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package javax.mail.internet;

import java.net.*;
import java.util.concurrent.atomic.AtomicInteger;
import javax.mail.Session;

This is a utility class that generates unique values. The generated
String contains only US-ASCII characters and hence is safe for use
in RFC822 headers. 

This is a package private class.
Author:
John Mani, Max Spivak, Bill Shannon/**
 * This is a utility class that generates unique values. The generated
 * String contains only US-ASCII characters and hence is safe for use
 * in RFC822 headers. <p>
 *
 * This is a package private class.
 *
 * @author John Mani
 * @author Max Spivak
 * @author Bill Shannon
 */

class UniqueValue {
    
A global unique number, to ensure uniqueness of generated strings.
/**
     * A global unique number, to ensure uniqueness of generated strings.
     */
    private static AtomicInteger id = new AtomicInteger();

    
Get a unique value for use in a multipart boundary string.
This implementation generates it by concatenating a global
part number, a newly created object's hashCode(),
and the current time (in milliseconds).
/**
     * Get a unique value for use in a multipart boundary string.
     *
     * This implementation generates it by concatenating a global
     * part number, a newly created object's <code>hashCode()</code>,
     * and the current time (in milliseconds).
     */
    public static String getUniqueBoundaryValue() {
	StringBuilder s = new StringBuilder();
	long hash = s.hashCode();

	// Unique string is ----=_Part_<part>_<hashcode>.<currentTime>
	s.append("----=_Part_").append(id.getAndIncrement()).append("_").
	  append(hash).append('.').
	  append(System.currentTimeMillis());
	return s.toString();
    }

    
Get a unique value for use in a Message-ID.
This implementation generates it by concatenating a newly
created object's hashCode(), a global ID
(incremented on every use), the current time (in milliseconds),
and the host name from this user's local address generated by 
InternetAddress.getLocalAddress().
(The host name defaults to "localhost" if
getLocalAddress() returns null.)
Params:
ssn – Session object used to get the local address
See Also:
InternetAddress/**
     * Get a unique value for use in a Message-ID.
     *
     * This implementation generates it by concatenating a newly
     * created object's <code>hashCode()</code>, a global ID
     * (incremented on every use), the current time (in milliseconds),
     * and the host name from this user's local address generated by 
     * <code>InternetAddress.getLocalAddress()</code>.
     * (The host name defaults to "localhost" if
     * <code>getLocalAddress()</code> returns null.)
     *
     * @param ssn Session object used to get the local address
     * @see javax.mail.internet.InternetAddress
     */
    public static String getUniqueMessageIDValue(Session ssn) {
	String suffix = null;

	InternetAddress addr = InternetAddress.getLocalAddress(ssn);
	if (addr != null)
	    suffix = addr.getAddress();
	else {
	    suffix = "javamailuser@localhost"; // worst-case default
	}
	int at = suffix.lastIndexOf('@');
	if (at >= 0)
	    suffix = suffix.substring(at);

	StringBuilder s = new StringBuilder();

	// Unique string is <hashcode>.<id>.<currentTime><suffix>
	s.append(s.hashCode()).append('.').
	  append(id.getAndIncrement()).append('.').
	  append(System.currentTimeMillis()).
	  append(suffix);
	return s.toString();
    }
}