alvinalexander.com | career | drupal | java | mac | mysql | perl | scala | uml | unix  
</thead> <tbody> <tr> <tr> </tbody> </table> <h4>FIELD annotations <table> <thead> <tr> </thead> <tbody> <tr> <tr> </tbody> </table> <h4>METHOD annotations <table> <thead> <tr> </thead> <tbody> <tr> <tr> <tr> <tr> </tbody> </table> <h4>PARAMETER annotations <table> <thead> <tr> </thead> <tbody> <tr> <tr> <tr> <tr> </tbody> </table> </subsection> <subsection name="Bootstrapping"> <p>The core of Digester annotations rules processor is the <code>org.apache.commons.digester.annotations.DigesterLoader class.

<p>A org.apache.commons.digester.annotations.DigesterLoader instance is able to analyze <code>Class<?> graphs and builds the relative <code>org.apache.commons.digester.RuleSet to create <code>org.apache.commons.digester.Digester instances.

<p>The bootstrap sequence has been designed to be as simple as possible, all that's needed is creating a new <code>org.apache.commons.digester.annotations.DigesterLoaderBuilder instance, plugging the desired <code>org.apache.commons.digester.annotations.spi.AnnotationRuleProviderFactory and <code>org.apache.commons.digester.annotations.spi.DigesterLoaderHandlerFactory. using a chaining builders pattern.</p> <p>An org.apache.commons.digester.annotations.spi.AnnotationRuleProviderFactory implementation performs the creation of <code>org.apache.commons.digester.annotations.AnnotationRuleProvider<A extends Annotation, E extends AnnotatedElement, R extends Rule> instances; the default implementation is limited to create the provider by invoking the default empty constructor of the required class, but users are free to give their implementation if they need a more complex factory, i.e. providers requires components that could be injected from a context, etc. etc.</p> <h5>Note <p>It is strongly descouraged caching AnnotationRuleProvider instances!!!</p> <p>Same thing for the org.apache.commons.digester.annotations.spi.DigesterLoaderHandlerFactory, which implementation performs the creation of <code>DigesterLoaderHandler<A extends Annotation, E extends AnnotatedElement> instances; the default implementation is limited to create the handler by invoking the default empty constructor of the required class, but users are free to give their implementation if they need a more complex factory, i.e. providers requires components that could be injected from a context, etc. etc.</p> <p>Said that, to obtain a fresh new <code>org.apache.commons.digester.annotations.DigesterLoader instance with default factories, it is enough invoking the default empty constructor:</p> <source>DigesterLoader digesterLoader = new DigesterLoaderBuilder() .useDefaultAnnotationRuleProviderFactory() .useDefaultDigesterLoaderHandlerFactory();</source> <p>Otherwise, if users need specify theyr custom factories:

<source>DigesterLoader digesterLoader = new DigesterLoaderBuilder() .useAnnotationRuleProviderFactory(new MyAnnotationRuleProviderFactory()) .useDigesterLoaderHandlerFactory(new MyDigesterLoaderHandlerFactory());</source> </subsection> <subsection name="Example: a simple RSS parser"> <p>Let's assume there is the need to parse the following (simplified) XML/RSS feed:</p> <source><rss version="2.0"> <channel> <title>Apache</title> <link>http://www.apache.org</link> <description>The Apache Software Foundation</description> <language>en-US</language> <rating>(PICS-1.1 "http://www.rsac.org/ratingsv01.html" 2 gen true comment "RSACi North America Server" for "http://www.rsac.org" on "1996.04.16T08:15-0500" r (n 0 s 0 v 0 l 0))</rating> <image> <title>Apache</title> <url>http://jakarta.apache.org/images/jakarta-logo.gif</url> <link>http://jakarta.apache.org</link> <width>505</width> <height>480</height> <description>The Jakarta project. Open source, serverside java.</description> </image> <item> <title>Commons Attributes 2.1 Released</title> <link>http://jakarta.apache.org/site/news/news-2004-2ndHalf.html#20040815.1</link> <description>The Apache Commons team is happy to announce the release of Commons Attributes 2.1. This is the first release of the new Commons-Attributes code.</description> </item> <item> <title>Cloudscape Becomes Apache Derby</title> <link>http://jakarta.apache.org/site/news/elsewhere-2004-2ndHalf.html#20040803.1</link> <description>IBM has submitted a proposal to the Apache DB project for a Java-based package to be called 'Derby'.</description> </item> <item> <title>Commons BeanUtils 1.7 Released</title> <link>http://jakarta.apache.org/site/news/news-2004-2ndHalf.html#20040802.1</link> <description/> </item> <item> <title>Commons JXPath 1.2 Released</title> <link>http://jakarta.apache.org/site/news/news-2004-2ndHalf.html#20040801.2</link> <description/> </item> </channel> </rss></source> <p>So, let's define the Java entities and annotate them; first the Channel entity:

