Adding attachments
to a HumanTask is a feature that exists in
Oracle HWF (Human Workflow) since 10g.
However, in 11g there have been many improvements on this feature and this entry will try
to summarize them.
Oracle BPM 11g 11.1.1.5.1 (aka PS4 Feature Pack or PS4FP) introduced two great features:
Ability
to link attachments at a Task scope or at a Process scope:
"Task" attachments are only visible within the scope (lifetime) of a task. This means that, initially, any member of the assignment pattern of the Human Task will be able
to handle (add, review or remove) attachments. However, once the task is completed, subsequent human tasks will not have access
to them. This does not mean those attachments got lost. Once the human task is completed, attachments can be retrieved in order
to, i.e., check them in
to a Content Server or
to inject them
to a new and different human task.
Aside note: a "re-initiated" human task will inherit comments and attachments, along with history and -optionally- payload. See here for more info.
"Process" attachments are visible within the scope of the process. This means that subsequent human tasks in the same process instance will have access
to them.
Ability
to use
Oracle WebCenter Content (previously known as "Oracle UCM") as the backend for the attachments instead of using HWF database backend. This feature adds all content server document lifecycle capabilities
to HWF attachments (versioning, RBAC, metadata management, etc). As of today, only
Oracle WCC is supported. However,
Oracle BPM Suite does include a license of
Oracle WCC for the solely usage of document management within BPM scope.
Here are some code samples that leverage the above features.
Retrieving uploaded attachments -Non UCM-
Non UCM attachments (default ones or those that have existed from 10g, and are stored "as-is" in HWK database backend) can be retrieved after the completion of the Human Task. Firstly, we need
to know whether any attachment has been effectively uploaded
to the human task. There are two ways
to find it out:
Through an XPath function:
Checking the execData/attachment[] structure. For example:
Once we are sure one ore more attachments were uploaded
to the Human Task, we want
to get them. In this example, by "get" I mean
to get the attachment name and the payload of the file. Aside note:
Oracle HWF lets you
to upload two kind of [non-UCM] attachments: a desktop document and a Web URL. This example focuses just on the desktop document one. In order
to "retrieve" an uploaded Web URL, you can get it directly from the execData/attachment[] structure.
Attachment content (payload) is retrieved through the getTaskAttachmentContents() XPath function:
This example shows how
to retrieve as many attachments as those had been uploaded
to the Human Task and write them
to the server using the File Adapter service.
The sample process excerpt is as follows:
A dummy UserTask using "HumanTask1" Human Task followed by a Embedded Subprocess that will retrieve the attachments (we're assuming at least one attachment is uploaded):
and once retrieved, we will write each of them back
to a file in the server using a File Adapter service:
In detail:
We've defined an XSD structure that will hold the attachments (both name and payload):
Then, we can create a BusinessObject based on such element (attachmentCollection) and create a variable (named attachmentBPM) of such BusinessObject type.
We will also need
to keep a copy of the HumanTask output's execData structure. Therefore we need
to create a variable of type TaskExecutionData...
...and copy the HumanTask output execData
to it:
Now we get into the embedded subprocess that will retrieve the attachments' payload. First, and using an XSLT transformation, we feed the attachmentBPM variable with the name of each attachment and setting an empty value
to the payload:
Please note that we're using the XSLT for-each node
to create as many target structures as necessary. Also note that we're setting an Empty text
to the payload variable. The reason for this is
to make sure the <payload></payload> tag gets created. This is needed when we map the payload
to the XML variable later.
Aside note: We are assuming that we're retrieving non-UCM attachments. However in real life you might want
to check the type of attachment you're handling. The execData/attachment[]/storageType contains the values "UCM" for UCM type attachments, "TASK" for non-UCM ones or "URL" for Web URL ones. Those values are part of the "Ext.Com.
Oracle.Xmlns.Bpel.Workflow.Task.StorageTypeEnum" enumeration.
Once we have fed the attachmentsBPM structure and so it now contains the name of each of the attachments, it is time
to iterate through it and get the payload. Therefore we will use a new embedded subprocess of type MultiInstance, that will iterate over the attachmentsBPM/attachment[] element:
In every iteration we will use a Script activity
to map the corresponding payload element with the result of the XPath function getTaskAttachmentContents(). Please, note how the target array element is indexed with the loopCounter predefined variable, so that we make sure we're feeding the right element during the array iteration:
The XPath function used looks as follows:
hwf:getTaskAttachmentContents(bpmn:getDataObject('UserTask1LocalExecData')/ns1:systemAttributes/ns1:taskId, bpmn:getDataObject('attachmentsBPM')/ns:attachment[bpmn:getActivityInstanceAttribute('SUBPROCESS3067107484296', 'loopCounter')]/ns:fileName)
where the input parameters are:
taskId of the just completed Human Task
attachment name we're retrieving the payload from
array index (loopCounter predefined variable)
Aside note: The reason whereby we're iterating the execData/attachment[] structure through embedded subprocess and not, i.e., using XSLT and for-each nodes, is mostly because the getTaskAttachmentContents() XPath function is currently not available in XSLT mappings. So all this example might be considered as a workaround until this gets fixed/enhanced in future releases.
Once this embedded subprocess ends, we will have all attachments (name + payload) in the attachmentsBPM variable, which is the main goal of this sample. But in order
to test everything runs fine, we finish the sample writing each attachment
to a file.
To that end we include a final embedded subprocess
to concurrently iterate through each attachmentsBPM/attachment[] element:
On each iteration we will use a Service activity that invokes a File Adapter write service. In here we have two important parameters
to set. First, the payload itself. The file adapter awaits binary data in base64 format (string). We have
to map it using XPath (Simple mapping doesn't recognize a String as a base64-binary valid target):
Second, we must set the target filename using the Service Properties dialog box:
Again, note how we're making use of the loopCounter index variable
to get the right element within the embedded subprocess iteration.
Handling UCM attachments will be part of a different and upcoming blog entry. Once I finish will all posts on this matter, I will upload the whole sample project
to java.net.
