无法将响应存储在邮件存储中

Question

需要将请求（URl，标头，有效负载）和响应日志发送到其余的api。我们使用WSO2 Message Broker使用Message store和Message处理器。下面是我们配置的api。

<api xmlns="http://ws.apache.org/ns/synapse" name="plants-logging" context="/plants-logging">
<resource methods="POST GET DELETE PUT">
  <inSequence>
     <log level="custom">
        <property name="HTTP_METHOD IS###########" expression="$axis2:HTTP_METHOD"></property>
        <property name="ip address" expression="get-property('axis2','REMOTE_ADDR')"></property>
        <property name="In Time : " expression="get-property('SYSTEM_TIME')"></property>
     </log>
     <property name="TIME_IN" expression="get-property('SYSTEM_TIME')" scope="default" type="LONG"></property>
     <log level="custom">
        <property name="Message Flow" value="ACCEPTED@"></property>
     </log>
     <send>
        <endpoint>
           <address uri="/test/api/"></address>
        </endpoint>
     </send>
     <property name="messageType" value="application/json" scope="axis2"></property>
     <property name="REST_URL_POSTFIX" scope="axis2" action="remove"></property>
     <switch source="$axis2:HTTP_METHOD">
        <case regex="POST">
           <store messageStore="JMSMS"></store>
        </case>
        <case regex="PUT">
           <store messageStore="JMSMS"></store>
        </case>
     </switch>
     <property name="TIME_OUT" expression="get-property('SYSTEM_TIME')" scope="default" type="LONG"></property>
     <script language="js">var time1 = mc.getProperty("TIME_IN");var time2 = mc.getProperty("TIME_OUT");var timeTaken = time2 - time1;mc.setProperty("RESPONSE_TIME", timeTaken);</script>
     <log level="custom">
        <property name="Time Duration in ms:" expression="get-property('RESPONSE_TIME') "></property>
     </log>
  </inSequence>
  <outSequence>
     <log level="custom">
        <property name="Out Sequence" value="ACCEPTED@"></property>
     </log>
     <switch source="$axis2:HTTP_METHOD">
        <case regex="GET">
            <property name="messageType" value="application/json" scope="axis2"></property>
            <property name="REST_URL_POSTFIX" scope="axis2" action="remove"></property>
            <store messageStore="JMSMS"></store>
        </case>
     </switch>
  </outSequence>
  <faultSequence>
     <log level="custom">
        <property name="Fault Sequence" value="ACCEPTED@"></property>
     </log>
     <property name="messageType" value="application/json" scope="axis2"></property>
     <property name="REST_URL_POSTFIX" scope="axis2" action="remove"></property>
     <store messageStore="JMSMS"></store>
  </faultSequence>
</resource>
</api>

对于POST请求，有效负载能够成功发送到我们的api api。但是对于我们得到的回应。

org.apache.axis2.AxisFault: Payload could not be written as JSON.
    at org.apache.synapse.commons.json.JsonUtil.writeAsJson(JsonUtil.java:109)
    at org.apache.synapse.commons.json.JsonStreamFormatter.writeTo(JsonStreamFormatter.java:60)
    at org.apache.axis2.transport.http.AxisRequestEntity.writeRequest(AxisRequestEntity.java:84)
    at org.apache.commons.httpclient.methods.EntityEnclosingMethod.writeRequestBody(EntityEnclosingMethod.java:499)
    at org.apache.commons.httpclient.HttpMethodBase.writeRequest(HttpMethodBase.java:2114)
    at org.apache.commons.httpclient.HttpMethodBase.execute(HttpMethodBase.java:1096)
    at org.apache.commons.httpclient.HttpMethodDirector.executeWithRetry(HttpMethodDirector.java:398)
    at org.apache.commons.httpclient.HttpMethodDirector.executeMethod(HttpMethodDirector.java:171)
    at org.apache.commons.httpclient.HttpClient.executeMethod(HttpClient.java:397)
    at org.apache.axis2.transport.http.AbstractHTTPSender.executeMethod(AbstractHTTPSender.java:622)
    at org.apache.axis2.transport.http.HTTPSender.sendViaPost(HTTPSender.java:193)
    at org.apache.axis2.transport.http.HTTPSender.send(HTTPSender.java:75)
    at org.apache.axis2.transport.http.CommonsHTTPTransportSender.writeMessageWithCommons(CommonsHTTPTransportSender.java:451)
    at org.apache.axis2.transport.http.CommonsHTTPTransportSender.invoke(CommonsHTTPTransportSender.java:278)
    at org.apache.axis2.engine.AxisEngine.send(AxisEngine.java:442)
    at org.apache.axis2.description.OutInAxisOperationClient.send(OutInAxisOperation.java:430)
    at org.apache.axis2.description.OutInAxisOperationClient.executeImpl(OutInAxisOperation.java:225)
    at org.apache.axis2.client.OperationClient.execute(OperationClient.java:149)
    at org.apache.synapse.message.senders.blocking.BlockingMsgSender.sendReceive(BlockingMsgSender.java:217)
    at org.apache.synapse.message.senders.blocking.BlockingMsgSender.send(BlockingMsgSender.java:146)
    at org.apache.synapse.message.processor.impl.forwarder.ForwardingService.dispatch(ForwardingService.java:288)
    at org.apache.synapse.message.processor.impl.forwarder.ForwardingService.execute(ForwardingService.java:128)
    at org.quartz.core.JobRunShell.run(JobRunShell.java:213)
    at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:557)

[2014-11-28 18：27：33,615]错误 - 消息处理器[SMFP]的ForwardingService BlockingMessageSender无法向端点发送消息 [2014-11-28 18：27：33,615] WARN - ForwardingService无法通过故障序列发送消息，序列名称null不存在。 [2014-11-28 18：27：37,634]错误 - JsonUtil #writeAsJson。 Payload无法写为JSON。消息ID：urn：uuid：20310054-7f03-4e7e-853e-9bc98f27a063 [2014-11-28 18：27：37,634]错误 - JsonUtil #writeAsJson。 Payload无法写为JSON。消息ID：urn：uuid：20310054-7f03-4e7e-853e-9bc98f27a063

请帮我解决这个问题。