Content Event

A message or an event is called Content Event in SAMOA. As the name suggests, it is an event which contains content which needs to be processed by the processors.

###1. Implementation ContentEvent has been implemented as an interface in SAMOA. Users need to implement ContentEvent interface to create their custom message classes. As it can be seen in the following code, key is the necessary part of a message.

package samoa.core;

public interface ContentEvent extends java.io.Serializable {
	
	public String getKey();
	
	public void setKey(String str);
	
	public boolean isLastEvent();
}

###2. Methods Following is a brief description of methods. ####2.1 String getKey() Each message is identified by a key in SAMOA. All user-defined message classes should have a key state variable. Each instance of the custom message should be assigned a key. This method should return the key of the respective message. ####2.2 void setKey(String str) This method is used to assign a key to the message. ####2.3 boolean isLastEvent() This method lets SAMOA know that this message is the last message. ###3. Example Following is the example of a Message class which implements ContentEvent interface. As ContentEvent is an interface, it can not hold variables. A user-defined message class should have its own data variables and its getter methods. In the following example, value variable of type Object is added to the class. Using a generic type Object is beneficial in the sense that any object can be passed to it and later it can be casted back to the original type. The following example also adds a streamId variable which stores the id of the stream the message belongs to. This is not a requirement but can be beneficial in certain applications.

package samoa.fpm.messages;

import samoa.core.ContentEvent;


/**
 * * @author Faisal Moeen
 * A general key-value message class which adds a stream id in the class variables
 * Stream id information helps in determining to which stream does the message belongs to.
 */
public class Message implements ContentEvent {

	/**
	 * To tell if the message is the last message of the stream. This may be required in some applications where
	 * a stream can cease to exist
	 */
	private boolean last=false;
	/**
	 * Id of the stream to which the message belongs
	 */
	private String streamId;
	/**
	 * The key of the message. Can be any sting value. Duplicates are allowed.
	 */
	private String key;
	/**
	 * The value of the message. Can be any object. Casting may be necessary to the desired type.
	 */
	private Object value;
	
	public Message()
	{}
	/**
	 * @param key
	 * @param value
	 * @param isLastEvent
	 * @param streamId
	 */
	public Message(String key, Object value, boolean isLastEvent, String streamId)
	{
		this.key=key;
		this.value = value;
		this.last = isLastEvent;
		this.streamId=streamId;
	}
	
	@Override
	public String getKey() {
		return key;
	}

	@Override
	public void setKey(String str) {
		this.key = str;
	}

	@Override
	public boolean isLastEvent() {
		// TODO Auto-generated method stub
		return last;
	}
	
	/**
	 * @return value of the message
	 */
	public String getValue()
	{
		return value.toString();
	}
	
	/**
	 * @return id of the stream to which the message belongs
	 */
	public String getStreamId() {
		return streamId;
	}
	/**
	 * @param streamId
	 */
	public void setStreamId(String streamId) {
		this.streamId = streamId;
	}

}