BasicIdGenerator.java

/*
 * ====================================================================
 * 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.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */
package com.apigee.sdk.apm.http.impl.client.cache;

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Formatter;
import java.util.Locale;

import com.apigee.sdk.apm.http.annotation.Immutable;

/**
 * Should produce reasonably unique tokens.
 */
@Immutable
class BasicIdGenerator {

	private final String hostname;
	private final SecureRandom rnd;

	private long count;

	public BasicIdGenerator() {
		super();
		String hostname;
		try {
			hostname = InetAddress.getLocalHost().getHostName();
		} catch (UnknownHostException ex) {
			hostname = "localhost";
		}
		this.hostname = hostname;
		try {
			this.rnd = SecureRandom.getInstance("SHA1PRNG");
		} catch (NoSuchAlgorithmException ex) {
			throw new Error(ex);
		}
		this.rnd.setSeed(System.currentTimeMillis());
	}

	public synchronized void generate(final StringBuilder buffer) {
		this.count++;
		int rndnum = this.rnd.nextInt();
		buffer.append(System.currentTimeMillis());
		buffer.append('.');
		Formatter formatter = new Formatter(buffer, Locale.US);
		formatter.format("%1$016x-%2$08x", this.count, rndnum);
		formatter.close();
		buffer.append('.');
		buffer.append(this.hostname);
	}

	public String generate() {
		StringBuilder buffer = new StringBuilder();
		generate(buffer);
		return buffer.toString();
	}

}