Java代码实现SIP通话

在 Java 中实现 SIP 通话可以使用 SIP API，比如 SIP API for Java (SIPServer API) 或者 MJSip。

使用 SIP API for Java (SIPServer API) 可以这样写代码：

import java.io.IOException;
import java.net.InetAddress;
import javax.sip.ClientTransaction;
import javax.sip.Dialog;
import javax.sip.DialogState;
import javax.sip.DialogTerminatedEvent;
import javax.sip.IOExceptionEvent;
import javax.sip.ListeningPoint;
import javax.sip.RequestEvent;
import javax.sip.ResponseEvent;
import javax.sip.ServerTransaction;
import javax.sip.SipFactory;
import javax.sip.SipListener;
import javax.sip.SipProvider;
import javax.sip.SipStack;
import javax.sip.TimeoutEvent;
import javax.sip.TransactionTerminatedEvent;
import javax.sip.address.Address;
import javax.sip.address.AddressFactory;
import javax.sip.address.SipURI;
import javax.sip.header.CSeqHeader;
import javax.sip.header.CallIdHeader;
import javax.sip.header.ContactHeader;
import javax.sip.header.ContentTypeHeader;
import javax.sip.header.FromHeader;
import javax.sip.header.HeaderFactory;
import javax.sip.header.MaxForwardsHeader;
import javax.sip.header.ToHeader;
import javax.sip.header.ViaHeader;
import javax.sip.message.MessageFactory;
import javax.sip.message.Request;
import javax.sip.message.Response;

public class SIPClient implements SipListener {
    private static SipStack sipStack;
    private static SipProvider sipProvider;
    private static AddressFactory addressFactory;
    private static MessageFactory messageFactory;
    private static HeaderFactory headerFactory;
    private static ListeningPoint listeningPoint;
    private static SipFactory sipFactory;
    private static Dialog dialog;

    public static void main(String[] args) {
        SIPClient sipClient = new SIPClient();
        sipClient.init();
        sipClient.sendInvite();
    }

    public void init() {
        sipFactory = SipFactory.getInstance();
        sipFactory.setPathName("gov.nist");
        Properties properties = new Properties();
        properties.setProperty("javax.sip.STACK_NAME", "SIPClient");
        try {
            // Create SipStack object
            sipStack = sipFactory.createSipStack(properties);
            System.out.println("createSipStack " + sipStack);
        } catch (PeerUnavailableException e) {