SPR-6464 Polish FlashMap changes.

org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/DispatcherServlet.java

@@ -671,7 +671,8 @@ public class DispatcherServlet extends FrameworkServlet {
 
 	/**
 	 * Initialize the {@link FlashMapManager} used by this servlet instance.
-	 * <p>If no implementation is configured then we default to DefaultFlashMapManager.
+	 * <p>If no implementation is configured then we default to 
+	 * {@code org.springframework.web.servlet.support.DefaultFlashMapManager}.
 	 */
 	private void initFlashMapManager(ApplicationContext context) {
 		try {

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

@@ -21,7 +21,6 @@ import java.util.LinkedHashMap;
 import java.util.Map;
 
 import org.springframework.beans.BeanUtils;
-import org.springframework.util.Assert;
 
 /**
  * A FlashMap provides a way for one request to store attributes intended for 
@@ -33,11 +32,14 @@ import org.springframework.util.Assert;
  * <p>A FlashMap can be set up with a request path and request parameters to 
  * help identify the target request. Without this information, a FlashMap is
  * made available to the next request, which may or may not be the intended 
- * result. Before a redirect, the target URL is known and when using the
- * {@code org.springframework.web.servlet.view.RedirectView}, FlashMap 
- * instances are automatically updated with redirect URL information.
+ * recipient. On a redirect, the target URL is known and for example
+ * {@code org.springframework.web.servlet.view.RedirectView} has the
+ * opportunity to automatically update the current FlashMap with target
+ * URL information .
  * 
- * <p>Annotated controllers will usually not access a FlashMap directly.. TODO
+ * <p>Annotated controllers will usually not use this type directly.
+ * See {@code org.springframework.web.servlet.mvc.support.RedirectAttributes}
+ * for an overview of using flash attributes in annotated controllers. 
  * 
  * @author Rossen Stoyanchev
  * @since 3.1
@@ -58,13 +60,6 @@ public class FlashMap extends HashMap<String, Object> implements Comparable<Flas
 
 	private final int createdBy;
 
-	/**
-	 * Create a new instance.
-	 */
-	public FlashMap() {
-		this.createdBy = 0;
-	}
-
 	/**
 	 * Create a new instance with an id uniquely identifying the creator of 
 	 * this FlashMap.
@@ -72,20 +67,26 @@ public class FlashMap extends HashMap<String, Object> implements Comparable<Flas
 	public FlashMap(int createdBy) {
 		this.createdBy = createdBy;
 	}
+	
+	/**
+	 * Create a new instance.
+	 */
+	public FlashMap() {
+		this.createdBy = 0;
+	}
 
 	/**
 	 * Provide a URL path to help identify the target request for this FlashMap.
 	 * The path may be absolute (e.g. /application/resource) or relative to the
 	 * current request (e.g. ../resource).
-	 * @param path the URI path, never {@code null}
+	 * @param path the URI path
 	 */
 	public void setTargetRequestPath(String path) {
-		Assert.notNull(path, "Expected path must not be null");
 		this.targetRequestPath = path;
 	}
 
 	/**
-	 * Return the URL path of the target request, or {@code null} if none.
+	 * Return the target URL path or {@code null}.
 	 */
 	public String getTargetRequestPath() {
 		return targetRequestPath;
@@ -93,10 +94,9 @@ public class FlashMap extends HashMap<String, Object> implements Comparable<Flas
 
 	/**
 	 * Provide request parameter pairs to identify the request for this FlashMap. 
-	 * If not set, the FlashMap will match to requests with any parameters.
-	 * Only simple value types, as defined in {@link BeanUtils#isSimpleValueType}, 
-	 * are used.
+	 * Only simple type, non-null parameter values are used.
 	 * @param params a Map with the names and values of expected parameters.
+	 * @see BeanUtils#isSimpleValueType(Class)
 	 */
 	public FlashMap addTargetRequestParams(Map<String, ?> params) {
 		if (params != null) {
@@ -112,10 +112,8 @@ public class FlashMap extends HashMap<String, Object> implements Comparable<Flas
 
