Update Jetty 8.x to 8.1.15
Remove unused variable

(cherry picked from commit b8ebc24b3e19b598e11f8b5dfa7923b1229d4f3e)
Fix typos in javadoc

(cherry picked from commit 1ac237de24ac4412ef5e3d98807b8063e9f1806a)
Optimize imports

(cherry picked from commit 2fbfa72bd6aac319806f2bd20b8e8008fa7acff7)