code: public List<Map<String, String>> getMetadataByTable(String schema, String tableName) throws SQLException {
  		
  		List<Map<String, String>> table = new ArrayList<Map<String, String>>();
  
  		DatabaseMetaData metadata = conn.getMetaData();
  		ResultSet rs = metadata.getColumns(null, schema, tableName, null);
  		
  		while (rs.next()) {
  			
  			Map<String, String> field = new HashMap<String, String>();
  			
  			field.put("NAME",  rs.getString("COLUMN_NAME"));// 字段名称
  			field.put("TYPE", rs.getString("TYPE_NAME")); //字段类型名称(例如：VACHAR2)
  			field.put("SIZE", Integer.toString(rs.getInt("COLUMN_SIZE"))); //字段长度
  			field.put("NULLABLE", rs.getString("IS_NULLABLE")); //是否为空
  			field.put("REMARK", rs.getString("REMARKS")); //字段注释
  			
  			table.add(field);
  			
  		}
  
  		return table;
  	}
docs: 通过表名获取元数据信息
  
  @param schema 模式名称
  @param tableName 表名称
  
  @return 元数据信息
  
  @throws SQLException SQL执行异常