从Digester解析xml说起

想弄清楚struts1到底是怎么解析struts-config.xml文件。于是在源代码中发现用的是apache的Digester库。第一次接触这个，于是好好的查阅了一番。

下面的代码，是从http://soft901.iteye.com/blog/335452上面弄过来的，自己改造了一下，只为了自己更清楚的理解。

待读取的XML文件datasource.xml: 

 

<?xml version="1.0"?>
<datasources>
	<datasource>
		<name>mysqldatasource</name>
		<driver>com.jdbc.mysql.Driver</driver>
		<url>jdbc:mysql://localhost:3306/test</url>
		<username>root</username>
		<password>1234</password>
	</datasource>
	<datasource>
		<name>oracledatasource</name>
		<driver>oracle.jdbc.driver.oracledriver</driver>
		<url>jdbc:oracle:thin:@localhost:1521:orcl</url>
		<username>scott</username>
		<password>tiger</password>
	</datasource>
</datasources>

 此xml文件分2层结构，分别为： 

 

<datasources>节点 其下包含2个<datasource>节点 
<datasource>节点，其下包含各种信息节点 ： 如：<name> 、<url>等。 
我们的操作目标是把datasource中的信息节点的内容提取出来。 
把每个<datasource>看做为一个对象，<datasource>中信息节点的内容为对象中的元素。

设定一个类DatasourceConfig.java 其内容如下： 

 

package xmlParse.digester;

public class DataSourceConfig {
	private String name;
	private String driver;
	private String url;
	private String username;
	private String password;

	public String getName() {
		return name;
	}

	public String getDriver() {
		return driver;
	}

	public String getUrl() {
		return url;
	}

	public String getUsername() {
		return username;
	}

	public String getPassword() {
		return password;
	}

	public void setName(String name) {
		this.name = name;
	}

	public void setDriver(String driver) {
		this.driver = driver;
	}

	public void setUrl(String url) {
		this.url = url;
	}

	public void setUsername(String username) {
		this.username = username;
	}

	public void setPassword(String password) {
		this.password = password;
	}
	
	 public String toString() {  
	        return "DataSource : " + "name : " + name + " Driver : " + driver  
	                + " URL : " + url + " Username : " + username + " Password : "  
	                + password;  
	 }  
}

 

其中设置解析的rule规则的方法有四种，一一列出代码。

 

第一种 使用addCallMethod方法,映射XML所对应的节点与这个Call method的参数即可,这个call method将读取的一个标签内所有的值存入对象,然后再存入一个集合中。

 

 

package xmlParse.digester;
/**
 * 利用digester来解析xml.
 */
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import org.apache.commons.digester.Digester;
import org.xml.sax.SAXException;

public class DigesterParseTest {
	private List<DataSourceConfig> dataSources;

	public static void main(String[] args) {
		DigesterParseTest sd = new DigesterParseTest();
		sd.digester();
		System.out.println(sd.toString());
	}

	void digester() {
		Digester digester = new Digester();
		setDataSources(new ArrayList<DataSourceConfig>());
		// 把当前对象压入到digester栈中。
		digester.push(this);
		/* 设定解析此xml文件的规则 */
		// 将XML文件解析所对应的方法.this.addDataSource();参数个数为5个.
		digester.addCallMethod("datasources/datasource", "addDataSource", 5);
		digester.addCallParam("datasources/datasource/name", 0);
		digester.addCallParam("datasources/datasource/driver", 1);
		digester.addCallParam("datasources/datasource/url", 2);
		digester.addCallParam("datasources/datasource/username", 3);
		digester.addCallParam("datasources/datasource/password", 4);

		try {
			digester.parse("config/datasource.xml");
		} catch (IOException e) {
			e.printStackTrace();
		} catch (SAXException e) {
			e.printStackTrace();
		}
	}
	
	public void addDataSource(final String name, final String driver,
			final String url, final String username, final String password) {
		DataSourceConfig dataSource = new DataSourceConfig();
		dataSource.setName(name);
		dataSource.setDriver(driver);
		dataSource.setUrl(url);
		dataSource.setUsername(username);
		dataSource.setPassword(password);
		getDataSources().add(dataSource);
	}
	
