Apache Commons Digester 三（规则注解）

Posted 2020-09-21

前言

Digester规则的定义除了可以在代码中直接new规则添加到 Digester对象外，还可以用xml配置规则，如下所示：

<digester-rules>
  <pattern value="*/foo">
    <object-create-rule pattern="bar" classname="Foobar" />
    <set-properties-rule pattern="bar" />
  </pattern>
</digester-rules>

显然，xml的规则配置目前已经不是主流方法了，今后的大趋势肯定是用注解，所以本文将主要关注如何在javabean上使用注解来配置Digester规则；

Digester规则注解

简单描述下Digester 有哪几类注解，详细信息建议看api文档，其实也比较简单了，熟悉Digester规则的话，基本不用看也知道；

类型注解

• @ObjectCreate 绑定Digester的ObjectCreateRule规则
• @FactoryCreate  绑定Digester的FactoryCreateRule规则

属性注解

• @BeanPropertySetter 绑定Digester的BeanPropertySetterRule规则
• @SetProperty  绑定Digester的SetPropertiesRule规则

方法注解

• @CallMethod ----> org.apache.commons.digester3.CallMethodRule
• @SetNext ----> org.apache.commons.digester3.SetNextRule
• @SetRoot ----> org.apache.commons.digester3.SetRootRule
• @SetTop ----> org.apache.commons.digester3.SetTopRule

参数注解

• @CallParam ----> org.apache.commons.digester3.rule.CallParamRule

Digester注解例子

看了半天，可能也还没有清晰直观的认识，直接看个例子，基本也就差不多了

如下是我们要解析的xml文件：

<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>

首先，观察分析要解析的xml文档，创建javabean对象，加上Digester元注解，

先创建一个Channel对象，如下所示，感觉也不需要过多解析，很直观了，注意下@SetNext注解，是根据方法参数对象里定义的注解匹配的

package apache.commons.digester3.example.annotations;

import java.util.ArrayList;
import java.util.List;

import org.apache.commons.digester3.annotations.rules.BeanPropertySetter;
import org.apache.commons.digester3.annotations.rules.ObjectCreate;
import org.apache.commons.digester3.annotations.rules.SetNext;

/**
 * 
 * 
 * @author http://www.cnblogs.com/chenpi/
 * @version 2017年6月7日
 */
@ObjectCreate(pattern = "rss/channel")
public class Channel
{

    private final List<Item> items = new ArrayList<Item>();

    private Image image;
    
    @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;


    @SetNext
    public void setImage(Image image)
    {
        this.image = image;
    }

    @SetNext
    public void addItem(Item item)
    {
        this.items.add(item);
    }

    /**
     * @return the title
     */
    public String getTitle()
    {
        return title;
    }

    /**
     * @param title the title to set
     */
    public void setTitle(String title)
    {
        this.title = title;
    }

    /**
     * @return the link
     */
    public String getLink()
    {
        return link;
    }

    /**
     * @param link the link to set
     */
    public void setLink(String link)
    {
        this.link = link;
    }

    /**
     * @return the description
     */
    public String getDescription()
    {
        return description;
    }

    /**
     * @param description the description to set
     */
    public void setDescription(String description)
    {
        this.description = description;
    }

    /**
     * @return the language
     */
    public String getLanguage()
    {
        return language;
    }

    /**
     * @param language the language to set
     */
    public void setLanguage(String language)
    {
        this.language = language;
    }

    /**
     * @return the items
     */
    public List<Item> getItems()
    {
        return items;
    }

    /**
     * @return the image
     */
    public Image getImage()
    {
        return image;
    }

}

在定义两个对象Image和Item，如下所示，至此，我们就已经把xml中所有元素需要匹配的规则定义完了

package apache.commons.digester3.example.annotations;

import org.apache.commons.digester3.annotations.rules.BeanPropertySetter;
import org.apache.commons.digester3.annotations.rules.ObjectCreate;

/**
 * 
 * 
 * @author http://www.cnblogs.com/chenpi/
 * @version 2017年6月7日
 */
@ObjectCreate(pattern = "rss/channel/item")
public 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;

