I would trace tomcat and recreate a servlet request .. see if I could
hack it in that way (assuming that localhost traffic isn't fast
enough). Normalizing on HTTP/TCP will be more maintainable, though?
Can somebody suggest a good place for a breakpoint?
Any other suggestions?
John
On 5/6/19, Paul Carter-Brown <paul.carter-br...@jini.guru> wrote:
> Hi John,
>
> See original request. It's pretty much a Kafka/Servlet proxy/gateway:
>
> I'm trying to design a Kafka consumer and producer that will run inside the
> tomcat jvm and pick up messages off a Kafka topic and translate them into a
> servlet request and pass it through tomcat and then when the response is
> complete then translate it into a Kafka message and put it onto another
> topic as a reply. This way I can reuse our existing jax-rs rest services
> and expose them as an async api over Kafka. The idea is to make the Kafka
> messages similar to http in that they would consist of headers and a body.
> The body would be json.
>
>
> On Mon, May 6, 2019 at 6:13 PM John Dale <jcdw...@gmail.com> wrote:
>
>> You could try debugging the tomcat code and find out how, right after
>> it parses the TCP request, it invokes the servlet. You can then
>> create your own harness for tomcat code after initializing the
>> appropriate context for the request to tomcat. I don't know off hand
>> where in the tomcat code this cut point can be found.
>>
>> Is this a performance issue, or are you building a proxy?
>>
>> What is the problem you're trying to solve?
>>
>> On 5/6/19, Paul Carter-Brown <paul.carter-br...@jini.guru> wrote:
>> > Yea, but the issue is that only works when calling in the context of a
>> > current servlet call.
>> >
>> > Here is the kind of problem I want to solve:
>> >
>> > @WebServlet(name = "MyExample", urlPatterns = {"/example"},
>> loadOnStartup =
>> > 1)
>> > public class Example extends HttpServlet {
>> >
>> > @PersistenceContext
>> > private EntityManager em;
>> >
>> > @Override
>> > public void init(ServletConfig config) {
>> > Thread t = new Thread(() -> {
>> > while (true) {
>> > try {
>> > // Do a GET to /example/ and get the response
>> > without
>> > going out on localhost and back in....
>> > // We cant just call doGet as we want the request
>> > to
>> > flow through the servlet filters, do the entitymanager injection etc
>> > Thread.sleep(10000);
>> > } catch (Exception e) {
>> > }
>> > }
>> > });
>> > t.start();
>> >
>> > }
>> >
>> > @Override
>> > protected void doGet(HttpServletRequest req, HttpServletResponse
>> resp)
>> > throws ServletException, IOException {
>> > // do stuff like use em
>> > resp.setStatus(200);
>> > resp.getWriter().write("Hello World");
>> > }
>> >
>> > }
>> >
>> >
>> >
>> >
>> > On Mon, May 6, 2019 at 5:35 PM John Dale <jcdw...@gmail.com> wrote:
>> >
>> >> For reference, I did find this after searching "calling a servlet
>> >> programmatically":
>> >> https://docs.oracle.com/cd/E19146-01/819-2634/abxbn/index.html
>> >>
>> >> On 5/6/19, Paul Carter-Brown <paul.carter-br...@jini.guru> wrote:
>> >> > I think we are completely missing each other. Forget sockets - that
>> was
>> >> > just an example. I have code running in a Tomcat App server which is
>> >> > not
>> >> > managed by Tomcat and is not initiated by anything within Tomcat.
>> >> > That
>> >> code
>> >> > now wants to call a servlet hosted in that very same JVM. Any way to
>> do
>> >> > that without going out and back in on TCP?
>> >> >
>> >> >
>> >> > On Mon, May 6, 2019 at 5:14 PM John Dale <jcdw...@gmail.com> wrote:
>> >> >
>> >> >> Sockets are an implementation of TCP/UDP inherently.
>> >> >>
>> >> >> Perhaps a mountaintop signal fire?
>> >> >>
>> >> >> ;)
>> >> >>
>> >> >> John
>> >> >>
>> >> >>
>> >> >> On 5/6/19, Paul Carter-Brown <paul.carter-br...@jini.guru> wrote:
>> >> >> > lol on the Semaphore Telegraph,
>> >> >> >
>> >> >> > I can't use a request dispatcher as the request is being
>> >> >> > initiated
>> >> from
>> >> >> > code that has no context. I already have it working with HTTP
>> >> >> > using
>> >> >> > asynchttp library, but I want to avoid the overhead. E.g. lets
>> >> >> > say
>> I
>> >> >> wrote
>> >> >> > my own server socket listener on port 10000 running in the Tomcat
>> >> >> > JVM
>> >> >> > and
>> >> >> > got some request in some propriatary protocol called X. Now I
>> >> >> > want
>> >> >> > to
>> >> >> call
>> >> >> > a Tomcat servlet in the current JVM with some info I got over X
>> >> without
>> >> >> > going out on TCP and back in....
