Il also supports several mechanisms to retrieve information and data from a job.
Before going further, it must be clear that no configuration for this component is intended to be created by hand. Neither by the Petals Studio.
In fact, only Talend Open Studio and Talend Integration Suite have the ability to generate a correct configuration for this component.
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h1. Recommended usage
The Petals-SE-Talend component is intended to execute jobs created with Talend Open Studio and Talend Integration Suite.
Whenever you want to work with both Talend and Petals ESB, it is the component to use.
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There are three ways of seeing the jobs that will be executed in Petals ESB.
First, they can be seen as *an extension of the platform capabilities*.
Indeed, a job can easily interact with almost any database, any kind of file, or other systems (SAP, Alfresco, etc...). Rather than developping a specific component, it can be interesting to create a job to cover this task, and expose it as a service through Petals. *The job here acts as a mediation way with data stores or systems.*
Second, a job can be seen as *a set of transformation means*.
Indeed, Talend products provide _Talend components_ that are very efficient and convenient for transformations (e.g. the tMap component). However, it must be clear that these transformations only cover flat structures, like schemas of relational databases. Object or XML schemas are not covered. From this point of view, *the Petals-SE-Talend component cannot replace the Petals-SE-XSLT component*. But it can be an alternative in few cases. Hence, transformations will either rely on attachment files (these files content are transformed by the job) or on Talend components for Petals (known as tPetalsInput and tPetalsOutput). The later solution provides a means to place the content to transform inside the XML message, rather than as an attachment. But still with constraints on the XML shape.
Eventually, the last way to apprehend a Talend job inside Petals, is to see it as a *an application to execute inside Petals*.
This application may work with data stores (files, databases...), may involve data transformations, but may also use other (if not redundant with Petals) features. As an example, it is possible to send mails inside a job, connect to FTPs, etc... Obviously, these features are also available inside Petals. But in some cases, it can be more interesting and more simple to integrate them directly in the job than use the Petals'ones (where you will have to use EIPs or BPELs to link the calls). In some other cases though, the exact opposite may be the best option, i.e. externalize some parts to Petals components. *It all depends on the expected granularity and reusability*.
The wide variety of possibilities (allowed by the non-less important variety of _Talend components_, and by the features of the Petals-SE-Talend component) makes this solution a very flexible one. However, as a swiss-knife component, *the Petals-SE-Talend component should mainly be seen as a functional service-engine*. Performances, without being bad, cannot be the best ones offered. People looking for a very specific and performant usage will prefer develop their own Petals component, or use Petals-SE-Pojo or Petals-SE-Jsr181.
h1. Message Processing
This section deals with the way messages (or requests) are processed by the Petals-SE-Talend component.
As a user, it is important to understand the logic of the component to use it efficiently.
A request received by this component may have only one goal: execute the target Talend job.
The request processing is made up of the different steps involved between the message reception and the response.
There are five steps in the processing of a request.
h2. Validating the request
When a request is received and started to be processed in the Petals-SE-Talend component, it is validated before being really processed.
Here are the different steps involved in this validation process.
The first step is the WSDL-based validation of the request's XML payload.
If the *validate-exchange-by-wsdl* parameter is set to *true*, either in the component or in the service-unit, then the XML payload is validated against the WSDL of the service-unit.
If the validation fails, a fault is raised. Otherwise, the validation goes on.
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Be careful, WSDL-based validation does not work when the input message contains attachments.
The Talend export for Petals does prevent that from happening.
Just remember it if you modify the jbi.xml by hand.
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The WSDL-based validation checks three elements:
# The called operation is defined in the service's WSDL.
# The called operation is associated with the called Message Exchange Pattern (MEP).
# The XML payload is validated against the WSDL's XML schemas.
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Be careful, the current implementation of this feature makes disk access, thus reducing the performances.
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Besides, it must be noticed that this component only supports *InOut* pattern.
No other pattern is or will be supported, unless the component undergoes a severe refactoring. It is up to the client to manage the call correctly.
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The second and last step in the validation is a check about the singleton property of a job.
If a job is singleton, it means that only one instance of this job can be executed at once.
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One typical example of a singleton job is a job which moves data from one database to another one.
It would make no sense for two instances of this job to run at the same time, especially if they work on the same databases.
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If the job is singleton and already running, then a fault is raised.
Otherwise, a new job instance is created. If the job is singleton, then the running state of this job is set to true and locked until it is this state is released (i.e. the job is executed).
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The job creation strategy is a lazy strategy. A job instance is created on every received and validated message.
The consequence for singleton jobs is that all the messages sent to a singleton job while it is running will be rejected.
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Once accepted, the request can now be parsed to prepare the job's input.
h2. Preparing the job's input
Once the request has been accepted, it is parsed to get the different possible parameters for the job.
The message input contains up to 4 parts, that are described in the serivce's WSDL.
# The first parameters are the context parameters, child elements of the *contexts* element from the input message. These parameters will be passed to the job in its main method.
# Then, the data flow to be passed to a tPetalsIOnput instance is retrieved from the request. This data flow may not be present.
# The third kind of parameters is the input attachments.
# Eventually, the component processes the native options to be passed to the job.
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If a job does not support to be passed data flow (for a tPetalsInput), an entry is logged, but no fault is raised. The execution goes on normally.
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Input attachments must respect some constraints:
* Each input attachments is serialized as a temporary file.
* Its location will be passed to the job through a context variable. This is why attachments are associated with context variables.
* Be careful, attachments are expected to be passed in MTOM mode. That is to say the attachment element has a grand-child element "xop:include" whose href attribute references an attachment.
* Besides, the name of the attachment element is the name of the context variable that will be associated with the temporary file location.
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As a user, you do not have to worry about this appearing complexity.
The configuration and the WSDL creation are made by the tools, during the export.
And hopefully, clients to call such a service can be generated automatically from the WSDL.{info}
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As you can see, from one JBI message (an XML payload and attachments), the Petals-SE-Talend component gets at most 4 kinds of parameter to pass to the jobs.
Three of them are merged together, since they are passed as contexts to the job. The remaining one concerns the tPetalsInput data.
Notice that the input message may not define any of these parameters. In this case, the component will pass nothing to the job.
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In fact, the WSDL content and the expected parameters depend on the job's content and on the defined options during the export operation.
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h2. Executing the job
At this point, the Petals-SE-Talend has built the job instance and prepared the parameters.
If the job contains a tPetalsInput component, the data for this component is passed to the job.
The Talend contexts and options are then passed to the job, right before its execution is launched.
h2. Getting the job's output
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