 	/**
 	 * Provide a request parameter to identify the request for this FlashMap.
-	 * If not set, the FlashMap will match to requests with any parameters.
-	 * 
-	 * @param name the name of the expected parameter (never {@code null})
-	 * @param value the value for the expected parameter (never {@code null})
+	 * @param name the name of the expected parameter, never {@code null}
+	 * @param value the value for the expected parameter, never {@code null}
 	 */
 	public FlashMap addTargetRequestParam(String name, String value) {
 		this.targetRequestParams.put(name, value.toString());
@@ -130,9 +128,8 @@ public class FlashMap extends HashMap<String, Object> implements Comparable<Flas
 	}
 
 	/**
-	 * Start the expiration period for this instance. After the given number of 
-	 * seconds calls to {@link #isExpired()} will return "true".
-	 * @param timeToLive the number of seconds before flash map expires
+	 * Start the expiration period for this instance.
+	 * @param timeToLive the number of seconds before expiration
 	 */
 	public void startExpirationPeriod(int timeToLive) {
 		this.expirationStartTime = System.currentTimeMillis();
@@ -140,8 +137,8 @@ public class FlashMap extends HashMap<String, Object> implements Comparable<Flas
 	}
 
 	/**
-	 * Whether the flash map has expired depending on the number of seconds 
-	 * elapsed since the call to {@link #startExpirationPeriod}.
+	 * Whether this instance has expired depending on the amount of elapsed
+	 * time since the call to {@link #startExpirationPeriod}.
 	 */
 	public boolean isExpired() {
 		if (this.expirationStartTime != 0) {
@@ -160,8 +157,9 @@ public class FlashMap extends HashMap<String, Object> implements Comparable<Flas
 	}
 
 	/**
-	 * Compare two FlashMaps and select the one that has a target URL path or 
-	 * has more target request parameters. 
+	 * Compare two FlashMaps and prefer the one that specifies a target URL 
+	 * path or has more target URL parameters. Before comparing FlashMap
+	 * instances ensure that they match a given request.
 	 */
 	public int compareTo(FlashMap other) {
 		int thisUrlPath = (this.targetRequestPath != null) ? 1 : 0;
@@ -178,8 +176,8 @@ public class FlashMap extends HashMap<String, Object> implements Comparable<Flas
 	public String toString() {
 		StringBuilder result = new StringBuilder();
 		result.append("[Attributes=").append(super.toString());
-		result.append(", expecteRequestUri=").append(this.targetRequestPath);
-		result.append(", expectedRequestParameters=" + this.targetRequestParams.toString()).append("]");
+		result.append(", targetRequestPath=").append(this.targetRequestPath);
+		result.append(", targetRequestParams=" + this.targetRequestParams.toString()).append("]");
 		return result.toString();
 	}
 

org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/FlashMapManager.java

@@ -16,20 +16,22 @@
 
 package org.springframework.web.servlet;
 
-import java.util.Map;
-
 import javax.servlet.http.HttpServletRequest;
 
 /**
- * A strategy interface for storing and retrieving {@code FlashMap} instances.
- * See {@link FlashMap} for a general overview of using flash attributes.
+ * A strategy interface for storing, retrieving, and managing {@code FlashMap}
+ * instances. See {@link FlashMap} for a general overview of flash attributes.
+ * 
+ * <p>A FlashMapManager is invoked at the beginning and at the end of requests.
+ * For each request it retrieves an "input" FlashMap with attributes passed 
+ * from a previous request (if any) and creates an "output" FlashMap with 
+ * attributes to pass to a subsequent request. "Input" and "output" FlashMap 
+ * instances are exposed as request attributes and are accessible via methods
+ * in {@code org.springframework.web.servlet.support.RequestContextUtils}.
  * 
- * <p>A FlashMapManager is invoked at the beginning and at the end of a request.
- * For each request, it exposes an "input" FlashMap with attributes passed from
- * a previous request (if any) and an "output" FlashMap with attributes to pass 
- * to a subsequent request. Both FlashMap instances are exposed via request
- * attributes and can be accessed through methods in
- * {@code org.springframework.web.servlet.support.RequestContextUtils}.
+ * <p>Annotated controllers are most likely to store and access flash attributes
+ * through their model. 
+ * See {@code org.springframework.web.servlet.mvc.support.RedirectAttributes}.
  * 
  * @author Rossen Stoyanchev
  * @since 3.1
@@ -39,42 +41,39 @@ import javax.servlet.http.HttpServletRequest;
 public interface FlashMapManager {
 
