import org.jivesoftware.smack.util.TLSUtils; //导入依赖的package包/类
private XMPPConnection login(final Configuration config) throws IOException, XMPPException, SmackException, KeyManagementException, NoSuchAlgorithmException {
    final String serviceName = isNullOrEmpty(config.getString(CK_SERVICE_NAME))
            ? config.getString(CK_HOSTNAME) : config.getString(CK_SERVICE_NAME);

    final XMPPTCPConnectionConfiguration.Builder configBuilder = XMPPTCPConnectionConfiguration.builder()
            .setHost(config.getString(CK_HOSTNAME))
            .setPort(config.getInt(CK_PORT))
            .setServiceName(serviceName)
            .setSendPresence(false);

    if (config.getBoolean(CK_ACCEPT_SELFSIGNED)) {
        TLSUtils.acceptAllCertificates(configBuilder);
    }

    final boolean requireSecurity = config.getBoolean(CK_REQUIRE_SECURITY);
    configBuilder.setSecurityMode(requireSecurity ?
            ConnectionConfiguration.SecurityMode.required : ConnectionConfiguration.SecurityMode.ifpossible);

    final XMPPTCPConnectionConfiguration connectionConfiguration = configBuilder.build();
    if (LOG.isDebugEnabled()) {
        LOG.debug("Supported SASL authentications: {}", SASLAuthentication.getRegisterdSASLMechanisms());
        LOG.debug("require_security: {}", requireSecurity);
        LOG.debug("Security mode: {}", connectionConfiguration.getSecurityMode());
        LOG.debug("Socket factory: {}", connectionConfiguration.getSocketFactory());
        LOG.debug("Keystore: {}", connectionConfiguration.getKeystorePath());
        LOG.debug("Keystore type: {}", connectionConfiguration.getKeystoreType());
    }

    final XMPPTCPConnection xmppConnection = new XMPPTCPConnection(connectionConfiguration);

    xmppConnection.connect();
    xmppConnection.login(config.getString(CK_USERNAME), config.getString(CK_PASSWORD));

    return xmppConnection;
}