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>