FlowHandler (Java(TM) EE 8 Specification APIs)

java.lang.Object
- javax.faces.flow.FlowHandler

```
public abstract class FlowHandler
extends Object
```
FlowHandler is the main entry point that enables the runtime to interact with the faces flows feature. NavigationHandler uses this class when it needs to make navigational decisions related to flows. The faces flow feature entirely depends on the ClientWindow feature and also on CDI.
Defining Flows

The implementation must support defining faces flows using the <flow-definition> element as specified in the Application Configuration Resources XML Schema Definition, or by using the FlowBuilder API. Additional means of defining flows may be provided by decorating the FlowHandlerFactory.

Managing Flows
The singleton instance of this class must be thread safe, and therefore must not store any per-user state. Flows are, however, traversed in a per-user manner, and must be associated with the current ClientWindow. Furthermore, Flows may be nested. These requirements strongly suggest managing the flows with a stack-like runtime data structure, stored in a per-user fashion and associated with the ClientWindow. Because Flow instances are immutable, yet the flow stack is per-user, implementations must make allowance for flow scoped data (managed beans declared to be FlowScoped and data stored in the Map returned by getCurrentFlowScope()) to be fully re-entrant. For example, consider an application with two flows, A and B, each with a single FlowScoped bean MyBeanA and MyBeanB, respectively. Entry into flow A causes MyBeanA to become active. Calling from A into B causes MyBeanB to become active. Calling back into A causes a new instance of MyBeanA to become active, rather than reactivating the earlier instance of MyBeanA.

The Flow Graph

Prior versions of the specification defined a flow graph but the only kind of node in the graph was a VDL view. The Faces Flow feature currently defines the following node types.
- View
  
  This is the regular JSF VDL View that has been in the specification since the beginning.
- Switch
  
  This is a list of EL expressions. When control is passed to a switch node, each expression in the list is evaluated and the first one that returns true is used to define the id of the next node to which control must be passed. If none of the expressions evaluates to true, control passes to the specified default id.
- Return
  
  This node type specifies an outcome that is returned to the calling flow.
- Method Call
  
  This node type allows invocation of arbitrary application logic at any point in the executiong of the flow. An outcome can be specified that will cause a navigation case to be navigated to after the method has been invoked.
- Faces Flow Call
  
  This node type allows one flow to call another flow. The calling flow remains active and is not exited until control returns from the called flow.
Edges in the graph are defined by the existing JSF navigation rule system.

Flows and Model Objects

Managed beans annotated with the CDI annotation FlowScoped are created lazily, when referenced, after a user agent's entry into the named scope, and must be made available for garbage collection when the user agent leaves the flow.

The flowScope EL implicit object is also available to store values in the "current" slope. Values stored in this scope must be made available for garbage collection when the user agent leaves the flow.
Since:

2.2

Field Summary

Fields
Modifier and Type	Field and Description
`static String`	`FLOW_ID_REQUEST_PARAM_NAME` Components that are rendered by `Renderers` of component-family `javax.faces.OutcomeTarget` must use this constant as the parameter name for a parameter representing the flow id of the flow that this component will cause to be entered.
`static String`	`NULL_FLOW` Components that are rendered by `Renderers` of component-family `javax.faces.OutcomeTarget` must use this constant as the value of the parameter named by `TO_FLOW_DOCUMENT_ID_REQUEST_PARAM_NAME` when returning from a flow (without entering another flow) using such a component.
`static String`	`TO_FLOW_DOCUMENT_ID_REQUEST_PARAM_NAME` Components that are rendered by `Renderers` of component-family `javax.faces.OutcomeTarget` must use this constant as the parameter name for a parameter representing the defining document id of the flow that this component will cause to be entered.

