Selectors in Ant

## Selectors

Selectors are a mechanism whereby the files that make up a fileset can be selected based on criteria other than filename as provided by the `<include>` and `<exclude>` tags.

### How to use a Selector

A selector is an element of FileSet, and appears within it. It can also be defined outside of any target by using the <selector> tag and then using it as a reference.

Different selectors have different attributes. Some selectors can contain other selectors, and these are called `Selector Containers`. There is also a category of selectors that allow user-defined extensions, called `Custom Selectors`. The ones built in to Ant are called `Core Selectors`.

### Core Selectors

Core selectors are the ones that come standard with Ant. They can be used within a fileset and can be contained within Selector Containers.

The core selectors are:

- <contains> - Select files that contain a particular text string
- <date> - Select files that have been modified either before or after a particular date and time
- <depend> - Select files that have been modified more recently than equivalent files elsewhere
- <depth> - Select files that appear so many directories down in a directory tree
- <filename> - Select files whose name matches a particular pattern. Equivalent to the include and exclude elements of a patternset.
- <present> - Select files that either do or do not exist in some other location
- <size> - Select files that are larger or smaller than a particular number of bytes.

#### Contains Selector

The `<contains>` tag in a FileSet limits the files defined by that fileset to only those which contain the string specified by the `text` attribute. .

Attribute | Description | Required
text | Specifies the text that every file must contain | Yes
casesensitive | Whether to pay attention to case when looking for the string in the `text` attribute. Default is true. | No

Here is an example of how to use the Contains Selector:

>     <fileset dir="${doc.path}" includes="**/*.html">
>         <contains text="script" casesensitive="no"/>
>     </fileset>

Selects all the HTML files that contain the string `script`.

#### Date Selector

The `<date>` tag in a FileSet will put a limit on the files specified by the include tag, so that tags whose last modified date does not meet the date limits specified by the selector will not end up being selected.

Attribute | Description | Required
datetime | Specifies the date and time to test for using a string of the format MM/DD/YYYY HH:MM AM_or_PM. | At least one of the two.
millis | The number of milliseconds since 1970 that should be tested for. It is usually much easier to use the datetime attribute.
granularity | The number of milliseconds leeway to give before deciding whether a files modification time matches a date. This is needed because not every file system supports tracking the last modified time to the millisecond level. The file will be selected provided the condition could be true were the granularity added or subtracted from the actual time. Default is 0 milliseconds except on Windows systems, where it is 2000 milliseconds (2 seconds). | No
when | Indicates how to interpret the date, whether the files to be selected are those whose last modified times should be before, after, or equal to the specified value. Acceptable values for this attribute are: before - select files whose last modified date is before the indicated date after - select files whose last modified date is after the indicated date equal - select files whose last modified date is this exact date The default is equal. | No

Here is an example of how to use the Date Selector:

>     <fileset dir="${jar.path}" includes="**/*.jar">
>         <date datetime="01/01/2001 12:00 AM" when="before"/>
>     </fileset>

Selects all JAR files which were last modified before midnight January 1, 2001.

#### Depend Selector

The `<depend>` tag selects files whose last modified date is later than another, equivalent file in another location.

The `<depend>` tag supports the use of a contained `<mapper>` element to define the location of the file to be compared against. If no `<mapper>` element is specified, the `identity` type mapper is used.

Attribute | Description | Required
targetdir | The base directory to look for the files to compare against. The precise location depends on a combination of this attribute and the `<mapper>` element, if any. | Yes
granularity | The number of milliseconds leeway to give before deciding a file is out of date. This is needed because not every file system supports tracking the last modified time to the millisecond level. Default is 0 milliseconds except on Windows systems, where it is 2000 milliseconds (2 seconds). | No

Here is an example of how to use the Depend Selector:

>     <fileset dir="${ant.1.5}/src/main" includes="**/*.java">
>         <depend targetdir="${ant.1.4.1}/src/main"/>
>     </fileset>

Selects all the Java source files which were modified in the 1.5 release.

#### Depth Selector

The `<depth>` tag selects files based on how many directy levels deep they are in relation to the base directory of the fileset.

Attribute | Description | Required
min | The minimum number of directory levels below the base directory that a file must be in order to be selected. Default is no limit. | At least one of the two.
max | The maximum number of directory levels below the base directory that a file can be and still be selected. Default is no limit.

Here is an example of how to use the Depth Selector:

>     <fileset dir="${doc.path}" includes="**/*">
>         <depth max="1"/>
>     </fileset>

Selects all files in the base directory and one directory below that.

#### Filename Selector

The `<filename>` tag acts like the `<include>` and `<exclude>` tags within a fileset. By using a selector instead, however, one can combine it with all the other selectors using whatever selector container is desired.

