Mule：如何从 IMAP 连接器捕获附件？

Question

我的测试流程成功查询了一个 imap 收件箱。我正在尝试捕获附件并将它们保存到输出文件夹。到目前为止，我还没有取得任何成功。我尝试过 "Attachment" 转换以及从 IMAP 传输文档中复制和粘贴示例。我不确定该示例是否已过时或什么，但我一直收到错误消息。

这是来自 IMAP 文档中 "Configuration Example" 的代码：

<?xml version="1.0" encoding="UTF-8"?>
<mule xmlns="http://www.mulesoft.org/schema/mule/core"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:spring="http://www.springframework.org/schema/beans"
       xmlns:imap="http://www.mulesoft.org/schema/mule/imap"
       xmlns:vm="http://www.mulesoft.org/schema/mule/vm"
       xmlns:file="http://www.mulesoft.org/schema/mule/file"
       xmlns:email="http://www.mulesoft.org/schema/mule/email"
       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/3.6/mule.xsd
       http://www.mulesoft.org/schema/mule/file http://www.mulesoft.org/schema/mule/file/3.6/mule-file.xsd
       http://www.mulesoft.org/schema/mule/imap http://www.mulesoft.org/schema/mule/imap/3.6/mule-imap.xsd
       http://www.mulesoft.org/schema/mule/email http://www.mulesoft.org/schema/mule/email/3.6/mule-email.xsd
       http://www.mulesoft.org/schema/mule/vm http://www.mulesoft.org/schema/mule/vm/3.6/mule-vm.xsd">

    <imap:connector name="imapConnector"  />

    <expression-transformer name="returnAttachments">
        <return-argument evaluator="attachments-list" expression="*" optional="false"/> ❶
    </expression-transformer>

    <file:connector name="fileName"> 
        <file:expression-filename-parser/> 
    </file:connector>

        <flow name="incoming-orders">
            <imap:inbound-endpoint user="bob" password="password" host="emailHost"
                     port="143" transformer-refs="returnAttachments" disableTransportTransformer="true"/> ❷
            <collection-splitter/>
            <file:outbound-endpoint path="./received" outputPattern="#[function:datestamp].dat"> ❹
                <expression-transformer>
                    <return-argument expression="payload.inputStream" evaluator="groovy" /> ❺
                </expression-transformer>
            </file:outbound-endpoint>                    
        </flow>
</mule>

这是我得到的错误（更改所有连接详细信息后）：

Element 'expression-transformer' cannot have character [children], because the type's content type is element-only.

Mule：如何从 IMAP 连接器捕获附件？

Mule: How to capture attachment from IMAP connector?

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