Package uk.ac.starlink.task


package uk.ac.starlink.task
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.

  • Class
    Description
    Exception generated when the user signals an intention to abort a task.
    Abstract superclass for parameters that permit choices from a given list of typed options.
    Parameter value representing a boolean value.
    Parameter whose legal value must be one of a disjunction of given values.
    Parameter representing a double precision number.
    Defines an execution environment within which tasks can operate.
    Defines an object which does the work of a task without any further user or environment interaction.
    Exception generated when a task does not complete correctly for some known reason.
    Parameter which can provide an input stream based on its value.
    Parameter representing an integer value.
    Provides some utility functions used by classes which invoke tasks.
    Execution environment for use from the command line.
    Compact log record formatter.
    Represents a single word on the command line used as by LineEnvironment.
    Parameter representing a long integer value.
    MultiParameter that returns an array of values from a given typed list of options.
    Marker interface which marks a parameter as one which can have multiple appearances on the command line.
    Invokes tasks from a command line when the tasks are available from an ObjectFactory.
    Parameter whose (user-supplied) string values correspond to nicknames from an ObjectFactory.
    Parameter for selecting an output stream to write to.
    A Parameter describes the function of one of a task's parameters.
    Exception generated when the value of a parameter is invalid.
    Invoker which only knows how to invoke a single given task.
    Parameter for holding string values.
    Defines a user-level task.
    Superclass for exceptions in the task package.
    Implementation of Environment which accepts an initial command line, and communicates with the user using standard input and standard output.
    Invokes Task objects in a way suitable for use from the main method, using a command line interface.
    Parameter representing a URL value.
    An Exception thrown when a task is invoked with the wrong usage.