org.eclipse.lyo.oslc.v3.sample.ETag.java Source code

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Here is the source code for org.eclipse.lyo.oslc.v3.sample.ETag.java

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/*******************************************************************************
 * Copyright (c) 2015 IBM Corporation.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * and Eclipse Distribution License v. 1.0 which accompanies this distribution.
 *
 * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
 * and the Eclipse Distribution License is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *
 *     Samuel Padgett       - initial API and implementation
 *******************************************************************************/
package org.eclipse.lyo.oslc.v3.sample;

import java.io.IOException;
import java.io.InputStream;
import java.io.PipedInputStream;
import java.io.PipedOutputStream;

import org.apache.commons.codec.digest.DigestUtils;
import org.apache.jena.atlas.io.IndentedWriter;
import org.apache.jena.atlas.json.JsonObject;
import org.apache.log4j.Logger;

import com.hp.hpl.jena.rdf.model.Model;

public class ETag {
    private static final Logger logger = Logger.getLogger(ETag.class);

    /**
     * Create an ETag value from a Jena model.
     *
     * @param m the model that represents the HTTP response body
     * @param lang the serialization language
     * @param base the base URI
     * @return an ETag value
     * @throws IOException on I/O errors
     *
     * @see <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.19">HTTP 1.1: Section 14.19 - ETag</a>
     */
    public static String generate(final Model m, final String lang, final String base) throws IOException {
        final PipedInputStream in = new PipedInputStream();
        final PipedOutputStream out = new PipedOutputStream(in);
        new Thread(new Runnable() {
            public void run() {
                m.write(out, lang, base);
                try {
                    out.close();
                } catch (IOException e) {
                    logger.error("Error creating MD5 hash of Model", e);
                }
            }
        }).start();

        return generate(in);
    }

    public static String generate(final JsonObject object) throws IOException {
        final PipedInputStream in = new PipedInputStream();
        final PipedOutputStream out = new PipedOutputStream(in);
        new Thread(new Runnable() {
            public void run() {
                object.output(new IndentedWriter(out));
                try {
                    out.close();
                } catch (IOException e) {
                    logger.error("Error creating MD5 hash of JSON", e);
                }
            }
        }).start();

        return generate(in);
    }

    private static String generate(final InputStream in) throws IOException {
        final String md5 = DigestUtils.md5Hex(in);
        return quote(md5);
    }

    public static String quote(String etag) {
        // ETags are quoted strings
        return "\"" + etag + "\"";
    }

    /**
     * Tests an If-Match or If-None-Match header value against an ETag, handling
     * wildcards and comma-separated header values.
     *
     * @param ifMatch
     *            the If-Match or If-None-Match header value (or null)
     * @param etag
     *            the entity tag
     * @return true iff the values match
     */
    public static boolean matches(String ifMatch, String etag) {
        if (ifMatch == null) {
            return false;
        }

        if (ifMatch.equals("*")) {
            return true;
        }

        for (String s : ifMatch.split(" *, *")) {
            if (s.equals(etag)) {
                return true;
            }
        }

        return false;
    }
}