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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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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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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 read the input from the console
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as this would make it impossible to embed Apache Ant in an IDE. Instead it asks an implementation
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of the <code class="code">org.apache.tools.ant.input.InputHandler</code> interface to prompt the
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user and hand the user input back to the task.</p>
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<p>To do this, the task creates an <code class="code">InputRequest</code> object and passes it to
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the <code class="code">InputHandler</code>. Such an <code class="code">InputRequest</code> may know
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whether a given user input is valid and the <code class="code">InputHandler</code> is supposed to
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reject all invalid input.</p>
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<p>Exactly one <code class="code">InputHandler</code> instance is associated with every Ant process,
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users can specify the implementation using the <kbd>-inputhandler</kbd> command line switch.</p>
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<h2>InputHandler</h2>
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<p>The <code class="code">InputHandler</code> interface contains exactly one 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;</pre>
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<p>with some pre- and postconditions. The main postcondition is that this method must not return
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unless the <code>request</code> considers the user input valid; it is allowed to throw an exception
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in this situation.</p>
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<p>Ant comes with three built-in implementations of this interface:</p>
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<h3 id="defaulthandler">DefaultInputHandler</h3>
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<p>This is the implementation you get, when you don't use the <kbd>-inputhandler</kbd> command line
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switch at all. This implementation will print the prompt encapsulated in the <code>request</code>
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object to Ant's logging system and re-prompt for input until the user enters something that is
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considered valid input by the <code>request</code> object. Input will be read from the console and
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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 processes. It reads all input
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from a properties file and makes the build fail if it cannot find valid input in this file. The
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name of the properties file must be specified in the Java system
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property <code>ant.input.properties</code>.</p>
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<p>The prompt encapsulated in a <code>request</code> will be used as the key when looking up the
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input inside the properties file. If no input can be found, the input is considered invalid and an
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exception will be thrown.</p>
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<p><strong>Note</strong> that <code>ant.input.properties</code> must be a Java system property, not
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an Ant property. I.e. you cannot define it as a simple parameter to <kbd>ant</kbd>, 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><em>Since Ant 1.7</em></p>
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<p>Like the default implementation, this InputHandler reads from standard input. However, it
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consumes <em>all</em> available input. This behavior is useful for sending Ant input via an OS
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pipe.</p>
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<h3>SecureInputHandler</h3>
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<p><em>Since Ant 1.7.1</em></p>
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<p>This InputHandler calls <code class="code">System.console().readPassword()</code>, available
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since Java 6. On earlier platforms it falls back to the behavior
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of <code class="code">DefaultInputHandler</code>.</p>
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<h2>InputRequest</h2>
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<p>Instances of <code class="code">org.apache.tools.ant.input.InputRequest</code> encapsulate the
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information necessary to ask a user for input and validate this input.</p>
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<p>The instances of <code class="code">InputRequest</code> itself will accept any input, but
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subclasses may use stricter
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validations. <code class="code">org.apache.tools.ant.input.MultipleChoiceInputRequest</code> should
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be used if the user input must be part of a predefined set of choices.</p>
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</body>
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</html>
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