Hi, Recently I am working on implementing a feature that can automatically register a ServletContextListerner instance, say A, to servletContext programmatically during startup.
I use ServletContainerInitializer and call the servletContext.addListener() method. This is fine for most of the cases. But if user has specified A in web.xml, it turns that A will be registered twice, which will lead to undesired behavior. My expected behavior will be registering A only once regardless of user specified A in web.xml or not. I can achieve this by specifying A in web-fragment.xml, since it will get merged into web.xml whenever A is defined in web.xml or not, which means duplicates can be removed. I am wondering why we can not achieve this using programatic API. I've checked servlet 4.0/3.1 spec, in 4.4.3.1 "void addListener(String className)", it says: If the class with the given name implements a listener interface whose invocation order corresponds to the declaration order, that is, if it implements javax.servlet.ServletRequestListener, javax.servlet.ServletContextListener or javax.servlet.http.HttpSessionListener, then the new listener will be added to the end of the ordered list of listeners of that interface. It looks tomcat's behavior is spec-compliant. My idea is if I can get all the existing listeners from servletContext, then I can decide whether to add A or not. But I can't find that kind of API from servletContext. I also noticed that there are getServletRegistrations() and getFilterRegistrations() in servletContext, why can't we have API like getListeners()? -- Best Regards！ Huxing --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@tomcat.apache.org For additional commands, e-mail: dev-h...@tomcat.apache.org
