com.threewks.thundr.view.negotiating.strategy.AcceptsHeaderNegotiationStrategy.java Source code

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Here is the source code for com.threewks.thundr.view.negotiating.strategy.AcceptsHeaderNegotiationStrategy.java

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/*
 * This file is a component of thundr, a software library from 3wks.
 * Read more: http://3wks.github.io/thundr/
 * Copyright (C) 2014 3wks, <thundr@3wks.com.au>
 *
 * 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 com.threewks.thundr.view.negotiating.strategy;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import javax.servlet.http.HttpServletRequest;

import org.apache.commons.lang3.StringUtils;

import com.atomicleopard.expressive.Expressive;
import com.threewks.thundr.http.Header;
import com.threewks.thundr.view.negotiating.NegotiatingView;
import com.threewks.thundr.view.negotiating.Negotiator;
import com.threewks.thundr.view.negotiating.ViewNegotiatorRegistry;
import com.threewks.thundr.view.negotiating.ViewNegotiatorRegistryImpl;

/**
 * Finds a {@link Negotiator} by looking at the Accept header provided on the request.
 * 
 * RFC: <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html">http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html</a>
 */
public class AcceptsHeaderNegotiationStrategy implements NegotiationStrategy {

    @Override
    public Negotiator<?> findNegotiator(HttpServletRequest req, NegotiatingView view,
            ViewNegotiatorRegistry viewNegotiatorRegistry) {
        String acceptsHeader = Header.getHeader(Header.Accept, req);
        if (StringUtils.isNotBlank(acceptsHeader)) {
            List<AcceptsComponent> orderedAcceptsHeader = cleanAndOrderAcceptHeader(acceptsHeader);
            for (AcceptsComponent acceptsComponent : orderedAcceptsHeader) {
                String accept = acceptsComponent.getAccept();
                Negotiator<?> negotiator = viewNegotiatorRegistry.getNegotiator(accept);
                if (negotiator != null) {
                    return negotiator;
                }
            }
        }
        return null;
    }

    private List<AcceptsComponent> cleanAndOrderAcceptHeader(String acceptsHeader) {
        List<AcceptsComponent> components = new ArrayList<AcceptsComponent>();
        for (String component : StringUtils.split(acceptsHeader, ",")) {
            components.add(new AcceptsComponent(ViewNegotiatorRegistryImpl.normaliseContentType(component)));
        }
        Collections.sort(components, AcceptsComponent.Comparator);
        return components;
    }

    protected static class AcceptsComponent {
        // This is a broad pattern to roughly match ;q=1 ;q=.5 and q=0.5 - it will also potentially match q= and q=. though.
        private static final Pattern QualityPattern = Pattern.compile("^(.+?);q=([0-9]*\\.?[0-9]+)");
        private String accept;
        private float quality;
        private int components;

        public AcceptsComponent(String component) {
            super();
            component = StringUtils.trim(component);
            this.quality = 1;
            Matcher matcher = QualityPattern.matcher(component);
            if (matcher.matches()) {
                this.accept = matcher.group(1);
                this.quality = Float.parseFloat(matcher.group(2));
            } else {
                this.accept = component;
            }
            this.components = StringUtils.countMatches(accept, ";") + 1;
        }

        public float getQuality() {
            return quality;
        }

        public int getComponents() {
            return components;
        }

        public String getAccept() {
            return accept;
        }

        @Override
        public String toString() {
            return accept;
        }

        public static final Comparator<AcceptsComponent> Comparator = Expressive.Comparators
                .compare(AcceptsComponent.class).on("quality").using(Collections.reverseOrder()).on("components")
                .using(Collections.reverseOrder());
    }
}