Constructor Summary

Constructors
Constructor and Description

FlowHandler()

Constructors
Constructor and Description
`FlowHandler()`

Method Summary

All Methods Instance Methods Abstract Methods Concrete Methods
Modifier and Type	Method and Description
`abstract void`	`addFlow(FacesContext context, Flow toAdd)` Add the argument `Flow` to the collection of `Flow`s known to the current application.
`abstract void`	`clientWindowTransition(FacesContext context)` Allow for flow transitions in the case of components rendered by the renderers from component-family `javax.faces.OutcomeTarget`.
`Flow`	`getCurrentFlow()` Convenience overload that calls `FacesContext.getCurrentInstance()` and then calls through to `getCurrentFlow(javax.faces.context.FacesContext)`.
`abstract Flow`	`getCurrentFlow(FacesContext context)` Return the currently active `Flow` for the argument `FacesContext`, or `null` if no flow is active.
`abstract Map<Object,Object>`	`getCurrentFlowScope()` Return the `Map` that backs the `#{flowScope}` EL implicit object or `null` if no flow is currently active.
`abstract Flow`	`getFlow(FacesContext context, String definingDocumentId, String id)` Return the `Flow` whose `id` is equivalent to the argument `id`, within the scope of the argument `definingDocument`.
`abstract String`	`getLastDisplayedViewId(FacesContext context)` Return the last displayed viewId for the current flow, as returned by `getCurrentFlow(javax.faces.context.FacesContext)`, or `null` if there is no current flow.
`abstract boolean`	`isActive(FacesContext context, String definingDocument, String id)` Return `true` if and only if the flow referenced by the argument `definingDocument` and `id` is currently active.
`abstract void`	`popReturnMode(FacesContext context)` Enable the correct handling of navigation when processing a return node.
`abstract void`	`pushReturnMode(FacesContext context)` Enable the correct handling of navigation when processing a return node.
`abstract void`	`transition(FacesContext context, Flow sourceFlow, Flow targetFlow, FlowCallNode outboundCallNode, String toViewId)` Perform a transition in the flow graph for the current user's `ClientWindow`.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - FLOW_ID_REQUEST_PARAM_NAME
```
public static final String FLOW_ID_REQUEST_PARAM_NAME
```
    Components that are rendered by Renderers of component-family javax.faces.OutcomeTarget must use this constant as the parameter name for a parameter representing the flow id of the flow that this component will cause to be entered.
    
    Since:
    
    2.2
    
    See Also:
    
    Constant Field Values
  - TO_FLOW_DOCUMENT_ID_REQUEST_PARAM_NAME
```
public static final String TO_FLOW_DOCUMENT_ID_REQUEST_PARAM_NAME
```
    Components that are rendered by Renderers of component-family javax.faces.OutcomeTarget must use this constant as the parameter name for a parameter representing the defining document id of the flow that this component will cause to be entered.
    
    Since:
    
    2.2
    
    See Also:
    
    Constant Field Values
  - NULL_FLOW
```
public static final String NULL_FLOW
```
    Components that are rendered by Renderers of component-family javax.faces.OutcomeTarget must use this constant as the value of the parameter named by TO_FLOW_DOCUMENT_ID_REQUEST_PARAM_NAME when returning from a flow (without entering another flow) using such a component.
    
    Since:
    
    2.2
    
    See Also:
    
    Constant Field Values
- Constructor Detail
  - FlowHandler
```
public FlowHandler()
```
- Method Detail
  - getCurrentFlowScope
```
public abstract Map<Object,Object> getCurrentFlowScope()
```
    Return the Map that backs the #{flowScope} EL implicit object or null if no flow is currently active.
    
    Returns:
    
    the Map for this flow scope.
    
    Since:
    
    2.2
  - getFlow
```
public abstract Flow getFlow(FacesContext context,
                             String definingDocumentId,
                             String id)
```
    Return the Flow whose id is equivalent to the argument id, within the scope of the argument definingDocument.
    
    Parameters:
    
    context - the FacesContext for the current request.
    
    definingDocumentId - An application unique identifier for the document in which the returned flow is defined.
    
    id - the id of a Flow, unique within the scope of the definingDocument.
    
    Returns:
    
    the Flow for the argument identifiers.
    
