高級隊列（AQ）是內(nèi)置在Oracle服務(wù)器上的一個靈活的信息交流機制，使用這個高級隊列，你可以將來自一個工作站或服務(wù)器的信息發(fā)送到一個或是多個工作站上。dotConnect for Oracle采用類集合來充分的利用這項技術(shù)。

首先來看一下高級隊列（AQ），主要通過下面的幾部分來具體的了解：

• AQ基本
• Oracle dotConnect中的AQ組件
• 點到點的信息示例
• 點到點信息的擴展示例
• 點到多點信息的示例

AQ基本

   高級隊列提供了數(shù)據(jù)庫集成的消息隊列功能，高級隊列信息可以持久存儲、不同數(shù)據(jù)或是數(shù)據(jù)庫上隊列之間的傳播、使用Oracle網(wǎng)絡(luò)服務(wù)的傳輸、HTTP、SMTP。

    由于Oracle高級隊列是在數(shù)據(jù)庫表上實現(xiàn)的，高可用性、可擴展性和可靠性完全適用于隊列的數(shù)據(jù)。這項技術(shù)是由DBMS_AQ 和DBMS_AQADM2個包實現(xiàn)，DBMS_AQ包管理隊列的信息，如入隊和出隊，DBMS_AQADM則是負責(zé)管理生命周期以及屬性。

    支持標準的數(shù)據(jù)庫功能，如恢復(fù)、重啟、安全性、以及隊列表的導(dǎo)入好和導(dǎo)出，還支持信息管理功能和異步通信功能。

    下面是AQ的兩種功能模式：點對點模型和發(fā)布訂閱模型。在第一個中，將會有應(yīng)用程序發(fā)送消息到隊列（稱為enqueuing），以及一個用于退出隊列信息的用戶應(yīng)用程序（稱為dequeuing）。可以有多個用戶應(yīng)用程序，但是任何的一條信息只能夠讀取一次，同時用戶可以瀏覽沒有退出隊列的信息。

  在發(fā)布訂閱模型中，有一些入隊和出隊信息的應(yīng)用程序，這些信息可以是針對特定的應(yīng)用程序，或是被目的地所接收，應(yīng)用程序接信息也被稱為代理。

dotConnect for Oracle中的AQ組件

    dotConnect for Oracle中有一些類用于提供AQ功能，這些類主要是以下幾種：

• OracleQueueMessage
• OracleQueue
• OracleQueueAdmin

OracleQueueMessage對象主要是代表了隊列信息，主要被用于排隊信息的參數(shù)，并被出對的方法返回。

OracleQueueMessages包含了系統(tǒng)生成的消息標志符和消息載荷，是char或用戶定義的對象類型。

點到點的消息的擴展示例

在這里有一個點到點的消息擴展的示例，方便大家理解：

[C#]

OracleConnection oracleConnection = new OracleConnection(
   "User Id=system;Password=manager;Server=ora;");
oracleConnection.Open();

OracleQueueTable oracleQueueTable = new OracleQueueTable(
   "QUEUE_TABLE_MESSAGE", oracleConnection);

// Set sort order by priority for the queue.  
// The messages with higher priority will reach the recipient first.
oracleQueueTable.Options.SortOrder = OracleQueueSortOrder.PriorityEnqueueTime;

// Specify type of the messages in the queue. 
//This time each message will be represented by just a string object. 
//We do so to simplify the unimportant details and concentrate on the advanced features of AQ
	
oracleQueueTable.Options.PayloadTypeName = "RAW";

// The following operations are same as in the previous example.
oracleQueueTable.CreateQueueTable();
OracleQueueAdmin oracleQueueAdmin = new OracleQueueAdmin("MESSAGE_QUEUE", 
"QUEUE_TABLE_MESSAGE", oracleConnection);
oracleQueueAdmin.CreateQueue();
oracleQueueAdmin.StartQueue();
OracleQueue oracleEnqueueQueue = new OracleQueue("MESSAGE_QUEUE", oracleConnection);

// Create and send the first message.
OracleQueueMessage message1 = new OracleQueueMessage();
message1.StringPayload = "First message.";
message1.MessageProperties.Priority = 7;
oracleEnqueueQueue.Enqueue(message1);

