JFinal - port: 80 already in use

When I run my JFinal application, I got this error:

java.lang.IllegalStateException: port: 80 already in use!
at com.jfinal.server.JettyServer.doStart(JettyServer.java:78)
at com.jfinal.server.JettyServer.start(JettyServer.java:64)
at com.jfinal.core.JFinal.main(JFinal.java:173)

Then I checked my port, but I could not find any process that used port 80…

The reason for this error is: I didn’t open eclipse as root!