Import Task

## Import

### Description

Imports another build file into the current project.

On execution it will select the proper ProjectHelper to parse the imported file, using the same algorithm as the one executed at startup. The selected ProjectHelper instance will then be responsible to actually parse the imported file.

Note as seen above, this task heavily relies on the ProjectHelper implementation and doesn't really perform any work of its own. If you have configured Apache Ant to use a ProjectHelper other than Ant's default, this task may or may not work.

In the common use case where only Ant's default project helper is used, it basically works like the Entity Includes as explained in the Ant FAQ, as if the imported file was contained in the importing file, minus the top `<project>` tag.

The `import` task may only be used as a top-level task. This means that it may not be used in a target.

There are two further functional aspects that pertain to this task and that are not possible with entity includes:

- target overriding
- special properties

#### Target overriding

If a target in the main file is also present in at least one of the imported files, the one from the main file takes precedence.

So if I import for example a `docsbuild.xml` file containing a project named builddocs that contains a docs target, I can define a docs target in my main buildfile and that is the one that will be called. This makes it easy to keep the same target name, so that the overriding target is still called by any other targets—in either the main or imported buildfile(s)—for which it is a dependency, with a different implementation. The target from `docsbuild.xml` is made available by the name builddocs.docs. This enables the new implementation to call the old target, thus enhancing it with tasks called before or after it.

If you use the as attribute of the task, its value will be used to prefix the overridden target's name instead of the name attribute of the `project` tag.

#### Special properties

Imported files are treated as they are present in the main buildfile. This makes it easy to understand, but it makes it impossible for them to reference files and resources relative to their path. Because of this, for every imported file, Ant adds a property that contains the path to the imported buildfile. With this path, the imported buildfile can keep resources and be able to reference them relative to its position.

So if I import for example a `docsbuild.xml` file named builddocs, I can get its path as `ant.file.builddocs`, similarly to the `ant.file` property of the main buildfile.

Note that builddocs is not the filename, but the name attribute present in the imported `project` tag.

If the imported file does not have a name attribute, the `ant.file.projectname` property will not be set.

Since Ant 1.8.0, the task can also import resources from URLs or classpath resources (which are URLs, really). If you need to know whether the current build file's source has been a file or an URL you can consult the property `ant.file.type.projectname` (using the same example as above `ant.file.type.builddocs`) which either have the value file or url.

#### Resolving files against the imported file

Suppose your main build file called `importing.xml` imports a build file `imported.xml`, located anywhere on the file system, and `imported.xml` reads a set of properties from `imported.properties`:

    <!-- importing.xml -->
    <project name="importing" basedir="." default="...">
      <import file="${path_to_imported}/imported.xml"/>
    </project>

    <!-- imported.xml -->
    <project name="imported" basedir="." default="...">
      <property file="imported.properties"/>
    </project>

This snippet however will resolve `imported.properties` against the basedir of `importing.xml`, because the basedir of `imported.xml` is ignored by Ant. The right way to use `imported.properties` is:

    <!-- imported.xml -->
    <project name="imported" basedir="." default="...">
      <dirname property="imported.basedir" file="${ant.file.imported}"/>
      <property file="${imported.basedir}/imported.properties"/>
    </project>

As explained above `ant.file.imported` stores the path of the build script, that defines the project called imported, (in short it stores the path to `imported.xml`) and `<dirname>` takes its directory. This technique also allows `imported.xml` to be used as a standalone file (without being imported in other project).

The above description only works for imported files that actually are imported from files and not from URLs. For files imported from URLs using resources relative to the imported file requires you to use tasks that can work on non-file resources in the first place. To create a relative resource you'd use something like:

    <loadproperties>
      <url baseUrl="${ant.file.imported}"
           relativePath="imported.properties"/>
    </loadproperties>

### Parameters

Attribute | Description | Required
--- | --- | ---
file | The file to import. If this is a relative file name, the file name will be resolved relative to the importing file. Note: this is unlike most other Ant file attributes, where relative files are resolved relative to basedir. | Yes or a nested resource collection
optional | If true, do not stop the build if the file does not exist. | No; default is false
as | Specifies the prefix prepended to the target names. | No; defaults to name attribute of the `project` tag of the imported file
prefixSeparator | Specifies the separator to be used between the prefix and the target name. | No; defaults to .

### Parameters specified as nested elements

#### any resource or resource collection

Since Ant 1.8.0

The specified resources will be imported.

### Examples

    <import file="../common-targets.xml"/>

Imports targets from the `common-targets.xml` file that is in a parent directory.

    <import file="${deploy-platform}.xml"/>

Imports the project defined by the property `deploy-platform`

    <import>
      <javaresource name="common/targets.xml">
        <classpath location="common.jar"/>
      </javaresource>
    </import>

Imports targets from the `targets.xml` file that is inside the directory `common` inside the jar file `common.jar`.

### How is <import> different from <include>?

The short version: Use `import` if you intend to override a target, otherwise use `include`.

When `import` is used, the imported targets are available by up to two names: their "normal" name without any prefix and potentially with a prefixed name (the value of the as attribute or the imported project's name attribute, if any).

When `include` is used, the included targets are only available in the prefixed form.

When `import` is used, the imported target's depends attribute remains unchanged, i.e. it uses "normal" names and allows you to override targets in the dependency list.

When `include` is used, the included targets cannot be overridden and their depends attributes are rewritten so that prefixed names are used. This allows writers of the included file to control which target is invoked as part of the dependencies.

It is possible to `include` the same file more than once by using different prefixes; it is not possible to `import` the same file more than once.

#### Examples

`nested.xml` shall be:

    <project>
      <target name="setUp">
        <property name="prop" value="in nested"/>
      </target>

      <target name="echo" depends="setUp">
        <echo>prop has the value ${prop}</echo>
      </target>
    </project>

When using `import` like in

    <project default="test">
      <target name="setUp">
        <property name="prop" value="in importing"/>
      </target>

      <import file="nested.xml" as="nested"/>

      <target name="test" depends="nested.echo"/>
    </project>

Running the build file will emit:

    setUp:

    nested.echo:
         [echo] prop has the value in importing

    test:

When using `include` like in

    <project default="test">
      <target name="setUp">
        <property name="prop" value="in importing"/>
      </target>

      <include file="nested.xml" as="nested"/>

      <target name="test" depends="nested.echo"/>
    </project>

Running the target build file will emit:

    nested.setUp:

    nested.echo:
         [echo] prop has the value in nested

    test:

and there won't be any target named echo on the including build file.