    Throws:
    
    NullPointerException - if any of the parameters are null
    
    Since:
    
    2.2
  - addFlow
```
public abstract void addFlow(FacesContext context,
                             Flow toAdd)
```
    Add the argument Flow to the collection of Flows known to the current application. The implementation must be thread safe.
    
    Parameters:
    
    context - the FacesContext for the current request.
    
    toAdd - the Flow to add.
    
    Throws:
    
    NullPointerException - if any of the parameters are null
    
    IllegalStateException - if there is already a flow with the same id as the argument Flow within the scope of the definingDocument.
    
    IllegalArgumentException - if the id of the flow to add is null or the empty string.
    
    IllegalArgumentException - if the definingDocumentId of the toAdd is null.
    
    Since:
    
    2.2
  - getCurrentFlow
```
public abstract Flow getCurrentFlow(FacesContext context)
```
    Return the currently active Flow for the argument FacesContext, or null if no flow is active. A Flow must always be associated with exactly one ClientWindow, but a ClientWindow may have multiple Flows.
    
    If pushReturnMode(javax.faces.context.FacesContext) had been called with true as the argument before invoking this method, return the preceding flow on the stack instead of the actual current flow, or null if there is no preceding flow. Otherwise, return the current flow.
    
    Parameters:
    
    context - the FacesContext for the current request.
    
    Returns:
    
    the current Flow or null if no flow is active
    
    Throws:
    
    NullPointerException - if any of the parameters are null
    
    Since:
    
    2.2
  - getCurrentFlow
```
public Flow getCurrentFlow()
```
    Convenience overload that calls FacesContext.getCurrentInstance() and then calls through to getCurrentFlow(javax.faces.context.FacesContext).
    
    Returns:
    
    the current Flow or null if no flow is active
    
    Since:
    
    2.2
  - getLastDisplayedViewId
```
public abstract String getLastDisplayedViewId(FacesContext context)
```
    Return the last displayed viewId for the current flow, as returned by getCurrentFlow(javax.faces.context.FacesContext), or null if there is no current flow.
    
    Parameters:
    
    context - the FacesContext for the current request.
    
    Returns:
    
    the last displayed viewId.
    
    Throws:
    
    NullPointerException - if context is null
    
    Since:
    
    2.2
  - pushReturnMode
```
public abstract void pushReturnMode(FacesContext context)
```
    Enable the correct handling of navigation when processing a return node. The default NavigationHandler specification requires calling this method before processing the navigation rules for the flow return, and calling popReturnMode(javax.faces.context.FacesContext), from a finally block, immediately afterward.
    
    Parameters:
    
    context - the FacesContext for the current request.
    
    Throws:
    
    NullPointerException - if context is null.
    
    Since:
    
    2.2
  - popReturnMode
```
public abstract void popReturnMode(FacesContext context)
```
    Enable the correct handling of navigation when processing a return node. The default NavigationHandler specification requires calling this method from a finally block, immediately attempting to process the navigation rules in the context of a flow return.
    
    Parameters:
    
    context - the FacesContext for the current request.
    
    Throws:
    
    NullPointerException - if context is null.
    
    Since:
    
    2.2
  - transition
```
public abstract void transition(FacesContext context,
                                Flow sourceFlow,
                                Flow targetFlow,
                                FlowCallNode outboundCallNode,
                                String toViewId)
```
    Perform a transition in the flow graph for the current user's ClientWindow. Obtain references to the Flow instances corresponding to the origin and destination arguments. If the origin Flow is equal to the destination Flow, take no action and return null. Otherwise, if the outboundCallNode argument is non-null save aside the outbound parameters. For discussion evaluatedParams is a data structure that stores the evaluated values of any outbound parameters. It is necessary to evaluate these values before popping any flow scopes because the values may refer to scoped instances that need to be passed to the target flow, but will not be available once the new scope is activated. Save aside the outbound parameters using the following algorithm.
    
    If the outboundParameters property of outboundCallNode is non-null and not empty, and the inboundParameters property of the target flow is non-null and not empty, for each entry in the outbound parameters whose name matches an entry in the inbound parameters, evaluate the value of the parameter, and put the evaluated value into evaluatedParams under the corresponding name. Otherwise, consider evaluatedParams to be empty.
    
