| 1 | <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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| 2 | <html>
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| 3 | <head>
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| 4 | <meta http-equiv="Content-Language" content="en-us">
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| 5 | <title>InputHandler</title>
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| 6 | <link rel="stylesheet" type="text/css" href="stylesheets/antmanual.css">
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| 7 | </head>
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| 8 |
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| 9 | <body>
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| 10 | <h1>InputHandler</h1>
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| 11 |
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| 12 | <h2>Overview</h2>
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| 13 |
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| 14 | <p>When a task wants to prompt a user for input, it doesn't simply
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| 15 | read the input from the console as this would make it impossible to
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| 16 | embed Ant in an IDE. Instead it asks an implementation of the
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| 17 | <code>org.apache.tools.ant.input.InputHandler</code> interface to
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| 18 | prompt the user and hand the user input back to the task.</p>
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| 19 |
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| 20 | <p>To do this, the task creates an <code>InputRequest</code> object
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| 21 | and passes it to the <code>InputHandler</code> Such an
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| 22 | <code>InputRequest</code> may know whether a given user input is valid
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| 23 | and the <code>InputHandler</code> is supposed to reject all invalid
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| 24 | input.</p>
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| 25 |
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| 26 | <p>Exactly one <code>InputHandler</code> instance is associated with
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| 27 | every Ant process, users can specify the implementation using the
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| 28 | <code>-inputhandler</code> command line switch.</p>
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| 29 |
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| 30 | <h2>InputHandler</h2>
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| 31 |
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| 32 | <p>The <code>InputHandler</code> interface contains exactly one
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| 33 | method</p>
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| 34 |
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| 35 | <pre>
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| 36 | void handleInput(InputRequest request)
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| 37 | throws org.apache.tools.ant.BuildException;
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| 38 | </pre>
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| 39 |
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| 40 | <p>with some pre- and postconditions. The main postcondition is that
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| 41 | this method must not return unless the <code>request</code> considers
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| 42 | the user input valid, it is allowed to throw an exception in this
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| 43 | situation.</p>
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| 44 |
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| 45 | <p>Ant comes with two built-in implementations of this interface:</p>
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| 46 |
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| 47 | <h3><a name="defaulthandler">DefaultInputHandler</a></h3>
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| 48 |
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| 49 | <p>This is the implementation you get, when you don't use the
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| 50 | <code>-inputhandler</code> command line switch at all. This
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| 51 | implementation will print the prompt encapsulated in the
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| 52 | <code>request</code> object to Ant's logging system and re-prompt for
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| 53 | input until the user enters something that is considered valid input
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| 54 | by the <code>request</code> object. Input will be read from the
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| 55 | console and the user will need to press the Return key.</p>
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| 56 |
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| 57 | <h3>PropertyFileInputHandler</h3>
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| 58 |
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| 59 | <p>This implementation is useful if you want to run unattended build
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| 60 | processes. It reads all input from a properties file and makes the
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| 61 | build fail if it cannot find valid input in this file. The name of
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| 62 | the properties file must be specified in the Java system property
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| 63 | <code>ant.input.properties</code>.</p>
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| 64 |
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| 65 | <p>The prompt encapsulated in a <code>request</code> will be used as
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| 66 | the key when looking up the input inside the properties file. If no
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| 67 | input can be found, the input is considered invalid and an exception
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| 68 | will be thrown.</p>
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| 69 |
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| 70 | <p><strong>Note</strong> that <code>ant.input.properties</code> must
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| 71 | be a Java system property, not an Ant property. I.e. you cannot
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| 72 | define it as a simple parameter to <code>ant</code>, but you can
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| 73 | define it inside the <code>ANT_OPTS</code> environment variable.</p>
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| 74 |
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| 75 | <h2>InputRequest</h2>
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| 76 |
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| 77 | <p>Instances of <code>org.apache.tools.ant.input.InputRequest</code>
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| 78 | encapsulate the information necessary to ask a user for input and
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| 79 | validate this input.</p>
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| 80 |
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| 81 | <p>The instances of <code>InputRequest</code> itself will accept any
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| 82 | input, but subclasses may use stricter validations.
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| 83 | <code>org.apache.tools.ant.input.MultipleChoiceInputRequest</code>
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| 84 | should be used if the user input must be part of a predefined set of
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| 85 | choices.</p>
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| 86 |
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| 87 | <hr>
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| 88 | <p align="center">Copyright © 2002,2004 The Apache Software Foundation. All rights
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| 89 | Reserved.</p>
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| 90 | </html>
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