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/*
 * Copyright 2002-2023 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.http;

import java.time.Duration;
import java.util.concurrent.TimeUnit;

import org.springframework.lang.Nullable;
import org.springframework.util.StringUtils;

/**
 * A builder for creating "Cache-Control" HTTP response headers.
 *
 * 

Adding Cache-Control directives to HTTP responses can significantly improve the client * experience when interacting with a web application. This builder creates opinionated * "Cache-Control" headers with response directives only, with several use cases in mind. * *

    *
  • Caching HTTP responses with {@code CacheControl cc = CacheControl.maxAge(1, TimeUnit.HOURS)} * will result in {@code Cache-Control: "max-age=3600"}
  • *
  • Preventing cache with {@code CacheControl cc = CacheControl.noStore()} * will result in {@code Cache-Control: "no-store"}
  • *
  • Advanced cases like {@code CacheControl cc = CacheControl.maxAge(1, TimeUnit.HOURS).noTransform().cachePublic()} * will result in {@code Cache-Control: "max-age=3600, no-transform, public"}
  • *
* *

Note that to be efficient, Cache-Control headers should be written along HTTP validators * such as "Last-Modified" or "ETag" headers. * * @author Brian Clozel * @author Juergen Hoeller * @since 4.2 * @see rfc7234 section 5.2.2 * @see * HTTP caching - Google developers reference * @see Mark Nottingham's cache documentation */ public class CacheControl { @Nullable private Duration maxAge; private boolean noCache = false; private boolean noStore = false; private boolean mustRevalidate = false; private boolean noTransform = false; private boolean cachePublic = false; private boolean cachePrivate = false; private boolean proxyRevalidate = false; @Nullable private Duration staleWhileRevalidate; @Nullable private Duration staleIfError; @Nullable private Duration sMaxAge; private boolean immutable = false; /** * Create an empty CacheControl instance. * @see #empty() */ protected CacheControl() { } /** * Return an empty directive. *

This is well suited for using other optional directives without "max-age", * "no-cache" or "no-store". * @return {@code this}, to facilitate method chaining */ public static CacheControl empty() { return new CacheControl(); } /** * Add a "max-age=" directive. *

This directive is well suited for publicly caching resources, knowing that * they won't change within the configured amount of time. Additional directives * can be also used, in case resources shouldn't be cached ({@link #cachePrivate()}) * or transformed ({@link #noTransform()}) by shared caches. *

In order to prevent caches to reuse the cached response even when it has * become stale (i.e. the "max-age" delay is passed), the "must-revalidate" * directive should be set ({@link #mustRevalidate()} * @param maxAge the maximum time the response should be cached * @param unit the time unit of the {@code maxAge} argument * @return {@code this}, to facilitate method chaining * @see #maxAge(Duration) * @see rfc7234 section 5.2.2.8 */ public static CacheControl maxAge(long maxAge, TimeUnit unit) { return maxAge(Duration.ofSeconds(unit.toSeconds(maxAge))); } /** * Add a "max-age=" directive. *

This directive is well suited for publicly caching resources, knowing that * they won't change within the configured amount of time. Additional directives * can be also used, in case resources shouldn't be cached ({@link #cachePrivate()}) * or transformed ({@link #noTransform()}) by shared caches. *

In order to prevent caches to reuse the cached response even when it has * become stale (i.e. the "max-age" delay is passed), the "must-revalidate" * directive should be set ({@link #mustRevalidate()} * @param maxAge the maximum time the response should be cached * @return {@code this}, to facilitate method chaining * @since 5.2 * @see rfc7234 section 5.2.2.8 */ public static CacheControl maxAge(Duration maxAge) { CacheControl cc = new CacheControl(); cc.maxAge = maxAge; return cc; } /** * Add a "no-cache" directive. *

This directive is well suited for telling caches that the response * can be reused only if the client revalidates it with the server. * This directive won't disable cache altogether and may result with clients * sending conditional requests (with "ETag", "If-Modified-Since" headers) * and the server responding with "304 - Not Modified" status. *

