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111 lines
4.3 KiB
HTML
111 lines
4.3 KiB
HTML
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Licensed to the Apache Software Foundation (ASF) under one or more
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contributor license agreements. See the NOTICE file distributed with
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The ASF licenses this file to You under the Apache License, Version 2.0
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the License. You may obtain a copy of the License at
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Unless required by applicable law or agreed to in writing, software
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-->
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<meta http-equiv="Content-Language" content="en-us">
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<link rel="stylesheet" type="text/css" href="stylesheets/style.css">
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<title>InputHandler</title>
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</head>
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<body>
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<h1>InputHandler</h1>
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<h2>Overview</h2>
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<p>When a task wants to prompt a user for input, it doesn't simply
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read the input from the console as this would make it impossible to
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embed Ant in an IDE. Instead it asks an implementation of the
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<code>org.apache.tools.ant.input.InputHandler</code> interface to
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prompt the user and hand the user input back to the task.</p>
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<p>To do this, the task creates an <code>InputRequest</code> object
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and passes it to the <code>InputHandler</code> Such an
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<code>InputRequest</code> may know whether a given user input is valid
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and the <code>InputHandler</code> is supposed to reject all invalid
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input.</p>
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<p>Exactly one <code>InputHandler</code> instance is associated with
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every Ant process, users can specify the implementation using the
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<code>-inputhandler</code> command line switch.</p>
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<h2>InputHandler</h2>
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<p>The <code>InputHandler</code> interface contains exactly one
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method</p>
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<pre>
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void handleInput(InputRequest request)
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throws org.apache.tools.ant.BuildException;
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</pre>
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<p>with some pre- and postconditions. The main postcondition is that
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this method must not return unless the <code>request</code> considers
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the user input valid, it is allowed to throw an exception in this
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situation.</p>
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<p>Ant comes with three built-in implementations of this interface:</p>
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<h3><a name="defaulthandler">DefaultInputHandler</a></h3>
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<p>This is the implementation you get, when you don't use the
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<code>-inputhandler</code> command line switch at all. This
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implementation will print the prompt encapsulated in the
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<code>request</code> object to Ant's logging system and re-prompt for
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input until the user enters something that is considered valid input
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by the <code>request</code> object. Input will be read from the
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console and the user will need to press the Return key.</p>
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<h3>PropertyFileInputHandler</h3>
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<p>This implementation is useful if you want to run unattended build
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processes. It reads all input from a properties file and makes the
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build fail if it cannot find valid input in this file. The name of
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the properties file must be specified in the Java system property
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<code>ant.input.properties</code>.</p>
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<p>The prompt encapsulated in a <code>request</code> will be used as
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the key when looking up the input inside the properties file. If no
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input can be found, the input is considered invalid and an exception
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will be thrown.</p>
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<p><strong>Note</strong> that <code>ant.input.properties</code> must
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be a Java system property, not an Ant property. I.e. you cannot
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define it as a simple parameter to <code>ant</code>, but you can
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define it inside the <code>ANT_OPTS</code> environment variable.</p>
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<h3>GreedyInputHandler</h3>
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<p>Like the default implementation, this InputHandler reads from standard
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input. However, it consumes <i>all</i> available input. This behavior is
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useful for sending Ant input via an OS pipe. <b>Since Ant 1.7</b>.</p>
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<h2>InputRequest</h2>
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<p>Instances of <code>org.apache.tools.ant.input.InputRequest</code>
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encapsulate the information necessary to ask a user for input and
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validate this input.</p>
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<p>The instances of <code>InputRequest</code> itself will accept any
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input, but subclasses may use stricter validations.
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<code>org.apache.tools.ant.input.MultipleChoiceInputRequest</code>
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should be used if the user input must be part of a predefined set of
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choices.</p>
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</html>
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