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295 lines
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295 lines
16 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN" "strict.dtd">
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<HTML>
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<HEAD>
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<TITLE>Ant Specification, version 0.5</TITLE>
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</HEAD>
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<BODY>
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<H1>Ant Specification</H1>
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<P>Version 0.5 (2000/04/20)</P>
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<P>This document specifies the behavior of Ant. At this time, this is a
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working document with no implementation. It is hoped that this specification
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will lead to a simplier and more consistent implementation of Ant.</P>
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<P>This document is not intended to be used as an end user manual or user
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guide to Ant. To adequatly explain the concepts herein in a way appropriate to
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such a use would potentially complicate this document.</P>
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<H2>Design Goals</H2>
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<P>The following are the overall design goals of Ant:</P>
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<UL>
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<LI>Simplicity</LI>
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<LI>Understandability</LI>
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<LI>Extensibility</LI>
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</UL>
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<H3>Simplicity</H3>
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<P>Ant must be simple to use. Of course, as the definition of simple varies
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according to the audience of the program. For Ant, since it is a build tool
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aimed at programmers, the goal is to be simple to use for a competent
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programmer.</P>
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<H3>Understandability</H3>
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<P>Ant must be clearly understandible for a first time as well as a veteran
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user. This means that a new user should be able to use Ant comfortably the
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first time and understand how to modify a build file by looking at it. And it
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should not require much experience with Ant to understand how it works and how
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to configure it for particular situtations.</P>
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<H3>Extensibility</H3>
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<P>Ant must be easy to extend. The API used to extend Ant must be easy to
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use and the way in which these extensions are located and used by the core
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runtime should be clear.</P>
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<H2>Conceptual Overview</H2>
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<P>This is a conceptual overview of the components used by Ant. Full APIs
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will be defined later.</P>
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<H3>Project</H3>
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<P>The base unit of work in Ant is the <STRONG>Project</STRONG>. A Project
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is defined by an editable text file and is represented by an object of type
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<CODE>org.apache.ant.Project</CODE> at runtime.</P>
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<P>A Project is a collection of <STRONG>Properties</STRONG> and
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<STRONG>Targets</STRONG>.</P>
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<H3>Properties</H3>
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<P>Properties are mutable name-value pairs that are scoped to the Project
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and held in a table. Only one pair is allowed per name. It is anticipated that
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this data structure would be of type <CODE>java.util.Properties</CODE> or a type that has approximatly
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the same contract.</P>
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<P>Properties can be defined in a hierarchical manner. The order of
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precidence in this hiearchy is:</P>
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<UL>
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<LI>Properties defined on the command line or via a GUI tool</LI>
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<LI>Properties defined in the text file which defines the project.</LI>
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<LI>Properties defined in a file in the users <CODE>user.home</CODE> directory</LI>
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<LI>Properties defined in the installation directory that can be shared
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by multiple users.</LI>
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</UL>
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<P>Note: The current version of Ant allows the System property list to be
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consulted for a return value if the property list doesn't satisfy the requested
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property name. As all Java code has access to the system property list via the
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<CODE>java.lang.System</CODE> class, this functionality is considered to be confusing and to be
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removed.</P>
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<P>Note: The current version of Ant allows property substitution to be
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performed in the project file. This functionality is being removed.</P>
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<H3>Targets</H3>
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<P>Targets are ordered collections of <STRONG>Tasks</STRONG>, units of work
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to be performed if a Target is executed. </P>
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<P>Targets can define dependancies on other Targets within the Project. If
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a Target is deemed to be executed, either directly on the command line, or via
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a dependancy from some other Target, then all of its dependencies must first be
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executed. Circular depenancies are resolved by examination of the dependancy
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stack when a Target is evaluated. If a dependancy is already on the stack of
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targets to be executed, then the dependancy is considered to have been
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satisfied.</P>
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<P>After all dependancies of a Target have been satisfied, all of the Tasks
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contained by the target are configured and executed in sequential order. </P>
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<H3>Tasks</H3>
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<P>A Task is a unit of work. When a Task is to be executed, an instance of
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the class that defines the behavior of the particular task specified is
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instantiated and then configured. This class implements the <CODE>org.apache.ant.Task</CODE> interface.
