原创|使用教程|编辑:郝浩|2013-04-24 14:50:48.000|阅读 328 次
概述:OracleAlerter类是用于DBMS_ALERT包的接口,S_ALERT包支持异步通知数据库事件(警报)。今天主要的内容就是详解OracleAlerter组件的使用,主要是由以下的部分组成:Oracle警报基础、等待警报模式、开始模式。
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OracleAlerter类是用于DBMS_ALERT包的接口,仅仅在专业版和开发版中有。DBMS_ALERT包支持异步通知数据库事件(警报),通过恰当地使用这个包和数据库触发器,一个应用程序可以通知任何其他的应用程序,连接数据库、登记接受到的报警以及数据库的任何的改变等。
今天主要的内容就是详解OracleAlerter组件的使用,主要是由以下的部分组成:Oracle警报基础、等待警报模式、开始模式。
DBMS_ALERT提供API接口来发送警报、警报注册、并等待接收警报。这个解决方案主要采用了信号、寄存器和WAITANY。
OracleAlerter 类主要原则如下图所示:
OracleAlerter类支持两种工作模式,等待警报和开始模式。“等待警报”模式将会等待最近的警报,并将其返回给应用程序。“开始”模式就是启动一次,当接收到一个警报的时候就会提出一个事件,为了制止这种模式,叫做OracleAlerter 类实例的“停止”方法。
下面的示例就是演示的是OracleAlerter在等待模式的情况:
[C#]
static OracleConnection con = new OracleConnection(); static void Main(string[] args) { // Initialize and open a connection to the Oracle server. // We connect as Sys to have the privilieges to use the DBMS_Alert package. con.Server = "ora"; con.UserId = "sys"; con.Password = "pwd"; con.ConnectMode = OracleConnectMode.SysDba; con.Open(); // Execute a script needed to create the database objects used in our sample. // These objects are: // 1) table "alert_table" with two fields: an integer identification and a char value; // 2) trigger "alert_trigger", which initializes the "my_alert" Oracle Alert after each insert to alert_table. OracleScript createAll = new OracleScript(); createAll.Connection = con; createAll.ScriptText = @" create table scott.alert_table (""id"" number(38,0), ""value"" varchar2(4000 byte) ); create or replace trigger sys.alert_trigger after insert or update on scott.alert_table for each row begin dbms_alert.signal('my_alert', 'A row has been added.'); end; "; createAll.Execute(); // Now we create an instance of the OracleAlerter class, which is used to retrieve alerts. // This instance is registered for the "my_alert" Oracle Alert. // Timeout stands for the time in seconds during which OracleAlerter will be waiting for alerts. OracleAlerter alerter = new OracleAlerter(); alerter.Connection = con; alerter.AlertName = "my_alert"; alerter.Timeout = 10; // When waiting for alerts, OracleAlerter expectedly pauses the current thread. // Thus, we need another one to generate the alert while OracleAlerter is listening. // In the Insert() function, a row is added to alert_table. // As it is shown in the createAll script, this insert triggers the "my_alert" Oracle Alert. Thread insertThread = new Thread(new ThreadStart(Insert)); insertThread.Start(); // Waits until the "my_alert" alert is received, returns the corresponding OracleAlert object. // If it is not during the timeout period, returns null. OracleAlert alert = alerter.WaitAlert(); // Simple output operations to show the alert's content. Console.WriteLine("Got an alert: " + ((alert == null) ? "null" : alert.Message)); Console.Read(); // Drop table and trigger. OracleScript dropAll = new OracleScript(); dropAll.Connection = con; dropAll.ScriptText = @" drop trigger sys.alert_trigger; drop table scott.alert_table; "; dropAll.Execute(); // Close the connection. con.Close(); } // A simple insert command used to trigger the "my_alert" alert. // We take this command out to use multithreading. public static void Insert() { OracleCommand insert = new OracleCommand(); insert.CommandText = "insert into scott.alert_table values ('10', 'Some text')"; insert.Connection = con; insert.ExecuteNonQuery(); Console.WriteLine("Inserted a row"); }
[Visual Basic]
Private Shared con As New OracleConnection Shared Sub Main(ByVal args As String()) ' Initialize and open a connection to the Oracle server. ' We connect as Sys to have the privilieges to use the DBMS_Alert package. con.Server = "ora" con.UserId = "sys" con.Password = "pwd" con.ConnectMode = OracleConnectMode.SysDba con.Open ' Execute a script needed to create the database objects used in our sample. ' These objects are: ' 1) table "alert_table" with two fields: an integer identification and a char value; ' 2) trigger "alert_trigger", which initializes the "my_alert" Oracle Alert after each insert to alert_table. Dim createAll As New OracleScript createAll.Connection = con createAll.ScriptText = VbCrlf _ & " " _ & "create table scott.alert_table " & VbCrlf _ & " (""id"" number(38,0), " & VbCrlf _ & " ""value"" varchar2(4000 byte)" & VbCrlf & _ " );" & VbCrlf & VbCrlf _ & " create or replace trigger sys.alert_trigger " & VbCrlf & _ " after insert or update on scott.alert_table " & VbCrlf & _ " for each row " & VbCrlf & _ " begin" & VbCrlf _ & " dbms_alert.signal('my_alert', 'A row