learnjsf.com

A PRG Phase Listener for JSF

6 August, 2006 (03:47) | JavaServer Faces

I love the POST-REDIRECT-GET pattern for enabling bookmarks and the back button. JSF allows you to specify a redirect element in a navigation case, but what if you want to automatically redirect every request? This PostRedirectGetPhaseListener does just that.

Very simply, it intercepts all POST requests just before the render phase and redirects the browser to the view via a GET request. This way, you don’t have to put redirect elements in every navigation case in faces-config.xml. OTOH, the phase listener does this every time, which you may not want, either. Like using a redirect in a navigation case, you incur the overhead of storing and restoring the view twice for each action; however, the phase listener approach does ensure that the browser never saves a POST request in its history.

A few notes about the code. As someone noted earlier in the dicussion, you will lose any values in the Request scope between the redirect and the get. This includes the Faces message queue. I’ve handled this below by saving and restoring all Faces messages in the session between the redirect and the get, so <h:message> will still work. If you wish, you can modify this code to save and restore the entire request scope in session.

To use the PostRedirectGetListener, just declare as usual in faces-config:

Caveat emptor: I have tested this a little, but only for my narrow applications. YMMV. As usual, this code comes with no warranty whatsoever. I’ll try to answer questions on users@myfaces.apache.org as I have time, but I’m on two other projects like the rest of us….

package com.turbomanage.util.faces;

import java.io.IOException;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.Iterator;

import java.util.List;

import java.util.Map;

import java.util.Map.Entry;import javax.faces.application.FacesMessage;

import javax.faces.component.UIComponent;

import javax.faces.component.UIInput;

import javax.faces.component.UIViewRoot;

import javax.faces.context.FacesContext;

import javax.faces.event.PhaseEvent;

import javax.faces.event.PhaseId;

import javax.faces.event.PhaseListener;

import javax.servlet.http.HttpServletRequest;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

public class PostRedirectGetListener implements PhaseListener {

private static final Log log = LogFactory
.getLog(PostRedirectGetListener.class);

// a name under which to save messages between the redirect and the
// subsequent
// get
private static final String sessionToken = “MULTI_PAGE_MESSAGES_SUPPORT”;

public PostRedirectGetListener() {
}

public PhaseId getPhaseId() {
return PhaseId.ANY_PHASE;
}

/**
* Handle a notification that the processing for a particular phase has just
* been completed.
*/
public void afterPhase(PhaseEvent event) {
// Save messages in session so they’ll be avaiable on the
// subsequent GET request
if (event.getPhaseId() == PhaseId.APPLY_REQUEST_VALUES
|| event.getPhaseId() == PhaseId.PROCESS_VALIDATIONS
|| event.getPhaseId() == PhaseId.INVOKE_APPLICATION) {
FacesContext facesContext = event.getFacesContext();
saveMessages(facesContext);
}
}

public void beforePhase(PhaseEvent event) {

if (event.getPhaseId() != PhaseId.RENDER_RESPONSE) {
return;
}

// Implement POST-REDIRECT-GET pattern
FacesContext facesContext = event.getFacesContext();
UIViewRoot viewRoot = facesContext.getViewRoot();
HttpServletRequest req = (HttpServletRequest) facesContext
.getExternalContext().getRequest();
if (“POST”.equals(req.getMethod())) {
String nextViewID = facesContext.getViewRoot().getViewId();
String nextViewURL = facesContext.getApplication().getViewHandler()
.getActionURL(facesContext, nextViewID);
log.debug(“Redirecting to ” + nextViewURL);
try {
event.getFacesContext().getExternalContext().redirect(
nextViewURL);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
} else {
// Move saved messages from session back to request queue
restoreMessages(facesContext);
/*
* JSF normally clears input component values in the UpdateModel
* phase. However, this phase does not run for a GET request, so we
* must do it ourselves. Otherwise, the view will retain values from
* the first time it was loaded.
*/
resetComponentValues(viewRoot.getChildren());
}
}

/**
* Remove the messages that are not associated with any particular component
* from the user’s session and add them to the faces context.
*
* @return the number of removed messages.
*/
private int restoreMessages(FacesContext facesContext) {
// remove messages from the session
int numRestoredMessages = 0;
Map sessionMap = facesContext.getExternalContext().getSessionMap();
Map allMessages = (Map) sessionMap.remove(sessionToken);
if (allMessages == null) {
return 0;
}

// Move messages from session back to facesContext
for (Iterator i = allMessages.entrySet().iterator(); i.hasNext();) {
Entry e = (Entry) i.next();
String clientId = (String) e.getKey();
List clientMessages = (List) e.getValue();
for (Iterator j = clientMessages.iterator(); j.hasNext();) {
facesContext.addMessage(clientId, (FacesMessage) j.next());
numRestoredMessages++;
}
}
return numRestoredMessages;
}

/**
* Remove the messages that are not associated with any particular component
* from the faces context and store them to the user’s session.
*
* @return the number of removed messages.
*/
private int saveMessages(FacesContext facesContext) {
// Remove messages from the context
// Save as a map of lists so we can continue to messages with components
Map sessionMap = facesContext.getExternalContext().getSessionMap();
int numMessages = 0;

if (!sessionMap.containsKey(sessionToken)) {
sessionMap.put(sessionToken, new HashMap());
}
Map allMessages = (Map) sessionMap.get(sessionToken);

for (Iterator i = facesContext.getClientIdsWithMessages(); i.hasNext();) {
String clientId = (String) i.next();
// For each component (client ID), retrieve the messages to a list
List messages = new ArrayList();
for (Iterator j = facesContext.getMessages(clientId); j.hasNext();) {
messages.add(j.next());
j.remove();
numMessages++;
}

List clientMessages = (List) allMessages.get(clientId);
if (clientMessages != null)
// There are already messages for this component
{
clientMessages.addAll(messages);
} else
// Not yet messages for this component
{
allMessages.put(clientId, messages);
}
}
return numMessages;
}

/**
* Resets UIInput component values From http://
* forum.java.sun.com/thread.jspa?threadID=495087&messageID=3704164
*/
private void resetComponentValues(List childList) {
for (int i = 0; i < childList.size(); i++) {
UIComponent component = (UIComponent) childList.get(i);
if (component instanceof UIInput) {
UIInput input = (UIInput) component;
input.setSubmittedValue(null);
}
resetComponentValues(component.getChildren());
}
}
}

« JSF Tip of the Day: EL Conditional Operator

JSF Security Presentation at OWASP Atlanta Wed Aug 9 »

Comments

Comment from Anonymous
Date: October 19, 2006, 1:55 pm

Hi,

I tried to integrate the idea of the Post-Redirect-Get-PhaseListener of
http://turbomanage.wordpress.com/2006/08/06/prg-for-jsf/
into my project.

Now I face the problem that t:dataScroller doesn’t work anymore, because
it lost its navigations variables during the redirect phase.
These params are stored within the request scoped and get lost during
the redirect.

But I wonder if I could store the vars into session scope. This would
also enable me to save the current navigation state for a longer period.

Regards,

Comment from dchandler
Date: October 19, 2006, 2:02 pm

Ingo, you could replace the saveMessages() method with a method to iterate over all entries in the Request Map instead of saving only component messages. However, I suspect there are some variables in the Request scope that you would not want to overwrite on the subsequent request.

/dmc

A PRG Phase Listener for JSF

Comments

Subscribe