| Selector class that uses Algorithm, Cache and Comparator
for its work.
The Algorithm is used for computing a hashvalue for a file.
The Comparator decides whether to select or not.
The Cache stores the other value for comparison by the Comparator
in a persistent manner.
The ModifiedSelector is implemented as a CoreSelector and uses default
values for all its attributes therefore the simpliest example is
<copy todir="dest">
<filelist dir="src">
<modified/>
</filelist>
</copy>
The same example rewritten as CoreSelector with setting the all values
(same as defaults are) would be
<copy todir="dest">
<filelist dir="src">
<modified update="true"
cache="propertyfile"
algorithm="digest"
comparator="equal">
<param name="cache.cachefile" value="cache.properties"/>
<param name="algorithm.algorithm" value="MD5"/>
</modified>
</filelist>
</copy>
And the same rewritten as CustomSelector would be
<copy todir="dest">
<filelist dir="src">
<custom class="org.apache.tools.ant.type.selectors.ModifiedSelector">
<param name="update" value="true"/>
<param name="cache" value="propertyfile"/>
<param name="algorithm" value="digest"/>
<param name="comparator" value="equal"/>
<param name="cache.cachefile" value="cache.properties"/>
<param name="algorithm.algorithm" value="MD5"/>
</custom>
</filelist>
</copy>
If you want to provide your own interface implementation you can do
that via the *classname attributes. If the classes are not on Ant's core
classpath, you will have to provide the path via nested <classpath>
element, so that the selector can find the classes.
<modified cacheclassname="com.mycompany.MyCache">
<classpath>
<pathelement location="lib/mycompony-antutil.jar"/>
</classpath>
</modified>
All these three examples copy the files from src to dest
using the ModifiedSelector. The ModifiedSelector uses the PropertyfileCache
, the DigestAlgorithm and the EqualComparator for its
work. The PropertyfileCache stores key-value-pairs in a simple java
properties file. The filename is cache.properties. The update
flag lets the selector update the values in the cache (and on first call
creates the cache). The DigestAlgorithm computes a hashvalue using the
java.security.MessageDigest class with its MD5-Algorithm and its standard
provider. The new computed hashvalue and the stored one are compared by
the EqualComparator which returns 'true' (more correct a value not
equals zero (1)) if the values are not the same using simple String
comparison.
A useful scenario for this selector is inside a build environment
for homepage generation (e.g. with
Apache Forrest).
<target name="generate-and-upload-site">
<echo> generate the site using forrest </echo>
<antcall target="site"/>
<echo> upload the changed files </echo>
<ftp server="${ftp.server}" userid="${ftp.user}" password="${ftp.pwd}">
<fileset dir="htdocs/manual">
<modified/>
</fileset>
</ftp>
</target>
Here all changed files are uploaded to the server. The
ModifiedSelector saves therefore much upload time.
This selector uses reflection for setting the values of its three interfaces
(using org.apache.tools.ant.IntrospectionHelper) therefore no special
'configuration interfaces' has to be implemented by new caches, algorithms or
comparators. All present setXX methods can be used. E.g. the DigestAlgorithm
can use a specified provider for computing its value. For selecting this
there is a setProvider(String providername) method. So you can use
a nested <param name="algorithm.provider" value="MyProvider"/>.
since:
Ant 1.6 | 