net.nicoulaj.maven.plugins.checksum.digest.DigesterFactory.java Source code

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Here is the source code for net.nicoulaj.maven.plugins.checksum.digest.DigesterFactory.java

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/**
 * checksum-maven-plugin - http://checksum-maven-plugin.nicoulaj.net
 * Copyright  2010-2016 checksum-maven-plugin contributors
 *
 * 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 net.nicoulaj.maven.plugins.checksum.digest;

import net.nicoulaj.maven.plugins.checksum.Constants;
import org.bouncycastle.jce.provider.BouncyCastleProvider;

import java.security.NoSuchAlgorithmException;
import java.security.Security;
import java.util.HashMap;
import java.util.Map;

/**
 * Singleton class used to get instances of {@link FileDigester}.
 * 
 * <p>Each {@link FileDigester} object is a singleton itself.</p>
 *
 * @author <a href="mailto:julien.nicoulaud@gmail.com">Julien Nicoulaud</a>
 * @see FileDigester
 * @since 1.0
 */
public class DigesterFactory {
    /**
     * The instance of {@link net.nicoulaj.maven.plugins.checksum.digest.DigesterFactory}.
     */
    private static DigesterFactory instance;

    /**
     * The map (algorithm, digester).
     */
    protected Map<String, FileDigester> digesters = new HashMap<String, FileDigester>(
            Constants.SUPPORTED_ALGORITHMS.length);

    /**
     * Build a new {@link net.nicoulaj.maven.plugins.checksum.digest.DigesterFactory}.
     *
     * @see #getInstance()
     */
    private DigesterFactory() {
    }

    /**
     * Get the instance of {@link net.nicoulaj.maven.plugins.checksum.digest.DigesterFactory}.
     *
     * @return the only instance of {@link net.nicoulaj.maven.plugins.checksum.digest.DigesterFactory}.
     */
    public static synchronized DigesterFactory getInstance() {
        if (instance == null) {
            instance = new DigesterFactory();
        }
        return instance;
    }

    /**
     * Get an instance of {@link FileDigester} for the given checksum algorithm.
     *
     * @param algorithm the target checksum algorithm.
     * @return an instance of {@link FileDigester}.
     * @throws NoSuchAlgorithmException if the checksum algorithm is not supported or invalid.
     * @see FileDigester
     */
    public synchronized FileDigester getFileDigester(String algorithm) throws NoSuchAlgorithmException {
        FileDigester digester = digesters.get(algorithm);

        if (digester == null) {
            // Algorithms with custom digesters
            if (CRC32FileDigester.ALGORITHM.equals(algorithm)) {
                digester = new CRC32FileDigester();
            }

            else if (CksumFileDigester.ALGORITHM.equals(algorithm)) {
                digester = new CksumFileDigester();
            }

            // Default case: try to use Java Security providers.
            else {
                // Try with the current providers.
                try {
                    digester = new MessageDigestFileDigester(algorithm);
                } catch (NoSuchAlgorithmException e) {
                    // If the algorithm is not supported by default providers, try with Bouncy Castle.
                    if (Security.getProvider(BouncyCastleProvider.PROVIDER_NAME) == null) {
                        Security.addProvider(new BouncyCastleProvider());
                        digester = new MessageDigestFileDigester(algorithm);
                    }

                    // If Bouncy Castle was already used, fail.
                    else {
                        throw e;
                    }
                }
            }

            digesters.put(algorithm, digester);
        }

        return digester;
    }
}