JavaEE中关于ServletConfig的小结

     在Servlet的配置文件中，可以使用一个或多个<init-param>标签为servlet配置一些初始化参数。当servlet配置了初始化参数后，web容器在创建servlet实例对象时，会自动将这些初始化参数封装到ServletConfig对象中，并在调用servlet的init方法时，ServletConfig对象传递给servlet。进而，程序员通过ServletConfig对象就可以得到当前servlet的初始化参数信息。
示例代码如下：

 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 {

       //获取指定的初始化参数

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

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

         //获取所有的初始化参数

         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;

     }

 }

相应的web.xml如下：

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

 

 <web-app xmlns="http://java.sun.com/xml/ns/javaee"

     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

     xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"

     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>

测试结果如下：

 在上面的代码中，ServletConfigDemo1对象中有一个ServletConfig对象，其实这是不必要的。因为ServletConfigDemo1继承了HttpServlet，HttpServlet又继承了GenericServlet 。GenericServlet 已经在内部维护了一个ServletConfig对象。相关实现如下：

 public abstract class GenericServlet 

     implements Servlet, ServletConfig, java.io.Serializable

 {

     …    …

 private transient ServletConfig config;

 public ServletConfig getServletConfig() {

           return config;

     }

 }

因而我们可以通过我们写的Servlet对象的getServletConfig()方法直接拿到ServletConfig对象，示例代码如下:

 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);

     }

 

 }

web.xml文件：

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

<web-app xmlns="http://java.sun.com/xml/ns/javaee"

    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"

    version="2.5">

 <servlet>

    <servlet-name>ServletConfigDemo2</servlet-name>

    <servlet-class>com.yyz.servletconfig.ServletConfigDemo2</servlet-class>

     <init-param>

               <param-name>name</param-name>

               <param-value>yyz</param-value>

    </init-param>

  </servlet>

 <servlet-mapping>

    <servlet-name>ServletConfigDemo2</servlet-name>

    <url-pattern>/servlet/ServletConfigDemo2</url-pattern>

  </servlet-mapping>

</web-app>