org.apache.marmotta.commons.http.ETagGenerator.java Source code

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Here is the source code for org.apache.marmotta.commons.http.ETagGenerator.java

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/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you 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.apache.marmotta.commons.http;

import com.google.common.hash.HashFunction;
import com.google.common.hash.Hasher;
import com.google.common.hash.Hashing;
import org.apache.marmotta.commons.sesame.repository.ResourceUtils;
import org.openrdf.model.Resource;
import org.openrdf.model.Statement;
import org.openrdf.model.URI;
import org.openrdf.repository.RepositoryConnection;
import org.openrdf.repository.RepositoryException;
import org.openrdf.repository.RepositoryResult;

import java.nio.charset.Charset;

/**
 * HTTP ETag generator for Sesame
 * 
 * @author Sergio Fernndez
 *
 */
public class ETagGenerator {

    public static String getETag(RepositoryConnection conn, String uri) throws RepositoryException {
        URI resource = ResourceUtils.getUriResource(conn, uri);
        return getETag(conn, resource);
    }

    public static String getETag(RepositoryConnection conn, URI resource) throws RepositoryException {
        if (resource == null)
            return "";

        Hasher hasher = buildHasher();
        hasher.putString(resource.stringValue(), Charset.defaultCharset());
        //FIXME: The order of the statements is not defined -> might result in different hash!
        RepositoryResult<Statement> outgoing = conn.getStatements(resource, null, null, true);
        try {
            while (outgoing.hasNext()) {
                Statement statement = outgoing.next();
                hasher.putString(statement.getPredicate().stringValue(), Charset.defaultCharset());
                hasher.putString(statement.getObject().stringValue(), Charset.defaultCharset());
                //TODO: statement modification date?
            }
        } finally {
            outgoing.close();
        }
        RepositoryResult<Statement> incoming = conn.getStatements(null, null, resource, true);
        try {
            while (incoming.hasNext()) {
                Statement statement = incoming.next();
                hasher.putString(statement.getSubject().stringValue(), Charset.defaultCharset());
                hasher.putString(statement.getPredicate().stringValue(), Charset.defaultCharset());
                //TODO: statement modification date?
            }
        } finally {
            incoming.close();
        }
        return hasher.hash().toString();
    }

    public static String getWeakETag(RepositoryConnection conn, String resource) throws RepositoryException {
        if (resource.startsWith("http://")) {
            return getWeakETag(conn, ResourceUtils.getUriResource(conn, resource));
        } else {
            return getWeakETag(conn, ResourceUtils.getAnonResource(conn, resource));
        }
    }

    //    public static String getWeakETag(RepositoryConnection conn, Resource resource) throws RepositoryException {
    //       if (resource instanceof URI) {
    //          return getWeakETag(conn, (URI)resource);
    //       } else if (resource instanceof BNode) {
    //          return getWeakETag(conn, (BNode)resource);
    //       } else {
    //          return null;
    //       }
    //    }

    public static String getWeakETag(RepositoryConnection conn, Resource resource) throws RepositoryException {
        if (resource == null)
            return "";

        Hasher hasher = buildHasher();
        hasher.putString(resource.stringValue(), Charset.defaultCharset());
        //FIXME: The order of the statements is not defined -> might result in different hash!
        RepositoryResult<Statement> statements = conn.getStatements(resource, null, null, true);
        try {
            while (statements.hasNext()) {
                Statement statement = statements.next();
                hasher.putString(statement.getPredicate().stringValue(), Charset.defaultCharset());
                hasher.putString(statement.getObject().stringValue(), Charset.defaultCharset());
                //TODO: statement modification date?
            }
        } finally {
            statements.close();
        }
        return hasher.hash().toString();
    }

    private static Hasher buildHasher() {
        HashFunction function = Hashing.goodFastHash(16);
        Hasher hasher = function.newHasher();
        return hasher;
    }

}