 	/**
-	 * Name of request attribute that holds a read-only {@link Map} with 
-	 * "input" flash attributes from a previous request (if any).
+	 * Name of request attribute that holds a read-only 
+	 * {@code Map<String, Object>} with "input" flash attributes if any.
 	 * @see org.springframework.web.servlet.support.RequestContextUtils#getInputFlashMap(HttpServletRequest)
 	 */
 	public static final String INPUT_FLASH_MAP_ATTRIBUTE = FlashMapManager.class.getName() + ".INPUT_FLASH_MAP";
 
 	/**
 	 * Name of request attribute that holds the "output" {@link FlashMap} with
-	 * attributes to pass to a subsequent request.
+	 * attributes to save for a subsequent request.
 	 * @see org.springframework.web.servlet.support.RequestContextUtils#getOutputFlashMap(HttpServletRequest)
 	 */
 	public static final String OUTPUT_FLASH_MAP_ATTRIBUTE = FlashMapManager.class.getName() + ".OUTPUT_FLASH_MAP";
 
 	/**
-	 * Performs the following tasks unless the {@link #OUTPUT_FLASH_MAP_ATTRIBUTE} 
+	 * Perform the following tasks unless the {@link #OUTPUT_FLASH_MAP_ATTRIBUTE} 
 	 * request attribute exists:
 	 * <ol>
-	 * 	<li>Find the "input" FlashMap from a previous request (if any), expose it 
-	 * under the request attribute {@link #INPUT_FLASH_MAP_ATTRIBUTE}, and 
-	 * remove it from underlying storage.
-	 * 	<li>Create the "output" FlashMap where the current request can save 
-	 * flash attributes and expose it under the request attribute 
-	 * {@link #OUTPUT_FLASH_MAP_ATTRIBUTE}.
-	 * 	<li>Remove expired FlashMap instances.
+	 * 	<li>Find the "input" FlashMap, expose it under the request attribute 
+	 * {@link #INPUT_FLASH_MAP_ATTRIBUTE}, and remove it from underlying storage.
+	 * 	<li>Create the "output" FlashMap and expose it under the request 
+	 * attribute {@link #OUTPUT_FLASH_MAP_ATTRIBUTE}.
+	 * 	<li>Clean expired FlashMap instances.
 	 * </ol>
-	 * 
 	 * @param request the current request
 	 */
 	void requestStarted(HttpServletRequest request);
 
 	/**
-	 * Save the "output" FlashMap in underlying storage, start its expiration 
-	 * period, and decode/normalize its target request path. 
-	 * 
-	 * <p>The "output" FlashMap is not saved if it is empty or if it was not 
-	 * created by this FlashMapManager.
+	 * Start the expiration period of the "output" FlashMap save it in the
+	 * underlying storage.
+	 * <p>The "output" FlashMap should not be saved if it is empty or if it was
+	 * not created by the current FlashMapManager instance.
+	 * @param request the current request
 	 */
 	void requestCompleted(HttpServletRequest request);
 

org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/SmartView.java

@@ -17,7 +17,8 @@
 package org.springframework.web.servlet;
 
 /**
- * Interface to be implemented by Views that perform a redirect.
+ * Provides additional information about a View such as whether it 
+ * performs redirects. 
  *
  * @author Rossen Stoyanchev
  * @since 3.1

org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/mvc/method/annotation/support/RedirectAttributesMethodArgumentResolver.java

@@ -31,10 +31,10 @@ import org.springframework.web.servlet.mvc.support.RedirectAttributes;
 import org.springframework.web.servlet.mvc.support.RedirectAttributesModelMap;
 
 /**
- * Resolves {@link RedirectAttributesModelMap} method arguments. 
+ * Resolves method arguments of type {@link RedirectAttributes}. 
  * 
- * <p>This resolver must be listed ahead of the {@link ModelMethodProcessor}, 
- * which also resolves arguments of type {@link Map} and {@link Model}.  
+ * <p>This resolver must be listed before the {@link ModelMethodProcessor},
+ * which resolves {@link Map} and {@link Model} arguments.
  *
  * @author Rossen Stoyanchev
  * @since 3.1

org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/mvc/support/RedirectAttributes.java

