利用Jakarta Commons Digester匹配xml配置文件信息与其对应的xml规则文件形成Java Object
说明：在这里以一个简单的例子来说明如何使用Digester。
第一步：下载Digester
在http://jakarta.apache.org/commons/index.html页面找到Digester Project,并下载commons-digester-1.6.zip（我使用的）
第二步：所需主要lib
commons-digester.jar : 这个就是Digester主要的lib
(digester中解析xml利用的是Sax方法，有可能需要crimson.jar,在我的JBuilder环境就不需要，因为jdk已经带了解析xml文件的lib)
commons-beanutils.jar : 主要公用包(请查看http://www.apache.org)
commons-logging.jar : 其log包，由于commons-digester.jar该包中使用
第三步：书写xml配置文件(config.xml)、xml规则文件(rules.xml)与Java Object(Example.java)
1.config.xml
<?xml version="1.0" encoding="UTF-8"?>
<db-base-config>
<control>
<queue-connection-factory>java:/ConnectionFactory</queue-connection-factory>
<sender-queue>
<param name="Internet">queue/Email</param>
<param name="CDMA">queue/SmsCdma</param>
</sender-queue>
</control>
<db-foreign-exchange-sql>
<publication_id>1</publication_id>
<receiver-list>
<param>Telephone</param>
<param>Email</param>
</receiver-list>
</db-foreign-exchange-sql>
</db-base-config>
2. rules.xml
<?xml version="1.0" encoding="UTF-8"?>
<digester-rules>
<pattern value="db-base-config/control">
<call-method-rule pattern="queue-connection-factory" methodname="setQueueConnectionFactory" paramcount="0"/>
<pattern value="sender-queue/param">
<call-method-rule methodname="addSenderQueue" paramcount="2"/>
<call-param-rule paramnumber='0' attrname='name'/>
<call-param-rule paramnumber='1'/>
</pattern>
</pattern>
<pattern value="db-base-config/db-foreign-exchange-sql">
<call-method-rule pattern="publication_id" methodname="setExchangePublicationID" paramcount="0"/>
<pattern value="receiver-list/param">
<call-method-rule methodname="addReceiverList" paramcount="0"/>
</pattern>
</pattern>
</digester-rules>
3. Example.java
import java.net.*;
import java.util.*;
import org.apache.commons.digester.*;
import org.apache.commons.digester.xmlrules.*;
public class Example {
/*
以下两个String变量，严实在xml配置文件，在不同节点下查找
*/
private String queueConnectionFactory = null;
private String exchangePublicationID = null;
/*
以下两个主要演示xml配置文件，是怎样形成Collection的
*/
private HashMap senderQueueMap = new HashMap();
private LinkedList receiverList = new LinkedList();
public Example() {
try {
/*
请把两个xml放在该Example的class文件，使该类能找到xml文件
*/
URL inputURL = getClass().getResource("config.xml");
URL rulesURL = getClass().getResource("rules.xml");
Digester digester = DigesterLoader.createDigester(rulesURL);
digester.push(this);
digester.parse(inputURL.openStream());
}
catch (Exception e) {
System.out.print(
"Can not get configurations, system initialization failed." +
e.toString());
System.exit(1);
}
System.out.print("Get configurations is successful ");
}
public static void main(String[] args) {
Example paramconfig = new Example();
System.out.print(paramconfig.getSenderQueueMap());
System.out.println(paramconfig.getExchangePublicationID());
System.out.print(paramconfig.getReceiverList());
}
public String getQueueConnectionFactory() {
return queueConnectionFactory;
}
public HashMap getSenderQueueMap() {
return senderQueueMap;
}
public String getExchangePublicationID() {
return exchangePublicationID;
}
/*增加Map元素*/
public void addSenderQueue(String name, String value) {
senderQueueMap.put(name.toLowerCase(), value);
}
public LinkedList getReceiverList() {
return receiverList;
}
public void setQueueConnectionFactory(String queueConnectionFactory) {
this.queueConnectionFactory = queueConnectionFactory;
}
/*增加LinkedList元素*/
public void addReceiverList(String value) {
receiverList.addLast(value);
}
