com.sun.faces.context.flash

Class FlashELResolver

java.lang.Object

javax.el.ELResolver

com.sun.faces.context.flash.FlashELResolver

public class FlashELResolver
extends javax.el.ELResolver

Provide a feature semantically identical to the "flash" concept in Ruby on Rails.

The feature is exposed to users via a custom ELResolver which introduces a new implicit object, flash. The flash functions as Map and can be used in getValue( ) or setValue( ) expressions.

Usage

Consider three JSF views: viewA, viewB, and viewC. The user first views viewA, then clicks a button and is shown viewB, where she clicks a button and is shown viewC. If values are stored into the flash during the rendering or postback phases of viewA, they are available to during the rendering phase of viewB, but are not available during the rendering or postback phases of viewC. In other words, values stored into the flash on "this" request are accessible for the "next" request, but not thereafter.

There are three ways to access the flash.

1. Using an EL Expression, such as using #{flash.foo} as the value of an attribute in a JSP page.

2. Using the EL API, such as:

    FacesContext context = FacesContext.getCurrentInstance();
    ValueExpression flashExpression = context.getApplication().
       createValueExpression(context.getELContext(), "#{flash.foo}",
                             null, Object.class);
    flashExpression.setValue(context.getELContext(), "Foo's new value");
    

3. Using getting the ELFlash directly, such as:

    Map<String,Object> flash = ELFlash.getFlash();
    flash.put("foo", "Foo's new value");
    

The main entry point to this feature is the first one. This library includes a simple custom tag, jsfExt:set, that evaluates an expression and sets its value into another expression. jsfExt:set can be used to store values into the flash from JSP pages, like this:

<jsfExt:set var="#{flash.foo}" value="fooValue" />

or this:

<jsfExt:set var="#{flash.keep.bar}" value="#{user.name}" />

or even this:

 <jsfExt:set var="#{flash.now.baz}" value="#{cookie.userCookie}" />
 

 <h:outputText value="#{flash.now.baz}" />
 

 

Related Classes

The complete list of classes that make up this feature is

• FlashELResolver

• ELFlash

Field Summary

Fields inherited from class javax.el.ELResolver

RESOLVABLE_AT_DESIGN_TIME, TYPE

Constructor Summary

Constructors

Constructor and Description
FlashELResolver() Not intended for manual invocation.

Method Summary

Modifier and Type	Method and Description
Class<?>	getCommonPropertyType(javax.el.ELContext context, Object base) If base is non-null and is the literal string "flash", return Object.class.
Iterator<FeatureDescriptor>	getFeatureDescriptors(javax.el.ELContext elContext, Object base) Returns an iterator of FeatureDescriptors for the current contents of the flash.
Class<?>	getType(javax.el.ELContext elContext, Object base, Object property) Return the valid Class for a future set operation, which will always be null because sets happen via the MapELResolver operating on the ELFlash instance as a Map.
Object	getValue(javax.el.ELContext elContext, Object base, Object property) Hook into the EL resolution process to introduce the flash implicit object.
boolean	isReadOnly(javax.el.ELContext elContext, Object base, Object property) Returns true because write operations take place via the MapELResolver on the actual ELFlash instance.
void	setValue(javax.el.ELContext elContext, Object base, Object property, Object value) This method will throw PropertyNotWritableException if called with a null base and a property value equal to the literal string "flash".

Methods inherited from class javax.el.ELResolver

convertToType, invoke

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

FlashELResolver

public FlashELResolver()

Not intended for manual invocation. Only called by the JSF Runtime.

Method Detail

getValue

public Object getValue(javax.el.ELContext elContext,
                       Object base,
                       Object property)

Hook into the EL resolution process to introduce the flash implicit object. If property is null, take no action and return null. if base is null, return null. If base is an instance of ELFlash and property is the literal string "keep", set a ThreadLocal property that will be inspected by the flash on the next link in the resolution chain and return the ELFlash instance. If base is an instance of ELFlash and property is the literal string "now", return the result of calling getRequestMap( ) on the ExternalContext for the FacesContext for this request. Call setPropertyResolved(true) on the ELContext where appropriate.

Specified by:

getValue in class javax.el.ELResolver

Throws:

javax.el.PropertyNotFoundException - if property is null.

getType

public Class<?> getType(javax.el.ELContext elContext,
                        Object base,
                        Object property)

Return the valid Class for a future set operation, which will always be null because sets happen via the MapELResolver operating on the ELFlash instance as a Map.

Specified by:

getType in class javax.el.ELResolver

Throws:

javax.el.PropertyNotFoundException - if property is null.

setValue

public void setValue(javax.el.ELContext elContext,
                     Object base,
                     Object property,
                     Object value)

This method will throw PropertyNotWritableException if called with a null base and a property value equal to the literal string "flash". This is because set operations normally go through the MapELResolver via the ELFlash Map.

In other words, do not call this method directly to set a value into the flash! The only way to access the flash is either through JSP or via the EL API.

Specified by:

setValue in class javax.el.ELResolver

Throws:

javax.el.PropertyNotFoundException - if base is null and property is null.

javax.el.PropertyNotWritableException - if base is null and property is the literal string "flash".

isReadOnly

public boolean isReadOnly(javax.el.ELContext elContext,
                          Object base,
                          Object property)

Returns true because write operations take place via the MapELResolver on the actual ELFlash instance.

Specified by:

isReadOnly in class javax.el.ELResolver

Throws:

javax.el.PropertyNotFoundException - if base is null and property is null.

getFeatureDescriptors

public Iterator<FeatureDescriptor> getFeatureDescriptors(javax.el.ELContext elContext,
                                                         Object base)

Returns an iterator of FeatureDescriptors for the current contents of the flash.

Specified by:

getFeatureDescriptors in class javax.el.ELResolver

getCommonPropertyType

public Class<?> getCommonPropertyType(javax.el.ELContext context,
                                      Object base)

If base is non-null and is the literal string "flash", return Object.class.

Specified by:

getCommonPropertyType in class javax.el.ELResolver