ru.smsl.webkrona.util.FlashMap.java Source code

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Here is the source code for ru.smsl.webkrona.util.FlashMap.java

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/*
 * Copyright 2002-2008 the original author or authors.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
 * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations under the License.
 */
package ru.smsl.webkrona.util;

import java.util.HashMap;
import java.util.Map;

import org.springframework.web.context.request.RequestAttributes;
import org.springframework.web.context.request.RequestContextHolder;

import ru.smsl.webkrona.filter.FlashMapFilter;

/**
 * The Redirect-After-Post pattern is a solution for many problems and the flash map utility is able to store state
 * which persists to the next request. For instance, if you're having an error in the login handler, you could actually
 * store messages or any other state within the flash map and then redirect to an appropriate view where the state would
 * be still available. The content of the flash map is actually added as request parameters in the next request and then
 * being flushed out which is done by the {@link FlashMapFilter}.
 * <p>
 * If window management is activated, the flash map is stored within window scope to avoid concurrent tabs / windows
 * affecting each other, it falls back to the session, if window management is not activated.
 * <p>
 * Typically, you will use the flash map by manually adding parameters to it before redirecting which could look like:
 * 
 * <pre>
 * FlashMap.put(&quot;paramName&quot;, paramValue);
 * redirect(...);
 * </pre>
 * 
 * @author Micha Kiener
 * @since 3.1
 * 
 * @see FlashMapFilter
 */
public class FlashMap {
    public static final String FLASH_MAP_ATTRIBUTE = FlashMap.class.getName();

    /**
     * Stores the given name / value pair in the flash map to become available as a request parameter in the next
     * request using the same name.
     * 
     * @param <T> the type of the parameter value to put in the flash map
     * @param parameterName the name of the parameter under which the value will become available in the next request
     * @param parameterValue the parameter value to be stored in flash
     * @return any old value already in the flash map, if any, <code>null</code> otherwise
     */
    @SuppressWarnings("unchecked")
    public static <T> T put(String parameterName, T parameterValue) {
        Map<String, Object> flashMap = getFlashMap(true);
        return (T) flashMap.put(parameterName, parameterValue);
    }

    /**
     * Returns the flash map typically stored in window or session scope and creates a new one, if not existing and if
     * needed.
     * 
     * @param createIfNotExisting flag, indicating whether to create the flash map, if it does not exist already
     * @return the flash map currently bound to the session or window scope, if available
     */
    @SuppressWarnings("unchecked")
    public static Map<String, Object> getFlashMap(boolean createIfNotExisting) {
        RequestAttributes requestAttributes = RequestContextHolder.currentRequestAttributes();
        Map<String, Object> flashMap = (Map<String, Object>) requestAttributes.getAttribute(FLASH_MAP_ATTRIBUTE,
                getFlashMapScope());

        if (flashMap == null && createIfNotExisting) {
            flashMap = new HashMap<String, Object>();
            requestAttributes.setAttribute(FLASH_MAP_ATTRIBUTE, flashMap, getFlashMapScope());
        }

        return flashMap;
    }

    /**
     * Removes the flash map from the window or session scope.
     */
    public static void removeFlashMap() {
        RequestAttributes requestAttributes = RequestContextHolder.currentRequestAttributes();
        requestAttributes.removeAttribute(FLASH_MAP_ATTRIBUTE, getFlashMapScope());
    }

    /**
     * @return the scope to store the flash map in which is window scope by default, if window management is activated,
     * session otherwise
     */
    protected static int getFlashMapScope() {
        // TODO: check for window management and return value accordingly
        return RequestAttributes.SCOPE_SESSION;
    }

    /**
     * Private constructor as the map is only to be used using its static accessor methods.
     */
    private FlashMap() {
    }
}