    If the destination Flow is a sub-flow of the origin Flow push the destination Flow onto the flow data structure and return the destination Flow. Otherwise, pop the current Flow from the flow data structure. If the destination Flow is non-null, make the destination Flow the current flow, pushing it onto the data structure. If evaluatedParams is not empty, for each entry, find the corresponding parameter in the target flow's inbound parameters and call its setValue method, passing the value from evaluatedParams.
    
    Parameters:
    
    context - the FacesContext for the current request.
    
    sourceFlow - the current Flow, or null if there is no source flow.
    
    targetFlow - the destination Flow, or null if there is no destination flow.
    
    outboundCallNode - the flow call node causing this transition, or null if this transition is not caused by a flow call.
    
    toViewId - the viewId of the view being displayed as a result of this transition. This parameter makes it possible to implement getLastDisplayedViewId(javax.faces.context.FacesContext).
    
    Throws:
    
    NullPointerException - if context or toViewId is null.
    
    Since:
    
    2.2
  - clientWindowTransition
```
public abstract void clientWindowTransition(FacesContext context)
```
    Allow for flow transitions in the case of components rendered by the renderers from component-family javax.faces.OutcomeTarget. These transitions must happen at the front of the request processing lifecycle due to the HTTP GET based nature of such components. Therefore, this method is called from the restore view phase of the lifecycle.
    
    Let flowId be the value in the request parameter map for the parameter whose name is given by the value of FLOW_ID_REQUEST_PARAM_NAME. Let toFlowDocumentId be the value in the request parameter map for the paramater whose name is given by the value of TO_FLOW_DOCUMENT_ID_REQUEST_PARAM_NAME. If toFlowDocumentId is null, take no action and return. Otherwise, let sourceFlow be the return from getCurrentFlow(javax.faces.context.FacesContext). A null value indicates there is no current flow, which will be the case if this navigation is trying to enter a flow. If flowId is not null and toFlowDocumentId is not equal to the value of NULL_FLOW, let targetFlow be the result of calling getFlow(javax.faces.context.FacesContext, java.lang.String, java.lang.String), passing toFlowDocumentId and flowId as the last two arguments, respectively. If the result is non-null, let flowCallNode be the return from calling Flow.getFlowCall(javax.faces.flow.Flow) on the sourceFlow, passing targetFlow as the argument. Otherwise, targetFlow and flowCallNode must remain null, indicating that this is a flow return. Call FacesContext.getViewRoot() and let toViewId be the the return from calling UIViewRoot.getViewId() on it.
    
    Call, transition(javax.faces.context.FacesContext, javax.faces.flow.Flow, javax.faces.flow.Flow, javax.faces.flow.FlowCallNode, java.lang.String), passing the arguments gathered in the preceding algorithm.
    
    Parameters:
    
    context - the FacesContext for the current request.
    
    Throws:
    
    NullPointerException - if context is null.
    
    Since:
    
    2.2
  - isActive
```
public abstract boolean isActive(FacesContext context,
                                 String definingDocument,
                                 String id)
```
    Return true if and only if the flow referenced by the argument definingDocument and id is currently active.
    
    Parameters:
    
    context - the FacesContext for the current request.
    
    definingDocument - An application unique identifier for the document in which the returned flow is defined.
    
    id - the id of a Flow, unique within the scope of the definingDocument.
    
    Returns:
    
    true if and only if the referenced flow is active
    
    Throws:
    
    NullPointerException - if any of the parameters are null
    
    Since:
    
    2.2

Class FlowHandler

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

FLOW_ID_REQUEST_PARAM_NAME

TO_FLOW_DOCUMENT_ID_REQUEST_PARAM_NAME

NULL_FLOW

Constructor Detail

FlowHandler

Method Detail

getCurrentFlowScope

getFlow

addFlow

getCurrentFlow

getCurrentFlow

getLastDisplayedViewId

pushReturnMode

popReturnMode

transition

clientWindowTransition

isActive