postgresql jdbc 瞭解postgresql數據庫對jdbc的參數設置

  postgresql jdbc 鏈接到postgresql 數據庫時，postgresql數據庫會返回一些參數來設置jdbc。postgresql 是經過發送類型爲S的數據包給客戶端的。本文主要講解jdbc中針對哪些參數進行了使用。

  經過搜索jdbc的源碼，能夠找到只有三個函數中針對參數進行了處理，這三個函數分別爲：readStartupMessages，processCopyResults，processResults。第一個函數是處理創建鏈接時的數據包的。第二個參數從名字看應該是處理copy功能時的函數。第三個參數處理的大部分操做的數據包。

    在這三個函數中，readStartupMessages函數處理的參數分別爲：server_version_num，client_encoding，standard_conforming_strings，integer_datetimes。processCopyResults和processResults函數中只處理了client_encoding，DateStyle，standard_conforming_strings這三個參數，其餘的參數都被忽略掉了。

    可是從9.4的postgresql數據庫的通訊看，傳遞了不少參數給客戶端，下面是經過jdbc的調試功能獲得的數據庫端設置jdbc端的參數狀況：

<=BE ParameterStatus(application_name = )
<=BE ParameterStatus(client_encoding = UTF8)
<=BE ParameterStatus(DateStyle = ISO, YMD)
<=BE ParameterStatus(integer_datetimes = on)
<=BE ParameterStatus(IntervalStyle = postgres)
<=BE ParameterStatus(is_superuser = on)
<=BE ParameterStatus(server_encoding = UTF8)
<=BE ParameterStatus(server_version = 9.4.4)
<=BE ParameterStatus(session_authorization = db_user)
<=BE ParameterStatus(standard_conforming_strings = on)
<=BE ParameterStatus(TimeZone = Asia/Shanghai)
<=BE BackendKeyData(pid=22833,ckey=1140395019)

上面參數中integer_datetimes若是爲on，則表明日期能夠使用double類型來進行通訊。standard_conforming_strings則是針對字符串的處理的設置。若是爲on，則不把\當作轉義。

下面是上述三個函數的詳細代碼：

readStartupMessages

case 'S':
	// ParameterStatus
	int l_len = pgStream.ReceiveInteger4();
	String name = pgStream.ReceiveString();
	String value = pgStream.ReceiveString();
	
	if (logger.logDebug())
	    logger.debug(" <=BE ParameterStatus(" + name + " = " + value + ")");
	
	if (name.equals("server_version_num"))
	    protoConnection.setServerVersionNum(Integer.parseInt(value));
	if (name.equals("server_version"))
	    protoConnection.setServerVersion(value);
	else if (name.equals("client_encoding"))
	{
	    if (!value.equals("UTF8"))
	        throw new PSQLException(GT.tr("Protocol error.  Session setup failed."), PSQLState.PROTOCOL_VIOLATION);
	    pgStream.setEncoding(Encoding.getDatabaseEncoding("UTF8"));
	}
	else if (name.equals("standard_conforming_strings"))
	{
	    if (value.equals("on"))
	        protoConnection.setStandardConformingStrings(true);
	    else if (value.equals("off"))
	        protoConnection.setStandardConformingStrings(false);
	    else
	        throw new PSQLException(GT.tr("Protocol error.  Session setup failed."), PSQLState.PROTOCOL_VIOLATION);
	}
	else if (name.equals("integer_datetimes"))
	{
	    if (value.equals("on"))
	        protoConnection.setIntegerDateTimes(true);
	    else if (value.equals("off"))
	        protoConnection.setIntegerDateTimes(false);
	    else
	        throw new PSQLException(GT.tr("Protocol error.  Session setup failed."), PSQLState.PROTOCOL_VIOLATION);
	}
	
	break;

processCopyResults：

case 'S':    // Parameter Status
{
    int l_len = pgStream.ReceiveInteger4();
    String name = pgStream.ReceiveString();
    String value = pgStream.ReceiveString();
    if (logger.logDebug())
        logger.debug(" <=BE ParameterStatus(" + name + " = " + value + ")");

    if (name.equals("client_encoding") && !value.equalsIgnoreCase("UTF8") && !allowEncodingChanges)
    {
        protoConnection.close(); // we're screwed now; we can't trust any subsequent string.
        error = new PSQLException(GT.tr("The server''s client_encoding parameter was changed to {0}. The JDBC driver requires client_encoding to be UTF8 for correct operation.", value), PSQLState.CONNECTION_FAILURE);
        endReceiving = true;
    }

    if (name.equals("DateStyle") && !value.startsWith("ISO,"))
    {
        protoConnection.close(); // we're screwed now; we can't trust any subsequent date.
        error = new PSQLException(GT.tr("The server''s DateStyle parameter was changed to {0}. The JDBC driver requires DateStyle to begin with ISO for correct operation.", value), PSQLState.CONNECTION_FAILURE);
        endReceiving = true;
    }
    
    if (name.equals("standard_conforming_strings"))
    {
        if (value.equals("on"))
            protoConnection.setStandardConformingStrings(true);
        else if (value.equals("off"))
            protoConnection.setStandardConformingStrings(false);
        else
        {
            protoConnection.close(); // we're screwed now; we don't know how to escape string literals
            error = new PSQLException(GT.tr("The server''s standard_conforming_strings parameter was reported as {0}. The JDBC driver expected on or off.", value), PSQLState.CONNECTION_FAILURE);
            endReceiving = true;
        }
    }
}

processResults

case 'S':    // Parameter Status
  {
      int l_len = pgStream.ReceiveInteger4();
      String name = pgStream.ReceiveString();
      String value = pgStream.ReceiveString();
      if (logger.logDebug())
          logger.debug(" <=BE ParameterStatus(" + name + " = " + value + ")");

      if (name.equals("client_encoding") && !value.equalsIgnoreCase("UTF8") && !allowEncodingChanges)
      {
          protoConnection.close(); // we're screwed now; we can't trust any subsequent string.
          handler.handleError(new PSQLException(GT.tr("The server''s client_encoding parameter was changed to {0}. The JDBC driver requires client_encoding to be UTF8 for correct operation.", value), PSQLState.CONNECTION_FAILURE));
          endQuery = true;
      }

      if (name.equals("DateStyle") && !value.startsWith("ISO,"))
      {
          protoConnection.close(); // we're screwed now; we can't trust any subsequent date.
          handler.handleError(new PSQLException(GT.tr("The server''s DateStyle parameter was changed to {0}. The JDBC driver requires DateStyle to begin with ISO for correct operation.", value), PSQLState.CONNECTION_FAILURE));
          endQuery = true;
      }
      
      if (name.equals("standard_conforming_strings"))
      {
          if (value.equals("on"))
              protoConnection.setStandardConformingStrings(true);
          else if (value.equals("off"))
              protoConnection.setStandardConformingStrings(false);
          else
          {
              protoConnection.close(); // we're screwed now; we don't know how to escape string literals
              handler.handleError(new PSQLException(GT.tr("The server''s standard_conforming_strings parameter was reported as {0}. The JDBC driver expected on or off.", value), PSQLState.CONNECTION_FAILURE));
              endQuery = true;
          }
      }
  }