leosutic 2004/03/19 17:38:43
Modified: attributes/site/xdocs tutorial.xml navigation.xml
Added: attributes/site/xdocs reference.xml declaring.xml
compiler.xml
Removed: attributes/site/xdocs walkthrough.xml
Log:
Made the walkthrough a reference. Also added documentation for
the compiler.
Revision Changes Path
1.4 +2 -3 jakarta-commons-sandbox/attributes/site/xdocs/tutorial.xml
Index: tutorial.xml
===================================================================
RCS file: /home/cvs/jakarta-commons-sandbox/attributes/site/xdocs/tutorial.xml,v
retrieving revision 1.3
retrieving revision 1.4
diff -u -r1.3 -r1.4
--- tutorial.xml 18 Mar 2004 23:16:30 -0000 1.3
+++ tutorial.xml 20 Mar 2004 01:38:43 -0000 1.4
@@ -26,8 +26,7 @@
<body>
<section name="About this Tutorial">
- <p>This tutorial will walk you through Commons Attributes. The tutorial
is split into
- two parts: First, a quick demo of the package, and second, a
walkthrough of all features.</p>
+ <p>This tutorial will walk you through a quick start with Commons
Attributes.</p>
<ul>
<li>
@@ -42,7 +41,7 @@
</li>
<li>
<p>
- <a href="walkthrough.html">Complete Walkthrough of all
Features</a>
+ <a href="reference.html">Reference</a>
</p>
</li>
</ul>
1.5 +5 -1 jakarta-commons-sandbox/attributes/site/xdocs/navigation.xml
Index: navigation.xml
===================================================================
RCS file: /home/cvs/jakarta-commons-sandbox/attributes/site/xdocs/navigation.xml,v
retrieving revision 1.4
retrieving revision 1.5
diff -u -r1.4 -r1.5
--- navigation.xml 4 Mar 2004 00:39:17 -0000 1.4
+++ navigation.xml 20 Mar 2004 01:38:43 -0000 1.5
@@ -31,7 +31,11 @@
<item name="Tutorial" href="/tutorial.html">
<item name="Ant Demo" href="/ant_demo.html"/>
<item name="Maven Demo" href="/maven_demo.html"/>
- <item name="Walkthrough" href="/walkthrough.html"/>
+ </item>
+
+ <item name="Reference" href="/reference.html">
+ <item name="Declaring and Using" href="/declaring.html"/>
+ <item name="Compiling" href="/compiler.html"/>
</item>
</menu>
</body>
1.1 jakarta-commons-sandbox/attributes/site/xdocs/reference.xml
Index: reference.xml
===================================================================
<?xml version="1.0"?>
<!--
=
= Copyright 2003-2004 The Apache Software Foundation
=
= Licensed under the Apache License, Version 2.0 (the "License");
= you may not use this file except in compliance with the License.
= You may obtain a copy of the License at
=
= http://www.apache.org/licenses/LICENSE-2.0
=
= Unless required by applicable law or agreed to in writing, software
= distributed under the License is distributed on an "AS IS" BASIS,
= WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
= See the License for the specific language governing permissions and
= limitations under the License.
=
-->
<document>
<properties>
<author email="[EMAIL PROTECTED]">Leo Sutic</author>
<title>Reference</title>
</properties>
<body>
<section name="Reference">
<p>This reference is split into two parts: The stuff you do to your
source code,
and the stuff you do to your build scripts.</p>
<p><a href="declaring.html">Declaring and Using</a><br/>
This section describes how you add attributes to your source code
and how
you access them.
</p>
<p><a href="compiler.html">Compiling</a><br/>
This section describes the changes and additions you need to do to
your
build scripts if you are not using the Maven plugin.
</p>
</section>
</body>
</document>
1.1 jakarta-commons-sandbox/attributes/site/xdocs/declaring.xml
Index: declaring.xml
===================================================================
<?xml version="1.0"?>
<!--
=
= Copyright 2003-2004 The Apache Software Foundation
=
= Licensed under the Apache License, Version 2.0 (the "License");
= you may not use this file except in compliance with the License.
= You may obtain a copy of the License at
=
= http://www.apache.org/licenses/LICENSE-2.0
=
= Unless required by applicable law or agreed to in writing, software
= distributed under the License is distributed on an "AS IS" BASIS,
= WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
= See the License for the specific language governing permissions and
= limitations under the License.