In order to disable caching and minimize requests/responses exchanges, * the {@link #noStore()} directive should be used instead of {@code #noCache()}. * @return {@code this}, to facilitate method chaining * @see rfc7234 section 5.2.2.2 */ public static CacheControl noCache() { CacheControl cc = new CacheControl(); cc.noCache = true; return cc; } /** * Add a "no-store" directive. *

This directive is well suited for preventing caches (browsers and proxies) * to cache the content of responses. * @return {@code this}, to facilitate method chaining * @see rfc7234 section 5.2.2.3 */ public static CacheControl noStore() { CacheControl cc = new CacheControl(); cc.noStore = true; return cc; } /** * Add a "must-revalidate" directive. *

This directive indicates that once it has become stale, a cache MUST NOT * use the response to satisfy subsequent requests without successful validation * on the origin server. * @return {@code this}, to facilitate method chaining * @see rfc7234 section 5.2.2.1 */ public CacheControl mustRevalidate() { this.mustRevalidate = true; return this; } /** * Add a "no-transform" directive. *

This directive indicates that intermediaries (caches and others) should * not transform the response content. This can be useful to force caches and * CDNs not to automatically gzip or optimize the response content. * @return {@code this}, to facilitate method chaining * @see rfc7234 section 5.2.2.4 */ public CacheControl noTransform() { this.noTransform = true; return this; } /** * Add a "public" directive. *

This directive indicates that any cache MAY store the response, * even if the response would normally be non-cacheable or cacheable * only within a private cache. * @return {@code this}, to facilitate method chaining * @see rfc7234 section 5.2.2.5 */ public CacheControl cachePublic() { this.cachePublic = true; return this; } /** * Add a "private" directive. *

This directive indicates that the response message is intended * for a single user and MUST NOT be stored by a shared cache. * @return {@code this}, to facilitate method chaining * @see rfc7234 section 5.2.2.6 */ public CacheControl cachePrivate() { this.cachePrivate = true; return this; } /** * Add a "proxy-revalidate" directive. *

This directive has the same meaning as the "must-revalidate" directive, * except that it does not apply to private caches (i.e. browsers, HTTP clients). * @return {@code this}, to facilitate method chaining * @see rfc7234 section 5.2.2.7 */ public CacheControl proxyRevalidate() { this.proxyRevalidate = true; return this; } /** * Add an "s-maxage" directive. *

This directive indicates that, in shared caches, the maximum age specified * by this directive overrides the maximum age specified by other directives. * @param sMaxAge the maximum time the response should be cached * @param unit the time unit of the {@code sMaxAge} argument * @return {@code this}, to facilitate method chaining * @see #sMaxAge(Duration) * @see rfc7234 section 5.2.2.9 */ public CacheControl sMaxAge(long sMaxAge, TimeUnit unit) { return sMaxAge(Duration.ofSeconds(unit.toSeconds(sMaxAge))); } /** * Add an "s-maxage" directive. *

This directive indicates that, in shared caches, the maximum age specified * by this directive overrides the maximum age specified by other directives. * @param sMaxAge the maximum time the response should be cached * @return {@code this}, to facilitate method chaining * @since 5.2 * @see rfc7234 section 5.2.2.9 */ public CacheControl sMaxAge(Duration sMaxAge) { this.sMaxAge = sMaxAge; return this; } /** * Add a "stale-while-revalidate" directive. *

This directive indicates that caches MAY serve the response in which it * appears after it becomes stale, up to the indicated number of seconds. * If a cached response is served stale due to the presence of this extension, * the cache SHOULD attempt to revalidate it while still serving stale responses * (i.e. without blocking). * @param staleWhileRevalidate the maximum time the response should be used while being revalidated * @param unit the time unit of the {@code staleWhileRevalidate} argument * @return {@code this}, to facilitate method chaining * @see #staleWhileRevalidate(Duration) * @see rfc5861 section 3 */ public CacheControl staleWhileRevalidate(long staleWhileRevalidate, TimeUnit unit) { return staleWhileRevalidate(Duration.ofSeconds(unit.toSeconds(staleWhileRevalidate))); } /** * Add a "stale-while-revalidate" directive. *