<source>@ObjectCreate(pattern = "rss/channel") class Channel { private final List<Item> items = new ArrayList<Item>(); @BeanPropertySetter(pattern = "rss/channel/title") private String title; @BeanPropertySetter(pattern = "rss/channel/link") private String link; @BeanPropertySetter(pattern = "rss/channel/description") private String description; @BeanPropertySetter(pattern = "rss/channel/language") private String language; private Image image; // getters and setters @SetNext public void setImage(Image image) { this.image = image; } @SetNext public void addItem(Item item) { this.items.add(item); } }</source> <p>Then the Image entity:

<source>@ObjectCreate(pattern = "rss/channel/image") class Image { @BeanPropertySetter(pattern = "rss/channel/image/description") private String description; @BeanPropertySetter(pattern = "rss/channel/image/width") private int width; @BeanPropertySetter(pattern = "rss/channel/image/height") private int height; @BeanPropertySetter(pattern = "rss/channel/image/link") private String link; @BeanPropertySetter(pattern = "rss/channel/image/title") private String title; @BeanPropertySetter(pattern = "rss/channel/image/url") private String url; // getters and setters }</source> <p>and finally the Item entity:

<source>@ObjectCreate(pattern = "rss/channel/item") class Item { @BeanPropertySetter(pattern = "rss/channel/item/description") private String description; @BeanPropertySetter(pattern = "rss/channel/item/link") private String link; @BeanPropertySetter(pattern = "rss/channel/item/title") private String title; // getters and setters }</source> <p>It is now possible to create the Digester instance and parse the XML:

<source>DigesterLoader digesterLoader = new DigesterLoaderBuilder() .useDefaultAnnotationRuleProviderFactory() .useDefaultDigesterLoaderHandlerFactory(); ... Digester digester = digesterLoader.createDigester(Channel.class); try { Channel channel = (Channel) digester.parse(new URL("http://www.myfeedprovider.com/rss.xml").openStream()); } catch (Exception e) { // do something } </source> <h5>Notes <p>If asking to the DigesterLoader instance more then twice the <code>Digester for the same Class<?>, the <code>DigesterLoader won't analize the target class for each request, but rather will reuse cached results.</p> <p>The same DigesterLoader instance can be reused to create other <code>Digester instances.

</subsection> </section> </body> </document>

Other Commons Digester examples (source code examples)

Here is a short list of links related to this Commons Digester annotations.xml source code file:

Commons Digester example source code file (annotations.xml)

This example Commons Digester source code file (annotations.xml) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Commons Digester tags/keywords

annotatedelement, annotation, apache, beanpropertysetter, beanpropertysetter, commons, digester, digester, e, license, license, string, string, the

The Commons Digester annotations.xml source code

<?xml version="1.0" encoding="UTF-8"?>
<!--
Licensed to the Apache Software Foundation (ASF) under one or more
contributor license agreements.  See the NOTICE file distributed with
this work for additional information regarding copyright ownership.
The ASF licenses this file to You 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 xmlns="http://maven.apache.org/XDOC/2.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/XDOC/2.0 http://maven.apache.org/xsd/xdoc-2.0.xsd">
  <properties>
    <title>Download Commons Digester
    <author email="dev@commons.apache.org">Commons Documentation Team
  </properties>
  <body>
    <section name="Annotations">
      <p>The annotations package provides for Java5 Annotations
        meta-data based definition of rules for <code>Digester.
        This improves maintainability of both Java code and XML documents, as
        rules are now defined in POJOs and generating <code>Digester
        parsers at run-time, avoiding manual updates.</p>

