Java tutorial
/* * Copyright 2002-2018 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 * * https://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 org.springframework.web.method.annotation; import java.util.Collections; import java.util.HashMap; import java.util.HashSet; import java.util.Map; import java.util.Set; import java.util.concurrent.ConcurrentHashMap; import org.springframework.core.annotation.AnnotatedElementUtils; import org.springframework.lang.Nullable; import org.springframework.util.Assert; import org.springframework.web.bind.annotation.SessionAttributes; import org.springframework.web.bind.support.SessionAttributeStore; import org.springframework.web.bind.support.SessionStatus; import org.springframework.web.context.request.WebRequest; /** * Manages controller-specific session attributes declared via * {@link SessionAttributes @SessionAttributes}. Actual storage is * delegated to a {@link SessionAttributeStore} instance. * * <p>When a controller annotated with {@code @SessionAttributes} adds * attributes to its model, those attributes are checked against names and * types specified via {@code @SessionAttributes}. Matching model attributes * are saved in the HTTP session and remain there until the controller calls * {@link SessionStatus#setComplete()}. * * @author Rossen Stoyanchev * @author Juergen Hoeller * @since 3.1 */ public class SessionAttributesHandler { private final Set<String> attributeNames = new HashSet<>(); private final Set<Class<?>> attributeTypes = new HashSet<>(); private final Set<String> knownAttributeNames = Collections.newSetFromMap(new ConcurrentHashMap<>(4)); private final SessionAttributeStore sessionAttributeStore; /** * Create a new session attributes handler. Session attribute names and types * are extracted from the {@code @SessionAttributes} annotation, if present, * on the given type. * @param handlerType the controller type * @param sessionAttributeStore used for session access */ public SessionAttributesHandler(Class<?> handlerType, SessionAttributeStore sessionAttributeStore) { Assert.notNull(sessionAttributeStore, "SessionAttributeStore may not be null"); this.sessionAttributeStore = sessionAttributeStore; SessionAttributes ann = AnnotatedElementUtils.findMergedAnnotation(handlerType, SessionAttributes.class); if (ann != null) { Collections.addAll(this.attributeNames, ann.names()); Collections.addAll(this.attributeTypes, ann.types()); } this.knownAttributeNames.addAll(this.attributeNames); } /** * Whether the controller represented by this instance has declared any * session attributes through an {@link SessionAttributes} annotation. */ public boolean hasSessionAttributes() { return (!this.attributeNames.isEmpty() || !this.attributeTypes.isEmpty()); } /** * Whether the attribute name or type match the names and types specified * via {@code @SessionAttributes} on the underlying controller. * <p>Attributes successfully resolved through this method are "remembered" * and subsequently used in {@link #retrieveAttributes(WebRequest)} and * {@link #cleanupAttributes(WebRequest)}. * @param attributeName the attribute name to check * @param attributeType the type for the attribute */ public boolean isHandlerSessionAttribute(String attributeName, Class<?> attributeType) { Assert.notNull(attributeName, "Attribute name must not be null"); if (this.attributeNames.contains(attributeName) || this.attributeTypes.contains(attributeType)) { this.knownAttributeNames.add(attributeName); return true; } else { return false; } } /** * Store a subset of the given attributes in the session. Attributes not * declared as session attributes via {@code @SessionAttributes} are ignored. * @param request the current request * @param attributes candidate attributes for session storage */ public void storeAttributes(WebRequest request, Map<String, ?> attributes) { attributes.forEach((name, value) -> { if (value != null && isHandlerSessionAttribute(name, value.getClass())) { this.sessionAttributeStore.storeAttribute(request, name, value); } }); } /** * Retrieve "known" attributes from the session, i.e. attributes listed * by name in {@code @SessionAttributes} or attributes previously stored * in the model that matched by type. * @param request the current request * @return a map with handler session attributes, possibly empty */ public Map<String, Object> retrieveAttributes(WebRequest request) { Map<String, Object> attributes = new HashMap<>(); for (String name : this.knownAttributeNames) { Object value = this.sessionAttributeStore.retrieveAttribute(request, name); if (value != null) { attributes.put(name, value); } } return attributes; } /** * Remove "known" attributes from the session, i.e. attributes listed * by name in {@code @SessionAttributes} or attributes previously stored * in the model that matched by type. * @param request the current request */ public void cleanupAttributes(WebRequest request) { for (String attributeName : this.knownAttributeNames) { this.sessionAttributeStore.cleanupAttribute(request, attributeName); } } /** * A pass-through call to the underlying {@link SessionAttributeStore}. * @param request the current request * @param attributeName the name of the attribute of interest * @return the attribute value, or {@code null} if none */ @Nullable Object retrieveAttribute(WebRequest request, String attributeName) { return this.sessionAttributeStore.retrieveAttribute(request, attributeName); } }