This documentation is for WSO2 Enterprise Service Bus version 4.9.0 . View documentation for the latest release.
Skip to end of metadata
Go to start of metadata

A Sequence Template is a parametrized sequence , providing an abstract or generic form of a sequence defined in the ESB. Parameters of a template are defined in the form of XPath statement/s. Callers can invoke the template by populating the parameters with static values/XPath expressions using the Call Template Mediator, which makes a sequence template into a concrete sequence.



Configuration

Let's illustrate the sequence template with a simple example. Suppose we have a sequence that logs the text "hello world" in four different languages.

<sequence>
   <switch source="//m0:greeting/m0:lang" xmlns:m0="http://services.samples">
        <case regex="EN">
            <log level="custom">

      		  <property name=”GREETING_MESSAGE” value=”HELLO WORLD!!!!!!” />

   	    </log>
        </case>
        <case regex="FR">
	    <log level="custom">

      		  <property name=”GREETING_MESSAGE” value=”Bonjour tout le monde!!!!!!” />

   	    </log>
        </case>
	<case regex="IT">
	    <log level="custom">

      		  <property name=”GREETING_MESSAGE” value=”Ciao a tutti!!!!!!!” />

   	    </log>
        </case>
	<case regex="JPN">
	    <log level="custom">

      		  <property name=”GREETING_MESSAGE” value=”???????!!!!!!!” />

   	    </log>
        </case>
    </switch>

</sequence>

Instead of printing our "hello world" message for each and every language inside the sequence, we can create a generalized template of these actions, which will accept any greeting message (from a particular language) and log it on screen. For example, let's create the following template named "HelloWorld_Logger".

<template name="HelloWorld_Logger">
   <parameter name="message"/>
   <sequence>
        <log level="custom">
      		  <property name=”GREETING_MESSAGE” expression=”$func:message” />
   	</log>
   </sequence>
</template>

With our "HelloWorld_Logger" in place, the Call Template mediator can populate this template with actual hello world messages and execute the sequence of actions defined within the template like with any other sequence. This is illustrated below.

<sequence>
   <switch source="//m0:greeting/m0:lang" xmlns:m0="http://services.samples">
        <case regex="EN">
            <call-template target="HelloWorld_Logger">
		<with-param name="message" value="HELLO WORLD!!!!!!" />
	    </call-template>
        </case>
        <case regex="FR">
	    <call-template target="HelloWorld_Logger">
		<with-param name="message" value="Bonjour tout le monde!!!!!!" />
	    </call-template>
        </case>
	<case regex="IT">
	    <call-template target="HelloWorld_Logger">
		<with-param name="message" value="Ciao a tutti!!!!!!!" />
	    </call-template>
        </case>
	<case regex="JPN">
	    <call-template target="HelloWorld_Logger">
		<with-param name="message" value="???????!!!!!!!" />
	    </call-template>
        </case>
    </switch>

</sequence>

The Call Template mediator points to the same template "HelloWorld_Logger" and passes different arguments to it. In this way, sequence templates make it easy to stereotype different workflows inside ESB.

 


Syntax

<template name="string">
   <!-- parameters this sequence template will be supporting -->
   (
   <parameter name="string"/>
   ) *
   <!--this is the in-line sequence of the template     -->
   <sequence>
        mediator+
   </sequence>
 </template>

The sequence template is a top-level element defined by the name attribute in the ESB configuration. Both endpoint and sequence template starts with a template element.

The parameters available to configure the Sequence Template are as follows.

Parameter Name
Description
NameThe name of the Sequence Template
onErrorSelect the error sequence that needs to be invoked.
Trace EnabledWhether or not trace is to be enabled for the sequence.
Statistics EnabledWhether or not statistics is to be enabled for the sequence.
Template ParametersThe input parameter that are supported by this Sequence Template.

Sequence template parameters can be referenced using an XPath expression defined inside the in-line sequence. For example, the parameter named "foo" can be referenced by the Property mediator (defined inside the in-line sequence of the template) in the following ways:

<property name=”fooValue” expression=”$func:foo” />

or

<property name=”fooValue” expression=”get-property('foo','func')” />

Using function scope or "?func?" in the XPath expression allows us to refer to a particular parameter value passed externally by an invoker such as the Call Template mediator.

 


Call Template Mediator

The Call Template mediator allows you to construct a sequence by passing values into a sequence template.

This is currently only supported for special types of mediators such as the Iterator and Aggregate Mediators, where actual XPath operations are performed on a different SOAP message, and not on the message coming into the mediator.

Syntax

<call-template target="string">
   <!-- parameter values will be passed on to a sequence template -->
   (
    <!--passing plain static values -->
   <with-param name="string" value="string" /> |
    <!--passing xpath expressions -->
   <with-param name="string" value="{string}" /> |
    <!--passing dynamic xpath expressions where values will be compiled
dynamically-->
   <with-param name="string" value="{{string}}" /> |
   ) *
   <!--this is the in-line sequence of the template    -->
 </call-template>

You use the target attribute to specify the sequence template you want to use. The <with-param> element is used to parse parameter values to the target sequence template. The parameter names should be the same as the names specified in target template. The parameter value can contain a string, an XPath expression (passed in with curly braces { }), or a dynamic XPath expression (passed in with double curly braces) of which the values are compiled dynamically.

UI Configuration

The parameters available to configure the Call-Template mediator are as follows.

Parameter NameDescription
Target TemplateThe sequence template to which values should be passed. You can select a template from the Available Templates list

When a target template is selected, the parameter section will be displayed as shown below if the sequence template selected has any parameters. This enables parameter values to be parsed into the sequence template selected.

Parameter NameDescription
Parameter NameThe name of the parameter.
Parameter Type

The type of the parameter. Possible values are as follows.

  • Value: Select this to define the parameter value as a static value. This value should be entered in the Value / Expression parameter.
  • Expression: Select this to define the parameter value as a dynamic value. The XPath expression to calculate the parameter value should be entered in the Value / Expression parameter.
Value / ExpressionThe parameter value. This can be a static value, or an XPath expression to calculate a dynamic value depending on the value you selected for the Parameter Type parameter.
ActionClick Delete to delete a parameter.

Example

The following four Call Template mediator configurations populate a sequence template named HelloWorld_Logger with the "hello world" text in four different languages.

<call-template target="HelloWorld_Logger">
	<with-param name="message" value="HELLO WORLD!!!!!!" />
</call-template>
<call-template target="HelloWorld_Logger">
	<with-param name="message" value="Bonjour tout le monde!!!!!!" />
</call-template>
<call-template target="HelloWorld_Logger">
	<with-param name="message" value="Ciao a tutti!!!!!!!" />
</call-template>
<call-template target="HelloWorld_Logger">
	<with-param name="message" value="???????!!!!!!!" />
</call-template>

The sequence template can be configured as follows to log any greetings message passed to it by the Call Template mediator. Thus, due to the availability of the Call Template mediator, you are not required to have the message entered in all four languages included in the sequence template configuration itself.

<template name="HelloWorld_Logger">
   <parameter name="message"/>
   <sequence>
        <log level="custom">
      		  <property name=”GREETING_MESSAGE” expression=”$func:message” />
   	</log>
   </sequence>
</template>

See Sequence Template for a more information about this scenario.

For more information, see the following topics:

  • No labels