	public List<DataSourceConfig> getDataSources() {
		return dataSources;
	}

	public void setDataSources(List<DataSourceConfig> dataSources) {
		this.dataSources = dataSources;
	}

	public String toString() {
		String newline = System.getProperty("line.separator");
		StringBuffer buff = new StringBuffer();
		if (getDataSources() != null) {
			for (DataSourceConfig ds : getDataSources()) {
				buff.append(newline).append(ds);
			}
			return buff.toString();
		}
		return "";
	}
}

 

 

第二种 使用addObjectCreate方法,创建对象映射XML文件的属性对java Bean. 读取完一个对象将对象加入到一个集合中,然后再读取XML文件的下一个标签: 

 

package xmlParse.digester;
/**
 * 利用digester来解析xml.
 */
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import org.apache.commons.digester.Digester;
import org.xml.sax.SAXException;

public class DigesterParseTest2 {
	private List<DataSourceConfig> dataSources;

	public static void main(String[] args) {
		DigesterParseTest sd = new DigesterParseTest();
		sd.digester();
		System.out.println(sd.toString());
	}
	private void digester() {
		Digester digester = new Digester();
		setDataSources(new ArrayList<DataSourceConfig>());
		// 把当前对象压入到digester栈中。
		digester.push(this);
		
		/* 设定解析此xml文件的规则 */
		digester.addObjectCreate("datasources/datasource", DataSourceConfig.class);
		
		//效果跟addSetProperties一样
//		digester.addBeanPropertySetter("datasources/datasource/name","name");
//		digester.addBeanPropertySetter("datasources/datasource/driver", "driver");
//		digester.addBeanPropertySetter("datasources/datasource/url", "url");
//		digester.addBeanPropertySetter("datasources/datasource/username", "username");
//		digester.addBeanPropertySetter("datasources/datasource/password", "password");

		digester.addSetProperties("datasources/datasource/name");
		digester.addSetProperties("datasources/datasource/driver");
		digester.addSetProperties("datasources/datasource/url");
		digester.addSetProperties("datasources/datasource/username");
		digester.addSetProperties("datasources/datasource/password");
		digester.addSetNext("datasources/datasource", "addDataSource");
		try {
			digester.parse("config/datasource.xml");
		} catch (IOException e) {
			e.printStackTrace();
		} catch (SAXException e) {
			e.printStackTrace();
		}
	}
	
	public void addDataSource(final DataSourceConfig datasource){
		getDataSources().add(datasource);
	}
	public List<DataSourceConfig> getDataSources() {
		return dataSources;
	}

	public void setDataSources(List<DataSourceConfig> dataSources) {
		this.dataSources = dataSources;
	}

	public String toString() {
		String newline = System.getProperty("line.separator");
		StringBuffer buff = new StringBuffer();
		if (getDataSources() != null) {
			for (DataSourceConfig ds : getDataSources()) {
				buff.append(newline).append(ds);
			}
			return buff.toString();
		}
		return "";
	}
}

 

 

第三种：使用addRule方法来解析datasource.xml: 

 

private void digester() {
	Digester digester = new Digester();

	setDataSources(new Vector<DataSource>());
	// 把当前对象压入到digester栈中。
	digester.push(this);

	Rule objectCreate = new ObjectCreateRule(DataSource.class);
	digester.addRule("datasources/datasource", objectCreate);

	digester.addRule("datasources/datasource", new SetNextRule(
			"addDataSource"));

	digester.addRule("datasources/datasource/name", new CallMethodRule(
			"setName", 0, new Class[] { String.class }));
	digester.addRule("datasources/datasource/driver", new CallMethodRule(
			"setDriver", 0, new Class[] { String.class }));
	digester.addRule("datasources/datasource/url", new CallMethodRule(
			"setUrl", 0, new Class[] { String.class }));
	digester.addRule("datasources/datasource/username", new CallMethodRule(
			"setUsername", 0, new Class[] { String.class }));
	digester.addRule("datasources/datasource/password", new CallMethodRule(
			"setPassword", 0, new Class[] { String.class }));
	try {
		digester.parse("datasource.xml");
	} catch (IOException e) {
		e.printStackTrace();
	} catch (SAXException e) {
		e.printStackTrace();
	}
}