    /**
     * @return the description
     */
    public String getDescription()
    {
        return description;
    }

    /**
     * @param description the description to set
     */
    public void setDescription(String description)
    {
        this.description = description;
    }

    /**
     * @return the link
     */
    public String getLink()
    {
        return link;
    }

    /**
     * @param link the link to set
     */
    public void setLink(String link)
    {
        this.link = link;
    }

    /**
     * @return the title
     */
    public String getTitle()
    {
        return title;
    }

    /**
     * @param title the title to set
     */
    public void setTitle(String title)
    {
        this.title = title;
    }

}

package apache.commons.digester3.example.annotations;

import org.apache.commons.digester3.annotations.rules.BeanPropertySetter;
import org.apache.commons.digester3.annotations.rules.ObjectCreate;

/**
 * 
 * 
 * @author http://www.cnblogs.com/chenpi/
 * @version 2017年6月7日
 */
@ObjectCreate(pattern = "rss/channel/image")
public 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;

    /**
     * @return the description
     */
    public String getDescription()
    {
        return description;
    }

    /**
     * @param description the description to set
     */
    public void setDescription(String description)
    {
        this.description = description;
    }

    /**
     * @return the width
     */
    public int getWidth()
    {
        return width;
    }

    /**
     * @param width the width to set
     */
    public void setWidth(int width)
    {
        this.width = width;
    }

    /**
     * @return the height
     */
    public int getHeight()
    {
        return height;
    }

    /**
     * @param height the height to set
     */
    public void setHeight(int height)
    {
        this.height = height;
    }

    /**
     * @return the link
     */
    public String getLink()
    {
        return link;
    }

    /**
     * @param link the link to set
     */
    public void setLink(String link)
    {
        this.link = link;
    }

    /**
     * @return the title
     */
    public String getTitle()
    {
        return title;
    }

    /**
     * @param title the title to set
     */
    public void setTitle(String title)
    {
        this.title = title;
    }

    /**
     * @return the url
     */
    public String getUrl()
    {
        return url;
    }

    /**
     * @param url the url to set
     */
    public void setUrl(String url)
    {
        this.url = url;
    }

    // getters and setters

}

规则与javabean绑定完后，就可以开始解析了，注意我们这里使用DigesterLoader来创建Digester实例对象，而DigesterLoader实例是通过FromAnnotationsRuleModule创建的，该类允许我们从一个注解的类上加载规则集：

/*
 * File Name: Main.java
 * Description: 
 * Author: http://www.cnblogs.com/chenpi/
 * Create Date: 2017年6月7日
 */
package apache.commons.digester3.example.annotations;

import org.apache.commons.digester3.Digester;
import org.apache.commons.digester3.annotations.FromAnnotationsRuleModule;
import org.apache.commons.digester3.binder.DigesterLoader;

/**
 * 
 * @author http://www.cnblogs.com/chenpi/
 * @version 2017年6月7日
 */

public class Main
{
    public static void main(String[] args)
    {
        try
        {

            DigesterLoader loader = DigesterLoader.newLoader(new FromAnnotationsRuleModule()
            {
                @Override
                protected void configureRules()
                {
                    bindRulesFrom(Channel.class);
                }

            });

            Digester digester = loader.newDigester();

            Channel channel = digester
                .parse(Main.class.getClassLoader().getResourceAsStream("rss.xml"));

            System.out.println(channel.getTitle());
            System.out.println(channel.getImage().getDescription());
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }

    }

}

结语

至此，Digester 的学习就告一段落了，除了使用xml定义规则（有注解了，感觉没必要在使用xml配置规则）和Digester插件模块（感觉很少会使用，不过参考代码里有例子）没详细说明外，基本涵盖了所有内容；

有兴趣的还可以深入研究，看看源码，相对而言也不难；

参考资料

http://commons.apache.org/proper/commons-digester/guide/annotations.html

参考代码

https://github.com/peterchenhdu/apache-commons-digester-example