// Create and send the second message. This message is assigned a higher priority value.
// The message will be consumed first, regardless of the fact that it was sent later.
OracleQueueMessage message2 = new OracleQueueMessage();
message2.StringPayload = "Second message with high priority.";
message2.MessageProperties.Priority = 1;
oracleEnqueueQueue.Enqueue(message2);

// Create an object that receives the two messages.
OracleQueue oracleDequeueQueue = new OracleQueue("MESSAGE_QUEUE", oracleConnection);
oracleDequeueQueue.DequeueOptions.WaitTimeout = 1;

// Retrieve the messages in a loop. Once there are two messages received, quit.
// (ex.Code == 25228) specifies that the error occured is ORA-25228; it is thrown when the dequeuing timeout expires 
// or the end of the queue is reached without dequeuing a message.

int messageCount = 0;
while (messageCount < 2) {
  try {
    OracleQueueMessage msg = oracleDequeueQueue.Dequeue();
    messageCount++;
    if (msg != null && msg.StringPayload != null) {
      Console.WriteLine(msg.StringPayload);
    }
  }
  catch(OracleException ex) {
    if (ex.Code == 25228) {
      continue;
    }
    else
      throw ex;
  }
}

//Stop and destroy the queue and the queue table
oracleQueueAdmin.StopQueue();
oracleQueueAdmin.DropQueue();
oracleQueueTable.DropQueueTable();
oracleConnection.Close();

[Visual Basic]

Dim oracleConnection As New OracleConnection((
"User Id=system;Password=manager;Server=ora;")
oracleConnection.Open()

Dim oracleQueueTable As New OracleQueueTable("QUEUE_TABLE_MESSAGE", oracleConnection)

' Set sort order by priority for the queue. 
' The messages  with higher priority will reach the recipient first.
oracleQueueTable.Options.SortOrder = OracleQueueSortOrder.PriorityEnqueueTime

' Specify type of the messages in the queue. This time each message will be represented by just a string object. 
' We do so to simplify the unimportant 

oracleQueueTable.Options.PayloadTypeName = "RAW"

' The following operations are same as in the previous example.
oracleQueueTable.CreateQueueTable()
Dim oracleQueueAdmin As New OracleQueueAdmin("MESSAGE_QUEUE", _
   "QUEUE_TABLE_MESSAGE", oracleConnection)
oracleQueueAdmin.CreateQueue()
oracleQueueAdmin.StartQueue()
Dim oracleEnqueueQueue As New OracleQueue("MESSAGE_QUEUE", oracleConnection)

' Create and send the first message.
Dim message1 As New OracleQueueMessage
message1.StringPayload = "First message."
message1.MessageProperties.Priority = 1
oracleEnqueueQueue.Enqueue(message1)

' Create and send the second message. This message is assigned a higher priority value.
' The message will be consumed first, regardless of the fact that it was sent later.
Dim message2 As New OracleQueueMessage
message2.StringPayload = "Second message with high priority."
message2.MessageProperties.Priority = 7
oracleEnqueueQueue.Enqueue(message2)

' Create an object that receives the two messages.
Dim oracleDequeueQueue As New OracleQueue("MESSAGE_QUEUE", oracleConnection)
oracleDequeueQueue.DequeueOptions.WaitTimeout = 1

' Retrieve the messages in a loop. Once there are two messages received, quit.
' (ex.Code == 25228) specifies that the error occured is ORA-25228; 
' it is thrown when the dequeuing timeout expires or the end of the queue is reached 
' without dequeuing a message.

Dim messageCount As Integer = 0
Do While (messageCount < 2)
  Try
    Dim msg As OracleQueueMessage = oracleDequeueQueue.Dequeue()
    messageCount += 1
    if ((Not msg Is Nothing) AndAlso (Not msg.StringPayload Is Nothing)) Then
      Console.WriteLine(msg.StringPayload)
    End If
  Catch ex As OracleException
    If (ex.Code = 25228) Then
      Continue Do
    Else
      Throw ex
    End If
  End Try
Loop

oracleQueueAdmin.StopQueue()
oracleQueueAdmin.DropQueue()
oracleQueueTable.DropQueueTable()
oracleConnection.Close()