-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Huxing,
On 7/25/18 11:28 AM, Huxing Zhang wrote: > 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()? Can you think of a use-case where addListener() shouldn't automatically perform de-duplication? I'm thinking that Tomcat should simply take a call to addListener() and ignore any registrations after the first one. Would that make sense? Would it violate any spec-defined behavior? - -chris -----BEGIN PGP SIGNATURE----- Comment: GPGTools - http://gpgtools.org Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQIzBAEBCAAdFiEEMmKgYcQvxMe7tcJcHPApP6U8pFgFAltYyDIACgkQHPApP6U8 pFhSmA//We21JrL+KwpbPrNgicIM0T77/WFMQyNoaFrW0+QdJ96CUAWYr6NKn17t 0Y0mk9WpRDSIsknpXPTYfisO1RllO7Mde1KuGH6EUMZyYWr84E9YhqBVyOHG48if Y/COneCHK3Gs7QlywgRhyKDZFogDFS/X5zW+AGctFIdcdgBu0z8U85a/wlPLUTuk XA00qPLrIWSXerB97nsqcdreh7Qs2Uyx3Eye74JE4RwzRYkGVYrMuPpPQwudbAUF f2fgAHC5lrJBGLK4yiFce53KcwTzeyBM2yskux/1y02NUyHIASpjV8DqADthV61o SOFgG25PJChShsLQipjhcNQtqiluP4FNo1sN78ieMABfOm1zlIh4T4/4M8VD0MqP qdoXgqC8vEsCiGUY7rqQKIRTAe6Hpf2yz6Oygwhfk+6z2CpJ4RQfsAFMVJMf2KOM wjb6akXnrEzxPG6UEVxtep2cLLVraHlbjDHzNqMrecBC2EYHU/Ovh+gpsHXtJG8v +Koh9HR2Ps5h92PI5ND39JsD1KyNhO+zayYD/a+I9ryrQEKV584JyU6q3vyWIwXk m8eDlYo0ChCeiGwQ22bAOsdKYTJHruGPEg92VbbDipPLJ+8uzAbtEAlXmiGYkv2B Q3EtprVkD1sI88v/iRU8QZg7ux5ebKDHGIk1f33BP3AYUWnwcyY= =jKMW -----END PGP SIGNATURE----- --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@tomcat.apache.org For additional commands, e-mail: dev-h...@tomcat.apache.org
