问题
I'm using Eclipse EE Juno and my current web application is using Dynamic web modules 2.4. I'm trying to bump the version up to 3.0 but for some reason I'm unable to. when I try to change the version in project facets I get Cannot change version of project facet Dynamic Web Module to 3.0. Is it possible that there some bunk line in my web.xml file that determines this? How do I change the Dynamic web modules version if not from Eclipse project facet setting alone?
回答1:
Servlet 2.4 in web.xml:
<web-app version="2.4"
xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
Servlet 3.0 in web.xml:
<web-app version="3.0"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
That's the only difference. The rest is your IDE configuration. In order to use Servlet 3.0 you must have 3.0 JARs on the CLASSPATH so that new annotations and other classes are available. But do not include servlet JAR in your WAR, the implementation should come from the servlet container.
来源：https://stackoverflow.com/questions/12146247/java-web-app-what-determines-my-servlet-api-version-does-it-get-specified-in