org.apache.juneau.http.Accept Maven / Gradle / Ivy
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package org.apache.juneau.http;
import static org.apache.juneau.http.Constants.*;
import static org.apache.juneau.internal.StringUtils.*;
import java.util.*;
import org.apache.juneau.internal.*;
/**
* Represents a parsed Accept HTTP request header.
*
*
* Content-Types that are acceptable for the response.
*
*
Example
*
* Accept: text/plain
*
*
* RFC2616 Specification
*
* The Accept request-header field can be used to specify certain media types which are acceptable for the response.
* Accept headers can be used to indicate that the request is specifically limited to a small set of desired types, as
* in the case of a request for an in-line image.
*
*
* Accept = "Accept" ":
* #( media-range [ accept-params ] )
*
* media-range = ( "* /*"
* | ( type "/" "*" )
* | ( type "/" subtype )
* ) *( ";" parameter )
* accept-params = ";" "q" "=" qvalue *( accept-extension )
* accept-extension = ";" token [ "=" ( token | quoted-string ) ]
*
*
*
* The asterisk "*" character is used to group media types into ranges, with "* /*" indicating all media types and
* "type/*" indicating all subtypes of that type.
* The media-range MAY include media type parameters that are applicable to that range.
*
*
* Each media-range MAY be followed by one or more accept-params, beginning with the "q" parameter for indicating a
* relative quality factor.
* The first "q" parameter (if any) separates the media-range parameter(s) from the accept-params.
* Quality factors allow the user or user agent to indicate the relative degree of preference for that media-range,
* using the qvalue scale from 0 to 1 (section 3.9).
* The default value is q=1.
*
*
* Note: Use of the "q" parameter name to separate media type parameters from Accept extension parameters is due to
* historical practice.
* Although this prevents any media type parameter named "q" from being used with a media range, such an event is
* believed to be unlikely given the lack of any "q" parameters in the IANA
* media type registry and the rare usage of any media type parameters in Accept.
* Future media types are discouraged from registering any parameter named "q".
*
*
* The example
*
* Accept: audio/*; q=0.2, audio/basic
*
*
* SHOULD be interpreted as "I prefer audio/basic, but send me any audio type if it is the best available after an 80%
* mark-down in quality."
*
*
* If no Accept header field is present, then it is assumed that the client accepts all media types.
*
*
* If an Accept header field is present, and if the server cannot send a response which is acceptable according to the
* combined Accept field value, then the server SHOULD send a 406 (not acceptable) response.
*
*
* A more elaborate example is
*
* Accept: text/plain; q=0.5, text/html,
* text/x-dvi; q=0.8, text/x-c
*
*
*
* Verbally, this would be interpreted as "text/html and text/x-c are the preferred media types, but if they do not
* exist, then send the
* text/x-dvi entity, and if that does not exist, send the text/plain entity."
*
*
* Media ranges can be overridden by more specific media ranges or specific media types.
* If more than one media range applies to a given type, the most specific reference has precedence.
* For example,
*
* Accept: text/ *, text/html, text/html;level=1, * /*
*
*
* have the following precedence:
*
* - text/html;level=1
*
- text/html
*
- text/*
*
- * /*
*
*
*
* The media type quality factor associated with a given type is determined by finding the media range with the highest
* precedence which matches that type.
* For example,
*
* Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
* text/html;level=2;q=0.4, * /*;q=0.5
*
*
* would cause the following values to be associated:
*
* text/html;level=1 = 1
* text/html = 0.7
* text/plain = 0.3
* image/jpeg = 0.5
* text/html;level=2 = 0.4
* text/html;level=3 = 0.7
*
*
*
* Note: A user agent might be provided with a default set of quality values for certain media ranges.
* However, unless the user agent is a closed system which cannot interact with other rendering agents, this default
* set ought to be configurable by the user.
*
*
Additional Information
*
*/
public final class Accept {
private static final Cache cache = new Cache(NOCACHE, CACHE_MAX_SIZE);
/**
* Returns a parsed Accept header.
*
* @param value The Accept header string.
* @return The parsed Accept header, or null if the string was null.
*/
public static Accept forString(String value) {
if (value == null)
return null;
Accept a = cache.get(value);
if (a == null)
a = cache.put(value, new Accept(value));
return a;
}
private final MediaTypeRange[] mediaRanges;
private final List mediaRangesList;
private Accept(String value) {
this.mediaRanges = MediaTypeRange.parse(value);
this.mediaRangesList = Collections.unmodifiableList(Arrays.asList(mediaRanges));
}
/**
* Returns the list of the media ranges that make up this header.
*
*
* The media ranges in the list are sorted by their q-value in descending order.
*
* @return An unmodifiable list of media ranges.
*/
public List asRanges() {
return mediaRangesList;
}
/**
* Given a list of media types, returns the best match for this Accept header.
*
*
* Note that fuzzy matching is allowed on the media types where the Accept header may
* contain additional subtype parts.
*
For example, given identical q-values and an Accept value of "text/json+activity" ,
* the media type "text/json" will match if "text/json+activity" or "text/activity+json"
* isn't found.
*
The purpose for this is to allow serializers to match when artifacts such as id properties are
* present in the header.
*
*
* See
* ActivityPub / Retrieving Objects
*
* @param mediaTypes The media types to match against.
* @return The index into the array of the best match, or -1 if no suitable matches could be found.
*/
public int findMatch(MediaType[] mediaTypes) {
int matchQuant = 0, matchIndex = -1;
float q = 0f;
// Media ranges are ordered by 'q'.
// So we only need to search until we've found a match.
for (MediaTypeRange mr : mediaRanges) {
float q2 = mr.getQValue();
if (q2 < q || q2 == 0)
break;
for (int i = 0; i < mediaTypes.length; i++) {
MediaType mt = mediaTypes[i];
int matchQuant2 = mr.getMediaType().match(mt, false);
if (matchQuant2 > matchQuant) {
matchIndex = i;
matchQuant = matchQuant2;
q = q2;
}
}
}
return matchIndex;
}
/**
* Convenience method for searching through all of the subtypes of all the media ranges in this header for the
* presence of a subtype fragment.
*
*
* For example, given the header "text/json+activity" , calling
* hasSubtypePart("activity" ) returns true .
*
* @param part The media type subtype fragment.
* @return true if subtype fragment exists.
*/
public boolean hasSubtypePart(String part) {
for (MediaTypeRange mr : this.mediaRanges)
if (mr.getQValue() > 0 && mr.getMediaType().getSubTypes().indexOf(part) >= 0)
return true;
return false;
}
@Override /* Object */
public String toString() {
return join(mediaRanges, ',');
}
}