Apache Tomcat 8.0.20 发布，该版本值得关注的 bug 修复包括：
– Fix a performance regression in the new resources implementation
when signed JARs are used in a web application.
– Fix several bugs that could cause multiple registrations for write
events for a single socket when using Servlet 3.0 async. Typically,
the side effects of these multiple registrations would be
exceptions appearing in the logs.
– Enhance the bean factory used for JNDI resources. The new
attribute forceString allows to support non-standard string
argument property setters.