@@ -20,70 +20,66 @@ import java.util.Collection;
 import java.util.Map;
 
 import org.springframework.ui.Model;
+import org.springframework.web.servlet.FlashMap;
 
 /**
- * A {@link Model} that can also store attributes candidate for flash storage.
+ * A specialization of the {@link Model} interface that controllers can use to
+ * select attributes for a redirect scenario. Since the intent of adding 
+ * redirect attributes is very explicit --  i.e. to be used for a redirect URL, 
+ * attribute values may be formatted as Strings and stored that way to make 
+ * them eligible to be appended to the query string or expanded as URI 
+ * variables in {@code org.springframework.web.servlet.view.RedirectView}.
+ * 
+ * <p>This interface also provides a way to add flash attributes. For a 
+ * general overview of flash attributes see {@link FlashMap}. You can use 
+ * {@link RedirectAttributes} to store flash attributes and they will be 
+ * automatically propagated to the "output" FlashMap of the current request. 
+ * 
+ * <p>Example usage in an {@code @Controller}:
+ * <pre>
+ * &#064;RequestMapping(value = "/accounts", method = RequestMethod.POST)
+ * public String handle(Account account, BindingResult result, RedirectAttributes redirectAttrs) {
+ *   if (result.hasErrors()) {
+ *     return "accounts/new";
+ *   }
+ *   // Save account ...
+ *   redirectAttrs.addAttribute("id", account.getId()).addFlashAttribute("message", "Account created!");
+ *   return "redirect:/accounts/{id}";
+ * }
+ * </pre>
+ * 
+ * <p>After the redirect, flash attributes are automatically added to the model
+ * of the controller serving the redirect URL.
  * 
  * @author Rossen Stoyanchev
  * @since 3.1
  */
 public interface RedirectAttributes extends Model {
 
-	/**
-	 * Add the supplied attribute under the supplied name.
-	 * @param attributeName the name of the model attribute (never <code>null</code>)
-	 * @param attributeValue the model attribute value (can be <code>null</code>)
-	 */
 	RedirectAttributes addAttribute(String attributeName, Object attributeValue);
 
-	/**
-	 * Add the supplied attribute to this <code>Map</code> using a
-	 * {@link org.springframework.core.Conventions#getVariableName generated name}.
-	 * <p><emphasis>Note: Empty {@link java.util.Collection Collections} are not added to
-	 * the model when using this method because we cannot correctly determine
-	 * the true convention name. View code should check for <code>null</code> rather
-	 * than for empty collections as is already done by JSTL tags.</emphasis>
-	 * @param attributeValue the model attribute value (never <code>null</code>)
-	 */
 	RedirectAttributes addAttribute(Object attributeValue);
 
-	/**
-	 * Copy all attributes in the supplied <code>Collection</code> into this
-	 * <code>Map</code>, using attribute name generation for each element.
-	 * @see #addAttribute(Object)
-	 */
 	RedirectAttributes addAllAttributes(Collection<?> attributeValues);
-
-	/**
-	 * Copy all attributes in the supplied <code>Map</code> into this <code>Map</code>.
-	 * @see #addAttribute(String, Object)
-	 */
-	Model addAllAttributes(Map<String, ?> attributes);
-
-	/**
-	 * Copy all attributes in the supplied <code>Map</code> into this <code>Map</code>,
-	 * with existing objects of the same name taking precedence (i.e. not getting
-	 * replaced).
-	 */
-	RedirectAttributes mergeAttributes(Map<String, ?> attributes);
 	
+	RedirectAttributes mergeAttributes(Map<String, ?> attributes);
+
 	/**
-	 * Add the given attribute as a candidate for flash storage. 
-	 * @param attributeName the flash attribute name; never null
-	 * @param attributeValue the flash attribute value; may be null
+	 * Add the given flash attribute. 
+	 * @param attributeName the attribute name; never {@code null}
+	 * @param attributeValue the attribute value; may be {@code null}
 	 */
 	RedirectAttributes addFlashAttribute(String attributeName, Object attributeValue);
 
