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封装的ServLet及servletContext

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说明

　原生的ServLet在实际生活中很少使用，可当作了解其发展历程使用。

步骤

封装的ServLet：

  1. 新建Dynamic Web Project
  2. 在src上，右键 new ——> Servlet
  3. 根据实际情况配置
  4. 之后我们会得到一个封装好的ServLet
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    package com.rexyan.servlet_auto;

    import java.io.IOException;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;

    /**
     * Servlet implementation class servlet_auto_create
     */
    public class servlet_auto_create extends HttpServlet {
    	private static final long serialVersionUID = 1L;
           
        /**
         * @see HttpServlet#HttpServlet()
         */
        public servlet_auto_create() {
            super();
            // TODO Auto-generated constructor stub
        }

    	/**
    	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
    	 */
    	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		// TODO Auto-generated method stub
    		response.getWriter().append("Served at: ").append(request.getContextPath());
    	}

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

    }

创建自己的ServLet模版

　我们可以创建自己的ServLet模版
window ——> Preferences ——> 搜索templates ———> 找到Java、Editor下在templates，右边选择new一个，名称为“severlet”，描述为“自定义severlet模版”，内容为：

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package ${enclosing_package};
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ${primary_type_name} extends HttpServlet {

	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		response.getWriter().write("Rex");
	}

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

用ServLet模版生成

　这是我们可以删除之前自动生成的ServLet，使用我们自己的模版创建的ServLet

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package com.rexyan.servlet2;

import java.io.IOException;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ServLet2 extends HttpServlet {
	public void init(){
		// 服务器创建一个ServLet的实例，init就会执行
		ServletContext servletContext = this.getServletContext();
		servletContext.setAttribute("test_name", 3);
		//往servletContext中设置一个名为test_name，值为3的属性
	}

	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		response.getWriter().write("Rex");
		// 返回Rex
		ServletContext servletContext = this.getServletContext();
		// 获取servletContext对象【此对象是全局的，只有一个，针对整个Web项目的，不像ServLet是可以有很多个】
		System.out.println(servletContext.getInitParameter("Driver"));
		// 获取web.xml配置，需要在web.xml中配置context-param
		System.out.println(servletContext.getRealPath("/1.txt"));
		// 获取文件的绝对路径，传入参数为相对路径
		System.out.println(servletContext.getAttribute("test_name"));
		// 输出servletContext中属性为test_name的值
		servletContext.setAttribute("test_name", 1);
		// 设置新的值
		System.out.println(servletContext.getAttribute("test_name"));
		// 再次输出servletContext中属性为test_name的值
		System.out.println("getServerInfo" + servletContext.getServerInfo());
		// 输出servletContext的一些信息
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// 在POST中可以调用GET方法
		doGet(request, response);
	}
}

配置web.xml

　web.xml的配置

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<?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_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>ServerLet2</display-name>
  
  <context-param>
  	<param-name>Driver</param-name>
  	<param-value>com.mysql.jdbc.Driver</param-value>
  </context-param>
  
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <description></description>
    <display-name>ServLet2</display-name>
    <servlet-name>ServLet2</servlet-name>
    <servlet-class>com.rexyan.servlet2.ServLet2</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>ServLet2</servlet-name>
    <url-pattern>/test2</url-pattern>
  </servlet-mapping>
</web-app>