Ant Specification

Version 0.5 (2000/04/20)

This document specifies the behavior of Ant. At this time, this is a working document with no implementation. It is hoped that this specification will lead to a simplier and more consistent implementation of Ant.

This document is not intended to be used as an end user manual or user guide to Ant. To adequatly explain the concepts herein in a way appropriate to such a use would potentially complicate this document.

Design Goals

The following are the overall design goals of Ant:

• Simplicity
• Understandability
• Extensibility

Simplicity

Ant must be simple to use. Of course, as the definition of simple varies according to the audience of the program. For Ant, since it is a build tool aimed at programmers, the goal is to be simple to use for a competent programmer.

Understandability

Ant must be clearly understandible for a first time as well as a veteran user. This means that a new user should be able to use Ant comfortably the first time and understand how to modify a build file by looking at it. And it should not require much experience with Ant to understand how it works and how to configure it for particular situtations.

Extensibility

Ant must be easy to extend. The API used to extend Ant must be easy to use and the way in which these extensions are located and used by the core runtime should be clear.

Conceptual Overview

This is a conceptual overview of the components used by Ant. Full APIs will be defined later.

Project

The base unit of work in Ant is the Project. A Project is defined by an editable text file and is represented by an object of type org.apache.ant.Project at runtime.

A Project is a collection of Properties and Targets.

Properties

Properties are mutable name-value pairs that are scoped to the Project and held in a table. Only one pair is allowed per name. It is anticipated that this data structure would be of type java.util.Properties or a type that has approximatly the same contract.

Properties can be defined in a hierarchical manner. The order of precidence in this hiearchy is:

• Properties defined on the command line or via a GUI tool
• Properties defined in the text file which defines the project.
• Properties defined in a file in the users user.home directory
• Properties defined in the installation directory that can be shared by multiple users.

Note: The current version of Ant allows the System property list to be consulted for a return value if the property list doesn't satisfy the requested property name. As all Java code has access to the system property list via the java.lang.System class, this functionality is considered to be confusing and to be removed.

Note: The current version of Ant allows property substitution to be performed in the project file. This functionality is being removed.

Targets

Targets are ordered collections of Tasks, units of work to be performed if a Target is executed.

Targets can define dependancies on other Targets within the Project. If a Target is deemed to be executed, either directly on the command line, or via a dependancy from some other Target, then all of its dependencies must first be executed. Circular depenancies are resolved by examination of the dependancy stack when a Target is evaluated. If a dependancy is already on the stack of targets to be executed, then the dependancy is considered to have been satisfied.

After all dependancies of a Target have been satisfied, all of the Tasks contained by the target are configured and executed in sequential order.

Tasks

A Task is a unit of work. When a Task is to be executed, an instance of the class that defines the behavior of the particular task specified is instantiated and then configured. This class implements the org.apache.ant.Task interface. It is then executed so that it may be able to perform its function. It is important to note that this configuration occurs just before execution of the task, and after execution of any previous tasks, so that configuration information that was modified by any other Task can be properly set.

When a Task is executed, it is provided access to the object representing the Project it is running in allowing it to examine the Property list of the project and access to various methods needed to operate.

Task Jar Layout

Tasks are defined within Java Archive files. The name of the JAR determines the name under which the task is known by in the system. For example, if a Task JAR is named mvdir.jar, the task is known to the system as "mvdir".

Question: Should we say that tasks belong in a JAR file with the .tsk extension?

The class within the Jar file that implements the org.apache.ant.Task interface is specified by a manifest attribute named Ant-Task-Class in the Jar manifest. An example manifest would look like:

    Manifest-Version: 1.0
    Ant-Task-Class: org.apache.ant.task.javac.JavacTask

When the task is used by Ant, a class loader is created that reads classes from the JAR file. This ensures that there is no chance of namespace collision in the classes of various task JAR files.

Installation

When Ant is installed on a user system, it installs a directory structure with the following form:

<installdir>/ant      (unix shell script)
            /ant.bat
            /ant.jar
            /ant.properties
            /tasks/[task jar files]
            /docs/[documentation]
            /README

Note: Current Jakarta practice is to name the Unix shell script with a .sh extension. This goes against Unix conventions and is unecessary. Testing has shown that the leaving the extension off on Unix will not interfere with the working of the Windows batch file.

Note: The ant.jar file has been moved from the lib/ directory and placed alongside the shell startup scripts (which have also been moved out of the bin/ directory). This is because on windows platforms, the .jar file is an executable file of sorts.

Ant Properties

The ant.properties file contains a list of all the properties that should be set by default when ant is run. In addition there are a few special properties that are used directly by ant. An example of these properties in use is:

    system.taskdir=tasks/
    user.taskdir=anttasks/

The system.taskdir property sets where the system looks for Java ARchive files containing tasks. If this property defines a relative path, then the path is taken as relative from the installation directory.

