起作用。

这是我的样本，非常粗糙。

                      if( size > 2000000 ) {
                        c = db.rawQuery("SELECT substr(PICTURE, 1, 1000000)  FROM PICS WHERE ID = 1, null);
                        if( c.moveToFirst() ) {
                            byte[] image1, image2, image3, image4, image5;
                            image2 = c.getBlob(0);
                            c = db.rawQuery("SELECT substr(PICTURE, 1000001, 2000000)  FROM PICS WHERE ID = 1, null);
                            if( c.moveToFirst() ) {
                                image3 = c.getBlob(0);
                                image4 = concatenateByteArrays(image2, image3);
                                c = db.rawQuery("SELECT substr(PICTURE, 2000001, 3000000) FROM PICS WHERE ID = 1, null);
                                if( c.moveToFirst() ) {
                                    image5 = c.getBlob(0);
                                    image1 = concatenateByteArrays(image4, image5);
                                    ByteArrayInputStream inputStream = new ByteArrayInputStream(image1);
                                    Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
                                    image.setImageBitmap(bitmap);
                                }
                            }
                        }

如有任何帮助，我们将不胜感激。

谢谢。

Answer 1

这是一个很好的例子，展示了如何从 blob 列中读取数据

Class.forName("YOUR_DB_DRIER"); Connection conn = DriverManager.getConnection(url, username, password);

String sql = "SELECT name, description, image FROM pictures ";
PreparedStatement stmt = conn.prepareStatement(sql);
ResultSet resultSet = stmt.executeQuery();
while (resultSet.next()) {
  String name = resultSet.getString(1);
  String description = resultSet.getString(2);
  File image = new File("D:\\java.gif");
  FileOutputStream fos = new FileOutputStream(image);

  byte[] buffer = new byte[512]; // as much as you increase this array  
             //   it will increase the performance of you data reading. 
  InputStream is = resultSet.getBinaryStream(3);
  while (is.read(buffer) > 0) {
    fos.write(buffer);
  }
  fos.close();
}