/*
* Copyright 2002-2016 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 org.springframework.http;
import java.util.concurrent.TimeUnit;
import org.springframework.util.StringUtils;
/**
* A builder for creating "Cache-Control" HTTP response headers.
*
* <p>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.
*
* <ul>
* <li>Caching HTTP responses with {@code CacheControl cc = CacheControl.maxAge(1, TimeUnit.HOURS)}
* will result in {@code Cache-Control: "max-age=3600"}</li>
* <li>Preventing cache with {@code CacheControl cc = CacheControl.noStore()}
* will result in {@code Cache-Control: "no-store"}</li>
* <li>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"}</li>
* </ul>
*
* <p>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 <a href="https://tools.ietf.org/html/rfc7234#section-5.2.2">rfc7234 section 5.2.2</a>
* @see <a href="https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/http-caching">
* HTTP caching - Google developers reference</a>
* @see <a href="https://www.mnot.net/cache_docs/">Mark Nottingham's cache documentation</a>
*/
public class CacheControl {
private long maxAge = -1;
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;
private long staleWhileRevalidate = -1;
private long staleIfError = -1;
private long sMaxAge = -1;
/**
* Create an empty CacheControl instance.
* @see #empty()
*/
protected CacheControl() {
}
/**
* Return an empty directive.
* <p>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.
* <p>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.
* <p>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 <a href="https://tools.ietf.org/html/rfc7234#section-5.2.2.8">rfc7234 section 5.2.2.8</a>
*/
public static CacheControl maxAge(long maxAge, TimeUnit unit) {
CacheControl cc = new CacheControl();
cc.maxAge = unit.toSeconds(maxAge);
return cc;
}
/**
* Add a "no-cache" directive.
* <p>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.
* <p>In order to disable caching and minimize requests/responses exchanges, the {@link #noStore()} directive
* should be used instead of {@link #noCache()}.
* @return {@code this}, to facilitate method chaining
* @see <a href="https://tools.ietf.org/html/rfc7234#section-5.2.2.2">rfc7234 section 5.2.2.2</a>
*/
public static CacheControl noCache() {
CacheControl cc = new CacheControl();
cc.noCache = true;
return cc;
}
/**
* Add a "no-store" directive.
* <p>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 <a href="https://tools.ietf.org/html/rfc7234#section-5.2.2.3">rfc7234 section 5.2.2.3</a>
*/
public static CacheControl noStore() {
CacheControl cc = new CacheControl();
cc.noStore = true;
return cc;
}
/**
* Add a "must-revalidate" directive.
* <p>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 <a href="https://tools.ietf.org/html/rfc7234#section-5.2.2.1">rfc7234 section 5.2.2.1</a>
*/
public CacheControl mustRevalidate() {
this.mustRevalidate = true;
return this;
}
/**
* Add a "no-transform" directive.
* <p>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 <a href="https://tools.ietf.org/html/rfc7234#section-5.2.2.4">rfc7234 section 5.2.2.4</a>
*/
public CacheControl noTransform() {
this.noTransform = true;
return this;
}
/**
* Add a "public" directive.
* <p>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 <a href="https://tools.ietf.org/html/rfc7234#section-5.2.2.5">rfc7234 section 5.2.2.5</a>
*/
public CacheControl cachePublic() {
this.cachePublic = true;
return this;
}
/**
* Add a "private" directive.
* <p>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 <a href="https://tools.ietf.org/html/rfc7234#section-5.2.2.6">rfc7234 section 5.2.2.6</a>
*/
public CacheControl cachePrivate() {
this.cachePrivate = true;
return this;
}
/**
* Add a "proxy-revalidate" directive.
* <p>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 <a href="https://tools.ietf.org/html/rfc7234#section-5.2.2.7">rfc7234 section 5.2.2.7</a>
*/
public CacheControl proxyRevalidate() {
this.proxyRevalidate = true;
return this;
}
/**
* Add an "s-maxage" directive.
* <p>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 <a href="https://tools.ietf.org/html/rfc7234#section-5.2.2.9">rfc7234 section 5.2.2.9</a>
*/
public CacheControl sMaxAge(long sMaxAge, TimeUnit unit) {
this.sMaxAge = unit.toSeconds(sMaxAge);
return this;
}
/**
* Add a "stale-while-revalidate" directive.
* <p>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 <a href="https://tools.ietf.org/html/rfc5861#section-3">rfc5861 section 3</a>
*/
public CacheControl staleWhileRevalidate(long staleWhileRevalidate, TimeUnit unit) {
this.staleWhileRevalidate = unit.toSeconds(staleWhileRevalidate);
return this;
}
/**
* Add a "stale-if-error" directive.
* <p>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 <a href="https://tools.ietf.org/html/rfc5861#section-4">rfc5861 section 4</a>
*/
public CacheControl staleIfError(long staleIfError, TimeUnit unit) {
this.staleIfError = unit.toSeconds(staleIfError);
return this;
}
/**
* Return the "Cache-Control" header value.
* @return {@code null} if no directive was added, or the header value otherwise
*/
public String getHeaderValue() {
StringBuilder ccValue = new StringBuilder();
if (this.maxAge != -1) {
appendDirective(ccValue, "max-age=" + Long.toString(this.maxAge));
}
if (this.noCache) {
appendDirective(ccValue, "no-cache");
}
if (this.noStore) {
appendDirective(ccValue, "no-store");
}
if (this.mustRevalidate) {
appendDirective(ccValue, "must-revalidate");
}
if (this.noTransform) {
appendDirective(ccValue, "no-transform");
}
if (this.cachePublic) {
appendDirective(ccValue, "public");
}
if (this.cachePrivate) {
appendDirective(ccValue, "private");
}
if (this.proxyRevalidate) {
appendDirective(ccValue, "proxy-revalidate");
}
if (this.sMaxAge != -1) {
appendDirective(ccValue, "s-maxage=" + Long.toString(this.sMaxAge));
}
if (this.staleIfError != -1) {
appendDirective(ccValue, "stale-if-error=" + Long.toString(this.staleIfError));
}
if (this.staleWhileRevalidate != -1) {
appendDirective(ccValue, "stale-while-revalidate=" + Long.toString(this.staleWhileRevalidate));
}
String ccHeaderValue = ccValue.toString();
return (StringUtils.hasText(ccHeaderValue) ? ccHeaderValue : null);
}
private void appendDirective(StringBuilder builder, String value) {
if (builder.length() > 0) {
builder.append(", ");
}
builder.append(value);
}
}