2018-02-16 0:35 GMT+03:00 Mark Thomas <ma...@apache.org>: > Hi, > > I've been looking at: > https://bz.apache.org/bugzilla/show_bug.cgi?id=43866 > > In short, this bug is looking for a way to tell Tomcat an object set as > a session attribute has been mutated and therefore needs to be > replicated. The 'standard' way to do this is by calling setAttribute() > but this triggers listeners. > > While thinking about ways to implement an option for this, I stumbled > across the following. When setAttribute() is called with an object that > is already in the session then StandardSession.setAttribute() calls > listeners inconsistently. > > Any HttpSessionBindingListener will not be called because the old and > new values are the same (see line 1426 in trunk). > > Any HttpSessionAttributeListener will be called since the old and new > values are not compared (see line 1466 in trunk). > > I can find no reason in the spec for this difference. > > I think these should be consistent. In the case where setAttribute() is > called with the same value as is already bound either both types of > listener should be called or neither. >
I disagree. Javadoc (Servlet 4.0): https://javaee.github.io/javaee-spec/javadocs/javax/servlet/http/HttpSessionAttributeListener.html https://javaee.github.io/javaee-spec/javadocs/javax/servlet/http/HttpSessionBindingListener.html 1) HttpSessionAttributeListener is "@since Servlet 2.3", HttpSessionBindingListener does not have "@since" clause. Thus it looks that the attribute listener is a newer and improved API. 2) The "binding" listener is not a listener (it is not in the list of listeners, it cannot be declared in web.xml). It is an interface implemented by the value itself. 3) I think that once value.valueUnbound() is called, the expectation is that the value is never going to be used again and can be destroyed. I think it is not safe to call valueBound() on it. Thus the reason for (value != oldValue) check (line 1426 in trunk). 4) A HttpSessionAttributeListener has three methods as opposed to two in binding listener. Its attributeReplaced() method can be coded to handle the (value == oldValue) case. Best regards, Konstantin Kolinko --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@tomcat.apache.org For additional commands, e-mail: dev-h...@tomcat.apache.org
