hello,everyone!I wrote a rule with Drools,but the error told me that the field Server.Message is not visible, I can't find how it happens. Please help me, I am almost exhausted with it. thank you.

the rules are as follows:

 

package com.sample

import com.sample.Server;

 

rule "system will execute 'tc' command"
 when
    eval(Server.Message>8388608)
 then
     System.out.println("The network is so crowd that it needs repairing.");
  Runtime.getRuntime().exec("tc");#execute the "tc" command
end

 

rule "caution"
    when
        eval(Server.Message==8388608)
    then
        System.out.println("caution!The network maybe will get blocked very soon.");
end

 

rule "fluent network"
  when
  eval(Server.Message<8388608)#conditions
 then
  System.out.println("the current network is very good");#actions
end