JSP Web应用程序中使用XML文件存储系统配置参数

在使用J2EE编写Web应用程序时，经常把参数设置在一个XML文件中，在Web应用程序启动时来读取。下面就是一个实际应用中的例子。

XML文件存放在WEB-INF目录下，文件名是SysConfig.xml，其内容如下：

<?xml version="1.0" encoding="utf-8"?>
<DocRoot>
<SysConfig>
  <BaseFolder>D:/DocLib</BaseFolder>
  <TempUploadFolder>D:/DocLib/temp</TempUploadFolder>
  <DocFolder>D:/DocLib/docs</DocFolder>
  <IndexFolder>D:/DocLib/index</IndexFolder>
  <LiusConfig>D:/DocLib/Config/liusConfig.xml</LiusConfig>
  <Log4jConfig>D:/DocLib/Config/log4j/log4j.properties</Log4jConfig>
  <Database>D:/DocLib/database/database.mdb</Database>
</SysConfig>
</DocRoot>

为了在Web应用程序启动时读取这些配置值，编写了一个Servlet如下

package bootstrap;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

import util.XMLHelper;
import util.XMLHelperException;

/**
* LoadConfig is a sevlet which load config properties from XML files named SysConfig.xml
* when the web application start.
* All these properties are stored in servlet context. The key is the same as the node name
* in XML file.
* @author jimshen
*
*/

public class LoadConfig extends HttpServlet {

public void init(ServletConfig config) throws ServletException {
  super.init(config);
  String configFile = getServletContext().getRealPath("/")
    + "WEB-INF\\SysConfig.xml";
  Document doc = null;
  ServletContext application = getServletContext();
  try {
   doc = XMLHelper.parseXMLFromFile(configFile);
   Element root = doc.getDocumentElement();
   NodeList nodes = root.getElementsByTagName("SysConfig");
   NodeList children = nodes.item(0).getChildNodes();
   for (int i = 0; i < children.getLength(); i++) {
    Node node = children.item(i);
if (node.getNodeType() != Node.ELEMENT_NODE)
     continue;
    String key=node.getNodeName();
    String = node.getFirstChild().getNode().trim();
    application.setAttribute(key,);
   }
  } catch (XMLHelperException e) {
   throw new ServletException(e.toString());
  }
}

public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  PrintWriter out = response.getWriter();
  out.println("This Servlet does not service requests!");
}

public void doPost(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  PrintWriter out = response.getWriter();
  out.println("This Servlet does not service requests!");
}

}

web.xml文件中将servlet配置为启动时加载

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4"
xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
  <servlet>
    <deion>Load Configuration Information From SysConfig.xml</deion>
    <display-name>LoadConfig</display-name>
    <servlet-name>LoadConfig</servlet-name>
    <servlet-class>bootstrap.LoadConfig</servlet-class>
<load-on-startup>1</load-on-startup>
  </servlet>

  <servlet-mapping>
    <servlet-name>LoadConfig</servlet-name>
    <url-pattern>/servlet/LoadConfig</url-pattern>
  </servlet-mapping>

</web-app>