The user.taskdir property defines where users can locate Java Archive files containing tasks. If this property defines a realtive path, then the path is taken as relative from the users home directory (as defined by the user.home system property). Task JAR files in this directory take precendence of those in the system directory.

Note: It has been suggested to add a properties file hook to the command line to roll in props. Pending investigation.

User Preferences

In addition to the Ant installation directory, an ant.properties file can be located in the user's home directory (as found by the system property user.home) which can define user preferences such as the location of a user tasks directory. Properties defined in this file take precidence over those set in the installation's ant.properties file. Such a file could look like:

    user.taskdir=anttasks/
    javac.debug=off

Properties starting with "system." in the user's ant.properties file are not allowed and must cause a warning to be thrown.

Project Configuration

Ant's Project text file is structured using XML and reflects the structure of the various components described in the Conceptual Overview.

A sample Project file:

<project name="projectname" defaulttarget="main" taskdir="tasks/">
  <property name="javac.debug" value="on"/>
  <target name="main">
    <taskimpl ...>
       ...
    </taskimpl>
  </target>
</project>

The Project Element

The project element has the following required attributes:

• defaulttarget defining the default target to be executed if no other target is specified when Ant is run

It also has the following optional allowed attributes:

• name defining a name for this project
• taskdir defining a directory in which project specific tasks can be located. Tasks in this directory take precedence over those in the either the user taskdir or the installation taskdir.

The following elements are allowed as children of the project element:

• property defining a property scoped to the project
• target defining a target

The Property Element

asdf

The Target Element

asfd

Configuration of Tasks

The Task section of the configuration file is structured as such:

  <[taskname] [attname=value] [attname=value]...]>
    [<[elementname] [attname=value] ...> ... </[elementname]>]
  </[taskname]>

The taskname is used to find the class of the Task. Once the class has been located and an instance of it created, all of the attributes of the Task are reflected into the task instance using bean patterns. For example, if a Task contains an attribute named "directory", the method named setDirectory would be called with the attribute value cast to the appropriate type desired by the method. (What to do if the type isn't a file or a simple type, look for the class and see if it has a setString method?)

Text blocks contained by the element are added to task using an addText method. Place an example...

For each element contained in the Task definition, an addElementname method is found on the task. The parameter type of the method defines an object that will be loaded and instantiated. The attributes of the element are reflected into the object using bean methods. Any text is set using the addText method. Any elements are recursed in the same fashion.

Search order of tasks.... project/user/system

Command Line

The command line utility provided with Ant must support the following allowable syntax:

ant projectfile [prop=value [prop=value...]] [target]

Internally, the command line shell scripts should call the org.apache.ant.Main class with the following arguments:

java -Dant.home=installdir org.apache.ant.Main $*

or its equivalent on the host platform. Note that the ant installation directory is a System property. The above syntax results in ant.home being placed in the System property list.

Note: On unix, finding the directory of the script that was launched is relatively easy. However on Windows, I'm not sure the best way of handling this.

File Naming Conventions

File naming in a cross platform tool is tricky. For maximum portability and understandiblity it is recommended that project files use the following conventions:

• The '/' character is used as a directory seperator
• The ':' character is used as a path seperator
• Only relative paths are used

However, to allow for maximum flexibility and to allow project authors to use conventions that make sense on their native platform, Ant allows for a representation of file names which has the following rules:

• Directories are seperated by the forward slash ('/') or backwards slash ('\') character.
• File names starting with either of the above directory seperators are considered to be absolute paths.
• On systems that support multiple file roots (e.g. Windows), a file name that starts with a single alphabetical character followed by a colon (':') followed by a directory seperator defines an absolute path where the letter corresponds with a directory root.
• File names starting with any other character are considered to be relative paths. In project files, all relative paths are resolved relative to the directory in which the project file is located.

Absolute paths are not recommended for build files as they reduce the ability to share a project between u sers or machines.

In situtations where a set of filenames need to be specified, such as defining a classpath, both the colon (':') andsemicolon (';') are allowable characters to seperate each filename. The only case that has to be disambiguated is if a user specifies paths that contain windows style absolute paths. In this case, the colon is not treated as a path seperator if the following rules are met:

• The character two places before the colon is either of the allowable path seperators (':' or ';') or if the colon is the second character of the string.
• The character immediately before the colon is a alphabetic character in the range a-z or A-Z.
• The character immediately after the colon is either of the allowable directory seperators ('/' or '\').

Scripting Model

Sam, I'm leaving this to you.

Runtime Requirements

The following requirements are system requirements that Ant should have in order to run correctly. We should not bundle in any of these into the distribution of ant.

• JDK 1.1 or greater
• A JAXP compliant parser on the classpath

Note: When running on JDK 1.2 or greater, the tools.jar isn't on the classpath by default. There's a few different ways we can take care of this. One is to put it on the classpath in the execute script (I don't like this one). Another is to find the location of tools.jar at runtime and put it on the classpath of class loaders that load in task.jars so that, at least in the scope of the Tasks, the relevant classes are there.