Java：从Oracle读取Blob

我有这个代码将Treemap转换为字节并将它们存储在数据库（Oracle 11g）中。 现在存储似乎工作正常。 我想现在检索地图，但它在blob字段中以字节为单位。 如何检索和重新构建地图？

存储地图的代码是：

public void StoreMapDB(TreeMap map) throws IOException, FileNotFoundException{ try { Connection con = null; Class.forName("oracle.jdbc.driver.OracleDriver"); con=DriverManager.getConnection( "jdbc:oracle:thin:@dsds", "dsdsd", "XXdsdsX"); con.setAutoCommit(false); ByteArrayOutputStream bos = new ByteArrayOutputStream() ; ObjectOutputStream out = new ObjectOutputStream(bos); out = new ObjectOutputStream(bos) ; out.writeObject(map); out.close(); byte[] buf = bos.toByteArray(); PreparedStatement prepareStatement = con.prepareStatement("INSERT INTO SMD_DATESTREEMAP VALUES(?,?)"); prepareStatement.setLong(1, 2); prepareStatement.setBinaryStream(2, new ByteArrayInputStream(buf), buf.length); prepareStatement.executeUpdate(); // insertMap.executeUpdate(); con.commit(); } catch(Exception e){ System.err.print(e); } } 

PS我编辑了这段代码但不认为它有效，因为它将检索到的地图的大小显示为0，它应该是366。

  public TreeMap retrieveMapDB()throws IOException, SQLException{ try { Connection con = null; Class.forName("oracle.jdbc.driver.OracleDriver"); con=DriverManager.getConnection( "jdbc:oracle:thin:@oradbfdfdt05:f:fdfd", "cxcx", "hpdbcxcxsmb"); con.setAutoCommit(false); ResultSet rs = null; PreparedStatement pstmt = null; String query = "SELECT TREEMAP FROM SMD_DATESTREEMAP WHERE id = ?"; try { pstmt = con.prepareStatement(query); int id = 1; pstmt.setInt(1, id); rs = pstmt.executeQuery(); while(rs.next()){ ByteArrayInputStream bos = new ByteArrayInputStream(rs.getBytes("TREEMAP")) ; ObjectInputStream out = new ObjectInputStream(bos); retrievedmap=(TreeMap)out.readObject(); } }catch(IOException ioe){ System.err.print(ioe); } }catch(ClassNotFoundException cnfe){ System.err.print(cnfe); } return retrievedmap; } 

Answer 1

您可以通过ResultSet.getBinaryStream()方法获取InputStream对象。

 PreparedStatement prepareStatement = con.prepareStatement("select * from SMD_DATESTREEMAP"); ResultSet rs=prepareStatement.executeQuery(); while(rs.next()) { oracle.jdbc.driver.OracleBlobInputStream bos=(oracle.jdbc.driver.OracleBlobInputStream) rs.getBinaryStream(2) ; ObjectInputStream out = new ObjectInputStream(bos); map=(TreeMap)out.readObject(); ... } 

您可以编写字节数组而不是二进制流。

  ByteArrayOutputStream bos = new ByteArrayOutputStream() ; ObjectOutputStream out = new ObjectOutputStream(bos); out.writeObject(map); out.flush(); out.close(); byte[] buf = bos.toByteArray(); PreparedStatement prepareStatement = con.prepareStatement("INSERT INTO SMD_DATESTREEMAP VALUES(?,?)"); prepareStatement.setInt(1, 1); prepareStatement.setBytes(2, buf); prepareStatement.executeUpdate(); prepareStatement.close(); 

并读取字节数组：

  while(rs.next()) { byte []buf=rs.getBytes(2); ByteArrayInputStream bos=new ByteArrayInputStream(buf); ObjectInputStream out = new ObjectInputStream(bos); map=(TreeMap)out.readObject(); .. } 

Answer 2

感谢AVD的大力支持，这也最符合我的代码/问题。 所以答案就在这里…… 来自Oracle的BLOB

与AVD的答案相辅相成的片段是：

  Blob blob = rs.getBlob("col_blob"); // Get the number bytes in the BLOB long blobLength = blob.length(); // Get bytes from the BLOB in a byte array int pos = 1; // position is 1-based int len = 10; byte[] bytes = blob.getBytes(pos, len); 

希望这会有所帮助，如果有人需要澄清，我将不仅仅是快乐：D