Get the server port number from tomcat without a request

0 votes
asked Oct 5, 2010 by teja-kantamneni

Is there any Tomcat API or configuration available which can tell an application (probably on startup), what port its running on without a request?

Imagine a scenario where there are two web applications running in the same Tomcat and one of which need to invoke a web service from the other one. We don't want the request to leave the Tomcat (if you use the Apache server name or absolute URL, the request will go out and come back again and it can go to any instance) and come back in. For that I know the name of the machine but no way to get the port number. I know I can hard code this information but I don't want to do this as I want my war file to be application server agnostic.

I know that we can find it if we have a HTTPServletRequest

This works only for Tomcat 6 and will not work on Tomcat 7

11 Answers

0 votes
answered Oct 5, 2010 by jay

Hmm, how would an application get started in Tomcat without a request? Maybe I'm going brain dead for a moment here, but I don't think any classes will load until a request hits. Sure, you could have classes independent of any particular request, but they'd need a request to get them fired off at some point.

0 votes
answered Oct 5, 2010 by sarat

I am not entirely sure if you can access the Tomcat port from code in the environment configuration you need. Did you consider actually having the full URL to the web service passed as a configuration param/setting (probably in a .properties file) to the app?

This way you wouldn't have to hardcode the port and de-couple both your apps so that you could technically have the web service on an external tomcat but still access it by just changing the property, avoiding code re-build.

0 votes
answered Oct 7, 2010 by mschonaker

You could use crossContext. But I don't think that's app server agnostic.

I would share a custom class, behaving as a registry of running applications in the same tomcat instance through JNDI, as I explained here.

During startup, through a ContextListener or through an Spring container event, I would obtain the registry through a JNDI lookup, add my web app instance with an url obtained from the servletcontext.contextpath, and finally register a listener to hear other applications registering themselves. That's the more server agnostic I can think of.

Obtaining the port won't be server agnostic, you should use a context parameter.

EDIT: I'm sorry, forgot to say that what I've described is to share objects among contexts, but no, you can't not know the port unless you use some server API (not agnostic at all).

0 votes
answered Oct 16, 2010 by ashley-walton

Previously on a large distributed project, the design I used was to have the centralised service initialise the several services with the central service's URL(& port).

Obviously this means that the central service must maintain a list of the services (URL & port) to initialise.

0 votes
answered Oct 18, 2010 by ejp

The server port number doesn't exist. It can have any number of port numbers. So what you're asking doesn't make sense. The port number associated with a specific request does make sense.

0 votes
answered Oct 18, 2010 by puspendu-banerjee
  • Get Hold of MBean/JMX Object for Tomcat/Server Instance
  • Get Virtual Server Instance Related Data from there

Check http://svn-mirror.glassfish.org/glassfish-svn/tags/embedded-gfv3-prelude-b07/web/web-glue/src/main/java/com/sun/enterprise/web/WebContainer.java for reference

The content of the MBeanServer can then be exposed through various protocols, implemented by protocol connectors[RMI/IIOP], or protocol adapters[SNMP/HTTP]. In this case, use of SNMP adapter will be a better approach so that a SNMP trap can be placed without knowing the exact IP/port of other Application Servers

0 votes
answered Oct 19, 2010 by aaron-digulla

If you want to access an application on the same server instance, just omit the server part of the URL. Some examples what you can achieve. The current document is at http://example.com:8080/app2/doc.html

0 votes
answered Oct 21, 2010 by allen

These types of servers are designed to be able to listen on (almost) arbitrary ports and to hide these details from the contained applications which normally do not need to know.

The only way is to read the configuration files yourself and have access to the command line arguments that started the server where the configuration files may have been overridden. You have to know a lot about the system you are running on for this to work. There is no way of doing it portably.

Even if there were, there are cases in which it simply does not matter like being behind a NAT, certain firewalls, etc.

0 votes
answered Oct 22, 2011 by teja-kantamneni

For anybody who is interested in how we solved this, here is the mock code

Server server = ServerFactory.getServer();
        Service[] services = server.findServices();
        for (Service service : services) {
            for (Connector connector : service.findConnectors()) {
                ProtocolHandler protocolHandler = connector.getProtocolHandler();
                if (protocolHandler instanceof Http11Protocol
                    || protocolHandler instanceof Http11AprProtocol
                    || protocolHandler instanceof Http11NioProtocol) {
                    serverPort = connector.getPort();
                    System.out.println("HTTP Port: " + connector.getPort());
                }
            }


        }
0 votes
answered Oct 31, 2013 by ggrandes

With this:

List<String> getEndPoints() throws MalformedObjectNameException,
        NullPointerException, UnknownHostException, AttributeNotFoundException,
        InstanceNotFoundException, MBeanException, ReflectionException {
    MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
    QueryExp subQuery1 = Query.match(Query.attr("protocol"), Query.value("HTTP/1.1"));
    QueryExp subQuery2 = Query.anySubString(Query.attr("protocol"), Query.value("Http11"));
    QueryExp query = Query.or(subQuery1, subQuery2);
    Set<ObjectName> objs = mbs.queryNames(new ObjectName("*:type=Connector,*"), query);
    String hostname = InetAddress.getLocalHost().getHostName();
    InetAddress[] addresses = InetAddress.getAllByName(hostname);
    ArrayList<String> endPoints = new ArrayList<String>();
    for (Iterator<ObjectName> i = objs.iterator(); i.hasNext();) {
        ObjectName obj = i.next();
        String scheme = mbs.getAttribute(obj, "scheme").toString();
        String port = obj.getKeyProperty("port");
        for (InetAddress addr : addresses) {
            if (addr.isAnyLocalAddress() || addr.isLoopbackAddress() || 
                addr.isMulticastAddress()) {
                continue;
            }
            String host = addr.getHostAddress();
            String ep = scheme + "://" + host + ":" + port;
            endPoints.add(ep);
        }
    }
    return endPoints;
}

You will get a List like this:

[http://192.168.1.22:8080]
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