mxlist.java

Java与模式 源代码

package com.javapatterns.singleton.mxrecord1;

import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.Hashtable;
import java.util.StringTokenizer;
import java.util.Vector;
import javax.naming.NamingEnumeration;
import javax.naming.directory.Attribute;
import javax.naming.directory.Attributes;
import javax.naming.directory.DirContext;
import javax.naming.directory.InitialDirContext;


public class MXList
{
    private static MXList mxl = null;
    private Vector list = null;
    private static final String FACTORY_ENTRY =
    "java.naming.factory.initial";
    private static final String FACTORY_NAME =
    "com.sun.jndi.dns.DnsContextFactory";
    private static final String PROVIDER_ENTRY =
    "java.naming.provider.url";
    private static final String MX_TYPE = "MX";
    private String dnsUrl = null;
    private String domainName = null;
    private static Calendar updateTime;
    private MailServer aMailServer = null;

    private MXList() { }

    private MXList(String providerUrl,
    String domainName) throws Exception
    {
        this.dnsUrl = dnsUrl;
        this.domainName = domainName;

        this.list = getMXRecords(providerUrl, domainName);
    }

    public static synchronized MXList getInstance(
    String providerUrl,
    String domainName) throws Exception
    {
        if (mxl == null)
        {
            mxl = new MXList(providerUrl, domainName);
        }
        else
        {
            Calendar now = new GregorianCalendar();

            long timeDifference = now.getTime().getTime()
            - updateTime.getTime().getTime();

            if (timeDifference > 24 * 60 * 60 * 1000)
            {
                mxl.list = mxl.getMXRecords(providerUrl, domainName);
            }
        }
        return mxl;
    }

    public MailServer elementAt(int index)
    throws Exception
    {
        return (MailServer)list.elementAt(index);
    }

    public int size()
    {
        return list.size();
    }

    private Vector getMXRecords(
    String dnsUrl,
    String domainName) throws Exception
    {
        Hashtable env = new Hashtable();

        env.put(FACTORY_ENTRY, FACTORY_NAME);
        env.put(PROVIDER_ENTRY, dnsUrl);

        DirContext dirContext = new InitialDirContext(env);

        Vector records = new Vector(10);

        Attributes attrs = dirContext.getAttributes(
        domainName,
            new String[] { MX_TYPE });

        for (NamingEnumeration ae = attrs.getAll();
        ae != null && ae.hasMoreElements(); )
        {
            Attribute attr = (Attribute)ae.next();
            NamingEnumeration e = attr.getAll();
            while (e.hasMoreElements())
            {
                String element = e.nextElement().toString();

                StringTokenizer tokenizer =
                new StringTokenizer(element, " ");

                MailServer mailServer = new MailServer();

                String token1 = tokenizer.nextToken();
                String token2 = tokenizer.nextToken();

                if (token1 != null && token2 != null)
                {
                    mailServer.setPriority(
                    Integer.valueOf(token1).intValue());
                    mailServer.setServer(token2);
                    records.addElement(mailServer);
                }
            }
        }

        updateTime = new GregorianCalendar();
        System.out.println("List created.");
        return records;
    }
}