javaee学习-servlet初始化参数

1.需要定义ServletConfig对象来接收servlet配置的初始化参数。

2.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，将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。

3.注意：获取servlet初始值（需要在init（）方法中初始化）//注意，这里必须设置，自动加载，<load-on-startup>1</load-on-startup>//或者配置映射才能初始化servlet初始化参数，直接在类中不能初始化。

以下是代码：

*helloworld.java

 package myweb;

 import java.io.IOException;
 import java.io.PrintWriter;
 import java.util.Enumeration;

 import javax.servlet.ServletConfig;
 import javax.servlet.ServletException;
 import javax.servlet.annotation.WebServlet;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;

 /**
  * Servlet implementation class helloworld
  */
 public class helloworld extends HttpServlet {
     private static final long serialVersionUID = 1L;
     /**
      * 定义ServletConfig对象来接收servlet配置的初始化参数
      */
     private ServletConfig config;
     /**
           * 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，
           * 将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。
           */
          @Override
          public void init(ServletConfig config) throws ServletException {
              this.config = config;
          }
     /**
      * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
      */
     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

         //.获取servlet初始值（需要在init（）方法中初始化）
         //注意，这里必须设置，自动加载，<load-on-startup>1</load-on-startup>
         //或者配置映射才能初始化servlet初始化参数，直接在类中不能初始化
         //获取在web.xml中配置的初始化参数
                  String paramVal = this.config.getInitParameter("name");//获取指定的初始化参数
                  response.getWriter().print(paramVal);
                  response.getWriter().print("<hr/>");
                  //获取所有的初始化参数
                  Enumeration<String> e = config.getInitParameterNames();
                  while(e.hasMoreElements()){
                      String name = e.nextElement();
                      String value = config.getInitParameter(name);
                      response.getWriter().print(name + "=" + value + "<br/>");
                  }
     }

     /**
      * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
      */
     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
         // TODO Auto-generated method stub
     }

 }

web.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">

 <servlet>
     <servlet-name>helloworld</servlet-name>
     <servlet-class>myweb.helloworld</servlet-class>

     <!--配置helloworld(servlet)的初始化参数 -->
     <init-param>
         <param-name>name</param-name>
         <param-value>xianghu</param-value>
     </init-param>
      <init-param>
         <param-name>password</param-name>
         <param-value>123456</param-value>
     </init-param>
     <init-param>
         <param-name>charset</param-name>
         <param-value>UTF-8</param-value>
     </init-param>
 </servlet>
 <servlet-mapping>
     <servlet-name>helloworld</servlet-name>
     <url-pattern>/Default</url-pattern>
 </servlet-mapping>
 </web-app>