       <subsection name="Introduction">
         <p>This is a brief overview of the digester-rules-in-Java5 Annotations
        feature. Inspired by the basic idea behind the JPA, BeanValidation and
        JAXB's specifications, this feature lets you define Digester rules
        directly in target POJOs, instead of creating and initializing the Rules
        objects programmatically, which can become tedious.</p>
       </subsection>

       <subsection name="Annotation Rules">
         <p>A digester rule on a POJO is expressed through one or more annotations.
        An annotation is considered a digester rule definition if its retention
        policy contains RUNTIME and if the annotation itself is annotated with
        <code>org.apache.commons.digester.annotations.DigesterRule.


        <p>The DigesterRule is defined by the combination of:

        <ul>
            <li>the reflected Class<? extends org.apache.commons.digester.Rule>
            by the annotation;</li>
            <li>the org.apache.commons.digester.annotations.DigesterLoaderHandler
            class that has to be invoked during the target class traversal
            (if not specifyied, the annotation processor will supply the 
            <code>org.apache.commons.digester.annotations.handlers.DefaultLoaderHandler);
            <li>the org.apache.commons.digester.annotations.AnnotationRuleProvider
            provider that produces the <code>pattern, rule pair.
        </ul>

        <p>Digester annotations can target any of the following ElementTypes:

        <ul>
            <li>FIELD for Digester rules concerning attributes;
            <li>METHOD for Digester rules concerning methods calls;
            <li>PARAMETER for Digester rules concerning methods parameters setting;
            <li>TYPE for Digester rules concerning types creation.
        </ul>
        <p>While other ElementTypes are not forbidden, the Digester
        annotations processor does not have to recognize and process annotation
        rules placed on such types.</p>

        <p>Every Digester rule annotation must define a pattern
        element of type <code>String that represents the element matching
        path pattern.</p>

        <source>@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@CreationRule
@DigesterRule(
        reflectsRule = ObjectCreateRule.class,
        providedBy = ObjectCreateRuleProvider.class
)
public @interface ObjectCreate {

    String pattern();

}</source>
       </subsection>

       <subsection name="Applying multiple annotation rule of the same type">
         <p>It is often useful to declare the same annotation rule more than once
        to the same target, with different properties. To support this requirement,
        the Digester annotation processor treats annotations annotated by
        <code>@org.apache.commons.digester.annotations.DigesterRuleList
        whose <code>value element has a return type of an array of rule
        annotations in a special way. Each element in the value array are processed
        by the Digester annotation processor as regular annotation rule annotations.
        This means that each Digester rule specified in the <code>value
        element is applied to the target. The annotation must have retention
        <code>RUNTIME and can be applied on a type, field, method or
        method parameter. It is recommended to use the same set of targets as
        the initial Digester annotation rule.</p>

        <p>Note to designers: each Digester annotation rule should be coupled
        with its corresponding multi-valued annotation.
        It is recommended, though not mandated, the definition of
        an inner annotation named <code>List.


         <source>@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@CreationRule
@DigesterRule(
    reflectsRule = ObjectCreateRule.class,
    providedBy = ObjectCreateRuleProvider.class
)
public @interface ObjectCreate {

    String pattern();

    @Documented
    @Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.TYPE)
    @DigesterRuleList
    @interface List {
        ObjectCreate[] value();
    }

}</source>
       </subsection>

       <subsection name="Rule provider implementation">
         <p>A Digester rule provider implementation performs the rule creation
        of a given annotation for a given annotated element. The implementation
        classes are specified by the <code>providedBy element of the
        <code>@DigesterRule annotation that decorates the rule annotation
        definition. The rule provider implementation implements the
        <code>org.apache.commons.digester.annotations.AnnotationRuleProvider<A extends Annotation, E extends AnnotatedElement, R extends Rule>
        interface.</p>

