如何在jdbc中使用ResultSet.getBinaryStream()从所有列中获取值?

Question

如何使用jdbc将整个表写入平面文件(文本文件)?到目前为止，我尝试了以下操作:

Statement statement = connection.createStatement();
   ResultSet result = statement.executeQuery("SELECT * FROM tablename");
   BufferedInputStream buffer;
   FileOutputStream out = new FileOutputStream("flatfile.txt");
   while(result.next() )
   {
      buffer =  new BufferedInputStream(result.getBinaryStream("????") );
      byte[] buf = new byte[4 * 1024]; //4K buffer
      int len;
      while( (len = buffer.read(buf, 0, buf.length) ) != -1 )
      {
          out.write(buf, 0, len );
      }
   }
   out.close();

"????"只是我的占位符。

Answer 1

可以使用下面的代码从表中获取所有列名和整个数据。writeToFile方法将包含写入文件的逻辑(如果这还不够明显:))

    ResultSetMetaData metadata = rs.getMetaData();
    int columnCount = metadata.getColumnCount();    
    for (int i = 1; i <= columnCount; i++) {
        writeToFile(metadata.getColumnName(i) + ", ");      
    }
    System.out.println();
    while (rs.next()) {
        String row = "";
        for (int i = 1; i <= columnCount; i++) {
            row += rs.getString(i) + ", ";          
        }
        System.out.println();
        writeToFile(row);
    }

Answer 2

下面是我如何从JDBC连接中转储表的，如果您想查看内存中(例如:HSQL) DB中的所有行，这对于调试非常有用:

  public static void spitOutAllTableRows(String tableName, Connection conn) {
    try {
      System.out.println("current " + tableName + " is:");
      try (PreparedStatement selectStmt = conn.prepareStatement(
              "SELECT * from " + tableName, ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);
           ResultSet rs = selectStmt.executeQuery()) {
        if (!rs.isBeforeFirst()) {
          System.out.println("no rows found");
        }
        else {
          System.out.println("types:");
          for (int i = 0; i < rs.getMetaData().getColumnCount(); i++) {
            System.out.print(rs.getMetaData().getColumnName(i + 1) + ":" + rs.getMetaData().getColumnTypeName(i + 1) + " ");
          }
          System.out.println();
          while (rs.next()) {
            for (int i = 1; i < rs.getMetaData().getColumnCount() + 1; i++) {
              System.out.print(" " + rs.getMetaData().getColumnName(i) + "=" + rs.getObject(i));
            }
            System.out.println("");
          }
        }
      }
    }
    catch (SQLException e) {
      throw new RuntimeException(e);
    }
  }

输出类似于

 current <yourtablename> is:
 types:ID:INT YOURCOLUMN1:VARCHAR YOURCOLUMN2:VARCHAR
 ID=1 YOURCOLUMN1=abc YOURCOLUMN2=null
 ID=2 YOURCOLUMN1=def YOURCOLUMN2=ghi
 ...

Answer 3

result.getBinaryStream("????")将只返回作为占位符的列的值。

如果您想获得所有列，则需要使用ResultSet

中的ResultSetMetaData

    ResultSetMetaData metadata = resultSet.getMetaData();
    int columnCount = metadata.getColumnCount();
    for (int i=1; i<=columnCount; i++) 
    {
        String columnName = metadata.getColumnName(i);
        System.out.println(columnName);
    }