Servlet取得初始化配置信息及内置对象

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

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="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">
<servlet>
    <servlet-name>InitParamServlet</servlet-name>
    <servlet-class>com.ls.servletd_01.InitParamServlet</servlet-class>
  	<init-param>
  		<param-name>ref</param-name>
  		<param-value>liusheng</param-value>
  	</init-param>
 </servlet>
 <servlet-mapping>
    <servlet-name>InitParamServlet</servlet-name>
    <url-pattern>/InitParamServlet</url-pattern>
  </servlet-mapping>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>  

 

程序运行结果：在Tomcat后台打印

                   初始化参数：liusheng

用<init-param>直接配置初始化

<param-name>表示参数名称

<param-value>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

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="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">
 <servlet>
    <servlet-name>HttpSession</servlet-name>
    <servlet-class>com.ls.servlet_02.HttpSessionservlet</servlet-class>
  </servlet>
 <servlet-mapping>
    <servlet-name>HttpSession</servlet-name>
    <url-pattern>/servlet_HttpSession</url-pattern>
  </servlet-mapping>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>

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

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="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">
 <servlet>
    <servlet-name>ServletContext</servlet-name>
    <servlet-class>com.ls.servlet_03.ServletContext</servlet-class>
  </servlet>
<servlet-mapping>
    <servlet-name>ServletContext</servlet-name>
    <url-pattern>/servlet_ServletContext</url-pattern>
  </servlet-mapping>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>

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。