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diff --git a/framework/src/ant/apache-ant-1.9.6/manual/properties.html b/framework/src/ant/apache-ant-1.9.6/manual/properties.html new file mode 100644 index 00000000..e42d3a2a --- /dev/null +++ b/framework/src/ant/apache-ant-1.9.6/manual/properties.html @@ -0,0 +1,399 @@ +<!-- + Licensed to the Apache Software Foundation (ASF) under one or more + contributor license agreements. See the NOTICE file distributed with + this work for additional information regarding copyright ownership. + The ASF licenses this file to You under the Apache License, Version 2.0 + (the "License"); you may not use this file except in compliance with + the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. +--> +<html> + +<head> + <meta http-equiv="Content-Language" content="en-us"/> + <link rel="stylesheet" type="text/css" href="stylesheets/style.css"/> + <title>Properties and PropertyHelpers</title> +</head> + +<body> + <h1>Properties</h1> + + <p>Properties are key-value-pairs where Apache Ant tries to + expand <code>${key}</code> to <code>value</code> at runtime.</p> + + <p>There are many tasks that can set properties, the most common one + is the <a href="Tasks/property.html">property</a> task. In + addition properties can be defined + via <a href="running.html">command line arguments</a> or similar + mechanisms from outside of Ant.</p> + + <p>Normally property values can not be changed, once a property is + set, most tasks will not allow its value to be modified. In + general properties are of global scope, i.e. once they have been + defined they are available for any task or target invoked + subsequently - it is not possible to set a property in a child + build process created via + the <a href="Tasks/ant.html">ant</a>, antcall or subant tasks + and make it available to the calling build process, though.</p> + + <p>Starting with Ant 1.8.0 + the <a href="Tasks/local.html">local</a> task can be used to + create properties that are locally scoped to a target or + a <a href="Tasks/sequential.html">sequential</a> element like + the one of the <a href="Tasks/macrodef.html">macrodef</a> + task.</p> + + <h2><a name="built-in-props">Built-in Properties</a></h2> + + <p>Ant provides access to all system properties as if they had been + defined using a <code><property></code> task. For + example, <code>${os.name}</code> expands to the name of the + operating system.</p> + <p>For a list of system properties see + <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/System.html#getProperties%28%29">the Javadoc of System.getProperties</a>. + </p> + + <p>In addition, Ant has some built-in properties:</p> +<pre><!-- TODO use <dl><dt><code>...</code></dt><dd>...</dd></dl> instead --> +basedir the absolute path of the project's basedir (as set + with the basedir attribute of <a href="using.html#projects"><project></a>). +ant.file the absolute path of the buildfile. +ant.version the version of Ant +ant.project.name the name of the project that is currently executing; + it is set in the name attribute of <project>. +ant.project.default-target + the name of the currently executing project's + default target; it is set via the default + attribute of <project>. +ant.project.invoked-targets + a comma separated list of the targets that have + been specified on the command line (the IDE, + an <ant> task ...) when invoking the current + project. + This property is set when the first target is executed. + So you can't use it in the implicit target (directly + under the <project> tag). +ant.java.version the JVM version Ant detected; currently it can hold + the values "1.7", "1.6", "1.5", + "1.4", "1.3" and "1.2". +ant.core.lib the absolute path of the <code>ant.jar</code> file. +</pre> + + <p>There is also another property, but this is set by the launcher + script and therefore maybe not set inside IDEs:</p> +<pre> +ant.home home directory of Ant +</pre> + + <p>The following property is only set if Ant is started via the + Launcher class (which means it may not be set inside IDEs + either):</p> +<pre> +ant.library.dir the directory that has been used to load Ant's + jars from. In most cases this is ANT_HOME/lib. +</pre> + + <h1><a name="propertyHelper">PropertyHelpers</a></h1> + + <p>Ant's property handling is accomplished by an instance of + <code>org.apache.tools.ant.PropertyHelper</code> associated with + the current Project. You can learn more about this class by + examining Ant's Java API. In Ant 1.8 the PropertyHelper class was + much reworked and now itself employs a number of helper classes + (actually instances of + the <code>org.apache.tools.ant.PropertyHelper$Delegate</code> + marker interface) to take care of discrete tasks such as property + setting, retrieval, parsing, etc. This makes Ant's property + handling highly extensible; also of interest is the + new <a href="Tasks/propertyhelper.html">propertyhelper</a> + task used to manipulate the PropertyHelper and its delegates from + the context of the Ant buildfile. + + <p>There are three sub-interfaces of <code>Delegate</code> that may be + useful to implement.