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Micha Kiener
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SPR-6464, FlashMap implementation
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‎org.springframework.web/src/main/java/org/springframework/web/filter/FlashMapFilter.java

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/*
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* Copyright 2002-2008 the original author or authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
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* an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
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* specific language governing permissions and limitations under the License.
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*/
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package org.springframework.web.filter;
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import java.io.IOException;
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import java.util.Map;
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import javax.servlet.FilterChain;
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import javax.servlet.ServletException;
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import javax.servlet.http.HttpServletRequest;
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import javax.servlet.http.HttpServletResponse;
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import org.springframework.web.util.FlashMap;
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/**
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* The filter needed to be activated to support the {@link FlashMap}, writing parameters within the flash map to the
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* current request and flushing out the map afterwards.
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*
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* @author Micha Kiener
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* @since 3.1
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*/
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public class FlashMapFilter extends OncePerRequestFilter {
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/**
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* @see org.springframework.web.filter.OncePerRequestFilter#doFilterInternal(javax.servlet.http.HttpServletRequest,
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* javax.servlet.http.HttpServletResponse, javax.servlet.FilterChain)
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*/
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@Override
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protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
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throws ServletException, IOException {
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Map<String, Object> flashMap = FlashMap.getFlashMap(false);
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if (flashMap != null) {
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for (Map.Entry<String, ?> entry : flashMap.entrySet()) {
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Object currentValue = request.getAttribute(entry.getKey());
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if (currentValue == null) {
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request.setAttribute(entry.getKey(), entry.getValue());
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}
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}
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FlashMap.removeFlashMap();
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}
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filterChain.doFilter(request, response);
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}
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}

‎org.springframework.web/src/main/java/org/springframework/web/util/FlashMap.java

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/*
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* Copyright 2002-2008 the original author or authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
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* an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
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* specific language governing permissions and limitations under the License.
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*/
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package org.springframework.web.util;
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import java.util.HashMap;
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import java.util.Map;
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import org.springframework.web.context.request.RequestAttributes;
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import org.springframework.web.context.request.RequestContextHolder;
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import org.springframework.web.filter.FlashMapFilter;
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/**
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* The Redirect-After-Post pattern is a solution for many problems and the flash map utility is able to store state
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* which persists to the next request. For instance, if you're having an error in the login handler, you could actually
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* store messages or any other state within the flash map and then redirect to an appropriate view where the state would
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* be still available. The content of the flash map is actually added as request parameters in the next request and then
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* being flushed out which is done by the {@link FlashMapFilter}.
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* <p>
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* If window management is activated, the flash map is stored within window scope to avoid concurrent tabs / windows
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* affecting each other, it falls back to the session, if window management is not activated.
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*
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* @author Micha Kiener
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* @since 3.1
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*
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* @see FlashMapFilter
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*/
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public class FlashMap {
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public static final String FLASH_MAP_ATTRIBUTE = FlashMap.class.getName();
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/**
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* Stores the given name / value pair in the flash map to become available as a request parameter in the next
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* request using the same name.
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*
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* @param <T> the type of the parameter value to put in the flash map
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* @param parameterName the name of the parameter under which the value will become available in the next request
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* @param parameterValue the parameter value to be stored in flash
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* @return any old value already in the flash map, if any, <code>null</code> otherwise
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*/
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@SuppressWarnings("unchecked")
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public static <T> T put(String parameterName, T parameterValue) {
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Map<String, Object> flashMap = getFlashMap(true);
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return (T) flashMap.put(parameterName, parameterValue);
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}
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/**
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* Returns the flash map typically stored in window or session scope and creates a new one, if not existing and if
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* needed.
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*
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* @param createIfNotExisting flag, indicating whether to create the flash map, if it does not exist already
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* @return the flash map currently bound to the session or window scope, if available
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*/
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@SuppressWarnings("unchecked")
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public static Map<String, Object> getFlashMap(boolean createIfNotExisting) {
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RequestAttributes requestAttributes = RequestContextHolder.currentRequestAttributes();
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Map<String, Object> flashMap = (Map<String, Object>) requestAttributes.getAttribute(FLASH_MAP_ATTRIBUTE,
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getFlashMapScope());
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if (flashMap == null && createIfNotExisting) {
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flashMap = new HashMap<String, Object>();
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requestAttributes.setAttribute(FLASH_MAP_ATTRIBUTE, flashMap, getFlashMapScope());
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}
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return flashMap;
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}
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/**
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* Removes the flash map from the window or session scope.
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*/
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public static void removeFlashMap() {
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RequestAttributes requestAttributes = RequestContextHolder.currentRequestAttributes();
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requestAttributes.removeAttribute(FLASH_MAP_ATTRIBUTE, getFlashMapScope());
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}
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/**
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* @return the scope to store the flash map in which is window scope by default, if window management is activated,
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* session otherwise
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*/
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protected static int getFlashMapScope() {
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// TODO: check for window management and return value accordingly
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return RequestAttributes.SCOPE_SESSION;
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}
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/**
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* Private constructor as the map is only to be used using its static accessor methods.
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*/
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private FlashMap() {
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}
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}

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