goja.rapid.mvc.kits.SessionIds Maven / Gradle / Ivy

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/**
 * Copyright (c) 2011-2013, James Zhan 詹波 ([email protected]).
 * 
 * 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 goja.rapid.mvc.kits;

import java.security.SecureRandom;
import java.util.Random;

import javax.servlet.http.HttpServletRequest;

/**
 * SessionIds.
 */
public class SessionIds {

    private static final SessionIds me   = new SessionIds();
    private static final Object     lock = new Object();
    protected static Random  random;
    private static   boolean weakRandom;

    private SessionIds() {
        try {
            // This operation may block on some systems with low entropy. See
            // this page
            // for workaround suggestions:
            // http://docs.codehaus.org/display/JETTY/Connectors+slow+to+startup
            random = new SecureRandom();
            weakRandom = false;
        } catch (Exception e) {
            System.err.println("Could not generate SecureRandom for session-id randomness");
            random = new Random();
            weakRandom = true;
        }
    }

    public static SessionIds me() {
        return me;
    }

    public String generate(HttpServletRequest request) {
        synchronized (lock) {
            String id = null;
            while (id == null || id.length() == 0) {    //)||idInUse(id))
                long r0 = weakRandom ? (hashCode()
                        ^ Runtime.getRuntime().freeMemory()
                        ^ random.nextInt()
                        ^ (((long) request.hashCode()) << 32)) : random.nextLong();
                long r1 = random.nextLong();
                if (r0 < 0) r0 = -r0;
                if (r1 < 0) r1 = -r1;
                id = Long.toString(r0, 36) + Long.toString(r1, 36);
            }
            return id;
        }
    }
}