MEL逻辑AND表现奇怪，操作数的顺序很重要？

Question

任何人都可以解释为什么发生以下行为？为什么使用逻辑AND时操作数的顺序很重要？在mule-ce上运行3.3.1。

输出如下：

true 
true 
false 
true 


<?xml version="1.0" encoding="UTF-8"?> 

<mule xmlns:http="http://www.mulesoft.org/schema/mule/http" xmlns="http://www.mulesoft.org/schema/mule/core" xmlns:doc="http://www.mulesoft.org/schema/mule/documentation" xmlns:spring="http://www.springframework.org/schema/beans" version="EE-3.4.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-current.xsd 
http://www.mulesoft.org/schema/mule/core http://www.mulesoft.org/schema/mule/core/current/mule.xsd 
http://www.mulesoft.org/schema/mule/http http://www.mulesoft.org/schema/mule/http/current/mule-http.xsd"> 

    <flow name="testFlow1" doc:name="testFlow1"> 
     <http:inbound-endpoint exchange-pattern="request-response" host="localhost" port="20005" path="test" doc:name="HTTP"/> 

     <message-properties-transformer overwrite="true" scope="session" doc:name="Message Properties"> 
       <add-message-property key="productNumber" value="1" /> 
     </message-properties-transformer> 

     <logger level="INFO" message="#[(sessionVars['productNumber'] == '1' || sessionVars['productNumber'] == '2') and (sessionVars['quantity'] == null)]" doc:name="Logger"/> 
     <!-- true --> 

     <logger level="INFO" message="#[(sessionVars['quantity'] == null) and (sessionVars['productNumber'] == '1' || sessionVars['productNumber'] == '2')]" doc:name="Logger"/> 
     <!-- true --> 

     <message-properties-transformer overwrite="true" scope="session" doc:name="Message Properties"> 
       <add-message-property key="productNumber" value="3" /> 
     </message-properties-transformer> 

     <logger level="INFO" message="#[(sessionVars['productNumber'] == '1' || sessionVars['productNumber'] == '2') and (sessionVars['quantity'] == null)]" doc:name="Logger"/> 
     <!-- false --> 

     <logger level="INFO" message="#[(sessionVars['quantity'] == null) and (sessionVars['productNumber'] == '1' || sessionVars['productNumber'] == '2')]" doc:name="Logger"/> 
     <!-- true? it should not be true! -->   
    </flow> 
</mule> 

Answer 1

我不知道为什么会这样，但是我有3.4.0 CE同样的经历。一个解决方法，以实现正确的结果似乎是用“& &”，如

#[(sessionVars['quantity'] == null) && (sessionVars['productNumber'] == '1' || sessionVars['productNumber'] == '2')]

Answer 2

使用＆ampamp;而不是和。它会计算出正确的值。更新流程

<logger level="INFO" message="#[(sessionVars['productNumber'] == '1' || sessionVars['productNumber'] == '2') &amp;&amp; (sessionVars['quantity'] == null)]" doc:name="Logger"/> 
    <!-- false --> 


<logger level="INFO" message="#[(sessionVars['quantity'] == null) &amp;&amp; (sessionVars['productNumber'] == '1' || sessionVars['productNumber'] == '1')]" doc:name="Logger"/>