Package uk.ac.starlink.task

A framework for invoking user-level tasks.

See: Description

Interface Summary

Interface	Description
Environment	Defines an execution environment within which tasks can operate.
Executable	Defines an object which does the work of a task without any further user or environment interaction.
MultiParameter	Marker interface which marks a parameter as one which can have multiple appearances on the command line.
Task	Defines a user-level task.

Class Summary

Class	Description
AbstractChoiceParameter<T,C>	Abstract superclass for parameters that permit choices from a given list of typed options.
BooleanParameter	Parameter value representing a boolean value.
ChoiceParameter<T>	Parameter whose legal value must be one of a disjunction of given values.
DoubleParameter	Parameter representing a double precision number.
InputStreamParameter	Parameter which can provide an input stream based on its value.
IntegerParameter	Parameter representing an integer value.
InvokeUtils	Provides some utility functions used by classes which invoke tasks.
LineEnvironment	Execution environment for use from the command line.
LineFormatter	Compact log record formatter.
LineWord	Represents a single word on the command line used as by LineEnvironment.
LongParameter	Parameter representing a long integer value.
MultiChoiceParameter<C>	MultiParameter that returns an array of values from a given typed list of options.
MultiTaskInvoker	Invokes tasks from a command line when the tasks are available from an ObjectFactory.
ObjectFactoryParameter<T>	Parameter whose (user-supplied) string values correspond to nicknames from an ObjectFactory.
OutputStreamParameter	Parameter for selecting an output stream to write to.
Parameter<T>	A Parameter describes the function of one of a task's parameters.
SingleTaskInvoker	Invoker which only knows how to invoke a single given task.
StringParameter	Parameter for holding string values.
TerminalEnvironment	Implementation of Environment which accepts an initial command line, and communicates with the user using standard input and standard output.
TerminalInvoker	Invokes Task objects in a way suitable for use from the main method, using a command line interface.
URLParameter	Parameter representing a URL value.

Exception Summary

Exception	Description
AbortException	Exception generated when the user signals an intention to abort a task.
ExecutionException	Exception generated when a task does not complete correctly for some known reason.
ParameterValueException	Exception generated when the value of a parameter is invalid.
TaskException	Superclass for exceptions in the task package.
UsageException	An Exception thrown when a task is invoked with the wrong usage.

Package uk.ac.starlink.task Description

A framework for invoking user-level tasks.

This package provides the necessary infrastructure for writing tasks that do things for users, along the same lines as ADAM A-tasks. An example of use is given in the separate NDTools package.

At the moment all the necessary machinery is provided for invoking tasks from the command line in a way that looks ADAM-like, but it is designed so that, for instance, a GUI-style invoker could be written to invoke the same tasks.

The provided components are as follows:

Parameter

is an object which knows about the name, default value, data type, validity constraints etc of a parameter of a task. It also stores the actual value of the parameter when it has been obtained from the environment. When it has obtained a value it can return it as a string. Parameter can be subclassed to enforce different validity constraints or so it knows how to return itself as some object other than a string (see for instance IntegerParameter).

Environment

is an interface which defines how to request the value of a parameter. It can also tell you about what output stream to use for messages to be dispatched to the user.

TerminalEnvironment

is an implementation of Environment which assumes a user is sitting at a terminal with standard input and standard output.

TerminalInvoker

given a map of task names to Task objects will use a TerminalEnvironment to invoke tasks from an args-style string array.

Task

is the interface which user tasks themselves have to implement. A Task must be able to return a list of the parameters which it uses; since each parameter knows its name, default value, order on the command line, prompt string etc, this tells the Environment everything it needs to know about how to get the value, including what to prompt the user etc. It must also be able to invoke itself on request. During invocation, it can interrogate its parameters to find out what their values are.

Setting up a user-level package containing tasks is then a case of writing a top-level class with a main method which invokes TerminalInvoker, and writing a number of classes which implement Task. See the NDTools package for an example.

To invoke the same tasks from a GUI you'd want to write something like a GUIEnvironment and GUIInvoker class.