If you want to write some code that make makes the Pentaho BI Platform talk to an external system, this may be what you are looking for, so read on...

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What is an Action?

Actions are the lightweight alternative to Pentaho BI Components.  For an understanding of how and why they are different, let's take a step back and examine what a BI Component is and how it is used.  A BI Component is historically a Java class that does some work, yielding some output, when it is provided certain inputs and resources.  The work done as well as the inputs and resources required are entirely up to the component developer.  It's purpose is to perform some work in a sequential success-based workflow (action sequence).  A saavy BI Platform user with a bit of inclination for Java coding can implement his or her own custom component to do just about anything.  However, this is not an easy endeavour since developing your own BI Component requires intimate knowledge of internal Pentaho APIs.  When you are done writing your custom component, the code you have written will be tightly coupled to the Pentaho BI Platform, so much so, that it will be difficult to unit test and may be difficult to maintain.

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• IAction - advertises that your bean has something to do and gives the platform's solution engine a method to execute.  This is the API that identifies your bean an Action.
• IStreamingAction - indicates that your bean accepts output streams managed by action sequence content outputs, such as a ServletResponse output stream.  You would implement this if you intended to write to such an output stream during execution.
• ILoggingAction - if your bean implements this, it will be provided a logger instance to which it can write errors, warnings, and debug messages.
• ISessionAwareAction - supplies your bean with an instance of the current Pentaho session
• IVarArgsAction - Allows an Action to accept inputs from the action sequence that are unspecified by the Action itself
• IDefinitionAwareAction - Makes an Action privy to certain details about the action definition that is responsible for executing it
• IPreProcessingAction - Allows an Action to do some preliminary work prior to execution

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The Action framework expects Action objects to be Java bean compliant with respect to setting inputs, setting resources, and getting outputs.  In other words, if your action needs takes a string input, the action definition in the xaction solution file will specify this string input, and the Action framework will cause that value to be set via a setter method on the Action object.  You do not see parameter Maps and such in the Action API for this reason.  All inputs, output, and resources IO will involve Java bean reflection on your Action object to find the appropriate IO methods.

See the Echo Plugin - a sample plugin for the BI PlatformBIServer project for examples of how to get data into your IAction and how to expose the output of your IAction so something else can do something with it (i.e. display the results of your IAction, pipe them to another step in an action sequence, or bind them to a session parameter).

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Sometimes your Action bean will need to pass inputs through to another subsystem and not act on them directly. For these inputs, it is cumbersome and sometimes impossible to create setter methods for each possible input. If this is the case for you, then have your Action bean implement the IVarArgsAction interface. This will allow you to receive a map containing all the inputs that were specified in the action definition but had no setter method counterpart in your Action bean.

Collection Inputs

Your Action may need to operate on an array of similar items, such as sending an email with multiple attachments, like so:

<action-inputs>
<attachments_0>
<attachments_1>
<attachments_2>
</action-inputs>

Assuming these attachments are specified in your action definition inputs section, the possible options for getting those inputs to your bean are:

1. you would need to code a setter method for each attachment declared in the action definition, e.g. setAttachments_0(Object o), setAttachments_1(Object o), and so on.
2. have your Action bean implement IVarArgsAction and then loop through the inputs maps and find the attachment inputs
3. use an beanutils "indexed" input in your Action bean

The names of the attachment inputs are significant here if we wish to use index properties to set them on our Action bean. The Action framework will understand the inputs to be indexable if the name contain "_n" where n is an integer. Once we have this, all you would need to do to your Action bean to get the attachments as a Collection type is specify an "indexed" setter like this (note the scalar getter is required for compliance with Java Bean spec, but is never called):

public class MyAction implements IAction {
public void setAttachments(int index, Object o)
{     //do something   }
public Object getAttachments(int index)
 { //will not be called }
public void execute() throws Exception {}
}

Alternatively, you can specify a getter method that returns a reference to the array to which the attachment object will be added, e.g.

public class MyAction implements IAction {
private List<Object> attachments = new ArrayList<Object>();
public List<Object> getAttachments()
{     return attachments;   }
public void execute() throws Exception {}
}

These two behaviors are employed by BeanUtils to implement what they call indexed properties. In summary,

• if there is an indexed setter method bean utils will use that (note: a simple getter is required as well though it will not be invoked)
• if there is an array-based getter like List<String> getNames(), bean utils will insert the new value into the array reference it gets from the array getter

Outputs

Normal Outputs

At the end of a step in an action sequence, the Action framework will attempt to retrieve data from your Action bean (per the action-outputs section of the action definition) by calling various getter methods. The framework will loop through the listed outputs and set them to the appropriate context. A discussion about the "appropriate" context is out of scope here, but suffice it to say the output data will be stored in a session-like structure and will be made accessible if you should chose to bind it to the input of a subsequent step, or bound in a way that will direct the data to the user for viewing or to a data sync such as a file.  You will notice that the type attribute is not required for action outputs, other than the special case "content" type which behaves very differently from other outputs.

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Plugging in Actions

Of course writing an Action does no good unless you can use it in an action sequence, right? Well the way you make the Pentaho BI Platform aware of your Action is to write a plugin. See the wiki page on developing plugins for more information.