</p> + + <ul> + <li><code>org.apache.tools.ant.property.PropertyExpander</code> is + responsible for finding the property name inside a string in the + first place (the default extracts <code>foo</code> + from <code>${foo}</code>). + + <p>This is the interface you'd implement if you wanted to invent + your own property syntax - or allow nested property expansions + since the default implementation doesn't balance braces + (see <a href="https://git-wip-us.apache.org/repos/asf?p=ant-antlibs-props.git;a=blob;f=src/main/org/apache/ant/props/NestedPropertyExpander.java;hb=HEAD"><code>NestedPropertyExpander</code> + in the "props" Antlib</a> for an example).</p> + </li> + + <li><code>org.apache.tools.ant.PropertyHelper$PropertyEvaluator</code> + is used to expand <code>${some-string}</code> into + an <code>Object</code>. + + <p>This is the interface you'd implement if you want to provide + your own storage independent of Ant's project instance - the + interface represents the reading end. An example for this + would + be <code>org.apache.tools.ant.property.LocalProperties</code> + which implements storage + for <a href="Tasks/local.html">local properties</a>.</p> + + <p>Another reason to implement this interface is if you wanted + to provide your own "property protocol" like + expanding <code>toString:foo</code> by looking up the project + reference foo and invoking <code>toString()</code> on it + (which is already implemented in Ant, see below).</p> + </li> + + <li><code>org.apache.tools.ant.PropertyHelper$PropertySetter</code> + is responsible for setting properties. + + <p>This is the interface you'd implement if you want to provide + your own storage independent of Ant's project instance - the + interface represents the reading end. An example for this + would + be <code>org.apache.tools.ant.property.LocalProperties</code> + which implements storage + for <a href="Tasks/local.html">local properties</a>.</p> + </li> + + </ul> + + <p>The default <code>PropertyExpander</code> looks similar to:</p> + +<pre> +public class DefaultExpander implements PropertyExpander { + public String parsePropertyName(String s, ParsePosition pos, + ParseNextProperty notUsed) { + int index = pos.getIndex(); + if (s.indexOf("${", index) == index) { + int end = s.indexOf('}', index); + if (end < 0) { + throw new BuildException("Syntax error in property: " + s); + } + int start = index + 2; + pos.setIndex(end + 1); + return s.substring(start, end); + } + return null; + } +} +</pre> + + <p>The logic that replaces <code>${toString:some-id}</code> with the + stringified representation of the object with + id <code>some-id</code> inside the current build is contained in a + PropertyEvaluator similar to the following code:</p> + +<pre> +public class ToStringEvaluator implements PropertyHelper.PropertyEvaluator { + private static final String prefix = "toString:"; + public Object evaluate(String property, PropertyHelper propertyHelper) { + Object o = null; + if (property.startsWith(prefix) && propertyHelper.getProject() != null) { + o = propertyHelper.getProject().getReference( + property.substring(prefix.length())); + } + return o == null ? null : o.toString(); + } +} +</pre> + + + <h1>Property Expansion</h1> + + <p>When Ant encounters a construct <code>${some-text}</code> the + exact parsing semantics are subject to the configured property + helper delegates.</p> + + <h2><code>$$</code> Expansion</h2> + + <p>In its default configuration Ant will expand the + text <code>$$</code> to a single <code>$</code> and suppress the + normal property expansion mechanism for the text immediately + following it, i.e. <code>$${key}</code> expands + to <code>${key}</code> and not <code>value</code> even though a + property named <code>key</code> was defined and had the + value <code>value</code>. This can be used to escape + literal <code>$</code> characters and is useful in constructs that + only look like property expansions or when you want to provide + diagnostic output like in</p> + +<pre> <echo>$${builddir}=${builddir}</echo></pre> + + <p>which will echo this message:</p> + +<pre> ${builddir}=build/classes</pre> + + <p>if the property <code>builddir</code> has the + value <code>build/classes</code>.</p> + + <p>In order to maintain backward compatibility with older Ant + releases, a single '$' character encountered apart from a + property-like construct (including a matched pair of french + braces) will be interpreted literally; that is, as '$'. The + "correct" way to specify this literal character, however, is by + using the escaping mechanism unconditionally, so that "$$" is + obtained by specifying "$$$$". Mixing the two approaches yields + unpredictable results, as "$$$" results in "$$".</p> + + <h2>Nesting of Braces</h2> + + <p>In its default configuration Ant will not try to balance braces + in property expansions, it will only consume the text up to the + first closing brace when creating a property name. I.e. when + expanding something like <code>${a${b}}</code> it will be + translated into two parts:</p> + + <ol> + <li>the expansion of property <code>a${b</code> - likely nothing + useful.</li> + <li>the literal text <code>}</code> resulting from the second + closing brace</li> + </ol> + + <p>This means you can't use easily expand properties whose names are + given by properties, but there + are <a href="http://ant.apache.org/faq.html#propertyvalue-as-name-for-property">some + workarounds</a> for older versions of Ant. With Ant 1.8.0 and the + <a href="http://ant.apache.org/antlib/props/">the props Antlib</a> + you can configure Ant to use + the <code>NestedPropertyExpander</code> defined there if you need + such a feature.