has been added.');" _ & VbCrlf & " end;" & VbCrlf & " " createAll.Execute ' Now we create an instance of the OracleAlerter class, which is used to retrieve alerts. ' This instance is registered for the "my_alert" Oracle Alert. ' Timeout stands for the time in seconds during which OracleAlerter will be waiting for alerts. Dim alerter As New OracleAlerter alerter.Connection = con alerter.AlertName = "my_alert" alerter.Timeout = 10 ' When waiting for alerts, OracleAlerter expectedly pauses the current thread. ' Thus, we need another one to generate the alert while OracleAlerter is listening. ' In the Insert() function, a row is added to alert_table. ' As it is shown in the createAll script, this insert triggers the "my_alert" Oracle Alert. Dim insertThread As Thread = New Thread(New ThreadStart(insert)) insertThread.Start() ' Waits until the "my_alert" alert is received, returns the corresponding OracleAlert object. ' If it is not during the timeout period, returns null. Dim alert As OracleAlert = alerter.WaitAlert ' Simple output operations to show the alert's content. Console.WriteLine(("Got an alert: " & IIf((alert Is Nothing), "null", alert.Message))) Console.Read ' Drop table and trigger. Dim dropAll As New OracleScript dropAll.Connection = con dropAll.ScriptText = VbCrlf & _ " " & "drop trigger sys.alert_trigger;" & VbCrlf & _ " " & "drop table scott.alert_table;" & VbCrlf dropAll.Execute ' Close the connection. con.Close End Sub ' A simple insert command used to trigger the "my_alert" alert. ' We take this command out to use multithreading. Public Shared Sub Insert() Dim createAll As New OracleCommand createAll.CommandText = "insert into scott.alert_table values ('10', 'Some text')" createAll.Connection = con createAll.ExecuteNonQuery Console.WriteLine("Inserted a row") End Sub
在这个示例中讲会使用警报检索模式中的开始模式,OracleAlerter对象alerter将被初始化,并被设置为特定警报侦听。然后OracleAlerter类的另一个实例alertGenerator,将会发送带有名字的警报到服务器上,从而触发警报的事件。等待时间到期后,将会提出WaitTimeout事件,监听重新开始。然后WaitTimeout对象停下来显示停止事件。
[C#]
static void Main(string[] args) { // Initialize and open a connection to the Oracle server. // We connect as Sys to have the privilieges to use the DBMS_Alert package. OracleConnection con = new OracleConnection(); con.Server = "ora"; con.UserId = "sys"; con.Password = "pwd"; con.ConnectMode = OracleConnectMode.SysDba; con.Open(); // Create the OracleAlerter instance and register it for the "my_alert" Oracle Alert. // Set Interval to 0 so that there is no delay between two consequent periods of listening. OracleAlerter alerter = new OracleAlerter(); alerter.Connection = con; alerter.AlertName = "my_alert"; alerter.Timeout = 3; alerter.Interval = 0; // Set the event handlers for all possible OracleAlerter events. // The Alert event fires when an alert is received. // The Error event fires as any error occurs while receiving alerts. // The Stopped event fires when alerter becomes inactive, e.g. after the Stop() method. // The WaitTimeout event fires when the Timeout period ends without getting an alert. alerter.Alert += new OracleAlerterAlertEventHandler(Alerter_OnAlert); alerter.Error += new OracleAlerterErrorEventHandler(Alerter_OnError); alerter.Stopped += new OracleAlerterFinishEventHandler(Alerter_OnStop); alerter.WaitTimeout += new OracleAlerterFinishEventHandler(Alerter_OnTimeOut); // Start the alerter. It will wait for alerts during the Timeout period. // After that, it sleeps during Interval and then starts again. // As Interval is zero, there will be no sleeping periods. // Unlike the WaitAlert method, Start() does not hold the current thread. alerter.Start(); // We need to wait until the alerter begins listening. // Otherwise, the alert may fire before OracleAlerter is initialized. // In this case, the Alert event won't be triggered and alerter will just wait // until Timeout, producing the WaitTimeout event. Thread.Sleep(2000); // In this sample, we use another instance of OracleAlerter instead of database triggers to generate the alert. // alertGenerator uses the same connection and alert name as the alerter object. OracleAlerter alertGenerator = new OracleAlerter(); alertGenerator.Connection = con; alertGenerator.AlertName = "my_alert"; // Send an alert to the server. At this moment alerter should raise the Alert event. alertGenerator.Signal("An alert message."); // In contrast to WaitAlert(), the Start() method allows to receive alerts continuously. // Thus, we can process all alerts that are available on the server. alertGenerator.Signal("One more alert"); // After the alert is