WSO2 API如何修正外部服务响应被字符串包裹的问题

场景 #

我在API中集成了一个外部服务，想要在外部服务的响应基础上新增几个JSON键值对。

API配置 #

<?xml version="1.0" encoding="UTF-8"?>
<api context="/PhoneVerify" name="PhoneVerifi" xmlns="http://ws.apache.org/ns/synapse">
    <resource methods="POST">
        <inSequence>
            <payloadFactory media-type="xml">
                <format>
                    <soapenv:Envelope xmlns:cmpa="http://XXX.XXX.com" xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsd="http://object.pmd.com/xsd">
                        <soapenv:Header/>
                        <soapenv:Body>
                            <cmpa:verify>
                                <!--Optional:-->
                                <cmpa:userName>XXXXX</cmpa:userName>
                                <!--Optional:-->
                                <cmpa:passwd>XXXXX</cmpa:passwd>
                                <!--Optional:-->
                                <cmpa:request>
                                    <!--Optional:-->
                                    <xsd:cnic>$1</xsd:cnic>
                                    <!--Optional:-->
                                    <xsd:msisdn>$2</xsd:msisdn>
                                    <!--Optional:-->
                                    <xsd:transactionID>$3</xsd:transactionID>
                                </cmpa:request>
                            </cmpa:verify>
                        </soapenv:Body>
                    </soapenv:Envelope>
                </format>
                <args>
                    <arg evaluator="json" expression="$.cnic"/>
                    <arg evaluator="json" expression="$.msisdn"/>
                    <arg evaluator="json" expression="$.transactionID"/>
                </args>
            </payloadFactory>
            <log category="DEBUG" level="full"/>
            <header name="Action" scope="default" value="verify"/>
            <send>
                <endpoint>
                    <address format="soap11" uri="https://XXXXX.com/CMPA/services/CnicMsisdnPairing.CnicMsisdnPairingHttpsSoap11Endpoint/">
                        <suspendOnFailure>
                            <initialDuration>-1</initialDuration>
                            <progressionFactor>1</progressionFactor>
                        </suspendOnFailure>
                        <markForSuspension>
                            <retriesBeforeSuspension>0</retriesBeforeSuspension>
                        </markForSuspension>
                    </address>
                </endpoint>
            </send>
        </inSequence>
        <outSequence>
            <property name="messageType" scope="axis2" type="STRING" value="application/json"/>
                       <payloadFactory media-type="json">
                <format>&#xd;
{&#xd;
    "status" : "success"&#xd;
    "response": "$1"
}</format>
                <args>
                    <arg evaluator="json" expression="$.verifyResponse.return"/>
                </args>
            </payloadFactory>
            <property name="messageType" scope="axis2" type="STRING" value="application/json"/>
            <respond/>
        </outSequence>
        <faultSequence>
                       <payloadFactory media-type="json">
                <format>&#xd;
{&#xd;
    "status" : "failure"&#xd;
}</format>
                <args/>
            </payloadFactory>
        </faultSequence>
    </resource>
</api>

外部服务响应 #

"verifyResponse":{
    "return" : {
        "@type":"ax21:Response",
        "message":"Duplicate Transaction ID",
        "responseCode":"08",
        "status":"00"
    }
}

期望响应 #

{
    "status": "success",
    "response": {
        "@type":"ax21:Response",
        "message":"Duplicate Transaction ID",
        "responseCode":"08",
        "status":"00"
    }
}

当前问题 #

我按上述配置尝试实现需求时，得到的响应里response字段的值被双引号包裹，变成了字符串类型，而非期望的JSON对象结构：

{
    "status": "success",
    "response": "{"@type":"ax21:Response","message":"Duplicate Transaction ID","responseCode":"08","status":"00"}"
}

问题出在payloadFactory的使用逻辑上：当用"$1"引用外部服务返回的JSON对象时，Synapse会自动将该对象序列化为字符串，导致它被双引号包裹。要保留JSON对象的嵌套结构，需要改用以下两种方式之一：

方案1：使用JavaScript脚本构建响应 #

通过script中介直接操作JSON对象，避免字符串拼接：

<outSequence>
    <!-- 确保消息以JSON格式处理 -->
    <property name="messageType" scope="axis2" type="STRING" value="application/json"/>
    <!-- 用JS脚本重组响应结构 -->
    <script language="js"><![CDATA[
        var originalPayload = mc.getPayloadJSON();
        var newPayload = {
            "status": "success",
            "response": originalPayload.verifyResponse.return
        };
        mc.setPayloadJSON(newPayload);
    ]]></script>
    <respond/>
</outSequence>

方案2：使用enrich中介合并消息 #

如果不想用脚本，可通过enrich中介将外部服务的响应对象嵌入到新结构中：

<outSequence>
    <property name="messageType" scope="axis2" type="STRING" value="application/json"/>
    <!-- 先创建基础的success结构 -->
    <payloadFactory media-type="json">
        <format>{"status": "success"}</format>
        <args/>
    </payloadFactory>
    <!-- 将外部服务的return对象添加到response字段 -->
    <enrich>
        <source type="json" expression="$.verifyResponse.return"/>
        <target type="json" action="child" xpath="$.response"/>
    </enrich>
    <respond/>
</outSequence>

额外注意 #

原配置中的payloadFactory存在JSON语法错误："status" : "success"后缺少逗号，这会导致JSON解析失败，修复后才能保证响应格式合法。

内容的提问来源于stack exchange，提问作者Ayub Jamal