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It is then executed so that it may be able to perform its function. It is
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important to note that this configuration occurs just before execution of the
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task, and after execution of any previous tasks, so that configuration
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information that was modified by any other Task can be properly set.</P>
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<P>When a Task is executed, it is provided access to the object
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representing the Project it is running in allowing it to examine the Property
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list of the project and access to various methods needed to operate.</P>
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<H2>Task Jar Layout</H2>
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<P>Tasks are defined within Java Archive files. The name of the JAR
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determines the name under which the task is known by in the system. For
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example, if a Task JAR is named mvdir.jar, the task is known to the system as
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<CODE>"mvdir"</CODE>.</P>
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<P><EM>Question: Should we say that tasks belong in a JAR file with the
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.tsk extension?</EM></P>
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<P>The class within the Jar file that implements the <CODE>org.apache.ant.Task</CODE> interface is
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specified by a manifest attribute named <CODE>Ant-Task-Class</CODE> in the Jar manifest. An example
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manifest would look like:</P>
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<PRE> Manifest-Version: 1.0
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Ant-Task-Class: org.apache.ant.task.javac.JavacTask</PRE>
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<P>When the task is used by Ant, a class loader is created that reads
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classes from the JAR file. This ensures that there is no chance of namespace
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collision in the classes of various task JAR files.</P>
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<H2>Installation</H2>
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<P>When Ant is installed on a user system, it installs a directory
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structure with the following form:</P>
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<PRE><installdir>/ant (unix shell script)
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/ant.bat
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/ant.jar
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/ant.properties
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/tasks/[task jar files]
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/docs/[documentation]
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/README</PRE>
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<P>Note: Current Jakarta practice is to name the Unix shell script with a
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.sh extension. This goes against Unix conventions and is unecessary. Testing
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has shown that the leaving the extension off on Unix will not interfere with
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the working of the Windows batch file.</P>
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<P>Note: The ant.jar file has been moved from the lib/ directory and placed
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alongside the shell startup scripts (which have also been moved out of the bin/
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directory). This is because on windows platforms, the .jar file is an
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executable file of sorts.</P>
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<H3>Ant Properties</H3>
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<P>The <CODE>ant.properties</CODE> file contains a list of all the properties that should be
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set by default when ant is run. In addition there are a few special properties
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that are used directly by ant. An example of these properties in use is:</P>
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<PRE> system.taskdir=tasks/
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user.taskdir=anttasks/</PRE>
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<P>The <CODE>system.taskdir</CODE> property sets where the system looks for Java ARchive files
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containing tasks. If this property defines a relative path, then the path is
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taken as relative from the installation directory.</P>
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<P>The <CODE>user.taskdir</CODE> property defines where users can locate Java Archive files
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containing tasks. If this property defines a realtive path, then the path is
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taken as relative from the users home directory (as defined by the <CODE>user.home</CODE>
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system property). Task JAR files in this directory take precendence of those in
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the system directory.</P>
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<P>Note: <EM>It has been suggested to add a properties file hook to the
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command line to roll in props. Pending investigation.</EM></P>
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<H3>User Preferences</H3>
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<P>In addition to the Ant installation directory, an <CODE>ant.properties</CODE> file can be
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located in the user's home directory (as found by the system property <CODE>user.home</CODE>)
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which can define user preferences such as the location of a user tasks
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directory. Properties defined in this file take precidence over those set in
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the installation's <CODE>ant.properties</CODE> file. Such a file could look like:</P>
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<PRE> user.taskdir=anttasks/
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javac.debug=off</PRE>
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<P>Properties starting with <CODE>"system."</CODE> in the user's <CODE>ant.properties</CODE> file are not
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allowed and must cause a warning to be thrown.</P>
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<H2>Project Configuration</H2>
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<P>Ant's Project text file is structured using XML and reflects the
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structure of the various components described in the Conceptual Overview.</P>
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<P>A sample Project file:</P>
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<PRE><project name="projectname" defaulttarget="main" taskdir="tasks/">
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<property name="javac.debug" value="on"/>
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<target name="main">
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<taskimpl ...>
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...