</p> + + <h2>Expanding a "Property Name"</h2> + + <p>In its most simple form <code>${key}</code> is supposed to look + up a property named <code>key</code> and expand to the value of + the property. Additional <code>PropertyEvaluator</code>s may + result in a different interpretation of <code>key</code>, + though.</p> + + <p>The <a href="http://ant.apache.org/antlibs/props/">props + Antlib</a> provides a few interesting evaluators but there are + also a few built-in ones.</p> + + <h3><a name="toString">Getting the value of a Reference with + ${toString:}</a></h3> + + <p>Any Ant type which has been declared with a reference can also + its string value extracted by using the <code>${toString:}</code> + operation, with the name of the reference listed after + the <code>toString:</code> text. The <code>toString()</code> + method of the Java class instance that is referenced is invoked + -all built in types strive to produce useful and relevant output + in such an instance.</p> + + <p>For example, here is how to get a listing of the files in a fileset,<p> + +<pre> +<fileset id="sourcefiles" dir="src" includes="**/*.java" /> +<echo> sourcefiles = ${toString:sourcefiles} </echo> +</pre> + + <p>There is no guarantee that external types provide meaningful + information in such a situation</p> + + <h3><a name="ant.refid">Getting the value of a Reference with + ${ant.refid:}</a></h3> + + <p>Any Ant type which has been declared with a reference can also be + used as a property by using the <code>${ant.refid:}</code> + operation, with the name of the reference listed after + the <code>ant.refid:</code> text. The difference between this + operation and <a href="#toString"><code>${toString:}</code></a> is + that <code>${ant.refid:}</code> will expand to the referenced + object itself. In most circumstances the toString method will be + invoked anyway, for example if the <code>${ant.refid:}</code> is + surrounded by other text.</p> + + <p>This syntax is most useful when using a task with attribute + setters that accept objects other than String. For example if the + setter accepts a Resource object as in</p> +<pre> +public void setAttr(Resource r) { ... } +</pre> + + <p>then the syntax can be used to pass in resource subclasses + previously defined as references like</p> +<pre> + <url url="http://ant.apache.org/" id="anturl"/> + <my:task attr="${ant.refid:anturl}"/> +</pre> + + <h2><a name="if+unless">If/Unless Attributes</a></h2> + <p> + The <code><target></code> element and various tasks (such as + <code><fail></code>) and task elements (such as <code><test></code> + in <code><junit></code>) support <code>if</code> and <code>unless</code> + attributes which can be used to control whether the item is run or otherwise + takes effect. + </p> + <p> + In Ant 1.7.1 and earlier, these attributes could only be property names. + The item was enabled if a property with that name was defined - even to be + the empty string or <tt>false</tt> - and disabled if the property was not + defined. For example, the following works but there is no way to override + the file existence check negatively (only positively): + </p> + <pre> +<target name="-check-use-file"> + <available property="file.exists" file="some-file"/> +</target> +<target name="use-file" depends="-check-use-file" <b>if="file.exists"</b>> + <!-- do something requiring that file... --> +</target> +<target name="lots-of-stuff" depends="use-file,other-unconditional-stuff"/> + </pre> + <p> + As of Ant 1.8.0, you may instead use property expansion; a value of + <tt>true</tt> (or <tt>on</tt> or <tt>yes</tt>) will enable the + item, while <tt>false</tt> (or <tt>off</tt> or <tt>no</tt>) will + disable it. Other values are still assumed to be property + names and so the item is enabled only if the named property is defined. + </p> + <p> + Compared to the older style, this gives you additional flexibility, because + you can override the condition from the command line or parent scripts: + </p> + <pre> +<target name="-check-use-file" <b>unless="file.exists"</b>> + <available property="file.exists" file="some-file"/> +</target> +<target name="use-file" depends="-check-use-file" <b>if="${file.exists}"</b>> + <!-- do something requiring that file... --> +</target> +<target name="lots-of-stuff" depends="use-file,other-unconditional-stuff"/> + </pre> + <p> + Now <code>ant -Dfile.exists=false lots-of-stuff</code> will run + <code>other-unconditional-stuff</code> but not <code>use-file</code>, + as you might expect, and you can disable the condition from another script + too: + </p> + <pre> +<antcall target="lots-of-stuff"> + <param name="file.exists" value="false"/> +</antcall> + </pre> + <p> + Similarly, an <code>unless</code> attribute disables the item if it is + either the name of property which is defined, or if it evaluates to a + <tt>true</tt>-like value. For example, the following allows you to define + <tt>skip.printing.message=true</tt> in <tt>my-prefs.properties</tt> with + the results you might expect: + </p> + <pre> +<property file="my-prefs.properties"/> +<target name="print-message" <b>unless="${skip.printing.message}"</b>> + <echo>hello!</echo> +</target> + </pre> + +</body> |