 	/**
-	 * Add the given attribute value as a candidate for flash storage using a
+	 * Add the given flash storage using a
 	 * {@link org.springframework.core.Conventions#getVariableName generated name}. 
-	 * @param attributeValue the flash attribute value; never null
+	 * @param attributeValue the flash attribute value; never {@code null}
 	 */
 	RedirectAttributes addFlashAttribute(Object attributeValue);
 
 	/**
-	 * Return the attributes candidate for flash storage.
+	 * Return the attributes candidate for flash storage or an empty Map.
 	 */
 	Map<String, ?> getFlashAttributes();
-
-}
+}

org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/mvc/support/RedirectAttributesModelMap.java

@@ -23,12 +23,10 @@ import org.springframework.ui.ModelMap;
 import org.springframework.validation.DataBinder;
 
 /**
- * A {@link ModelMap} that implements the {@link RedirectAttributes} interface.
- * 
- * <p>Attributes are formatted and stored as Strings so they can be used as URI 
- * variables or as query parameters in the redirect URL. Alternatively, 
- * attributes may also be added as flash attributes in order to request storing
- * them until the next request without affecting the redirect URL.
+ * A {@link ModelMap} implementation of {@link RedirectAttributes} that formats
+ * values as Strings using a {@link DataBinder}. Also provides a place to store 
+ * flash attributes so they can survive a redirect without the need to be 
+ * embedded in the redirect URL.
  * 
  * @author Rossen Stoyanchev
  * @since 3.1
@@ -41,33 +39,31 @@ public class RedirectAttributesModelMap extends ModelMap implements RedirectAttr
 	private final ModelMap flashAttributes = new ModelMap();
 
 	/**
-	 * Default constructor without a DataBinder. 
-	 * Redirect attribute values will be formatted via {@link #toString()}.
+	 * Class constructor.
+	 * @param dataBinder used to format attribute values as Strings.
 	 */
-	public RedirectAttributesModelMap() {
-		this(null);
+	public RedirectAttributesModelMap(DataBinder dataBinder) {
+		this.dataBinder = dataBinder;
 	}
-
+	
 	/**
-	 * Constructor with a DataBinder to use to format redirect attribute values.
-	 * @param dataBinder a DataBinder for converting attribute values to String.
+	 * Default constructor without a DataBinder. 
+	 * Attribute values are converted to String via {@link #toString()}.
 	 */
-	public RedirectAttributesModelMap(DataBinder dataBinder) {
-		this.dataBinder = dataBinder;
+	public RedirectAttributesModelMap() {
+		this(null);
 	}
 
 	/**
-	 * Return the attributes candidate for flash storage.
+	 * Return the attributes candidate for flash storage or an empty Map.
 	 */
 	public Map<String, ?> getFlashAttributes() {
-		return flashAttributes;
+		return this.flashAttributes;
 	}
 
 	/**
-	 * Format the attribute value as a String and add it. If the value is 
-	 * {@code null} it is not be added. 
-	 * @param attributeName the attribute name; never null
-	 * @param attributeValue the attribute value; skipped if null
+	 * {@inheritDoc}
+	 * <p>Formats the attribute value as a String before adding it.
 	 */
 	public RedirectAttributesModelMap addAttribute(String attributeName, Object attributeValue) {
 		if (attributeValue != null) {
@@ -81,10 +77,8 @@ public class RedirectAttributesModelMap extends ModelMap implements RedirectAttr
 	}
 
 	/**
-	 * Add an attribute using a 
-	 * {@link org.springframework.core.Conventions#getVariableName generated name}. 
-	 * Before being added the attribute value is formatted as a String.
-	 * @param attributeValue the attribute value; never null
+	 * {@inheritDoc}
+	 * <p>Formats the attribute value as a String before adding it.
 	 */
 	public RedirectAttributesModelMap addAttribute(Object attributeValue) {
 		super.addAttribute(attributeValue);
@@ -92,9 +86,8 @@ public class RedirectAttributesModelMap extends ModelMap implements RedirectAttr
 	}
 