received, alerter starts another Timeout period. // At its end, the WaitTimeout event will be generated. We pause the thread to get this event. // Besides, we need a small pause to let the last alert be sent to the server. Thread.Sleep(5000); // Disable alerter, raising the Stopped event. alerter.Stop(); Console.Read(); // Close the connection. con.Close(); } // Simple event handlers for alerter's events. public static void Alerter_OnAlert(object sender, OracleAlerterAlertEventArgs e) { Console.WriteLine("Got an alert: " + e.AlertMessage); } public static void Alerter_OnError(object sender, OracleAlerterErrorEventArgs e) { Console.WriteLine("Error: " + e.AlerterException.Message); } public static void Alerter_OnStop(object sender, OracleAlerterFinishEventArgs e) { Console.WriteLine("Stopped: " + e.ToString()); } public static void Alerter_OnTimeOut(object sender, OracleAlerterFinishEventArgs e) { Console.WriteLine("Time's up: " + e.ToString()); }
[Visual Basic]
Shared Sub Main(ByVal args As String()) ' Initialize and open a connection to the Oracle server. ' We connect as Sys to have the privilieges to use the DBMS_Alert package. Dim con As New OracleConnection con.Server = "ora" con.UserId = "sys" con.Password = "pwd" con.ConnectMode = OracleConnectMode.SysDba con.Open ' Create the OracleAlerter instance and register it for the "my_alert" Oracle Alert. ' Set Interval to 0 so that there is no delay between two consequent periods of listening. Dim alerter As New OracleAlerter alerter.Connection = con alerter.AlertName = "my_alert" alerter.Timeout = 3 alerter.Interval = 0 ' Set the event handlers for all possible OracleAlerter events. ' The Alert event fires when an alert is received. ' The Error event fires as any error occurs while receiving alerts. ' The Stopped event fires when alerter becomes inactive, e.g. after the Stop() method. ' The WaitTimeout event fires when the Timeout period ends without getting an alert. AddHandler alerter.Alert, New OracleAlerterAlertEventHandler(AddressOf Alerter_OnAlert) AddHandler alerter.Error, New OracleAlerterErrorEventHandler(AddressOf Alerter_OnError) AddHandler alerter.Stopped, New OracleAlerterFinishEventHandler(AddressOf Alerter_OnStop) AddHandler alerter.WaitTimeout, New OracleAlerterFinishEventHandler(AddressOf Alerter_OnTimeOut) ' Start the alerter. It will wait for alerts during the Timeout period. ' After that, it sleeps during Interval and then starts again. ' As Interval is zero, there will be no sleeping periods. ' Unlike the WaitAlert method, Start() does not hold the current thread. alerter.Start ' We need to wait until the alerter begins listening. ' Otherwise, the alert may fire before OracleAlerter is initialized. ' In this case, the Alert event won't be triggered and alerter will just wait ' until Timeout, producing the WaitTimeout event. Thread.Sleep(2000) ' In this sample, we use another instance of OracleAlerter instead of database triggers to generate the alert. ' alertGenerator uses the same connection and alert name as the alerter object. Dim alertGenerator As New OracleAlerter alertGenerator.Connection = con alertGenerator.AlertName = "my_alert" ' Send an alert to the server. At this moment alerter should raise the Alert event. alertGenerator.Signal("An alert message.") ' In contrast to WaitAlert(), the Start() method allows to receive alerts continuously. ' Thus, we can process all alerts that are available on the server. alertGenerator.Signal("One more alert") ' After the alert is received, alerter starts another Timeout period. ' At its end, the WaitTimeout event will be generated. We pause the thread to get this event. ' Besides, we need a small pause to let the last alert be sent to the server. Thread.Sleep(5000) ' Disable alerter, raising the Stopped event. alerter.Stop Console.Read ' Close the connection. con.Close End Sub Public Shared Sub Alerter_OnAlert(ByVal sender As Object, ByVal e As OracleAlerterAlertEventArgs) Console.WriteLine(("Got an alert: " & e.AlertMessage)) End Sub Public Shared Sub Alerter_OnError(ByVal sender As Object, ByVal e As OracleAlerterErrorEventArgs) Console.WriteLine(("Error: " & e.AlerterException.Message)) End Sub Public Shared Sub Alerter_OnStop(ByVal sender As Object, ByVal e As OracleAlerterFinishEventArgs) Console.WriteLine(("Stopped: " & e.ToString)) End Sub Public Shared Sub Alerter_OnTimeOut(ByVal sender As Object, ByVal e As OracleAlerterFinishEventArgs) Console.WriteLine(("Time's up: " & e.ToString)) End Sub
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