=
-->
<document>
<properties>
<author email="[EMAIL PROTECTED]">Leo Sutic</author>
<title>Reference - Declaring and Using</title>
</properties>
<body>
<section name="What are Attributes?">
<p>Attributes are value objects that can be added to language elements
such as
classes, methods and fields.</p>
<subsection name="Value Objects">
<p>What is a value object? Simply stated, a value object is an
object that is
read-only, constant and can be replaced with another object of
the same value
without it making any difference. For example, instances of the
class
<code>java.lang.Integer</code> are value objects. You can
replace any instance
of that class with any other instance, provided that they are
equal. An
<code>java.io.Socket</code> is not a value object, as you can't
replace an
instance of a socket with another - it corresponds to a real
resource, in
this case a connection.</p>
<p>You should therefore not allow your attribute classes to be
mutable, and not
use Sockets or similar classes as attributes.</p>
</subsection>
</section>
<section name="How Are They Added?">
<p>Let's look at the way attributes are added to the code. The general
form of the
attribute expression is (optional parts are in [brackets]):</p>
<source><![CDATA[@@[target] ClassName ([constructor args] [named
args])]]></source>
<subsection name="target">
<p>This name indicates what sub-element the attribute is to be
applied to.
Classes and fields have no sub-elements, but methods do. The
sub-elements
of a method are (1) the arguments and (2) the return value. In
order to
apply an element to a method argument, you let the target be
<code>.argument name</code>.
For example:</p>
<source><![CDATA[/**
* @@.arg1 MyAttribute()
*/
public Object myMethod (int arg1) { ... }]]></source>
<p>Will attach MyAttribute to the first argument of the method - not
to
the method itself. The attribute can be retrieved via
<code>Attributes.getParameterAttributes(Method,int)</code>.</p>
<p>Adding an attribute to the return value is done by the reserved
target
name <code>.return</code>:</p>
<source><![CDATA[/**
* @@.return MyAttribute()
*/
public Object myMethod (int arg1) { ... }]]></source>
<p>The attribute can then be retrieved via
<code>Attributes.getReturnAttributes(Method)</code>.</p>
</subsection>
<subsection name="ClassName">
<p>This is the name of the attribute class. You can use a qualified
or
unqualified name here - but if you use the unqualified name one
of
the following must be true:</p>
<ul>
<li>
<p>
The attribute class is in the same package as the class
you are attaching it to. (Standard Java rules for when
you need to import a class.)
</p>
</li>
<li>
<p>
You have an import statement that imports the attribute
class.
</p>
</li>
<li>
<p>
You have listed the package the attribute class is in in
the attributePackages
attribute of the attribute compiler in your build
script. <a href="compiler.html">See
here.</a>
</p>
</li>
</ul>
</subsection>
<subsection name="constructor args">
<p>
This is simply a list of arguments to pass to the constructor
when
instantiating the attribute class. For example, given an
attribute:</p>
<source><![CDATA[class MyAttribute {
private final String name;
public MyAttribute(String name) { this.name = name };
public String getName() { return name; }
}]]></source>
<p>You would specify the name by including it as a constructor
argument:</p>
<source><![CDATA[/**
* @@MyAttribute("this is a name")
*/]]></source>
</subsection>
<subsection name="named arguments">
<p>Commons Attributes provides a simple way of having named
arguments.
This is done by having setter metods in the attribute class.
Adding a
field and two methods to the attribute class above we get:</p>
<source><![CDATA[class MyAttribute {
private final String name;
private boolean optional = false;
public MyAttribute(String name) { this.name = name };
public String getName() { return name; }
public boolean isOptional { return optional; }
public void setOptional (boolean optional) { this.optional = optional; }
}]]></source>
<p>We can now set the <code>optional</code> field by using a named
parameter:</p>
<source><![CDATA[/**
* @@MyAttribute("this is a name", optional=true)
*/]]></source>
<p>The attribute compiler will pass any parameter up to the first
one that is
on the form <code><i>name</i> = <i>expression</i></code> to the
constructor.
For the remaining parameters, it will invoke a method named
<code>setName(expression)</code> on the attribute instance.
So for our example above, the following code will be
generated:</p>
<source><![CDATA[MyAttribute attr = new MyAttribute("this is a
name");
attr.setOptional(true);]]></source>
<p>Named parameters are always optional.</p>
</subsection>
</section>
<section name="How are they Retrieved?">
<p>You retrieve attributes by using the methods in the
org.apache.commons.attributes.Attributes
class. See the <a href="api/index.html">JavaDoc</a> for a
description of methods in this class.</p>
</section>
<section name="How are Attributes Stored?">
<p>
See the <a href="compiler.html">Compiling</a> section of the
reference.
</p>
</section>
<section name="Gotchas and Other Questions">
<subsection name="What happens if I add the same attribute twice?">
<p>Let's define the question via a use case. Suppose you have an
attribute (MyAttribute), and you have a class MyClass:</p>
<source><![CDATA[/**
* @@MyAttribute()
* @@MyAttribute()
*/
public class MyClass {}]]></source>
<p>The question is now, will the collection returned by
Attributes.getAttributes (MyClass.class) have one or
two elements? The answer is that it depends on the way
MyAttribute handles equality. The attributes associated
with a class, method or field always for a Set, meaning that
there are no duplicates. So if MyAttribute is
implemented this way:</p>
<source><![CDATA[public class MyAttribute {}]]></source>
<p>Then you will get two elements, since each instance of
MyAttribute is different from every other instance.
