Java EE CDI ConversationScoped

Conversation scope
The conversation scope holds state associated with a user of the system, and spans multiple requests to the server.A conversation represents a task—a unit of work from the point of view of the user.
 
The conversation context is active during any JSF request. Most conversations are destroyed at the end of the request. If a conversation should hold state across multiple requests, it must be explicitly promoted to a long-running conversation.
 
Conversation demarcation
 
CDI provides a built-in bean for controlling the lifecycle of conversations in a JSF application. This bean may be obtained by injection:
 

@Inject
Conversation conversation;

 
To promote the conversation associated with the current request to a long-running conversation, call the begin() method from application code. To schedule the current long-running conversation context for destruction at the end of the current request, call end().
 

public void beginConversation() {
    if (conversation.isTransient()) {
        conversation.begin();
        conversation.setTimeout(1000 * 60 * 30);
    }
}

public void endConversation() {
    conversation.end();
}

 
The container is permitted to destroy a conversation and all state held in its context at any time in order to conserve resources. The Conversation object provides a method to set the timeout. The timeout is the period of inactivity before the conversation is destroyed (as opposed to the amount of time the conversation is active).
 
The method beginConversation() may be called when the page is generated by the means of the JSF preRenderView event.
 

...
<f:event type="preRenderView" listener="#{action.beginConversation}"/>
<h:head>
  ...
</h:head>
...

 
 
Conversation propagation
 
The conversation context automatically propagates with any JSF faces request (JSF form submission) or redirect. It does not automatically propagate with non-faces requests, for example, navigation via a link.
 
We can force the conversation to propagate with a non-faces request by including the unique identifier of the conversation as a request parameter. The CDI specification reserves the request parameter named cid for this use. The unique identifier of the conversation may be obtained from the Conversation object, which has the EL bean name javax.enterprise.context.conversation.
 
Therefore, the following link propagates the conversation:
 

<a href="/addProduct.jsp?cid=#{javax.enterprise.context.conversation.id}">Add Product</a>

 
It's probably better to use one of the link components in JSF 2:
 

<h:link outcome="/addProduct.xhtml" value="Add Product">
   <f:param name="cid" value="#{javax.enterprise.context.conversation.id}"/>
</h:link>

 
In order to keep the code simple, you can define custom tags beginConversation and  conversationId:
 

<!DOCTYPE composition PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<ui:composition xmlns="http://www.w3.org/1999/xhtml"
                xmlns:ui="http://java.sun.com/jsf/facelets"
                xmlns:f="http://java.sun.com/jsf/core">
    <f:event type="preRenderView" listener="#{action.beginConversation}"/>
</ui:composition>

 

<!DOCTYPE composition PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<ui:composition xmlns="http://www.w3.org/1999/xhtml"
                xmlns:ui="http://java.sun.com/jsf/facelets"
                xmlns:f="http://java.sun.com/jsf/core">
    <f:param name="cid" value="#{javax.enterprise.context.conversation.id}"/>
</ui:composition>

 
Difference between JSF FlowScoped and CDI ConversationScoped
 
A flow is a group of views related by navigation rules. Flow-scoped beans stay alive as long as you navigate within this flow, and they die when you leave the flow.Conversation-scoped beans can also survive navigation, but their lifetime is delimited programmatically by calling Conversation.begin() and Conversation.end(). They are not directly related to a specific group of views.You can use conversation scoped beans without using JSF.
 
Reference
Java EE CDI ConversationScoped example
Java EE CDI bean scopes
Java EE 7 CDI bean scopes
Java EE CDI ViewScoped example
Java EE CDI TransactionScoped example
JSF Flow example
Weld reference documentation