This directive indicates that caches MAY serve the response in which it * appears after it becomes stale, up to the indicated number of seconds. * If a cached response is served stale due to the presence of this extension, * the cache SHOULD attempt to revalidate it while still serving stale responses * (i.e. without blocking). * @param staleWhileRevalidate the maximum time the response should be used while being revalidated * @return {@code this}, to facilitate method chaining * @since 5.2 * @see rfc5861 section 3 */ public CacheControl staleWhileRevalidate(Duration staleWhileRevalidate) { this.staleWhileRevalidate = staleWhileRevalidate; return this; } /** * Add a "stale-if-error" directive. *

This directive indicates that when an error is encountered, a cached stale response * MAY be used to satisfy the request, regardless of other freshness information. * @param staleIfError the maximum time the response should be used when errors are encountered * @param unit the time unit of the {@code staleIfError} argument * @return {@code this}, to facilitate method chaining * @see #staleIfError(Duration) * @see rfc5861 section 4 */ public CacheControl staleIfError(long staleIfError, TimeUnit unit) { return staleIfError(Duration.ofSeconds(unit.toSeconds(staleIfError))); } /** * Add a "stale-if-error" directive. *

This directive indicates that when an error is encountered, a cached stale response * MAY be used to satisfy the request, regardless of other freshness information. * @param staleIfError the maximum time the response should be used when errors are encountered * @return {@code this}, to facilitate method chaining * @since 5.2 * @see rfc5861 section 4 */ public CacheControl staleIfError(Duration staleIfError) { this.staleIfError = staleIfError; return this; } /** * Add an "immutable" directive. *

This directive indicates that the origin server will not update the * representation of that resource during the freshness lifetime of the response. * Adding a {@link #maxAge(Duration) max-age} directive is strongly advised * to enforce the actual freshness lifetime. * @return {@code this}, to facilitate method chaining * @since 6.0.5 * @see rfc8246 */ public CacheControl immutable() { this.immutable = true; return this; } /** * Return the "Cache-Control" header value, if any. * @return the header value, or {@code null} if no directive was added */ @Nullable public String getHeaderValue() { String headerValue = toHeaderValue(); return (StringUtils.hasText(headerValue) ? headerValue : null); } /** * Return the "Cache-Control" header value. * @return the header value (potentially empty) */ private String toHeaderValue() { StringBuilder headerValue = new StringBuilder(); if (this.maxAge != null) { appendDirective(headerValue, "max-age=" + this.maxAge.getSeconds()); } if (this.noCache) { appendDirective(headerValue, "no-cache"); } if (this.noStore) { appendDirective(headerValue, "no-store"); } if (this.mustRevalidate) { appendDirective(headerValue, "must-revalidate"); } if (this.noTransform) { appendDirective(headerValue, "no-transform"); } if (this.cachePublic) { appendDirective(headerValue, "public"); } if (this.cachePrivate) { appendDirective(headerValue, "private"); } if (this.proxyRevalidate) { appendDirective(headerValue, "proxy-revalidate"); } if (this.sMaxAge != null) { appendDirective(headerValue, "s-maxage=" + this.sMaxAge.getSeconds()); } if (this.staleIfError != null) { appendDirective(headerValue, "stale-if-error=" + this.staleIfError.getSeconds()); } if (this.staleWhileRevalidate != null) { appendDirective(headerValue, "stale-while-revalidate=" + this.staleWhileRevalidate.getSeconds()); } if (this.immutable) { appendDirective(headerValue, "immutable"); } return headerValue.toString(); } private void appendDirective(StringBuilder builder, String value) { if (builder.length() > 0) { builder.append(", "); } builder.append(value); } @Override public String toString() { return "CacheControl [" + toHeaderValue() + "]"; } }





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