{{tag>Programmers_Reference Adding_Custom_Channels Source_and_sink Writing_Sink example}}
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==== Writing a Sink ====

To write a custom Sink follow the steps below:

  - Inherit the Sink from the ''AbstractSimpleSink'' class.
  - If necessary override init method to provide the Sink-specific initialization (if there’s any) – this method is called once when the Sink is initialized. The Sink-specific properties would have been entered by the user in the Configuration Tool (see also section 4.3)
  - You must override the following method to provide your own handling of messages sent from //**AwareIM**//:<code java>public void processMessage (Message msg) 
throws PipelineException;</code> \\ You can translate messages from //**AwareIM**// using the following techniques:
      - get the array of DataObject’s from the message:<code java>DataObject [] dobs = msg.peekDataObjects ();</code>
      - use MessageInterpreter class to interpret the message (see also 4.1.3):<code java>MessageInterpreter mi = new MessageInterpreter (dobs);
INotification notif = mi.getNotification (); /**or**/
String serviceName  = mi.getServiceName ();</code>

As an example you can see the code snippet below that implements the Sink that sends outgoing e-mails from //**AwareIM**//. Note that this code is for illustration purposes only and certain details such as e-mail construction and sending and error handling are omitted.

<code java> public  class EmailSink extends AbstractSimpleSink
 {
    private Stringm_mailHost= null ;
    private Sessionm_session= null ;
    private Stringm_fromAddress= null ;
    /** Initializethesink. Mail host and 'from address' properties are specified in the user interface */
    public  void init(Stringname,Propertiesprops,Stringprefix,
        Controllercontroller)
    throws IbafException
    {
        try 
        {
            super .init(name,props,prefix,controller);
            m_mailHost=props.getProperty(prefix+"."+"MAIL_HOST");
            if (m_mailHost== null )
                throw  new IbafException("Mail host property for outgoing e-mails is not specified.");
            PropertiessessionProps=System.getProperties();
            sessionProps.put("mail.smtp.host",m_mailHost);
            m_fromAddress=props.getProperty(prefix+"."+"MAIL_FROM_ADDRESS");
            m_session=Session.getDefaultInstance(sessionProps,null);
        }
        catch (Exceptione)
        {
            e.printStackTrace();
            throw  new IbafException(e.toString());
        }
    }
    /**  Message handling method – must be provided */
    public  void processMessage(Message msg)
    throws PipelineException
    {
        Stringsubject= null ,toAddress= null ;
        StringsentDateStr= null ;
        try 
        {
            DataObject[]dobs=msg.peekDataObjects();
            // get all message parameters from data objects
            MessageInterpretermi= new MessageInterpreter(dobs);
            // get e-mail address from channel values
            DataObjectchvDob=mis.getChannelValues();
            if (chvDob== null )
            return ; // ignore the message
        try 
        {
            toAddress=(String)chvDob.getAttributeValue(EMAIL_ADDRESS);
        }
        catch (InvalidParameterExceptionipe)
        {

        }
        if (toAddress== null ) return ;//** ignore the message
        INotificationnotif=mis.getNotification();
        if (notif== null ) return ; // ignore the message
        // we expect notification of a certain structure – it must have "BODY" and SUBJECT attributes defined
        Stringbody= null ;
        try 
        {
            body=(String)notif.getAttributeValue (EMAIL_BODY_ATTR);
        }
        catch (InvalidParameterExceptionipe)
        {

        }
        if (body== null )
        return ; // ignore the message// subject is optional
        try
        {
            subject=(String)notif.getAttributeValue (EMAIL_SUBJECT_ATTR);
        }
        catch (Exceptione)
        {
        }
        if (subject== null ) subject="";
        // create MAPI e-mail message
        MimeMessageemail=createEmail(body,subject, toAddress);
        if (email!= null )
        {
            // send e-mail using MAPI
            sendEmail(email,toAddress,new Date ());
        }
    }
    catch (Exceptione)
    {        
    }
}

/**  Send the e-mail using MAPI. A lot of details are omitted  **/
private  boolean sendEmail(MimeMessageemail,StringtoAddress, StringsentDate)
{
    try
    {
        Transport.send(email);
    }
    catch (Exceptione)
    {
    }
    return true;
}

/** Create e-mailmessage using MAPI. Details are omitted */
private MimeMessagecreateEmail(Stringbody,Stringsubject,String toAddress,DatesentDate)
throws Exception 
{
    MimeMessagemailMessage= new MimeMessage(m_session);
    if (m_fromAddress!= null ) mailMessage.setFrom(InternetAddress.parse mailMessage.setRecipients(javax.mail.Message.RecipientType.TO, InternetAddress.parse(toAddress, false ));
        mailMessage.setSubject (subject);
        mailMessage.setSentDate(sentDate);
        return mailMessage;
}</code>