>> >> >> >
>> >> >> > On Mon, May 6, 2019 at 4:40 PM John Dale <jcdw...@gmail.com>
>> wrote:
>> >> >> >
>> >> >> >> If you're wanting to forward control to another servlet deployed
>> in
>> >> >> >> the same context:
>> >> >> >> https://www.javatpoint.com/requestdispatcher-in-servlet
>> >> >> >>
>> >> >> >> If you are okay going through TCP to facilitate some future or
>> >> current
>> >> >> >> distribution of services, Use HTTPURLConnection (not sure what
>> >> >> >> you're
>> >> >> >> wanting to do with the result of the request, if anything):
>> >> >> >>
>> >> >> >>
>> >> >>
>> >>
>> https://stackoverflow.com/questions/2793150/how-to-use-java-net-urlconnection-to-fire-and-handle-http-requests
>> >> >> >>
>> >> >> >> If you need more sophisticated HTTP interactions, Apache
>> >> >> >> maintains
>> >> >> >> a
>> >> >> >> very useful library for that: http://hc.apache.org/
>> >> >> >>
>> >> >> >> If these don't work-out for you, rather than using .NET, PHP,
>> >> >> >> Python,
>> >> >> >> or some other Java facsimile at best, I recommend using the
>> >> >> >> semaphore
>> >> >> >> telegraph:
>> >> >> >> https://en.wikipedia.org/wiki/Semaphore_telegraph
>> >> >> >>
>> >> >> >> Sincerely,
>> >> >> >>
>> >> >> >> John
>> >> >> >> DB2DOM
>> >> >> >>
>> >> >> >> On 5/6/19, Paul Carter-Brown <paul.carter-br...@jini.guru>
>> >> >> >> wrote:
>> >> >> >> > Hi John,
>> >> >> >> >
>> >> >> >> > Thanks for your feedback.
>> >> >> >> >
>> >> >> >> > The request I'm initiating should not or need not carry any
>> >> >> >> > context
>> >> >> >> > from
>> >> >> >> > the originating code. There is also no session to worry about
>> >> >> >> > as
>> >> its
>> >> >> >> > just
>> >> >> >> > for rest calls. So basically I have the headers, path and body
>> >> >> >> > and
>> >> >> need
>> >> >> >> to
>> >> >> >> > generate a http servlet request and get an http servlet
>> >> >> >> > response
>> >> (or
>> >> >> >> > similar) back. I have this working by calling into localhost
>> >> >> >> > but
>> >> >> >> > ideally
>> >> >> >> > want to skip the trombone out and back in.
>> >> >> >> >
>> >> >> >> > Have you got any basic code examples?
>> >> >> >> >
>> >> >> >> > Paul
>> >> >> >> >
>> >> >> >> > On Tue, Apr 30, 2019 at 5:27 PM John Dale <jcdw...@gmail.com>
>> >> wrote:
>> >> >> >> >
>> >> >> >> >> Another thought .. you can do some request dispatching, but
>> >> without
>> >> >> >> >> knowing more about the tools you're using, I can't say for
>> >> >> >> >> sure
>> >> >> >> >> if
>> >> >> >> >> this is the direction you'll want to go.
>> >> >> >> >>
>> >> >> >> >> On 4/29/19, Paul Carter-Brown <paul.carter-br...@jini.guru>
>> >> wrote:
>> >> >> >> >> > Hi
>> >> >> >> >> >
>> >> >> >> >> > I'm trying to design a Kafka consumer and producer that
>> >> >> >> >> > will
>> >> >> >> >> > run
>> >> >> >> inside
>> >> >> >> >> the
>> >> >> >> >> > tomcat jvm and pick up messages off a Kafka topic and
>> >> >> >> >> > translate
>> >> >> them
>> >> >> >> >> into a
>> >> >> >> >> > servlet request and pass it through tomcat and then when
>> >> >> >> >> > the
>> >> >> >> >> > response
>> >> >> >> >> > is
>> >> >> >> >> > complete then translate it into a Kafka message and put it
>> >> >> >> >> > onto
>> >> >> >> another
>> >> >> >> >> > topic as a reply. This way I can reuse our existing jax-rs
>> >> >> >> >> > rest
>> >> >> >> >> > services
>> >> >> >> >> > and expose them as an async api over Kafka. The idea is to
>> >> >> >> >> > make
>> >> >> >> >> > the
>> >> >> >> >> > Kafka
>> >> >> >> >> > messages similar to http in that they would consist of
>> headers
>> >> >> >> >> > and
>> >> >> a
>> >> >> >> >> body.
>> >> >> >> >> > The body would be json.
>> >> >> >> >> >
>> >> >> >> >> > Now I know this could be done by calling localhost with an
>> >> >> >> >> > http
>> >> >> call
>> >> >> >> to
>> >> >> >> >> > trombone the requests back into tomcat but I'd like to
>> >> >> >> >> > avoid
>> >> >> >> >> > the
>> >> >> >> >> associated
>> >> >> >> >> > latency and overhead. Is it possible to call tomcat
>> >> >> >> >> > directly
>> >> >> >> >> > in-process.
>> >> >> >> >> > This does not need to be portable to other containers so
>> >> >> >> >> > can
>> >> >> >> >> > be
>> >> >> >> >> > proprietary.
>> >> >> >> >> >
>> >> >> >> >> > I'm using tomcat 8. In fact its tomee 8 but guessed this is
>> >> >> >> >> > more
>> >> >> >> >> > a
>> >> >> >> >> > tomcat
>> >> >> >> >> > question than tomee but have sent to both groups just in
>> case.
>> >> >> >> >> >
>> >> >> >> >> > Thanks for any insights.
>> >> >> >> >> >
>> >> >> >> >> > Paul
>> >> >> >> >> >
>> >> >> >> >>
>> >> >> >> >
>> >> >> >>
>> >> >> >>
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>> >> >> >>
>> >> >> >>
>> >> >> >
>> >> >>
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>> >> >>
>> >> >>
>> >> >
>> >>
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>> >>
>> >>
>> >
>>
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