org.springframework.webflow.engine
Interface FlowAttributeMapper

All Known Implementing Classes:

AbstractFlowAttributeMapper, ConfigurableFlowAttributeMapper

public interface FlowAttributeMapper

A service interface that maps attributes between two flows. Used by the subflow state to map attributes between a parent flow and its sub flow.

An attribute mapper may map attributes of a parent flow down to a child flow as input when the child is spawned as a subflow. In addition, a mapper may map output attributes of a subflow into a resuming parent flow as output when the child session ends and control is returned to the parent flow.

For example, say you have the following parent flow session:

     Parent Flow Session
     -------------------
     -> flow = myFlow
     -> flowScope = [map-> attribute1=value1, attribute2=value2, attribute3=value3]
 

For the "Parent Flow Session" above, there are 3 attributes in flow scope ("attribute1", "attribute2" and "attribute3", respectively). Any of these three attributes may be mapped as input down to child subflows when those subflows are spawned. An implementation of this interface performs the actual mapping, encapsulating knowledge of which attributes should be mapped, and how they will be mapped (for example, will the same attribute names be used between flows or not?).

For example:

     Flow Attribute Mapper Configuration
     -----------------------------------
     -> inputMappings  = [map-> flowScope.attribute1->attribute1, flowScope.attribute3->attribute4]
     -> outputMappings = [map-> attribute4->flowScope.attribute3]
 

The above example "Flow Attribute Mapper" specifies inputMappings that define which parent attributes to map as input to the child. In this case, two attributes in flow scope of the parent are mapped, "attribute1" and "attribute3". "attribute1" is mapped with the name "attribute1" (given the same name in both flows), while "attribute3" is mapped to "attribute4", given a different name that is local to the child flow.

Likewise, when a child flow ends the outputMappings define which output attributes to map into the parent. In this case the subflow output attribute "attribute4" will be mapped up to the parent as "attribute3", updating the value of "attribute3" in the parent's flow scope. Note: only output attributes exposed by the end state of the ending subflow are eligible for mapping.

A FlowAttributeMapper is typically implemented using 2 distinct AttributeMapper implementations: one responsible for input mapping and one taking care of output mapping.

Note: because FlowAttributeMappers are singletons, take care not to store and/or modify caller-specific state in a unsafe manner. The FlowAttributeMapper methods run in an independently executing thread on each invocation so make sure you deal only with local data or internal, thread-safe services.

Author:

Keith Donald, Erwin Vervaet

See Also:

SubflowState, AttributeMapper

Method Summary

MutableAttributeMap	createFlowInput(RequestContext context) Create a map of attributes that should be passed as input to a spawning flow.
void	mapFlowOutput(AttributeMap flowOutput, RequestContext context) Map output attributes of an ended flow to a resuming parent flow session.

Method Detail

createFlowInput

MutableAttributeMap createFlowInput(RequestContext context)

Create a map of attributes that should be passed as input to a spawning flow.

Attributes set in the map returned by this method are availale as input to the subflow when its session is spawned.

Parameters:

context - the current request execution context, which gives access to the parent flow scope, the request scope, any event parameters, etcetera

Returns:

a map of attributes (name=value pairs) to pass as input to the spawning subflow

mapFlowOutput

void mapFlowOutput(AttributeMap flowOutput,
                   RequestContext context)

Map output attributes of an ended flow to a resuming parent flow session. This maps the output of the child as new input to the resuming parent, typically adding data to flow scope.

Parameters:

flowOutput - the output attributes exposed by the ended subflow

context - the current request execution context, which gives access to the parent flow scope