        <source>class ObjectCreateRuleProvider implements AnnotationRuleProvider<ObjectCreate, Class<?>, ObjectCreateRule> {

    private Class<?> clazz;

    public void init(ObjectCreate annotation, Class<?> element) {
        this.clazz = element;
    }

    public ObjectCreateRule get() {
        return new ObjectCreateRule(this.clazz);
    }

}</source>

         <h5>Notes
        <p>A new instance of the provider will be created each time the Digester
        annotations processor will meet the relative rule that requests it.</p>
        <p>To supply the missing AnnotatedElement for methods
        <code>PARAMETERs, the Digester annotation processor come with the
        <code>org.apache.commons.digester.annotations.reflect.MethodArgument
        class.</p>
       </subsection>

       <subsection name="Digester loader handler implementation">
         <p>The Digester loader handler is an AnnotatedElement
        interceptor invoked when meeting a particular Digester rule annotation
        while analyzing the target class.</p>

        <p>By default, the Digester annotations processor, when meeting a
        Digester annotation rule, extracts the rule pattern and the relative
        rule provider to store it in the
        <code>org.apache.commons.digester.annotations.FromAnnotationsRuleSet,
        an <code>org.apache.commons.digester.RuleSet implementation.


        <p>If designers have the need of a more elaborate annottaion processing,
        they can specify the <code>handledBy element of the
        <code>@DigesterRule annotation that decorates the rule annotation
        definition. The Digester loader handler implementation implements the
        <code>DigesterLoaderHandler<A extends Annotation, E extends AnnotatedElement>
        interface. Follows below an example:</p>

        <source>class SetPropertiesLoaderHandler implements DigesterLoaderHandler<SetProperty, Field> {

    public void handle(SetProperty annotation, Field element, FromAnnotationsRuleSet ruleSet) {
        SetPropertiesRuleProvider ruleProvider = ruleSet.getProvider(annotation.pattern(), SetPropertiesRuleProvider.class);

        if (ruleProvider == null) {
            ruleProvider = new SetPropertiesRuleProvider();
            ruleSet.addRuleProvider(annotation.pattern(), ruleProvider);
        }

        ruleProvider.addAlias(annotation, element);
    }

}</source>
       </subsection>

       <subsection name="Built-in Rules">
         <p>All built-in annotation rules are in the package
        <code>org.apache.commons.digester.annotations.rules.
        Here is the list of annotations and their usage.</p>

        <h4>TYPE annotations
        <table>
            <thead>
                <tr>
AnnotationReflect rule
@ObjectCreateorg.apache.commons.digester.ObjectCreateRule
@FactoryCreateorg.apache.commons.digester.FactoryCreateRule
AnnotationReflect rule
@BeanPropertySetterorg.apache.commons.digester.BeanPropertySetterRule
@SetPropertyorg.apache.commons.digester.SetPropertiesRule
AnnotationReflect rule
@CallMethodorg.apache.commons.digester.CallMethodRule
@SetNextorg.apache.commons.digester.SetNextRule
@SetRootorg.apache.commons.digester.SetRootRule
@SetToporg.apache.commons.digester.SetTopRule
AnnotationReflect rule
@AttributeCallParamorg.apache.commons.digester.Digester#addCallParam(String, int, String)
@CallParamorg.apache.commons.digester.Digester#addCallParam(String, int)
@PathCallParamorg.apache.commons.digester.Digester#addCallParamPath(String, int)
@StackCallParamorg.apache.commons.digester.Digester#addCallParam(String, int, int)
... this post is sponsored by my books ...

#1 New Release!
FP Best Seller

 

new blog posts

 

Copyright 1998-2021 Alvin Alexander, alvinalexander.com
All Rights Reserved.

A percentage of advertising revenue from
pages under the /java/jwarehouse URI on this website is
paid back to open source projects.