Spring MVC custom scope bean

Question

I would like to create my own custom scope bean which will use HTTP session (kind of Flash scope).

According to Spring Manual I need to implement org.springframewor

Answer 1

I hope it will be useful for someone in the future, so I would like to share it.

I made some reserch on it and have found that unfortunately, it is impossible to get HTTP Session for Spring MVC.

My purpose was Flash Scope implementation for my Spring MVC Controller using PRG pattern.

Making more research in Spring Forum I've found the way to do it using HandlerInterceptor.

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import java.util.*;
import java.util.Map.Entry;

import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

public class FlashScopeInterceptor implements HandlerInterceptor {

    public static final String DEFAULT_ATTRIBUTE_NAME = "flashScope";
    public static final String DEFAULT_SESSION_ATTRIBUTE_NAME = FlashScopeInterceptor.class.getName();
    public static final int DEFAULT_RETENTION_COUNT = 2;

    private String sessionAttributeName = DEFAULT_SESSION_ATTRIBUTE_NAME;
    private String attributeName = DEFAULT_ATTRIBUTE_NAME;
    private int retentionCount = DEFAULT_RETENTION_COUNT;

    /**
     * Unbinds current flashScope from session. Rolls request's flashScope to
     * the next scope. Binds request's flashScope, if not empty, to the session.
     * 
     */

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
            throws Exception {
        if (request.getSession( false ) != null)
        {
            request.getSession().removeAttribute( this.sessionAttributeName );
        }
        Object requestAttribute = request.getAttribute( this.attributeName );
        if (requestAttribute instanceof MultiScopeModelMap)
        {
            MultiScopeModelMap attributes = (MultiScopeModelMap) requestAttribute;
            if (!attributes.isEmpty())
            {
                attributes.next();
                if (!attributes.isEmpty())
                {
                    request.getSession( true ).setAttribute( this.sessionAttributeName, attributes );
                }
            }
        }
    }

    /**
     * merge modelAndView.model['flashScope'] to current flashScope
     */
    @Override
    public void postHandle( HttpServletRequest request, HttpServletResponse response, Object handler,
            ModelAndView modelAndView) throws Exception {
        if (modelAndView != null)
        {
            Map modelFlashScopeMap = null;
            for (Iterator> iterator = ((Map) modelAndView.getModel()).entrySet()
                    .iterator(); iterator.hasNext();)
            {
                Entry entry = iterator.next();
                if (this.attributeName.equals( entry.getKey() ) && entry.getValue() instanceof Map)
                {
                    if (modelFlashScopeMap == null)
                    {
                        modelFlashScopeMap = (Map) entry.getValue();
                    }
                    else
                    {
                        modelFlashScopeMap.putAll( (Map) entry.getValue() );
                    }
                    iterator.remove();
                }
                else if (entry.getKey().startsWith( this.attributeName + "." ))
                {
                    String key = entry.getKey().substring( this.attributeName.length() + 1 );
                    if (modelFlashScopeMap == null)
                    {
                        modelFlashScopeMap = new HashMap();
                    }
                    modelFlashScopeMap.put( key, entry.getValue() );
                    iterator.remove();
                }
            }
            if (modelFlashScopeMap != null)
            {
                MultiScopeModelMap flashScopeMap;
                if (request.getAttribute( this.attributeName ) instanceof MultiScopeModelMap)
                {
                    flashScopeMap = (MultiScopeModelMap) request.getAttribute( this.attributeName );
                }
                else
                {
                    flashScopeMap = new MultiScopeModelMap( this.retentionCount );
                }
                flashScopeMap.putAll( modelFlashScopeMap );
                request.setAttribute( this.attributeName, flashScopeMap );
            }
        }
    }

    /**
     * binds session flashScope to current session, if not empty. Otherwise cleans up empty
     * flashScope
     */
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {

        HttpSession session = request.getSession( false );
        if (session != null)
        {
            Object sessionAttribute = session.getAttribute( this.sessionAttributeName );
            if (sessionAttribute instanceof MultiScopeModelMap)
            {
                MultiScopeModelMap flashScope = (MultiScopeModelMap) sessionAttribute;
                if (flashScope.isEmpty())
                {
                    session.removeAttribute( this.sessionAttributeName );
                }
                else
                {
                    request.setAttribute( this.attributeName, flashScope );
                }
            }
        }
        return true;
    }
}

Now MultiScopeModelMap.java

import java.io.Serializable;
import java.util.Collection;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.Map;
import java.util.Set;

import org.apache.commons.collections.map.CompositeMap;
import org.apache.commons.collections.map.CompositeMap.MapMutator;

public class MultiScopeModelMap extends CompositeMap implements Serializable, MapMutator
{
    public MultiScopeModelMap(int num)
    {
        super();
        setMutator( this );
        for(int i = 0; i < num; ++i)
        {
            addComposited( new HashMap() );
        }
    }

    /** Shadows composite map. */
    private final LinkedList

Usage:

@RequestMapping(value="/login.do", method=RequestMethod.POST)
    public ModelAndView login(@Valid User user){
        ModelAndView mv = new ModelAndView("redirect:result.html");
        if (authService.authenticate(user.getUserName(), user.getPassword()))
            mv.addObject("flashScope.message", "Success");
        //else
            mv.addObject("flashScope.message", "Login Failed");
        return mv;
    }

@RequestMapping(value ="/result.html", method=RequestMethod.GET)
    public ModelAndView result(){
        ModelAndView mv = new ModelAndView("login/loginAction");
        return mv;
    }

In JSP the usage is very simple:

${flashScope.message}

In addition you need to configure FlashScopeInterceptor class as interceptor.