JavaEE中關(guān)于ServletConfig的小結(jié)

更新時(shí)間：2014年10月26日 10:31:44 投稿：hebedich

ServletConfig是針對(duì)特定的Servlet的參數(shù)或?qū)傩?。ServletConfig是表示單獨(dú)的Servlet的配置和參數(shù)，只是適用于特定的Servlet。從一個(gè)servlet被實(shí)例化后，對(duì)任何客戶端在任何時(shí)候訪問有效，但僅對(duì)本servlet有效，一個(gè)servlet的ServletConfig對(duì)象不能被另一個(gè)servlet訪問

在Servlet的配置文件中，可以使用一個(gè)或多個(gè)<init-param>標(biāo)簽為servlet配置一些初始化參數(shù)。當(dāng)servlet配置了初始化參數(shù)后，web容器在創(chuàng)建servlet實(shí)例對(duì)象時(shí)，會(huì)自動(dòng)將這些初始化參數(shù)封裝到ServletConfig對(duì)象中，并在調(diào)用servlet的init方法時(shí)，ServletConfig對(duì)象傳遞給servlet。進(jìn)而，程序員通過ServletConfig對(duì)象就可以得到當(dāng)前servlet的初始化參數(shù)信息。
示例代碼如下：

復(fù)制代碼代碼如下:

 package com.yyz.servletconfig;

 import java.io.IOException;

 import java.util.Enumeration;

 import javax.servlet.ServletConfig;

 import javax.servlet.ServletException;

 import javax.servlet.http.HttpServlet;

 import javax.servlet.http.HttpServletRequest;

 import javax.servlet.http.HttpServletResponse;

 public class ServletConfigDemo1 extends HttpServlet {

     ServletConfig config;

     public void doGet(HttpServletRequest request, HttpServletResponse response)

             throws ServletException, IOException {

       //獲取指定的初始化參數(shù)

         String value = config.getInitParameter("xxx");

         response.getOutputStream().write(value.getBytes());

         //獲取所有的初始化參數(shù)

         Enumeration e = cofig.getInitParameterNames();

         while(e.hasMoreElements()){

             String name = (String) e.nextElement();

             value = config.getInitParameter(name);

             response.getOutputStream().write((name+"="+value+"<br/>").getBytes());

         }

     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)

             throws ServletException, IOException {

         doGet(request,response);

     }

     @Override

     public void init(ServletConfig config) throws ServletException {

         this.config = config;

     }

 }

相應(yīng)的web.xml如下：

復(fù)制代碼代碼如下:

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="      xmlns:xsi="      xsi:schemaLocation="http://java.sun.com/xml/ns/javaee      version="2.5">
   <servlet>

     <servlet-name>ServletConfigDemo1</servlet-name>
     <servlet-class>com.yyz.servletconfig.ServletConfigDemo1</servlet-class>
     <init-param>
                <param-name>xxx</param-name>
                <param-value>yyy</param-value>
     </init-param>
       <init-param>
                <param-name>name</param-name>
                <param-value>yyz</param-value>
     </init-param>
       <init-param>
                <param-name>password</param-name>
                <param-value>yyy</param-value>
     </init-param>
   </servlet>
<servlet-mapping>
     <servlet-name>ServletConfigDemo1</servlet-name>
     <url-pattern>/servlet/ServletConfigDemo1</url-pattern>

   </servlet-mapping>
</web-app>

測(cè)試結(jié)果如下：

在上面的代碼中，ServletConfigDemo1對(duì)象中有一個(gè)ServletConfig對(duì)象，其實(shí)這是不必要的。因?yàn)镾ervletConfigDemo1繼承了HttpServlet，HttpServlet又繼承了GenericServlet 。GenericServlet 已經(jīng)在內(nèi)部維護(hù)了一個(gè)ServletConfig對(duì)象。相關(guān)實(shí)現(xiàn)如下：

復(fù)制代碼代碼如下:

 public abstract class GenericServlet 

     implements Servlet, ServletConfig, java.io.Serializable

 {

     …    …

 private transient ServletConfig config;

 public ServletConfig getServletConfig() {

           return config;

     }

 }

因而我們可以通過我們寫的Servlet對(duì)象的getServletConfig()方法直接拿到ServletConfig對(duì)象，示例代碼如下:

復(fù)制代碼代碼如下:

 package com.yyz.servletconfig;

 import java.io.IOException;

 import java.io.PrintWriter;

 import javax.servlet.ServletException;

 import javax.servlet.http.HttpServlet;

 import javax.servlet.http.HttpServletRequest;

 import javax.servlet.http.HttpServletResponse;

 public class ServletConfigDemo2 extends HttpServlet {

     public void doGet(HttpServletRequest request, HttpServletResponse response)

             throws ServletException, IOException {

         String value = this.getServletConfig().getInitParameter("name");

         System.out.println(value);

 }

     public void doPost(HttpServletRequest request, HttpServletResponse response)

             throws ServletException, IOException {

         doGet(request, response);

     }

 }