WSO2 ESB从后端流转时发送异常空JSON负载问题求助

Hey there, let's tackle this payload issue you're facing with WSO2 ESB and WireMock. I've run into similar scenarios while working with WSO2 integrations, so here's what's going on and how to fix it:

The Root Cause #

When you use the send mediator in your switch statement, it consumes the payload from the message context by default. That means once the send executes, the original payload stored in ESB's message context gets cleared out—this is why you see the payload is intact when it first enters the ESB, but turns empty when flowing to subsequent endpoints.

Fixes You Can Implement #

Here are three targeted solutions, ordered by how commonly they're used in this scenario:

1. Use the clone Mediator to Preserve the Original Payload

If you need to route the same payload to multiple endpoints (or run additional logic after the initial send), the clone mediator creates copies of the message context so each target sequence gets a full, unmodified payload. Example configuration:

<clone>
    <target>
        <sequence>
            <!-- Your existing switch + send logic for the first endpoint -->
            <switch source="$axis2:HTTP_SC">
                <case regex="2\d\d">
                    <send>
                        <endpoint>your-first-endpoint</endpoint>
                    </send>
                </case>
            </switch>
        </sequence>
    </target>
    <target>
        <sequence>
            <!-- Logic for your subsequent endpoint, with full payload intact -->
            <send>
                <endpoint>your-next-endpoint</endpoint>
            </send>
        </sequence>
    </target>
</clone>

2. Save the Payload to a Custom Property Before Using send

If you don't need multiple parallel routes, you can stash the original payload in a property before running send, then restore it later when you need to pass it to another endpoint. Example:

<!-- Save the original payload to a persistent property -->
<property name="OriginalPayload" expression="$body" scope="default" type="OM"/>

<!-- Your existing switch + send logic -->
<switch source="$axis2:HTTP_SC">
    <case regex="2\d\d">
        <send>
            <endpoint>your-first-endpoint</endpoint>
        </send>
    </case>
</switch>

<!-- Restore the payload back to the message context -->
<property name="RESPONSE" value="false" scope="axis2"/> <!-- Adjust this if you're working in request vs response flow -->
<payloadFactory media-type="xml">
    <format>$1</format>
    <args>
        <arg evaluator="xml" expression="$ctx:OriginalPayload"/>
    </args>
</payloadFactory>

<!-- Send to your next endpoint with the restored payload -->
<send>
    <endpoint>your-next-endpoint</endpoint>
</send>

Note: The RESPONSE property toggles whether ESB treats the context as a request or response—tweak it based on whether you're processing an incoming request or a backend response (like your WireMock return).

3. Verify Message Relay Configuration (Edge Case)

In rare cases, modified axis2.xml settings can cause premature payload clearing. Check if the messageRelay configuration has any flags that auto-discard payloads after mediation. This is usually a default setting issue, so prioritize the first two fixes before diving into this.

内容的提问来源于stack exchange，提问作者Crelley