/**
* Copyright 2009 Google Inc.
*
* 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 org.waveprotocol.box.server.util;
import com.google.common.annotations.VisibleForTesting;
import java.security.SecureRandom;
import java.util.Random;
/**
* Produces sequence of pseudo-random id strings.
* Thread-safe.
*
*
*/
public class RandomBase64Generator {
/** The 64 valid web-safe characters. */
@VisibleForTesting static final char[] WEB64_ALPHABET =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_"
.toCharArray();
private final Random random;
/**
* @param random Pseudo-random generator,
* use Random for speed, SecureRandom for cryptographic strength.
*/
public RandomBase64Generator(Random random) {
this.random = random;
}
/**
* Default constructor using Random.
*/
public RandomBase64Generator() {
this(new SecureRandom());
}
/**
* @param length The requested number of random base 64 characters.
* @return string with length many random base 64 characters.
*/
public String next(int length) {
StringBuilder result = new StringBuilder(length);
int bits = 0;
int bitCount = 0;
while (result.length() < length) {
if (bitCount < 6) {
bits = random.nextInt();
bitCount = 32;
}
result.append(WEB64_ALPHABET[bits & 0x3F]);
bits >>= 6;
bitCount -= 6;
}
return result.toString();
}
}