drools - 理解议程组流口水

Question

我尝试了一个示例来了解议程组的工作原理。最初我将 ksession 的焦点设置为议程组“ag1”并触发了规则。

package com.sample

import com.sample.DroolsTest.Message;

rule "Hello World"
  agenda-group "ag1"
    when
        m : Message( status == Message.HELLO, myMessage : message )
    then
        System.out.println( "Hello World" ); 
        m.setMessage( "Goodbye cruel world" );
        m.setStatus( Message.GOODBYE );
        update( m );
end

rule "Hello World 2"
  agenda-group "ag2"
    when
        m : Message( status == Message.HELLO, myMessage : message )
    then
        System.out.println( "Hello World 2" ); 
        m.setMessage( "Goodbye cruel world" );
        m.setStatus( Message.GOODBYE );
        update( m );
end

rule "GoodBye"
  agenda-group "ag1"
    when
        m : Message( status == Message.GOODBYE, myMessage : message )
    then
        System.out.println( "GoodBye" );
        drools.setFocus("ag2");
        System.out.println("comeon man");
        m.setStatus(com.sample.DroolsTest.Message.HELLO);
        update(m);
end

rule "GoodBye 2"
  agenda-group "ag2"
    when
        Message( status == Message.GOODBYE, myMessage : message )
    then
        System.out.println( "GoodBye 2" );
end

这是我得到的输出。

Hello World
GoodBye
comeon man
Hello World 2
GoodBye 2
GoodBye
comeon man
Hello World 2
GoodBye 2
GoodBye
comeon man
Hello World 2
GoodBye 2
GoodBye
comeon man
Hello World 2
GoodBye 2
GoodBye
comeon man
Hello World 2
...
...

我可以理解输出的前 5 行直到“GoodBye 2”。但是由于焦点设置为“ag2”，它如何回到“ag1”议程组的“再见”规则并因此递归。

谢谢。

Answer 1

议程组就像一个堆栈。当您将焦点设置到给定的议程组时，该组将放置在堆栈顶部。当引擎尝试触发下一个激活并且给定组中没有更多激活时，该组将从堆栈顶部移除，并且其下方的组再次获得焦点。

所以它是这样的(main 是始​​终存在的默认组):

* STACK: [MAIN, ag1]

Hello Word fires and activates both "GoodBye" rules
GoodBye fires, activates both "Hello World" rules and sets the focus to "ag2"

* STACK: [MAIN, ag1, ag2]

Hellow World 2 fires, cancels the "Hello World 1" rule and activates both "GoodBye" rules
GoodBye 2 fires because ag2 has the focus

* There are no more activations in ag2 to fire, so ag2 is removed from the stack
* STACK: [MAIN, ag1]
* The "GoodBye" rule is still active in ag1, so it fires

GoodBye fires, activates both "Hello World" rules and sets the focus to "ag2"

* STACK: [MAIN, ag1, ag2]

Hellow World 2 fires, cancels the "Hello World 1" rule and activates both "GoodBye" rules
...

并且循环重复。

如果您在 Eclipse IDE 中使用审计日志，这种行为是很容易看到的。

希望这可以帮助。