Attribute | Description | Required
name | The name of files to select. The name parameter can contain the standard Ant wildcard characters. | Yes
casesensitive | Whether to pay attention to case when looking at file names. Default is "true". | No
negate | Whether to reverse the effects of this filename selection, therefore emulating an exclude rather than include tag. Default is "false". | No

Here is an example of how to use the Filename Selector:

>     <fileset dir="${doc.path}" includes="**/*">
>         <filename name="**/*.css"/>
>     </fileset>

Selects all the cascading style sheet files.

#### Present Selector

The `<present>` tag selects files that have an equivalent file in another directory tree.

The `<present>` tag supports the use of a contained `<mapper>` element to define the location of the file to be tested against. If no `<mapper>` element is specified, the `identity` type mapper is used.

Attribute | Description | Required
targetdir | The base directory to look for the files to compare against. The precise location depends on a combination of this attribute and the `<mapper>` element, if any. | Yes
present | Whether we are requiring that a file is present in the src directory tree only, or in both the src and the target directory tree. Valid values are: srconly - select files only if they are in the src directory tree but not in the target directory tree both - select files only if they are present both in the src and target directory trees Default is both. Setting this attribute to "srconly" is equivalent to wrapping the selector in the <not> selector container. | No

Here is an example of how to use the Present Selector:

>     <fileset dir="${ant.1.5}/src/main" includes="**/*.java">
>         <present present="srconly" targetdir="${ant.1.4.1}/src/main"/>
>     </fileset>

Selects all the Java source files which are new in the 1.5 release.

#### Size Selector

The `<size>` tag in a FileSet will put a limit on the files specified by the include tag, so that tags which do not meet the size limits specified by the selector will not end up being selected.

Attribute | Description | Required
value | The size of the file which should be tested for. | Yes
units | The units that the `value` attribute is expressed in. When using the standard single letter SI designations, such as "k","M", or "G", multiples of 1000 are used. If you want to use power of 2 units, use the IEC standard: "Ki" for 1024, "Mi" for 1048576, and so on. The default is no units, which means the `value` attribute expresses the exact number of bytes. | No
when | Indicates how to interpret the size, whether the files to be selected should be larger, smaller, or equal to that value. Acceptable values for this attribute are: less - select files less than the indicated size more - select files greater than the indicated size equal - select files this exact size The default is equal. | No

Here is an example of how to use the Size Selector:

>     <fileset dir="${jar.path}">
>       <patternset>
>         <include name="**/*.jar"/>
>       </patternset>
>       <size value="4" units="Ki" when="more"/>
>     </fileset>

Selects all JAR files that are larger than 4096 bytes.

### Selector Containers

To create more complex selections, a variety of selectors that contain other selectors are available for your use. They combine the selections of their child selectors in various ways.

The selector containers are:

- <and> - select a file only if all the contained selectors select it.
- <majority> - select a file if a majority of its selectors select it.
- <none> - select a file only if none of the contained selectors select it.
- <not> - can contain only one selector, and reverses what it selects and doesn't select.
- <or> - selects a file if any one of the contained selectors selects it.
- <selector> - contains only one selector and forwards all requests to it without alteration. This is the selector to use if you want to define a reference. It is usable as an element of `<project>`.

All selector containers can contain any other selector, including other containers, as an element. Using containers, the selector tags can be arbitrarily deep. Here is a complete list of allowable selector elements within a container:

- <and>
- <contains>
- <custom>
- <date>
- <depend>
- <depth>
- <filename>
- <majority>
- <none>
- <not>
- <or>
- <present>
- <selector>
- <size>

#### And Selector

The `<and>` tag selects files that are selected by all of the elements it contains. It returns as soon as it finds a selector that does not select the file, so it is not guaranteed to check every selector.

Here is an example of how to use the And Selector:

>     <fileset dir="${dist}" includes="**/*.jar">
>         <and>
>             <size value="4" units="Ki" when="more"/>
>             <date datetime="01/01/2001 12:00 AM" when="before"/>
>         </and>
>     </fileset>

Selects all the JAR file larger than 4096 bytes which haven't been update since the last millenium.

#### Majority Selector

The `<majority>` tag selects files provided that a majority of the contained elements also select it. Ties are dealt with as specified by the `allowtie` attribute.