 	/**
-	 * Copy all attributes in the supplied <code>Collection</code> into this
-	 * Model using attribute name generation for each element. 
-	 * @see #addAttribute(Object)
+	 * {@inheritDoc}
+	 * <p>Each attribute value is formatted as a String before being added.
 	 */
 	public RedirectAttributesModelMap addAllAttributes(Collection<?> attributeValues) {
 		super.addAllAttributes(attributeValues);
@@ -102,8 +95,8 @@ public class RedirectAttributesModelMap extends ModelMap implements RedirectAttr
 	}
 
 	/**
-	 * Copy all supplied attributes into this model.
-	 * @see #addAttribute(String, Object)
+	 * {@inheritDoc}
+	 * <p>Each attribute value is formatted as a String before being added.
 	 */
 	public RedirectAttributesModelMap addAllAttributes(Map<String, ?> attributes) {
 		if (attributes != null) {
@@ -115,9 +108,8 @@ public class RedirectAttributesModelMap extends ModelMap implements RedirectAttr
 	}
 
 	/**
-	 * Copy all supplied attributes into this model with with existing 
-	 * attributes of the same name taking precedence (i.e. not getting replaced).
-	 * @see #addAttribute(String, Object)
+	 * {@inheritDoc}
+	 * <p>Each attribute value is formatted as a String before being merged.
 	 */
 	public RedirectAttributesModelMap mergeAttributes(Map<String, ?> attributes) {
 		if (attributes != null) {
@@ -134,21 +126,11 @@ public class RedirectAttributesModelMap extends ModelMap implements RedirectAttr
 		return this;
 	}
 
-	/**
-	 * Add the given attribute as a candidate for flash storage. 
-	 * @param attributeName the flash attribute name; never null
-	 * @param attributeValue the flash attribute value; may be null
-	 */
 	public RedirectAttributes addFlashAttribute(String attributeName, Object attributeValue) {
 		this.flashAttributes.addAttribute(attributeName, attributeValue);
 		return this;
 	}
 	
-	/**
-	 * Add the given attribute value as a candidate for flash storage using a
-	 * {@link org.springframework.core.Conventions#getVariableName generated name}. 
-	 * @param attributeValue the flash attribute value; never null
-	 */
 	public RedirectAttributes addFlashAttribute(Object attributeValue) {
 		this.flashAttributes.addAttribute(attributeValue);
 		return this;

org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/support/DefaultFlashMapManager.java

@@ -19,7 +19,6 @@ package org.springframework.web.servlet.support;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
-import java.util.Map;
 import java.util.concurrent.CopyOnWriteArrayList;
 
 import javax.servlet.http.HttpServletRequest;
@@ -34,7 +33,8 @@ import org.springframework.web.servlet.FlashMapManager;
 import org.springframework.web.util.UrlPathHelper;
 
 /**
- * A {@link FlashMapManager} that stores FlashMap instances in the HTTP session.
+ * A default {@link FlashMapManager} implementation keeps {@link FlashMap}
+ * instances in the HTTP session.
  * 
  * @author Rossen Stoyanchev
  * @since 3.1
@@ -50,8 +50,9 @@ public class DefaultFlashMapManager implements FlashMapManager {
 	private final UrlPathHelper urlPathHelper = new UrlPathHelper();
 
 	/**
-	 * The amount of time in seconds after a FlashMap is saved (after request
-	 * completion) before it is considered expired. The default value is 180.
+	 * Set the amount of time in seconds after a {@link FlashMap} is saved 
+	 * (at request completion) and before it expires. 
+	 * <p>The default value is 180 seconds.
 	 */
 	public void setFlashMapTimeout(int flashTimeout) {
 		this.flashTimeout = flashTimeout;
@@ -59,16 +60,16 @@ public class DefaultFlashMapManager implements FlashMapManager {
 
 	/**
 	 * {@inheritDoc}
-	 * <p>This method never causes the HTTP session to be created.
+	 * <p>An HTTP session is never created by this method.
 	 */
 	public void requestStarted(HttpServletRequest request) {
 		if (request.getAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE) != null) {
 			return;
 		}
 		
-		Map<String, ?> inputFlashMap = lookupFlashMap(request);
+		FlashMap inputFlashMap = lookupFlashMap(request);
 		if (inputFlashMap != null) {
-			request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, inputFlashMap);
+			request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
 		}
 