public void setSenderQueueMap(HashMap senderQueueMap) {
this.senderQueueMap = senderQueueMap;
}
public void setExchangePublicationID(String exchangePublicationID) {
this.exchangePublicationID = exchangePublicationID;
}
public void setReceiverList(LinkedList receiverList) {
this.receiverList = receiverList;
}
}
说明：请注意rules.xml的中pattern属性以及methodname属性
第四步：运行（在Jbuilder下调试通过）
第五步：（高级）形成DataSource的例子
以配置Oracle为例子，所增lib(class12.jar:oracle jdbc driver)
1.config.xml
<?xml version="1.0" encoding="UTF-8"?>
<db-base-config>
<database>
<user>user</user>
<password>pwd</password>
</database>
<db-provider class="oracle.jdbc.pool.OracleDataSource">
<user>user</user>
<password>pwd</password>
<driver-type>thin</driver-type>
<server-name>192.168.0.59</server-name>
<network-protocol>tcp</network-protocol>
<port-number>1521</port-number>
<database-name>example</database-name>
</db-provider>
</db-base-config>
2.rules.xml
<?xml version="1.0" encoding="UTF-8"?>
<digester-rules>
<pattern value="db-base-config/database">
<call-method-rule pattern="user" methodname="setDbUser" paramcount="0" />
<call-method-rule pattern="password" methodname="setDbPass" paramcount="0" />
</pattern>
<pattern value="db-base-config/db-provider">
<object-create-rule classname="oracle.jdbc.pool.OracleDataSource" attrname="class" />
<call-method-rule pattern="user" methodname="setUser" paramcount="0" />
<call-method-rule pattern="password" methodname="setPassword" paramcount="0" />
<call-method-rule pattern="driver-type" methodname="setDriverType" paramcount="0" />
<call-method-rule pattern="server-name" methodname="setServerName" paramcount="0" />
<call-method-rule pattern="network-protocol" methodname="setNetworkProtocol" paramcount="0" />
<call-method-rule pattern="port-number" methodname="setPortNumber" paramcount="0" paramtypes="java.lang.Integer" />
<call-method-rule pattern="database-name" methodname="setDatabaseName" paramcount="0" />
<set-next-rule methodname="setDs" />
</pattern>
</digester-rules>
3. Java Object
import javax.sql.DataSource;
import java.net.*;
import java.util.*;
import org.apache.commons.digester.*;
import org.apache.commons.digester.xmlrules.*;
public class Example {
private static DataSource ds = null;
private String dbUser = null;
private String dbPass = null;
public Example() {
try {
/*
请把两个xml放在该Example的class文件，使该类能找到xml文件
*/
URL inputURL = getClass().getResource("config.xml");
URL rulesURL = getClass().getResource("rules.xml");
Digester digester = DigesterLoader.createDigester(rulesURL);
digester.push(this);
digester.parse(inputURL.openStream());
}
catch (Exception e) {
System.out.print(
"Can not get configurations, system initialization failed." +
e.toString());
System.exit(1);
}
System.out.print("Get configurations is successful ");
}
public static void main(String[] args) {
Example paramconfig = new Example();
DataSource dataSource = paramconfig.getDs().getConnection();
//已经得到connection，就看你处理数据库的能力的，呵呵
java.sql.Connection conn = dataSource.getConnection(paramconfig.getDbUser(),paramconfig.getDbPass());
}
public DataSource getDs() {
return ds;
}
public void setDs(DataSource ds) {
this.ds = ds;
}
public String getDbPass() {
return dbPass;
}
public String getDbUser() {
return dbUser;
}
public void setDbPass(String dbPass) {
this.dbPass = dbPass;
}
public void setDbUser(String dbUser) {
this.dbUser = dbUser;
}
}
总结：Digester功能越来越强大，在这里我只是抛砖引玉。
Java Application Framework---Spring 的Dependency Injection是非常强大
大家可以有空研究一下。 
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