WSO2 ESB service orchestration

Question

Hello WSO2 community and hello Stackoverflow,

my testing of the SOA suite starting from the ESB is going good: now the ESB recognises external services, create correct proxies that return correct results.

SOLVED

About that, I have two issues: the first is that the "try it" functionality raises the exception:

"Cannot find dispatch method for {http://schemas.xmlsoap.org/soap/envelope/}Envelope

[tagOpened]/soapenv:Text[tagClosed]"

when i try to send a SOAP enveloped created for the mock service of the web service proxied.

Anyway, if I try the proxy service from an external client (created on Netbeans) it works great.

ANSWER

For the first part, the reason is most probably the cross domain issue as try-it is sending messages through a java script stub from the browser. You will notice that this works great when the service itself is hosted in the ESB itself, because the request passes through the same domain. This is why, although, it works perfectly through a normal client invocation, it does not work through try-it.

The second issue is that I'm not able to orchestrate two services. My objective is sending the input of the first service to the second service, and then to the user.

I'm working on the tutorial Tharindu Mathew suggested: everything now makes sense to me except on one thing: the XSLT transformation.

Here is the out sequence the tutorial suggests you to create:

<outSequence xmlns="http://ws.apache.org/ns/synapse">
   <switch source="get-property('STATE')">
      <case regex="PERSON_INFO_REQUEST">
         <log level="full">
            <property name="sequence" value="outSequence - STATE 01 - response from PersonInfoService" />
         </log>
         <xslt key="xslt">
            <property name="amount" expression="get-property('ORG_AMOUNT')" />
         </xslt>
         <log level="full">
            <property name="sequence" value="outSequence - STATE 01 - request for CreditService" />
         </log>
         <property name="STATE" value="CREDIT_REQUEST" />
         <send>
            <endpoint key="CreditEpr" />
         </send>
      </case>
      <case regex="CREDIT_REQUEST">
         <log level="full">
            <property name="sequence" value="outSequence - STATE 02 - response from CreditService" />
         </log>
         <send />
      </case>
   </switch>
</outSequence>

Now, focusing on the XSLT node of the first case of the switch, you can see that there's just a get for the amount property. So that I think we have an XML from the in sequence that states the ID, and this get on the amount property (and I don't know what it does).

The tutorial then suggests:

To create the request to this CrediService, we use the following XSLT with the XSLT mediator. Note, we are using the ORG_ID that we stored in this XSLT as a XSLT parameter and using the XSLT mediator as well.

And here is the XSLT showed in the tutorial:

<xsl:stylesheet version="2.0" 
        xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
        xmlns:fn="http://www.w3.org/2005/02/xpath-functions"
        xmlns:ns="http://samples.esb.wso2.org"
        xmlns:ax21="http://samples.esb.wso2.org/xsd"
        exclude-result-prefixes="ns fn">
<xsl:param name="amount"/>
<xsl:output method="xml" omit-xml-declaration="yes" indent="yes"/>

<xsl:template match="/">
  <xsl:apply-templates select="//ns:getResponse" />
</xsl:template>

<xsl:template match="ns:getResponse" xmlns:ns="http://samples.esb.wso2.org">
<sam:credit xmlns:sam="http://samples.esb.wso2.org" xmlns:xsd="http://samples.esb.wso2.org/xsd">
    <sam:info>
        <xsd:amount><xsl:value-of select="$amount"/></xsd:amount>
        <xsd:personInfo>
            <xsd:address><xsl:value-of select="ns:return/ax21:address"/></xsd:address>
            <xsd:id><xsl:value-of select="ns:return/ax21:id"/></xsd:id>
            <xsd:name><xsl:value-of select="ns:return/ax21:name"/></xsd:name>
        </xsd:personInfo>
    </sam:info>
</sam:credit>
</xsl:template>
</xsl:stylesheet>

I was asked to put a similar file into the resources directory of WSO2 ESB, but this file is never used in the tutorial:

Copy the personToCredit.xslt in the sample zip to resources directory of WSO2 ESB.

---------LITTLE PARENTHESIS-----------

The WSDL file was not used either after it was stated:

Copy the CreditProxy.wsdl in the sample zip to the resources directory of the WSO2 ESB.

I cannot find the WSDL file in the Configuration/Governance Registry, and I don't know how to address it, so I chose to specify it inline instead.

---------LITTLE PARENTHESIS END-----------

This sentence is followed by the XSLT file text. My main question now is:

Where should I put this XSLT? I do not know where to put the XSLT mediator, neither how to build it. Should I rely on registries?

A perfect answer could be the code of the out sequence, and the specified connection with the XSLT mediator suggested.

OverTheBitStair

Answer 1

Hi OverTheBitStair (nice nick!),

For the first part, the reason is most probably the cross domain issue as try-it is sending messages through a java script stub from the browser. You will notice that this works great when the service itself is hosted in the ESB itself, because the request passes through the same domain. This is why, although, it works perfectly through a normal client invocation, it does not work through try-it.

For the second part, the short answer is yes, it is possible. In terms of the ESB, we refer to it as a light-weight orchestration engine in addition to being a mediation engine. This means for light-weight and short-lived (<1 day) processes we can solve the orchestration requirements using the ESB without bringing in the Business Process Server.

To do this, we use this method called service chaining. What it does is introduce a method to get some output out of the initial service invocation and use it in a subsequent invocation. The article WSO2 ESB by example - Service Chaining should help you with implementation details on what you are looking for.

Hope this helps.

Answer 2

If you create a service chaining scenario where your proxy service calls two other services and return the result to the caller of the proxy service, it would look something like this:

Caller --> Proxy Service -- seq_A --> Service1 -- seq_B --> Service2 -- seq_C --> (proxy serviced response) --> Caller

In this case, seq_A would be the in sequence of the proxy service, seq_C the out sequence of the proxy service and seq_B another named sequence.

Input, i.e. the message body, to seq_A would be the input to proxy service. seq_A would contain a send mediator at the end and at that point in the sequence the message context would be the input to Service1. The send mediator also points to seq_B to be executed for the reply.

At start of seq_B the message body contains the output from Service1. If you want to keep some message data from before the service call you need to save that in properties in the context. At the end of seq_B you would have a send mediator; at that point the message body should contain the input to Service2, The send mediator would in this case not need to point to an explicit reply sequence, if seq_C is the out sequence of the proxy service - that one will be used by default then.

When seq_C is executing the message body at that point is the response from Service2. Again, if you need to use/combine with some data prior to the call to Service2, you need that to be saved into properties.

Depending on the particular needs for the input and transformations needed at each step it can be fairly straightforward or a bit cumbersome to handle. What also should taken into consideration is what needs to happen in error scenarios, as this may add some additional complexity, depending on the requirements.