 

 

第四种：把规则写在xml文件中。新建rules.xml

 

<? xml version = " 1.0 " ?>
<digester-rules>
	<object-create-rule pattern=" datasources "
		classname=" datasources " />
	<pattern value=" datasources/datasource ">
		<object-create-rule classname=" datasource " />
		<call-method-rule pattern=" name " methodname=" setName "
			paramcount=" 0 " />
		<call-method-rule pattern=" driver " methodname=" setDriver "
			paramcount=" 0 " />
		<call-method-rule pattern=" url " methodname=" setUrl "
			paramcount=" 0 " />
		<call-method-rule pattern=" username " methodname=" setUsername "
			paramcount=" 0 " />
		<call-method-rule pattern=" password " methodname=" setPassword "
			paramcount=" 0 " />
		<set-next-rule methodname=" addDatasource " />
	</pattern>
	
</digester-rules>

 

digester方法如下：

 

private void digester() {
		setDataSources(new ArrayList<DataSourceConfig>());
		try {
			File rules = new File("config/rules.xml");
			//创建digester对象并指定解析规则
			Digester digester = DigesterLoader.createDigester(rules.toURL());
			digester.parse("config/datasource.xml");
		} catch (IOException e) {
			e.printStackTrace();
		} catch (SAXException e) {
			e.printStackTrace();
		}
	}

 

以上是digester四种解析xml的方法。这些例子只是些直观的说明。竹笋炒肉的三篇有关digester的笔记更深入一步的讲解了有关digester的知识。链接见下：

digester学习笔记1

digester学习笔记2

digester学习笔记3

另附上commons-digester-2.0 API和官网

 

回到文章开头说的，其实了解digester是为了弄明白struts怎么解析配置文件的。本来想自己整理下，但是发现struts学习--初始化MoudleConfig 正好解释的很清楚，只以解析DataSourceConfig标签为例稍微补充下RuleSet配置说明。

通过ActionServlet的成员变量configDigester的初始化来深入理解struts-config.xml文件的加载，其中配置信息可以通过org.apache.struts.config.impl.ModuleConfigImpl类描述。 

configDigester上注册了RuleSet类为ConfigRuleSet，主要通过覆盖方法public void addRuleInstances(Digester digester)来为digester注册Rule，代码分析如下： 

1．处理ModuleConfigImpl对象中的数据源DataSourceConfig对象： 
/* 1.1当遇到struts-config/data-sources/data-source开始标记时便创建此标记className属性标示的类实例，如果没有className属性，则创建org.apache.struts.config.DataSourceConfig对象，并入栈；遇到结束标记时对象出栈。*/ 

digester.addObjectCreate 
("struts-config/data-sources/data-source", "org.apache.struts.config.DataSourceConfig", "className"); 
/*1.2 当遇到struts-config/data-sources/data-source开始标记时根据data-source标记的属性设置栈顶元素对象的属性 */ 
digester.addSetProperties 
("struts-config/data-sources/data-source"); 

/*1.3 遇到struts-config/data-sources/data-source结束标记时将调用次栈顶元素ModuleConfigImpl对象的addDataSourceConfig方法，将当前栈顶元素DataSourceConfig对象为值，struts-config/data-sources/data-source标记的key属性为键推入到ModuleConfigImpl的HashMap类型成员变量dataSources中。*/ 
digester.addSetNext 
("struts-config/data-sources/data-source", "addDataSourceConfig", "org.apache.struts.config.DataSourceConfig"); 

/*1.4 将遇到的set-property标记的property属性值为key，value属性值为值添加到栈顶DataSourceConfig对象的HashMap类型成员变量properties中。*/ digester.addRule 
("struts-config/data-sources/data-source/set-property", new AddDataSourcePropertyRule());