Attribute | Description | Required
allowtie | Whether files should be selected if there are an even number of selectors selecting them as are not selecting them. Default is true. | No

Here is an example of how to use the Majority Selector:

>     <fileset dir="${docs}" includes="**/*.html">
>         <majority>
>             <contains text="project" casesensitive="false"/>
>             <contains text="taskdef" casesensitive="false"/>
>             <contains text="IntrospectionHelper" casesensitive="true"/>
>         </majority>
>     </fileset>

Selects all the HTML files which contain at least two of the three phrases "project", "taskdef", and "IntrospectionHelper" (this last phrase must match case exactly).

#### None Selector

The `<none>` tag selects files that are not selected by any of the elements it contains. It returns as soon as it finds a selector that selects the file, so it is not guaranteed to check every selector.

Here is an example of how to use the None Selector:

>     <fileset dir="${src}" includes="**/*.java">
>         <none>
>             <present targetdir="${dest}"/>
>             <present targetdir="${dest}">
>                 <mapper type="glob" from="*.java" to="*.class"/>
>             </present>
>         </none>
>     </fileset>

Selects only Java files which do not have equivalent java or class files in the dest directory.

#### Not Selector

The `<not>` tag reverses the meaning of the single selector it contains.

Here is an example of how to use the Not Selector:

>     <fileset dir="${src}" includes="**/*.java">
>         <not>
>             <contains text="test"/>
>         </not>
>     </fileset>

Selects all the files in the src directory that do not contain the string "test".

#### Or Selector

The `<or>` tag selects files that are selected by any one of the elements it contains. It returns as soon as it finds a selector that selects the file, so it is not guaranteed to check every selector.

Here is an example of how to use the Or Selector:

>     <fileset dir="${basedir}">
>         <or>
>             <depth max="0"/>
>             <filename name="*.png"/>
>             <filename name="*.gif"/>
>             <filename name="*.jpg"/>
>         </or>
>     </fileset>

Selects all the files in the top directory along with all the image files below it.

#### Selector Reference

The `<selector>` tag is used to create selectors that can be reused through references. It is the only selector which can be used outside of any target, as an element of the `<project>` tag. It can contain only one other selector, but of course that selector can be a container.

Here is an example of how to use the Selector Reference:

>     <project default="all" basedir="./ant">

>         <selector id="completed">
>             <none>
>                 <depend targetdir="build/classes">
>                     <mapper type="glob" from="*.java" to="*.class"/>
>                 </depend>
>                 <depend targetdir="docs/manual/api">
>                     <mapper type="glob" from="*.java" to="*.html"/>
>                 </depend>
>             </none>
>         </selector>

>         <target>
>             <zip>
>                 <fileset dir="src/main" includes="**/*.java">
>                     <selector refid="completed"/>
>                 </fileset>
>             </zip>
>         </target>

>     </project>

Zips up all the Java files which have an up-to-date equivalent class file and javadoc file associated with them.

### Custom Selectors

You can write your own selectors and use them within the selector containers by specifying them within the <custom> tag.

First, you have to write your selector class in Java. The only requirement it must meet in order to be a selector is that it implements the `org.apache.tools.ant.types.selectors.FileSelector` interface, which contains a single method. See Programming Selectors in Ant for more information.

Once that is written, you include it in your build file by using the `<custom>` tag.

Attribute | Description | Required
classname | The name of your class that implements `org.apache.tools.ant.types.selectors.FileSelector`. | Yes
classpath | The classpath to use in order to load the custom selector class. If neither this classpath nor the classpathref are specified, the class will be loaded from the classpath that Ant uses. | No
classpathref | A reference to a classpath previously defined. If neither this reference nor the classpath above are specified, the class will be loaded from the classpath that Ant uses. | No

Here is how you use `<custom>` to use your class as a selector:

>     <fileset dir="${mydir}" includes="**/*">
>         <custom classname="com.mydomain.MySelector">
>             <param name="myattribute" value="myvalue"/>
>         </custom>
>     </fileset>

A number of core selectors can also be used as custom selectors by specifying their attributes using <param> elements. These are

- Contains Selector with classname `org.apache.tools.ant.types.selectors.ContainsSelector`
- Date Selector with classname `org.apache.tools.ant.types.selectors.DateSelector`
- Depth Selector with classname `org.apache.tools.ant.types.selectors.DepthSelector`
- Filename Selector with classname `org.apache.tools.ant.types.selectors.FilenameSelector`
- Size Selector with classname `org.apache.tools.ant.types.selectors.SizeSelector`

Here is the example from the Depth Selector section rewritten to use the selector through `<custom>`.

>     <fileset dir="${doc.path}" includes="**/*">
>         <custom classname="org.apache.tools.ant.types.selectors.DepthSelector">
>             <param name="max" value="1"/>
>         </custom>
>     </fileset>

Selects all files in the base directory and one directory below that.

For more details concerning writing your own selectors, consult Programming Selectors in Ant.

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