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.
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.
{warning}
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.
{warning}
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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.
{warning}
Be careful, the current implementation of this feature makes disk access, thus reducing the performances.
{warning}
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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.
{info}
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.
{info}
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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{note}
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.
{note}
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.
{note}
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.
{note}
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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.
{info}
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.
{note}
In fact, the WSDL content and the expected parameters depend on the job's content and on the defined options during the export operation.
{note}
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
The native job's output is an array of array of String, that is to say: {code:lang=java}String[][]{code}
This result may contain only an integer, in which case {code:lang=java}String[ 0 ][ 0 ]{code} is an integer and indicates the result of the job execution. Otherwise, this array contains raw data (which is the case if the job contains a tBufferOutput).
This can be a solution to determine whether the job execution succedded or not. The Petals-SE-Talend does not do it. It is the responsibility of the client to make this check (since in fact, it depends on the job itself).
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If the job contained a tPetalsOutput, then the output data flow is retreived from the job.
{note}
If a job does not support to be asked data flow (for a tPetalsOutput), an entry is logged, but no fault is raised. The execution goes on normally.
{note}
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Eventually, if it was specified during the job export that output attachments are to be expected after the job was executed, then they are taken back from the job.
These attachments must be passed from the job to the component through files. These files are loaded by the component in memory and then, deleted from the disk.
The deletion of these files is not an option. Letting them on the disk could represent important risks. Indeed, a malicious client could override the context on each call, thus creating an infinite number of files on the disk. Unfinite until the disk crashes, obviously.
Like input attachments, output attachments are returned in MTOM mode.
{note}
If a component expects output attachments to be returned by the job, and that this job does not support it, then a fault is thrown.
This can typically happen if you created your job with Talend Open Studio and exported a context as an "OUT-Attachment".
{note}
h2. Building the response
Now that everything has been gathered from the job, the response can be built and returned.
Hence, the response can count up to 3 parts:
# The job's result (remember, the array of array of String). This part is always returned.
# The output data beans, if the job contained a tPetalsOutput.
# The output attachments.
Like the input message, the structure of the output message is determined by the job content and the options which were checked during the export of the job for Petals.
h1. Talend Open Studio vs. Talend Integration Suite
Two products can be used to create Talend jobs and export them into Petals: Talend Open Studio, which is an open source product, and Talend Integration Suite, which is the upgraded version of Talend Open Studio (but not free).
There are slight differences between what can be made in these two products.
h2. Talend Open Studio
Talend Open Studio does not support any specific component for Petals.
It supports the following features for the Petals-SE-Component:
* Expose a context as a parameter into the service's WSDL.
* Pass attachment files to a job.
* Pass native parameters and options to a job.
* Get the job's execution result.
Other features are only supported by Talend Integration Suite.
However, it is possible to use alternative ways, depending on the desired feature.
h2. Talend Integration Suite
In Talend Integration Suite, all the features of Talend Open Studio are supported.
It also embeds additional capabilities to work with Petals ESB.
* You can use tPetalsInput and tPetalsOutput components in your jobs.
** These components respectively allow you to pass data from Petals to the job and from the job to Petals.
** These two components do not have any specific parameter. They just need their schema to be defined.
* You can simulate the Petals behavior for these two components, meaning you can execute your job in Talend Integration Suite if it contains a tPetalsInput or a tPetalsOutput component.
** Thus, for a tPetalsInput, you can provide what would be the Petals input from a file that will be loaded before the simulation.
** For the tPetalsOutput, the returned document will be printed into the console.
* Eventually, Talend Integration Suite allows to attach files in the responses.
h2. Limitations
There are some restrictions in the Petals export and in the use of the Talend components for Petals.
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About the export:
* Only one job can be exported at once for Petals.
** One job = One deployment archive for Petals.
* Some data types are not supported in the export for Petals:
** Lists, Objects, passwords, List of values are not supported.
** It also applies to exported contexts.
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About the tPetalsInput or the tPetalsOutput components:
* A job can contain several instances of any of these components.
* All the tPetalsInput must have the same schema.
** This is checked during the export.
* All the tPetalsOutput must have the same schema.
** This is checked during the export.
* All the tPetalsInput instances read the same input message.
* All the tPetalsOutput instances write in the same output message.
** If two instances of tPetalsOutput are on the same processing flow, the second will erase what is written by the first instance.
** tPetalsOutput instances should be placed on different _branches_ (onSubjobOK, onSubjobError and so on...).
h2. The Talend export for Petals
The export is the same in both Talend Open Studio and Talend Integration Suite.
The generated artifacts are the same in both of them. And the content of the jbi.xml is (almost) the same in both of them.
The only differences are the job's content (which Talend components have been added into the job) and the generated WSDL (which depends on the job content and the export options).
The service-unit structure and the jbi.xml are desribed farther.
This section only introduces the export options and their impact on the result.
The generated WSDL is not discussed in this documentation.
However, you will find samples in the simple use cases for this component.
Here is a snapshot version of the Talend export for Petals.
{center}
!SimpleJobExport.jpg!
{center}
The target file is the location of the service-assembly to generate.
The job version meaning is explicit.
The export options are the following:
|| Export Option || Description ||
| Singleton job | True to make the job singleton. A singleton job can have only one instance running at once on a given Petals-SE-Talend component. |
| Generate the end-point | True to let Petals generate the end-point at deployment time. If false, the end-point name is the job name with the suffix "Endpoint". |
| Validate Petals messages | True to validate all the messages / requests against the WSDL. \\
Be careful, enabling this option reduces the performances (disk access). \\ |
| User routines | Embed the user routines in the service-unit. |
| Source files | True to embed the source files in the generated service-unit. |
| Jobs contexts | Select the context that will be used by default by the job. |
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Eventually, there is the edition link to specify how contexts should be exposed in the generated WSDL.
{center}
!SimpleJobExportContext1.jpg!
{center}
When this link is clicked, a dialog shows up.
It lists all the job contexts, with their name, the type they will be associated with if exported, and the way they are exported.
By default, no context is exported. Said differently, the export mode for all the contexts is *Not exported*.
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Here is a small description of the export modes.
|| Export Mode || Description ||
| Not exported | The context is not exported (not visible as a parameter). But the context can still be overridden using the native parameters (options) of the job. |
| Parameter | The context is exported as a parameter in the WSDL's operation. |
| In-Attachment | The context will be passed the location of a temporary file whose content was attached in the input message. |
| Out-Attachment | The context will be read after the job was executed.
* This context must point to a file.
* The file content will be read by the Petals-SE-Talend component and put as an attachment into the response.
* The context name will be used as the attachment name.
* The file will be deleted by the component right after its content was loaded. |
| Parameter and Out-Attachment | A mix between the Parameter and the Out-Attachement modes.
* The context is exposed as a parameter.
* It will also be read after the job execution.
* The file will be deleted anyway.
* The advantage of this export mode is to define the output file destination dynamically. |
h1. Component Configuration
The component can be configured through its JBI descriptor file, as shown below.
{code:lang=xml}<?xml version="1.0" encoding="UTF-8"?>
<jbi:jbi
version="1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:petalsCDK="http://petals.ow2.org/components/extensions/version-5"
xmlns:jbi="http://java.sun.com/xml/ns/jbi"
xmlns:talend="http://petals.ow2.org/components/talend/version-1">
<jbi:component type="service-engine">
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