 		FlashMap outputFlashMap = new FlashMap(this.hashCode());
@@ -78,17 +79,17 @@ public class DefaultFlashMapManager implements FlashMapManager {
 	}
 
 	/**
-	 * Look up the "input" FlashMap by matching the target request path and 
-	 * the target request parameters configured in each available FlashMap
-	 * to the current request.
-	 */
-	private Map<String, ?> lookupFlashMap(HttpServletRequest request) {
+	 * Find the "input" FlashMap for the current request target by matching it
+	 * to the target request information of all stored FlashMap instances.
+	 * @return a FlashMap instance or {@code null}
+  	 */
+	private FlashMap lookupFlashMap(HttpServletRequest request) {
 		List<FlashMap> allFlashMaps = retrieveFlashMaps(request, false);
 		if (CollectionUtils.isEmpty(allFlashMaps)) {
 			return null;
 		}
 		if (logger.isDebugEnabled()) {
-			logger.debug("Retrieved flash maps: " + allFlashMaps);
+			logger.debug("Retrieved FlashMap(s): " + allFlashMaps);
 		}
 		List<FlashMap> result = new ArrayList<FlashMap>();
 		for (FlashMap flashMap : allFlashMaps) {
@@ -99,19 +100,19 @@ public class DefaultFlashMapManager implements FlashMapManager {
 		if (!result.isEmpty()) {
 			Collections.sort(result);
 			if (logger.isDebugEnabled()) {
-				logger.debug("Matching flash maps: " + result);
+				logger.debug("Found matching FlashMap(s): " + result);
 			}
 			FlashMap match = result.remove(0);
 			allFlashMaps.remove(match);
-			return Collections.unmodifiableMap(match);
+			return match;
 		}
 		return null;
 	}
 
 	/**
-	 * Compares the target request path and the target request parameters in the
-	 * given FlashMap and returns "true" if they match. If the FlashMap does not
-	 * have target request information, it matches any request.
+	 * Whether the given FlashMap matches the current request.
+	 * The default implementation uses the target request path and query params 
+	 * saved in the FlashMap.
 	 */
 	protected boolean isFlashMapForRequest(FlashMap flashMap, HttpServletRequest request) {
 		if (flashMap.getTargetRequestPath() != null) {
@@ -122,8 +123,8 @@ public class DefaultFlashMapManager implements FlashMapManager {
 			}
 		}
 		if (flashMap.getTargetRequestParams() != null) {
-			for (Map.Entry<String, String> entry : flashMap.getTargetRequestParams().entrySet()) {
-				if (!entry.getValue().equals(request.getParameter(entry.getKey()))) {
+			for (String paramName : flashMap.getTargetRequestParams().keySet()) {
+				if (!flashMap.getTargetRequestParams().get(paramName).equals(request.getParameter(paramName))) {
 					return false;
 				}
 			}
@@ -132,10 +133,13 @@ public class DefaultFlashMapManager implements FlashMapManager {
 	}
 
 	/**
-	 * Retrieve all available FlashMap instances from the HTTP session. 
+	 * Retrieve all FlashMap instances from the current HTTP session.
+	 * If {@code allowCreate} is "true" and no flash maps exist yet, a new list
+	 * is created and stored as a session attribute.
 	 * @param request the current request
-	 * @param allowCreate whether to create and save the FlashMap in the session
-	 * @return a Map with all FlashMap instances; or {@code null}
+	 * @param allowCreate whether to create the session if necessary
+	 * @return a List to add FlashMap instances to or {@code null} 
+	 * 	assuming {@code allowCreate} is "false".
 	 */
 	@SuppressWarnings("unchecked")
 	protected List<FlashMap> retrieveFlashMaps(HttpServletRequest request, boolean allowCreate) {
@@ -157,7 +161,7 @@ public class DefaultFlashMapManager implements FlashMapManager {
 	}
 	
