You are viewing a plain text version of this content. The canonical link for it is here.
Posted to dev@ant.apache.org by do...@apache.org on 2001/01/16 14:45:42 UTC
cvs commit: jakarta-ant/docs/ant2 original-specification.html
donaldp 01/01/16 05:45:42
Added: docs/ant2 original-specification.html
Log:
moved original specification to here
Revision Changes Path
1.1 jakarta-ant/docs/ant2/original-specification.html
Index: original-specification.html
===================================================================
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN" "strict.dtd">
<HTML>
<HEAD>
<TITLE>Ant Specification, version 0.5</TITLE>
</HEAD>
<BODY>
<H1>Ant Specification</H1>
<P>Version 0.5 (2000/04/20)</P>
<P>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.</P>
<P>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.</P>
<H2>Design Goals</H2>
<P>The following are the overall design goals of Ant:</P>
<UL>
<LI>Simplicity</LI>
<LI>Understandability</LI>
<LI>Extensibility</LI>
</UL>
<H3>Simplicity</H3>
<P>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.</P>
<H3>Understandability</H3>
<P>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.</P>
<H3>Extensibility</H3>
<P>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.</P>
<H2>Conceptual Overview</H2>
<P>This is a conceptual overview of the components used by Ant. Full APIs
will be defined later.</P>
<H3>Project</H3>
<P>The base unit of work in Ant is the <STRONG>Project</STRONG>. A Project
is defined by an editable text file and is represented by an object of type
<CODE>org.apache.ant.Project</CODE> at runtime.</P>
<P>A Project is a collection of <STRONG>Properties</STRONG> and
<STRONG>Targets</STRONG>.</P>
<H3>Properties</H3>
<P>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 <CODE>java.util.Properties</CODE> or a type that has approximatly
the same contract.</P>
<P>Properties can be defined in a hierarchical manner. The order of
precidence in this hiearchy is:</P>
<UL>
<LI>Properties defined on the command line or via a GUI tool</LI>
<LI>Properties defined in the text file which defines the project.</LI>
<LI>Properties defined in a file in the users <CODE>user.home</CODE> directory</LI>
<LI>Properties defined in the installation directory that can be shared
by multiple users.</LI>
</UL>
<P>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
<CODE>java.lang.System</CODE> class, this functionality is considered to be confusing and to be
removed.</P>
<P>Note: The current version of Ant allows property substitution to be
performed in the project file. This functionality is being removed.</P>
<H3>Targets</H3>
<P>Targets are ordered collections of <STRONG>Tasks</STRONG>, units of work
to be performed if a Target is executed. </P>
<P>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.</P>
<P>After all dependancies of a Target have been satisfied, all of the Tasks
contained by the target are configured and executed in sequential order. </P>
<H3>Tasks</H3>
<P>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 <CODE>org.apache.ant.Task</CODE> 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.</P>
<P>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.</P>
<H2>Task Jar Layout</H2>
<P>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
<CODE>"mvdir"</CODE>.</P>
<P><EM>Question: Should we say that tasks belong in a JAR file with the
.tsk extension?</EM></P>
<P>The class within the Jar file that implements the <CODE>org.apache.ant.Task</CODE> interface is
specified by a manifest attribute named <CODE>Ant-Task-Class</CODE> in the Jar manifest. An example
manifest would look like:</P>
<PRE> Manifest-Version: 1.0
Ant-Task-Class: org.apache.ant.task.javac.JavacTask</PRE>
<P>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.</P>
<H2>Installation</H2>
<P>When Ant is installed on a user system, it installs a directory
structure with the following form:</P>
<PRE><installdir>/ant (unix shell script)
/ant.bat
/ant.jar
/ant.properties
/tasks/[task jar files]
/docs/[documentation]
/README</PRE>
<P>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.</P>
<P>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.</P>
<H3>Ant Properties</H3>
<P>The <CODE>ant.properties</CODE> 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:</P>
<PRE> system.taskdir=tasks/
user.taskdir=anttasks/</PRE>
<P>The <CODE>system.taskdir</CODE> 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.</P>
<P>The <CODE>user.taskdir</CODE> 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 <CODE>user.home</CODE>
system property). Task JAR files in this directory take precendence of those in
the system directory.</P>
<P>Note: <EM>It has been suggested to add a properties file hook to the
command line to roll in props. Pending investigation.</EM></P>
<H3>User Preferences</H3>
<P>In addition to the Ant installation directory, an <CODE>ant.properties</CODE> file can be
located in the user's home directory (as found by the system property <CODE>user.home</CODE>)
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 <CODE>ant.properties</CODE> file. Such a file could look like:</P>
<PRE> user.taskdir=anttasks/
javac.debug=off</PRE>
<P>Properties starting with <CODE>"system."</CODE> in the user's <CODE>ant.properties</CODE> file are not
allowed and must cause a warning to be thrown.</P>
<H2>Project Configuration</H2>
<P>Ant's Project text file is structured using XML and reflects the
structure of the various components described in the Conceptual Overview.</P>
<P>A sample Project file:</P>
<PRE><project name="projectname" defaulttarget="main" taskdir="tasks/">
<property name="javac.debug" value="on"/>
<target name="main">
<taskimpl ...>
...
