servlet 配置信息及初始化参数

Servlet取得初始化配置信息：

 

通过config对象可以读取web.xml中的配置的初始化参数，此对象实际上是ServletConfig借口的实例。可以通过init()方法找到ServletConfig接口实例。

 

读取初始化配置信息------InitParamServlet.Java

 package com.ls.servlet_01;

 import java.io.IOException;
 import java.io.PrintWriter;

 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 InitParamServlet extends HttpServlet {

     String initParam=null;
     public void init(ServletConfig config) throws ServletException {
         this.initParam=config.getInitParameter("ref");
     }
     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         System.out.println("初始化参数："+this.initParam);

     }
     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         this.doGet(request, response);
     }
 }

在web.xml中配置初始化信息

 "1.0" encoding="UTF-8"?>
 "2.5"
     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">

     InitParamServlet
     class>com.ls.servletd_01.InitParamServletclass>

         ref
         liusheng



     InitParamServlet
     /InitParamServlet


     index.jsp

 

程序运行结果：在Tomcat后台打印

                   初始化参数：liusheng

用直接配置初始化

表示参数名称

表示参数的内容

 

 

注意：

    在Servlet中初始化方法一共有init（）和init（ServletConfig config）两个，如果两个初始化方法同时出现，则调用的是init（ServletConfig config）方法。

 

Servlet取得其他内置对象：

   

    1、取得HttpSession实例

在servlet程序中要想取得一个session对象，则可以通过HttpServletRequest接口完成，有以下操作方法：

public HttpSession getSession()      返回当前的session

public HttpSession  getSession（boolean  create）     返回当前的session，如果没有则创建一个新的session对象返回

 

取得HttpSession对象---HttpSessionservlet.java

 package com.ls.servlet_02;

 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;
 import javax.servlet.http.HttpSession;

 public class HttpSessionservlet extends HttpServlet {

     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         HttpSession ses = request.getSession();
         System.out.println("SESSION-->" + ses.getId());
         ses.setAttribute("username", "刘胜");
         System.out.println("username属性内容是：" + ses.getAttribute("username"));
     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         this.doGet(request, response);

     }

 }

配置web.xml文件

 "1.0" encoding="UTF-8"?>
 "2.5"
     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">

     HttpSession
     class>com.ls.servlet_02.HttpSessionservletclass>


     HttpSession
     /servlet_HttpSession


     index.jsp

程序运行结果： Tomcat后台显示

           

 本程序通过getSession()方法取得了一个HttpSession对象后，输出了Session Id以及属性的设置及取得操作。

 

      2、取得ServletContext实例

application内置对象是ServletContext 接口的实例，表示的是Servlet上下文。如果要在一个servlet中使用此现象，直接通过GenericServlet类提供的方法即可：

public ServletContext getServletContext（）      取得ServletContext对象

 

取得application对象-----ServletContext.java

 package com.ls.servlet_03;

 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 ServletContext extends HttpServlet {

     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         javax.servlet.ServletContext app =super.getServletContext();
         System.out.println("真实路径："+app.getRealPath("/"));
     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {

         this.doGet(request, response);
     }


 }

配置web.xml文件

 "1.0" encoding="UTF-8"?>
 "2.5"
     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">

     ServletContext
     class>com.ls.servlet_03.ServletContextclass>


     ServletContext
     /servlet_ServletContext


     index.jsp

程序运行结果：  Tomcat后台输出

           

 

    本程序通过getServletContext()方法取得ServletContext实例后，将虚拟目录所对应的真实路径输出。

 

 

 

 

 

                                                                                                        

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