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</taskimpl>
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</target>
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</project></PRE>
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<H3>The Project Element</H3>
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<P>The <CODE>project</CODE> element has the following required attributes:</P>
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<UL>
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<LI><CODE><STRONG>defaulttarget</STRONG></CODE> defining the default target to be executed if no other target
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is specified when Ant is run</LI>
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</UL>
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<P>It also has the following optional allowed attributes:</P>
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<UL>
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<LI><CODE><CODE><STRONG>name</STRONG></CODE></CODE> defining a name for this project</LI>
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<LI><CODE><STRONG>taskdir</STRONG></CODE> defining a directory in which project specific tasks can be
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located. Tasks in this directory take precedence over those in the either the
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user taskdir or the installation taskdir.</LI>
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</UL>
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<P>The following elements are allowed as children of the project
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element:</P>
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<UL>
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<LI><CODE><STRONG>property</STRONG></CODE> defining a property scoped to the project</LI>
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<LI><CODE><STRONG>target</STRONG></CODE> defining a target</LI>
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</UL>
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<H3>The Property Element</H3>
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<P>asdf</P>
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<H3>The Target Element</H3>
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<P>asfd</P>
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<H2>Configuration of Tasks</H2>
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<P>The Task section of the configuration file is structured as such:</P>
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<PRE> <[taskname] [attname=value] [attname=value]...]>
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[<[elementname] [attname=value] ...> ... </[elementname]>]
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</[taskname]></PRE>
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<P>The taskname is used to find the class of the Task. Once the class has
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been located and an instance of it created, all of the attributes of the Task
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are reflected into the task instance using bean patterns. For example, if a
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Task contains an attribute named "directory", the method named
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setDirectory would be called with the attribute value cast to the appropriate
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type desired by the method. <EM>(What to do if the type isn't a file or a
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simple type, look for the class and see if it has a setString method?)</EM></P>
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<P>Text blocks contained by the element are added to task using an addText
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method. <EM>Place an example...</EM></P>
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<P>For each element contained in the Task definition, an addElementname
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method is found on the task. The parameter type of the method defines an object
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that will be loaded and instantiated. The attributes of the element are
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reflected into the object using bean methods. Any text is set using the addText
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method. Any elements are recursed in the same fashion.</P>
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<P>Search order of tasks.... project/user/system</P>
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<H2>Command Line</H2>
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<P>The command line utility provided with Ant must support the following
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allowable syntax:</P>
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<P><CODE>ant projectfile [prop=value [prop=value...]] [target]</CODE></P>
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<P>Internally, the command line shell scripts should call the <CODE>org.apache.ant.Main</CODE> class
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with the following arguments:</P>
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<PRE>java -Dant.home=installdir org.apache.ant.Main $*</PRE>
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<P>or its equivalent on the host platform. Note that the ant installation
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directory is a System property. The above syntax results in ant.home being
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placed in the System property list.</P>
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<P>Note: <EM>On unix, finding the directory of the script that was launched
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is relatively easy. However on Windows, I'm not sure the best way of handling
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this.</EM></P>
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<H2>File Naming Conventions</H2>
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<P>File naming in a cross platform tool is tricky. For maximum portability
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and understandiblity it is recommended that project files use the following
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conventions:</P>
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<UL>
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<LI>The '/' character is used as a directory seperator</LI>
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<LI>The ':' character is used as a path seperator</LI>
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<LI>Only relative paths are used</LI>
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</UL>
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<P>However, to allow for maximum flexibility and to allow project authors
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to use conventions that make sense on their native platform, Ant allows for a
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representation of file names which has the following rules:</P>
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<UL>
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<LI>Directories are seperated by the forward slash ('/') or backwards
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slash ('\') character.</LI>
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<LI>File names starting with either of the above directory seperators are
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considered to be absolute paths.</LI>
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<LI>On systems that support multiple file roots (e.g. Windows), a file
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name that starts with a single alphabetical character followed by a colon (':')
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followed by a directory seperator defines an absolute path where the letter
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corresponds with a directory root.</LI>
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<LI>File names starting with any other character are considered to be
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relative paths. In project files, all relative paths are resolved relative to
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the directory in which the project file is located.</LI>
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</UL>
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<P>Absolute paths are not recommended for build files as they reduce the
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ability to share a project between u sers or machines.</P>
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<P>In situtations where a set of filenames need to be specified, such as
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defining a classpath, both the colon (':') andsemicolon (';') are allowable
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characters to seperate each filename. The only case that has to be
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disambiguated is if a user specifies paths that contain windows style absolute
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paths. In this case, the colon is not treated as a path seperator if the
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following rules are met:</P>
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<UL>
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<LI>The character two places before the colon is either of the allowable
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path seperators (':' or ';') or if the colon is the second character of the
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string.</LI>
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<LI>The character immediately before the colon is a alphabetic character
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in the range a-z or A-Z.</LI>
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<LI>The character immediately after the colon is either of the allowable
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directory seperators ('/' or '\').</LI>
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</UL>
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<H2>Scripting Model</H2>
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<P>Sam, I'm leaving this to you. </P>
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<H2>Runtime Requirements</H2>
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<P>The following requirements are system requirements that Ant should have
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in order to run correctly. We should not bundle in any of these into the
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distribution of ant.</P>
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<UL>
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<LI>JDK 1.1 or greater</LI>
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<LI>A JAXP compliant parser on the classpath</LI>
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</UL>
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<P>Note: <EM>When running on JDK 1.2 or greater, the tools.jar isn't on the
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classpath by default. There's a few different ways we can take care of this.
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One is to put it on the classpath in the execute script (I don't like this
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one). Another is to find the location of tools.jar at runtime and put it on the
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classpath of class loaders that load in task.jars so that, at least in the
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scope of the Tasks, the relevant classes are there. </EM></P>
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<P></P>
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<P></P> </BODY>
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</HTML>
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