使用XML文件來實(shí)現(xiàn)對(duì)Servlet的配置我們?cè)赪eb應(yīng)用中可以使用xml來配置servlet,給其提供初始化參數(shù),如下例:
我們創(chuàng)建的Servlet為:ServletDemo.java,代碼如下:
/*
* Created on 2005-8-29
*
* TODO To change the template for this generated file go to
* Window - Preferences - Java - Code Style - Code Templates
*/
package zy.pro.wd.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.sql.DataSource;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* @author zhangyi
*
* TODO To change the template for this generated type comment go to
* Window - Preferences - Java - Code Style - Code Templates
*/
public class ServletDemo extends HttpServlet {
String message;
DataSource ds;
/**
* Constructor of the object.
*/
public ServletDemo() {
super();
}
/**
* Destruction of the servlet. <br>
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}
/**
* The doGet method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out
.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
out.println("<HTML>");
out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");
out.println(" <BODY>");
out.print(" This is ");
out.print(this.getClass());
out.println(", using the GET method<br>");
out.println(this.getServletConfig().getInitParameter("message"));
out.println(" </BODY>");
out.println("</HTML>");
out.flush();
out.close();
}
/**
* The doPost method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void init() throws ServletException {
// Put your code here
}
}
在此Servlet中我們定義了兩個(gè)屬性message和ds。我們現(xiàn)在在web.xml中作如下配置：
<servlet>
<description>
This is the description of my J2EE component
</description>
<display-name>
This is the display name of my J2EE component
</display-name>
<servlet-name>ServletDemo</servlet-name>
<servlet-class>zy.pro.wd.servlet.ServletDemo</servlet-class>
<init-param>
<description>initialize the field of message</description>
<param-name>message</param-name>
<param-value>
welcome here ,thank you for visiting !!!
</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>ServletDemo</servlet-name>
<url-pattern>/servlet/ServletDemo</url-pattern>
</servlet-mapping>
加粗的部分是我們要作的配置。在其中我們給message屬性設(shè)置了初始值：
welcome here ,thank you for visiting !!!
注意：此處我們不能同時(shí)給ds設(shè)置初始值，因?yàn)閣eb.xml的DTD中約定了只能定義一個(gè)屬性也就是在配置文件中只允許聲明一個(gè)參數(shù)值對(duì)。這樣，在我們的servlet中就可以這樣來訪問此屬性：
this.getServletConfig().getInitParameter("message")。
但是，有時(shí)候我們需要同時(shí)對(duì)多個(gè)屬性用XML來初始化，那么我們就需要自己來寫XML文件，同時(shí)自己來解析了。
使用XML來配置Servlet的好處：
如果不在XML中對(duì)Servlet配置，那么我們修改Servlet的屬性的話就要重新啟動(dòng)服務(wù)器，而如果使用XML來配置的話就不需要重新啟動(dòng)服務(wù)器而可以自動(dòng)生效。服務(wù)器可以自動(dòng)監(jiān)視其改變而重新裝入文檔。對(duì)企業(yè)來說，系統(tǒng)的連續(xù)運(yùn)營(yíng)是很重要的。
XML來配置Servlet主要用在初始化參數(shù)在運(yùn)行過程中需要改變的情況下。
（如果可以實(shí)現(xiàn)配置多屬性的話，那么不是有點(diǎn)象Spring中的動(dòng)態(tài)注入？？？）
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