 	/**
-	 * Iterate available FlashMap instances and remove the ones that have expired.
+	 * Iterate all flash maps and remove expired ones.
 	 */
 	private void removeExpiredFlashMaps(HttpServletRequest request) {
 		List<FlashMap> allMaps = retrieveFlashMaps(request, false);
@@ -173,40 +177,52 @@ public class DefaultFlashMapManager implements FlashMapManager {
 				expiredMaps.add(flashMap);
 			}
 		}
-		allMaps.removeAll(expiredMaps);
+		if (!expiredMaps.isEmpty()) {
+			allMaps.removeAll(expiredMaps);
+		}
 	}
-	
+
+	/**
+	 * {@inheritDoc}
+	 * <p>An HTTP session is never created if the "output" FlashMap is empty.
+	 */
 	public void requestCompleted(HttpServletRequest request) {
 		FlashMap flashMap = (FlashMap) request.getAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE);
 		if (flashMap == null) {
-			throw new IllegalStateException(
-					"Did not find a FlashMap exposed as the request attribute " + OUTPUT_FLASH_MAP_ATTRIBUTE);
+			throw new IllegalStateException("requestCompleted called but \"output\" FlashMap was never created");
 		}
 		if (!flashMap.isEmpty() && flashMap.isCreatedBy(this.hashCode())) {
 			if (logger.isDebugEnabled()) {
 				logger.debug("Saving FlashMap=" + flashMap);
 			}
-			decodeAndNormalizeTargetPath(flashMap, request);
-			flashMap.startExpirationPeriod(this.flashTimeout);
+			onSaveFlashMap(flashMap, request);
 			retrieveFlashMaps(request, true).add(flashMap);
 		}
 	}
-
+	
 	/**
-	 * Ensure the target request path in the given FlashMap is decoded and also 
-	 * normalized (if it is relative) against the current request URL. 
+	 * Update a FlashMap before it is stored in the HTTP Session.
+	 * <p>The default implementation starts the expiration period and ensures the
+	 * target request path is decoded and normalized if it is relative. 
+	 * @param flashMap the flash map to be saved
+	 * @param request the current request
 	 */
-	private void decodeAndNormalizeTargetPath(FlashMap flashMap, HttpServletRequest request) {
-		String path = flashMap.getTargetRequestPath();
+	protected void onSaveFlashMap(FlashMap flashMap, HttpServletRequest request) {
+		String targetPath = flashMap.getTargetRequestPath();
+		flashMap.setTargetRequestPath(decodeAndNormalizePath(targetPath, request));
+		flashMap.startExpirationPeriod(this.flashTimeout);
+	}
+
+	private String decodeAndNormalizePath(String path, HttpServletRequest request) {
 		if (path != null) {
-			path = urlPathHelper.decodeRequestString(request, path);
+			path = this.urlPathHelper.decodeRequestString(request, path);
 			if (path.charAt(0) != '/') {
 				String requestUri = this.urlPathHelper.getRequestUri(request);
 				path = requestUri.substring(0, requestUri.lastIndexOf('/') + 1) + path;
 				path = StringUtils.cleanPath(path);
 			}
-			flashMap.setTargetRequestPath(path);
 		}
+		return path;
 	}
 
 }

org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/support/RequestContextUtils.java

@@ -157,9 +157,11 @@ public abstract class RequestContextUtils {
 	}
 
 	/**
-	 * Return a read-only Map with flash attributes saved during the previous request. 
+	 * Return a read-only {@link Map} with "input" flash attributes saved on a
+	 * previous request. 
 	 * @param request the current request
-	 * @return a read-only Map, or {@code null}
+	 * @return a read-only Map, or {@code null} 
+	 * @see FlashMap
 	 */
 	@SuppressWarnings("unchecked")
 	public static Map<String, ?> getInputFlashMap(HttpServletRequest request) {
@@ -167,9 +169,10 @@ public abstract class RequestContextUtils {
 	}
 
 	/**
-	 * Return a FlashMap to add attributes to during the current request.
-	 * @param request current HTTP request
-	 * @return the flash map for the current request; never {@code null}.
+	 * Return the "output" FlashMap with attributes to save for a subsequent request.
+	 * @param request current request
+	 * @return a {@link FlashMap} instance, never {@code null}
+	 * @see FlashMap
 	 */
 	public static FlashMap getOutputFlashMap(HttpServletRequest request) {
 		return (FlashMap) request.getAttribute(FlashMapManager.OUTPUT_FLASH_MAP_ATTRIBUTE);