When a task wants to prompt a user for input, it doesn't simply
read the input from the console as this would make it impossible to
embed Apache Ant in an IDE. Instead it asks an implementation of the
org.apache.tools.ant.input.InputHandler interface to
prompt the user and hand the user input back to the task.
To do this, the task creates an
and passes it to the
InputHandler Such an
InputRequest may know whether a given user input is valid
InputHandler is supposed to reject all invalid
InputHandler instance is associated with
every Ant process, users can specify the implementation using the
-inputhandler command line switch.
InputHandler interface contains exactly one
void handleInput(InputRequest request) throws org.apache.tools.ant.BuildException;
with some pre- and postconditions. The main postcondition is that
this method must not return unless the
the user input valid, it is allowed to throw an exception in this
Ant comes with three built-in implementations of this interface:
This is the implementation you get, when you don't use the
-inputhandler command line switch at all. This
implementation will print the prompt encapsulated in the
request object to Ant's logging system and re-prompt for
input until the user enters something that is considered valid input
request object. Input will be read from the
console and the user will need to press the Return key.
This implementation is useful if you want to run unattended build
processes. It reads all input from a properties file and makes the
build fail if it cannot find valid input in this file. The name of
the properties file must be specified in the Java system property
The prompt encapsulated in a
request will be used as
the key when looking up the input inside the properties file. If no
input can be found, the input is considered invalid and an exception
will be thrown.
be a Java system property, not an Ant property. I.e. you cannot
define it as a simple parameter to
ant, but you can
define it inside the
ANT_OPTS environment variable.
Like the default implementation, this InputHandler reads from standard input. However, it consumes all available input. This behavior is useful for sending Ant input via an OS pipe. Since Ant 1.7.
This InputHandler calls
available since Java 1.6. On earlier platforms it falls back to the
behavior of DefaultInputHandler. Since Ant 1.7.1.
encapsulate the information necessary to ask a user for input and
validate this input.
The instances of
InputRequest itself will accept any
input, but subclasses may use stricter validations.
should be used if the user input must be part of a predefined set of