# Libraries Task

## Libraries

### Description

Extensible library download mechanism, integrated with the Maven repository hosted at ibiblio.org.

This task can:

1. Download publicly published JAR files by version
2. Download JAR files from private file: or http: repositories
3. Cache the JAR files in a directory tree
4. Check for updates on a regular schedule
5. Build paths for compilation/execution
6. Fail the build if needed libraries are missing
7. Force an update of all libraries
8. Skip all downloading when offline

### Parameters

Attribute | Description | Required
destDir | Destination directory for all downloads | No - default is ${user.home}/.maven/repository
offline | Flag to indicate that the system is offline, and that no downloads should take place. | No
flatten | flag to indicate that files should be flattened when downloaded | No -default false
usetimestamp | flag to indicate that timestamps should be compared when probing for updates. | No -default false
pathID | Name of a path to create containing all libraries in this declaration. | No
repositoryRef | Reference to a predefined repository | No

The default destination is that used by Maven, ${user.home}/.maven/repository . It can be overridden by setting the property `ant.maven.repository.dir` to a new location.

### Nested Elements

#### library

This is the core of the system: a library to (potentially) download.

Attribute | Description | Required
project | Name of the project | Yes
version |  | Yes
archive | Name of the archive | No
destinationName | Filename of downloaded file | No, default remote name
suffix | Suffix of the archive | No -default ".jar"
enabled | flag to turn on or off specific download/use of an archive | No -default "true"

#### Repository

A repository is an Ant datatype that extends the `Repository` type. Ant only ships with one: the mavenrepository. If no repository is declared inline, and no repositoryref attribute set, the task will default to the maven repository.

Attribute | Description | Required
url | URL of the repository | No

Example:

        <repository ref="predefined.repository" />

#### mavenrepository

This connects to the Maven repository at ibiblio.org, or another chosen. Private repositories should copy the existing layout.

If no `url` is set, the default URL is `http://ibiblio.org/maven`, unless the property `ant.maven.repository.url` is set to something else.

Attribute | Description | Required
url | URL of the repository | No
checkMD5 | Flag to turn on MD5 checking (unimplemented) | No
username | HTTP authentication username | No
password | HTTP authentication password | Only if username is set

### UpdatePolicies

Update policies are an (extensible) means of tuning the download, running code before and possibly after a download. They can enable or disable checks for individual files, skip the download process, or perform some post-download validation.

All policies have at least the common set of attributes; some may have more, in which case an updated attribute list is shown.

Attribute | Description | Required
enabled | Enabled flag | No -default "true"

Policies can be chained by listing them in order. Before an update/download takes place, all policies will be executed in order. After the download, the policies will be invoked in reverse order. The compound policy in such a situation is left to the experimentor, though reading the source will help.

Developers may add new policies (such as signing incoming files) by adding new datatypes extending the `LibraryPolicy` class.

#### noupdate

This policy will disable remote downloads when enabled. It is the policy equivalent of the offline flag.

Example:

        <noupdate />

#### forceupdate

This policy forces all libraries to be downloaded. If any download failed, the build will halt.

Example:

        <forceupdate />

#### timestamp

This policy tells Ant to check the repository to see if the files have changed using timestamp checks. Any files which are up to date will not be downloaded again. It is equivalent to setting the `useTimestamp` flag.

Example:

        <timestamp />

#### scheduledupdate

This policy tells Ant to check the repository to see if the files have changed, but only intermittently. An interval of the size of the schedule has to have passed, or the set of files to check has to have changed.

Attribute | Description | Required
enabled | Enabled flag | No -default "true"
markerFile | Name of a file to cache download history | Yes
Days | number of days between update checks | No
Hours | number of hours between update checks | No
Minutes | number of minutes between update checks | No

Example:

        <scheduledupdate days="1" hours="3" minutes="17" />

Check for an update every 27 hours, 17 minutes.

#### assertdownloaded

This policy is really for testing the library. It does not alter the download policy, but after any download has taken place, it verifies that the number of files downloaded matches the number expected.

Attribute | Description | Required
count | number of downloaded files expected. | Yes
enabled | Enabled flag | No -default "true"

Example:

        <assertdownloaded count="4" />

### Examples

        <!--
        versions.properties says
        xdoclet.version=2.0
        commons-logging.version=1.0.3
        commons-collections.version=3.1
        -->
        <property file="versions.properties" />

        <libraries destDir="${lib.dir}" pathid="xdoclet.lib" >
          <mavenrepository />
          <library project="xdoclet"
            version="${xdoclet.version}" />
          <library project="commons-logging"
            version="${commons-logging.version}" />
          <library project="commons-collections"
            version="${commons-collections.version}" />
        </libraries>

Load in versions from a file, then download the relevant archives. No update schedule is defined, but a path is created for insertion into a classpath. This property file driven dependency model is what we recommend over hard coding versions in a build file.

       <libraries destDir="build/lib" offline="${offline}" flatten="true">
          <mavenrepository url="${private.server}"/>
          <library project="doomed" archive="dead-code"
            suffix=".war"
            destinationName="product.war"
            version="LATEST" />
          <scheduledupdate markerfile="build/lib/marker.properties"
            hours="11" />
        </libraries>

Download doomed/dead-code.LATEST.war from a private repository, save it to build/lib/product.war with an update schedule of every eleven hours.

Copyright © 2005 The Apache Software Foundation. All rights Reserved.