However, if MyAttribute is implemented like this:</p>
<source><![CDATA[public class MyAttribute {
public int hashCode () { return 0; }
public boolean equals (Object o) { return o instanceof MyAttribute; }
}]]></source>
<p>That is, every instance of MyAttribute is equal to any other
instance of the class, then you will only get
one element in the collection.</p>
<p>The above also holds true if the attribute has been inherited.</p>
</subsection>
<subsection name="What are the requirements for an attribute class?">
<p>It must have a public constructor. That's all.</p>
</subsection>
<subsection name="I tried adding attributes to an anonymous class and it
didn't work.">
<p>That's not supported (yet). It is also very hard to implement
since the class name is decided by the Java compiler.</p>
</subsection>
<subsection name="I want to add a constant value as an attribute.">
<p>So you have this</p>
<source><![CDATA[public class Values {
public static final Integer ONE = new Integer (1);
}]]></source>
<p>and now you'd like to add ONE as an attribute like this:</p>
<source><![CDATA[/**
* @@Values.ONE
*/
public class MyClass { ... }]]></source>
<p>how can this be done?</p>
<p>The best that can be offered is:</p>
<source><![CDATA[/**
* @@Integer(Values.ONE)
*/
public class MyClass { ... }]]></source>
<p>I'm afraid. The expression follwing the @@ must fit the template
"new (expression)" optionally suffixed by "()". This makes the compiler much simpler,
and the loss of functionality was considered worth it. You can also define a separate
ONE class:</p>
<source><![CDATA[public class One {}]]></source>
<p>and use it.</p>
</subsection>
</section>
</body>
</document>
1.1 jakarta-commons-sandbox/attributes/site/xdocs/compiler.xml
Index: compiler.xml
===================================================================
<?xml version="1.0"?>
<!--
=
= Copyright 2003-2004 The Apache Software Foundation
=
= Licensed under the Apache License, Version 2.0 (the "License");
= you may not use this file except in compliance with the License.
= You may obtain a copy of the License at
=
= http://www.apache.org/licenses/LICENSE-2.0
=
= Unless required by applicable law or agreed to in writing, software
= distributed under the License is distributed on an "AS IS" BASIS,
= WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
= See the License for the specific language governing permissions and
= limitations under the License.
=
-->
<document>
<properties>
<author email="[EMAIL PROTECTED]">Leo Sutic</author>
<title>Reference - Compiling</title>
</properties>
<body>
<section name="The AttributeCompiler Ant Task">
<p>This is the process your source files have to go through:</p>
<source><![CDATA[+------------+
+--------------------+
|Java Sources|----> Attribute Compiler ---->|Generated Java Files|
+------------+ +--------------------+
| |
| |
| +-------------+ |
+-------------->|Java Compiler|<------------------+
+-------------+
|
v
+-----------------+
|Java .class files|
+-----------------+]]></source>
<p>
This section will focus on the "Attribute Compiler" step. As is
implied by the diagram,
the Attribute Compiler compiles Java source files into other Java
source files.
</p>
<p>
This is how the compiler is used:
</p>
<source><![CDATA[<taskdef
resource="org/apache/commons/attributes/anttasks.properties"/>
<attribute-compiler
destdir="temp/"
attributepackages="my.attributes;my.otherattributes">
<fileset dir="src/" includes="*.java"/>
</attribute-compiler>]]></source>
<table>
<tr>
<th>
Parameter
</th>
<th>
Required
</th>
<th>
Description
</th>
</tr>
<tr>
<td>
destdir
</td>
<td>
Yes
</td>
<td>
Destination directory for generated source files
</td>
</tr>
<tr>
<td>
attributepackages
</td>
<td>
No
</td>
<td>
A semi-colon separated list of package names. Attributes in
these packages
can be used without specifying their fully-qualified names,
even if they are not
in the same package as the class they are being attached to,
and even if they
are not imported. (The compiler generates import statements
in the generated
source files.)
</td>
</tr>
</table>
<p>
After the attribute compiler has generated the new source files, you
should
feed them <b>and your own source files</b> to the Java compiler.
</p>
</section>
<section name="Do I Have to Use the Attribute Compiler?">
<p>
No, you don't. You can add attributes to a class by programmatically
creating an attribute repository in the class's static initializer.
See the Javadoc for
<a
href="api/org/apache/commons/attributes/RuntimeAttributeRepository.html">RuntimeAttributeRepository</a>
for an example. <i>It's not pretty, but it works.</i>
</p>
</section>
</body>
</document>
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