</taskimpl>
</target>
</project></PRE>
<H3>The Project Element</H3>
<P>The <CODE>project</CODE> element has the following required attributes:</P>
<UL>
<LI><CODE><STRONG>defaulttarget</STRONG></CODE> defining the default target to be executed if no other target
is specified when Ant is run</LI>
</UL>
<P>It also has the following optional allowed attributes:</P>
<UL>
<LI><CODE><CODE><STRONG>name</STRONG></CODE></CODE> defining a name for this project</LI>
<LI><CODE><STRONG>taskdir</STRONG></CODE> 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.</LI>
</UL>
<P>The following elements are allowed as children of the project
element:</P>
<UL>
<LI><CODE><STRONG>property</STRONG></CODE> defining a property scoped to the project</LI>
<LI><CODE><STRONG>target</STRONG></CODE> defining a target</LI>
</UL>
<H3>The Property Element</H3>
<P>asdf</P>
<H3>The Target Element</H3>
<P>asfd</P>
<H2>Configuration of Tasks</H2>
<P>The Task section of the configuration file is structured as such:</P>
<PRE> <[taskname] [attname=value] [attname=value]...]>
[<[elementname] [attname=value] ...> ... </[elementname]>]
</[taskname]></PRE>
<P>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. <EM>(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?)</EM></P>
<P>Text blocks contained by the element are added to task using an addText
method. <EM>Place an example...</EM></P>
<P>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.</P>
<P>Search order of tasks.... project/user/system</P>
<H2>Command Line</H2>
<P>The command line utility provided with Ant must support the following
allowable syntax:</P>
<P><CODE>ant projectfile [prop=value [prop=value...]] [target]</CODE></P>
<P>Internally, the command line shell scripts should call the <CODE>org.apache.ant.Main</CODE> class
with the following arguments:</P>
<PRE>java -Dant.home=installdir org.apache.ant.Main $*</PRE>
<P>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.</P>
<P>Note: <EM>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.</EM></P>
<H2>File Naming Conventions</H2>
<P>File naming in a cross platform tool is tricky. For maximum portability
and understandiblity it is recommended that project files use the following
conventions:</P>
<UL>
<LI>The '/' character is used as a directory seperator</LI>
<LI>The ':' character is used as a path seperator</LI>
<LI>Only relative paths are used</LI>
</UL>
<P>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:</P>
<UL>
<LI>Directories are seperated by the forward slash ('/') or backwards
slash ('\') character.</LI>
<LI>File names starting with either of the above directory seperators are
considered to be absolute paths.</LI>
<LI>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.</LI>
<LI>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.</LI>
</UL>
<P>Absolute paths are not recommended for build files as they reduce the
ability to share a project between u sers or machines.</P>
<P>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:</P>
<UL>
<LI>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.</LI>
<LI>The character immediately before the colon is a alphabetic character
in the range a-z or A-Z.</LI>
<LI>The character immediately after the colon is either of the allowable
directory seperators ('/' or '\').</LI>
</UL>
<H2>Scripting Model</H2>
<P>Sam, I'm leaving this to you. </P>
<H2>Runtime Requirements</H2>
<P>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.</P>
<UL>
<LI>JDK 1.1 or greater</LI>
<LI>A JAXP compliant parser on the classpath</LI>
</UL>
<P>Note: <EM>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. </EM></P>
<P></P>
<P></P> </BODY>
</HTML>